WO 2007/024425 PCT/US2006/029976
METHOD OF PRODUCING POLYCARBONATE ARTICLES BY ROTATION
MOLDING AND ROTATION MOLDED ARTICLES MADE BY THE METHOD
FIELD OF THE INVENTION
This invention relates to a method for making polycarbonate articles by rotation
molding. More specifically this invention relates to a method for making rotation
molded polycarbonate articles from a melt polycarbonate composition. In another
embodiment the invention relates to a light diffusing rotation molded article.
Rotation molding is a widely used technique to inexpensively prepare relatively large
molded polymer articles, such as canoes, dolls, light fixtures, furniture etc. In
comparison with injection molding, no expensive molds or high-pressure equipment
is needed, allowing for low investment, which affords the cost effective production of
a small series of articles. Rotation molded articles are produced with low-pressure
conditions and hence have very low molded-in stresses. Common polymers used for
rotation molding, or roto-molding as it is often called, are poly-olefins such as
polyethylene and polypropylene.
Aromatic polycarbonate is a polymer that is noted for its transparency and excellent
mechanical properties when used in a large variety of applications. For example,
polycarbonate is used for optical data carriers such as CDs and DVDs, automotive
parts, sheets and household appliances. Polycarbonate articles made by rotation
molding have the advantage of an intrinsically better chemical resistance because of
the low molded in stress. Chemical stress cracking is a known problem with injection
molded polycarbonate articles. Molded in stresses can be made visible by inspecting
an article under polarized light. Up to now rotation molding of polycarbonate has not
been widely practiced due to technical difficulties. Polycarbonate requires relatively
high processing temperatures and pressures for effective molding. Typically
temperatures above 300°C, and high pressures as employed with extrusion or
injection molding equipment are required. Only at these high pressures and
temperatures is the viscosity of polycarbonate low enough to efficiently fill a mold.
However, polycarbonate is known to be sensitive to degradation at the high
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temperatures and long residence times, commonly used in rotation molding. To
mitigate these viscosity problems, previous attempts to rotation mold polycarbonate
have focused on relatively low temperature molding of low molecular weight
polycarbonate, which has relatively low viscosity. Unfortunately, low molecular
weight polycarbonate does not exhibit very good mechanical properties, and in
particular lacks impact strength. Other troublesome issues encountered in rotation
molding of polycarbonate are surface defects and mold release problems. Because of
these problems, aromatic polycarbonates have not previously been widely used in
commercial roto-molding
Consequently there is a need for a method of rotation molding aromatic polycarbonate
that addresses one or more of the above issues.
SUMMARY OF THE INVENTION
Disclosed herein is a method for making a polycarbonate article comprising:
processing a melt aromatic polycarbonate in a rotation molding apparatus into a
rotation molded article characterized in that
1. said aromatic polycarbonate is produced by a melt reaction process comprising the
steps of:
transesterifying a diaryl carbonate and a dihydroxy compound in the presence of a
catalyst system to form an intermediate aromatic polycarbonate, wherein said catalyst
system comprises:
an alpha catalyst selected from the group consisting of alkali metal salts and alkaline
earth metal salts; and
a beta catalyst selected from the group consisting of quaternary ammonium
compounds and quaternary phosphonium compounds;
adding to said intermediate aromatic polycarbonate a catalyst quencher; and
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2. said aromatic polycarbonate is rotation molded into said article at a rotation
molding temperature between 305°C to 360°C.
Also disclosed is an aromatic polycarbonate article produced by rotation molding
wherein the aromatic polycarbonate is produced by a melt transesterification process
and has a weight average molecular weight from 25,000 up to about 36,000. Further
there is disclosed a light diffusive rotation molded article.
DETAILED DESCRIPTION OF THE INVENTION
Disclosed herein are several embodiments of a rotation molded polycarbonate article
and methods for making such rotation molded polycarbonate article.
In one embodiment there is disclosed a method for making a polycarbonate article
comprising the steps of:
1) producing an aromatic polycarbonate by a melt reaction process comprising the
steps of:
a) transesterifying a diaryl carbonate and a dihydroxy compound in the presence of a
catalyst system to form an intermediate aromatic polycarbonate, wherein said catalyst
system comprises,
(i) an alpha catalyst selected from the group consisting of alkali metal salts and
alkaline earth metal salts; and
(ii) a beta catalyst selected from the group consisting of quaternary ammonium
compounds and quaternary phosphonium compounds;
b) adding to said intermediate aromatic polycarbonate a catalyst quencher; and
2) rotation molding the polycarbonate into an article at a rotation molding temperature
between 305°C to 360°C.
In another embodiment there is disclosed an aromatic polycarbonate article produced
by rotation molding wherein the aromatic polycarbonate is produced by a melt
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transesterification process and has a weight average molecular weight from 25,000 up
to about 36,000 as measured by GPC against polycarbonate standards.
In another embodiment an article is produced by rotation molding from a
polycarbonate composition comprising
a melt polycarbonate resin;
0.01 to 5% by weight of the total composition of a poly alkyl silsesquioxane based
diffusing agent; and
0 to 0.5% by weight stabilizer based on the total composition including the stabilizer.
As stated above, the method of the present invention relates to articles produced by
rotation molding of melt aromatic polycarbonate. As used herein, the terms
"polycarbonate", "polycarbonate composition", "aromatic polycarbonate" and
"composition comprising aromatic carbonate chain units" includes polymers and
compositions having structural units of the formula (1):

wherein greater than or equal to about 60 percent of the total number of R1 groups are
aromatic radicals and the balance thereof are aliphatic, alicyclic, or aromatic radicals.
Specifically, R1 is an aromatic radical and, more specifically, a radical of the formula
(2):

wherein each of A1 and A2 is a monocyclic divalent aryl radical and Y1 is a bridging
radical having zero, one, or two atoms which separate A from A . In an exemplary
embodiment, one atom separates A1 from A2. Illustrative non-limiting examples of
the Y1 radicals are -O-, -S-, -S(O)-, -S(O)2-, -C(O)-( methylene, cyclohexyl-
methylene, 2-[2,2,l]-bicycloheptylidene, ethylidene, isopropylidene, neopentylidene,
cyclohexylidene, cyclopentadecylidene, cyclododecylidene and adamantylidene. In
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another embodiment, zero atoms separate A1 from A2, with an illustrative example
being biphenyl. The bridging radical Y1 can be a saturated hydrocarbon group such
as methylene, cyclohexylidene or isopropylidene.
The polycarbonate manufacturing process comprises the step of reacting an aromatic
dihydroxy compound with a compound capable of introducing a carbonate bond. In
the Schotten-Baumann reaction, commonly known as an 'interfacial' reaction, a
dihydroxy compound is reacted with a carbonyl halide in a solvent system containing
an organic solvent such as methylene chloride and water. Phosgene is often employed
as the carbonyl halide. A base is introduced during the reaction as an acid scavenger
for pH control.
Another process for producing polycarbonate utilizes a carbonic acid diester as the
carbonate source. The dihydroxy compound and the carbonic acid diester are reacted
in a transesterification reaction in the melt. This process has the advantage that it
does not employ the highly toxic phosgene, nor does it employ organic solvents.
Commonly used carbonic acid diesters are diaryl carbonates, such as diphenyl
carbonate (DPC) or bismethyl salicyl carbonate (BMSC).
Among these processes, the use of the melt transesterification process is the preferred
process for this invention.
Suitable dihydroxy compounds are those in which only one atom separates A1 and A2.
As used herein, the term "dihydroxy compound" includes, for example, bisphenol
compounds having the general formula (3) as follows:

wherein Ra and Rb each represent a halogen atom or a monovalent hydrocarbon group
and may be the same or different; p and q are each independently integers from 0 to 4;
and Xa represents one of the groups of formula (4):
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wherein Rc and Rd each independently represent a hydrogen atom or a monovalent
linear or cyclic hydrocarbon group and Re is a divalent hydrocarbon group.
Some illustrative, non-limiting examples of dihydroxy compounds suitable for
forming the polycarbonate oligomers include the dihydroxy-substituted aromatic
hydrocarbons disclosed by name or formula (generic or specific) in U.S. Patent
4,217,438. A nonexclusive list of specific examples of the types of bisphenol
compounds that may be represented by formula (3) includes bis(hydroxyaryl) alkanes
such as bis(4-hydroxyphenyl)methane; l,l-bis(4-hydroxyphenyl)ethane; 2,2-bis(4-
hydroxyphenyl)propane (also known as bisphenol A); 2,2-bis(4-
hydroxyphenyl)butane; 2,2-bis(4-hydroxyphenyl)octane; bis(4-
hydroxyphenyl)phenylmethane; 2,2-bis(4-hydroxy- l-methylphenyl)propane; 1,1-
bis(4-hydroxy-t-butylphenyl) propane; and 2,2-bis(4-hydroxy-3-
bromophenyl)propane; bis(hydroxyaryl)cycloalkanes such as l,l-(4-
hydroxyphenyl)cyclopentane and 1,1 -bis(4-hydroxyphenyl)cyclohexane;
dihydroxyaryl ethers such as 4,4'-dihydroxydiphenyl ether and 4,4'dihydroxy-3,3'-
dimethylphenyl ether; dihydroxydiaryl sulfides such as 4,4'-dihydroxydiphenyl sulfide
and 4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfide; dihydroxydiaryl sulfoxides such as
4,4'-dihydroxydiphenyl sulfoxide and4,4'-dihydroxy-3,3'-dimethyldiphenyl sulfoxide;
and dihydroxydiaryl sulfones such as 4,4'-dihydroxydiphenyl sulfone and 4,4'-
dihydroxy-3,3 '-dimethyldiphenyl sulfone.
It is also possible to employ two or more different dihydric phenols or a copolymer of
a dihydric phenol with a glycol or with a hydroxy- or acid-terminated polyester or
with a dibasic acid or hydroxy acid in the event a carbonate copolymer rather than a
homopolymer is desired for use. Polyarylates and polyester-carbonate resins or their
blends can also be employed. Preferably, the polycarbonates are linear
homopolycarbonates that are capable of branching upon addition of the branching
agent in accordance with this disclosure.
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Other bisphenol compounds that may be used in the polycondensation of
polycarbonate include those of formula (5):

wherein, Rf is a halogen atom of a hydrocarbon group having 1 to 10 carbon atoms or
a halogen substituted hydrocarbon group; n is a value from 0 to 4. When n is at least
2, Rf may be the same or different. Non-limiting examples of bisphenol compounds
that may be represented by the formula (5), are resorcinol, substituted resorcinol
compounds such as 5-methyl resorcinol, 5-ethyl resorcinol, 5-propyl resorcinol, 5-
butyl resorcinol, 5-t-butyl resorcinol, 5-phenyl resorcinol and 5-cumyl resorcinol;
catechol, hydroquinone, substituted hydroquinones, such as 3-methyl hydroquinone,
3-ethyl hydroquinone, 3-propyl hydroquinone, 3-butyl hydroquinone, 3-t-butyl
hydroquinone, 3-phenyl hydroquinone and 3-cumyl hydroquinone; or combinations
comprising at least two of the foregoing bisphenol compounds.
Bisphenol compounds such as 2,2,2',2'-tetrahydro-3,3,3',3'-tetramethyl-l,r-spirobi-
[IH-indene]-6,6'- diol represented by formula (6) may also be used.

Suitable polycarbonates further include those derived from bisphenols containing
alkyl cyclohexane units. Such polycarbonates have structural units corresponding to
the formula (7):
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wherein Ra-Rd are each independently hydrogen, C1-12 alkyl, or halogen; and Re-R1 are
each independently hydrogen, C1-12 alkyl. The residue may be aliphatic or aromatic,
straight-chain, cyclic, bicyclic, branched, saturated, or unsaturated. The alkyl residue
may contain heteroatoms over and above the carbon and hydrogen members of the
substituent residue. Thus, when specifically noted as containing such heteroatoms,
the alkyl residue may also contain carbonyl groups, amino groups and hydroxyl
groups, or it may contain heteroatoms within the backbone of the alkyl residue.
Alkyl cyclohexane containing bisphenols, for example the reaction product of two
moles of a phenol with one mole of a hydrogenated isophorone, are useful for making
polycarbonate polymers with high glass transition temperatures and high heat
distortion temperatures. Such isophorone bisphenol-containing polycarbonates have
structural units corresponding to the formula (8):

wherein Ra-Rd are as defined above. These isophorone bisphenol based polymers,
including polycarbonate copolymers made containing non-alkyl cyclohexane
bisphenols and blends of alkyl cyclohexyl bisphenol containing polycarbonates with
non-alkyl cyclohexyl bisphenol polycarbonates, are supplied by Bayer Co. under the
APEC trade name
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In some more typical embodiments, the aromatic dihydroxy has the structure of
formula (9):

wherein each G1 is independently an aromatic group, such as, for example phenylene,
biphenylene, naphthylene, etc. E may be an alkylene or alkylidene group such as
methylene, ethylene, ethylidene, propylene, propylidene, isopropylidene, butylene,
butylidene, isobutylidene, amylene, amylidene, isoamylidene, etc. and may consist of
two or more alkylene or alkylidene groups connected by a moiety different from
alkylene or alkylidene, such as an aromatic linkage; a tertiary amino linkage; an ether
linkage; a carbonyl linkage; a silicon-containing linkage; a sulfur-containing linkage
such as sulfide, sulfoxide, sulfone, etc.; or a phosphorus-containing linkage such as
phosphinyl, phosphonyl, etc. In addition, E may be a cycloaliphatic group. R3 is
hydrogen or a monovalent hydrocarbon group such as alkyl, aryl, aralkyl, alkaryl, or
cycloalkyl. Y1 may be an inorganic atom such as halogen (fluorine, bromine, chlorine,
iodine); an inorganic group such as nitro; an organic group such as alkenyl, allyl,
hydrogen or a monovalent hydrocarbon group, or an oxy group such as OR; it being
only desirable that Y1 be inert to and unaffected by the reactants and reaction
conditions used to prepare the polymer. The letter m is a whole number from and
including zero through the number of positions on G1 available for substitution; p is a
whole number from and including zero through the number of positions on E
available for substitution; t is a natural number equal to at least one; s is either zero or
one; and u is any natural number including zero. Suitable particular examples of E
include cyclopentylidene, cyclohexylidene, 3,3,5-trimethylcyclohexylidene,
methylcyclohexylidene, 2-[2.2.1]-bicycloheptylidene, neopentylidene,
cyclopentadecylidene, cyclododecylidene, adamantylidene, etc.; a sulfur-containing
linkage, such as sulfide, sulfoxide or sulfone; a phosphorus-containing linkage, such
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as phosphinyl, phosphonyl; an ether linkage; a carbonyl group; a tertiary nitrogen
group; or a silicon-containing linkage such as silane or siloxy.
In the aromatic dihydroxy compound (9) above, when more than one Y1 substituent is
present, they may be the same or different. The same holds true for the R3
substituent. Where s is zero in formula (9) and u is not zero, the aromatic rings are
directly joined with no intervening alkylidene or other bridge (e.g., 4,4'-
dihydroxybiphenyl). The positions of the hydroxyl groups and Y1 on the aromatic
nuclear residues G1 can be varied in the ortho, meta, or para positions and the
groupings can be in vicinal, asymmetrical or symmetrical relationship, where two or
more ring carbon atoms of the hydrocarbon residue are substituted with Y1 and
hydroxyl groups. In some particular embodiments, the parameters t, s, and u are each
one; both G1 radicals are unsubstituted phenylene radicals; and E is an alkylidene
group such as isopropylidene. In some particular embodiments, both G1 radicals are
p-phenylene, although both may be o- or m-phenylene or one o- or m-phenylene and
the other p-phenylene.
Some non-limiting examples of aromatic dihydroxy compounds of formula (9) are
illustrated by the following list: 2,4'-dihydroxydiphenylmethane, bis(2-
hydroxyphenyl)methane, bis(4-hydroxyphenyl)methane, bis(4-hydroxy-5-
nitrophenyl)methane, bis(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)methane, 1,1-
bis(4-hydroxyphenyl)ethane, 1, l-bis(4-hydroxy-2-chlorophenyl)ethane, 2,2-bis(4-
hydroxyphenyl)propane (bisphenol A); 2,2-bis(3-chloro-4-hydroxyphenyl)propane;
2,2-bis(3-bromo-4-hydroxyphenyl)propane; 2,2-bis(4-hydroxy-3-
methylphenyl)propane; 2,2-bis(4-hydroxy-3-isopropylphenyl)propane; 2,2-bis(3-t-
butyl-4-hydroxyphenyl)propane; 2,2-bis(3 -phenyl-4-hydroxyphenyl)propane; 2,2-
bis(3,5-dichloro-4-hydroxyphenyl)propane; 2,2-bis(3,5-dibromo-4-
hydroxyphenyl)propane; 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane; 2,2-bis(3-
chloro-4-hydroxy-5-methylphenyl)propane; 2,2-bis(3-bromo-4-hydroxy-5-
methylphenyl)propane; 2,2-bis(3-chloro-4-hydroxy-5-isopropylphenyl)propane; 2,2-
bis(3-bromo-4-hydroxy-5-isopropylphenyl)propane; 2,2-bis(3-t-butyl-5-chloro~4-
hydroxyphenyl)propane; 2,2-bis(3 -bromo-5-t-butyl-4-hydroxyphenyl)propane; 2,2-
bis(3-chloro-5-phenyl-4-hydroxyphenyl)propane; 2,2-bis(3-bromo-5-phenyl-4-
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hydroxyphenyl)propane; 2,2-bis(3,5-disopropyl-4-hydroxyphenyl)propane; 2,2-
bis(3,5-di-t-butyl-4-hydroxyphenyl)propane; 2,2-bis(3,5-diphenyl-4-
hydroxyphenyl)propane; 2,2-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)propane; 2,2-
bis(4-hydroxy-2,3,5,6-tetrabromophenyl)propane; 2,2-bis(4-hydroxy-2,3,5,6-
tetramethylphenyl)propane; 2,2-bis(2,6-dichloro-3,5-dimethyl-4-
hydroxyphenyl)propane; 2,2-bis(2,6-dibromo-3,5-dimethyl-4-
hydroxyphenyl)propane; 2,2-bis(4-hydroxy-3-ethylphenyl)propane, 2,2-bis(4-
hydroxy-3,5-dimethylphenyl)propane, 2,2-bis(3,5,3' ,5' -tetrachloro-4,4' -
dihydroxyphenyl)propane, bis(4-hydroxyphenyl)cyclohexylmethane, 2,2-bis(4-
hydroxyphenyl)-l-phenylpropane, l,l-bis(4-hydroxyphenyl)cyclohexane; l,l-bis(3-
chloro-4-hydroxyphenyl)cyclohexane; 1,1 -bis(3-bromo-4-
hydroxyphenyl)cyclohexane; 1 ,l-bis(4-hydroxy-3-methylphenyl)cyclohexane; 1,1-
bis(4-hydroxy-3-isopropylphenyl)cyclohexane; 1, l-bis(3-t-butyl-4-
hydroxyphenyl)cyclohexane; 1, l-bis(3-phenyl-4-hydroxyphenyl)cyclohexane; 1,1-
bis(3,5-dichloro-4-hydroxyphenyl)cyclohexane; l,l-bis(3,5-dibromo-4-
hydroxyphenyl)cyclohexane; 1, l-bis(4' -hydroxy-3' methylphenyl) cyclohexane
(DMBPC), l,l-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane; 4,4'-[l-methyl-4-(l-
methyl-ethyl)-l,3-cyclohexandiyl]bisphenol (1,3 BHPM), 4-[l-[3-(4-hydroxyphenyl)-
4-methylcyclohexyl]-l-methyl-ethyl]-phenol (2,8 BHPM), 3,8-dihydroxy-5a,10b-
diphenylcoumarano-2',3',2,3-coumarane (DCBP), 2-phenyl-3,3-bis(4-
hydroxyphenyl)phthalimidine (PPPBP) l,l-bis(3-chloro-4-hydroxy-5-
methylphenyl)cyclohexane; 1, l-bis(3-bromo-4-hydroxy-5-
methylphenyl)cyclohexane; 1, l-bis(3-chloro-4-hydroxy-5-
isopropylphenyl)cyclohexane; l,l-bis(3-bromo-4-hydroxy-5-
isopropylphenyl)cyclohexane; l,l-bis(3-t-butyl-5-chloro-4-
hydroxyphenyl)cyclohexane; l,l-bis(3-bromo-5-t-butyl-4-
hydroxyphenyl)cyclohexane; 1, l-bis(3-chloro-5-phenyl-4-
hydroxyphenyl)cyclohexane; l,l-bis(3-bromo-5-phenyl-4-
hydroxyphenyl)cyclohexane; l,l-bis(3,5-disopropyl-4-hydroxyphenyl)cyclohexane;
l,l-bis(3,5-di-t-butyl-4-hydroxyphenyl)cyclohexane; l,l-bis(3,5-diphenyl-4-
hydroxyphenyl)cyclohexane; l,l-bis(4-hydroxy-2,3,5,6-
tetrachlorophenyl)cyclohexane; 1, l-bis(4-hydroxy-2,3,5,6-
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tetrabromophenyl)cyclohexane; 1, l-bis(4-hydroxy-2,3,5,6-
tetramethylphenyl)cyclohexane; l,l-bis(2,6-dichloro-3,5-dimethyl-4-
hydroxyphenyl)cyclohexane; l,l-bis(2,6-dibromo-3,5-dimethyl-4-
hydroxyphenyl)cyclohexane; l,l-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;
l,l-bis(3-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane; l,l-bis(3-bromo-4-
hydroxyphenyl)-3,3,5-trimethylcyclohexane; l,l-bis(4-hydroxy-3-methylphenyl)-
3,3,5-trimethylcyclohexane; l,l-bis(4-hydroxy-3-isopropylphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(3-t-butyl-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(3-phenyl-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; 1,1 -bis(3,5-dichloro-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; 1, l-bis(3,5-dibromo-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; 1,1 -bis(3,5-dimethyl-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(3-chloro-4-hydroxy-5-methylphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(3-bromo-4-hydroxy-5-methylphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(3-chloro-4-hydroxy-5-isopropylphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(3-bromo-4-hydroxy-5-isopropylphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; bis(3-chloro-5-phenyl-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(3-bromo-5-phenyl-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(3,5-disopropyl-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; 1, l-bis(3,5-di-t-butyl-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(3,5-diphenyl-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; 1, l-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)-3,3,5-
trimethylcyclohexane; l,l-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; 1,1 -bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-
trimethylcyclohexane; 4,4-bis(4-hydroxyphenyl)heptane, 4,4' dihydroxy-1,1-
biphenyl; 4,4'-dihydroxy-3, 3'-dimethyl-l,l-biphenyl; 4,4'-dihydroxy-3,3'-dioctyl-
1,1-biphenyl; 4,4'-(3,3,5-trimethylcyclohexylidene)diphenol, 4,4'-bis(3,5-
dimethyl)diphenol, 4,4'-dihydroxydiphenylether; 4,4'-dihydroxydiphenylthioether;
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1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene; 1,3-bis(2-(4-hydroxy-3-
methylphenyl)-2-propyl)benzene; l,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene,
l,4-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene 2,4'-dihydroxyphenyl
sulfone, 4,4'-dihydroxydiphenylsulfone (BPS), BPF, 2,6-dihydroxy naphthalene;
hydroquinone; resorcinol, Cl-3 alkyl-substituted resorcinols, 3-(4-hydroxyphenyl)-
l,l,3-trimethylindan-5-ol, l-(4-hydroxyphenyl)-l,3,3-trimethylindan-5-ol, and
2,2,2l,2l-tetrahydro-3,3,3',3I-tetramethyl-l,r-spirobi[lH-indene]-6,6'-diol. The most
typical aromatic dihydroxy compound is Bisphenol A (BPA).
In preparing the polycarbonate, usually about 1.0 mole to about 1.30 moles of a
carbonic acid diester are utilized for every 1 mole of the dihydroxy compound. In one
embodiment, about 1.01 moles to about 1.20 moles of the carbonic diester are
utilized. Optionally, the carbonic diester acid component for preparing the
polycarbonate may contain a portion, up to 50 mole% of a dicarboxylic acid or its
ester, such as terephthalic acid or diphenyl isophthalate, to prepare polyester
polycarbonates.
The synthesis of polycarbonates may be conducted in the presence of a catalyst, for
example, to promote the transesterification reaction. Examples of suitable catalysts
include quaternary ammonium compounds, quaternary phosphonium compounds,
alkali metal salts and alkaline earth metal salts, such as alkali metal or alkaline earth
metal oxides, hydroxides, amide compounds, alcoholates, and phenolates, basic metal
oxides such as ZnO, PbO, and Sb2O3, organotitanium compounds, soluble manganese
compounds, nitrogen-containing basic compounds; acetates of calcium, magnesium,
zinc, lead, tin, manganese, cadmium, and cobalt; and compound catalyst systems such
as a nitrogen-containing basic compound and a boron compound; a combination of a
nitrogen-containing basic compound and an alkali (alkaline earth) metal compound; a
combination of a nitrogen-containing basic compound, an alkali (alkaline earth) metal
compound, and a boron compound; or combinations comprising at least two of the
foregoing catalysts. When more than one catalyst is employed, each may be
incorporated into the melt at the same stage or at different stages of the reaction.
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Preferably, the catalyst is a quaternary ammonium compound or a quaternary
phosphonium compound. Illlustrative non-limiting examples include tetramethyl
ammonium hydroxide, tetramethyl ammonium acetate, tetramethyl ammonium
fluoride, tetramethyl ammonium tetraphenyl borate, tetraphenyl phosphonium
fluoride, tetraphenyl phosphonium tetraphenyl borate, tetrabutyl phosphonium
hydroxide, tetrabutyl phosphonium acetate and dimethyl diphenyl ammonium
hydroxide.
The appropriate level of catalyst will depend in part on how many catalysts are being
employed. In general, the total amount of catalyst is usually in the range of about 1 x
10"8 to about 1.0 mole per mole of the dihydroxy compound. Optionally, when more
than one catalyst is employed, each may be incorporated into the melt at a different
stage of the reaction.
In a particularly preferred embodiment a catalyst system comprising an alkali metal
salt or an earth alkaline metal salt, (known as an alpha catalyst) in combination with a
quaternary ammonium or a quaternary phosphonium compound (known as a beta
catalyst) is used. In one embodiment both catalysts are added to the reaction mixture
at the same time. In another embodiment the beta catalyst is added to the reaction
mixture in a first oligomerization step, and the alpha catalyst is subsequently added in
a second step.
Terminators or endcapping agents may also be used during the manufacture of the
polycarbonate. Examples of terminators include phenol, p-tert-butylphenol, p-
cumylphenol, octylphenol, nonylphenol and other endcapping agents well-known in
the art.
In order to obtain a faster and/or greater build in molecular weight of the
polycarbonate a coupling agent such as a bis-alkylsalicyl carbonate may also be added
to the polycarbonate. Examples of bis-alkylsalicyl carbonates include, but are not
limited to, bis-rnethyl, ethyl or propyl salicyl carbonate, bis-phenyl or benzyl salicyl
carbonate, bis(2-benzoylphenyl) carbonate, BPA-bis-2-alkoxyphenylcarbonate, BPA-
bis-2-aryloxyphenylcarbonate, andBPA-bis-2-benzoylphenylcarbonate.
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The process of manufacturing polycarbonates generally takes place in a series of
reactors, commonly referred to as a reactor train in the art. In general, the temperature
is increased and the pressure is reduced along the reactor train. Since the reaction is
an equilibrium reaction, byproduct aryl alcohol (e.g. phenol) is continuously removed
from the reactors to ensure the desired or targeted molecular weight. The reaction
preferably occurs at temperatures greater than about 230°C, with about 270°C to about
310°C more preferred. The pressure of the reaction is preferably reduced to a
pressure less than about 100 Pa, with about 20 to about 50 Pa more preferred. Once
the final polycarbonate target specifications have been reached, a quencher
composition may be added if desired. The mixture is passed through an extruder and
pelletized. The reaction can be carried out by either a batch mode or a continuous
mode.
The quencher composition generally comprises an acid or acid derivative dissolved in
a carrier. Suitable quencher compounds are sulfonic acid class compounds or
derivatives thereof. Non-limiting examples of sulfonic acid class compounds include
sulfonates such as benzenesulfonate, p-toluenesulfonate, methyl benzenesulfonate,
ethylbenzene sulfonate, butyl benzenesulfonate, octyl benzenesulfonate and phenyl
benzenesulfonate, sulfonic acid esters such as methyl p-toluenesulfonate, ethyl p-
toluenesulfonate, butyl p-toluene sulfonate, octyl p-toluenesulfonate and phenyl p-
toluenesulfonate, and sulfonic acid ammonium salts such as ammonium p-toluene
sulfonate. Moreover, sulfonic acid compounds such as trifluoromethanesulfonic acid,
and naphtalenesulfonic acid may also be used. Another class of quencher compounds
include compounds having at least one acid or acid ester moiety and at least one
amine moiety. Non-limiting examples include N-(2-hydroxyethyl)piperazine-N'-3-
propanesulfonic acid, 1,4-piperazine bis (ethanesulfonic acid) and 5-dimethylamino-
1-naphthalenesulfonic acid. Among these substances methyl p-toluenesulfonate, ethyl
p-toluenesulfonate and butyl p-toluenesulfonate are preferred. In one embodiment the
quencher composition is added in a carrier comprising monomers employed in the
reaction optionally in combination with a solvent. An exemplary embodiment utilizes
butyl p-toluenesulfonate in a diphenyl carbonate/toluene carrier.
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Generally the quencher composition is added in a 2 to 20-fold molar excess of active
quencher compound in the quencher composition relative to the alkali metal or earth
alkaline metal catalyst, hi one embodiment the quencher is added in about 5 to 10 fold
molar excess of active quencher compound in the quencher composition. The amount
of active quencher compound in the total quencher composition (active quencher
compound + carrier) generally varies from 1 to 30% by weight of the total quencher
composition.
In one embodiment of the method of the present Invention, a first reaction stage
comprises charging at least one dihydroxy aromatic compound, at least one diaryl
carbonate and at least one quaternary ammonium or quaternary phosphonium (beta)
transesterification catalyst to a reactor and reacting under conditions which comprise
heating at a temperature in a range between about 150 and about 300°C, preferably
between about 170 and about 280°C, and pressure of between about 2 atmospheres
and about 1.0 mmHg, preferably between about atmospheric pressure and about 10
mmHg, for a time period of between about 15 minutes and about 3 hours, preferably
between about 30 minutes and about 2 hours. The first stage reaction provides an
oligomeric polycarbonate having a weight average molecular weight, Mw, of less than
about 10,000 Daltons and comprising structural units derived from the diaryl
carbonate and dihydroxy aromatic compounds employed. The diaryl carbonate and
dihydroxy aromatic compounds are each employed in an amount corresponding to
between about 0.90 and about 1.30, preferably between about 0.95 and about 1.20
moles diaryl carbonate per mole of dihydroxy aromatic compound. The beta
transesterification catalyst is employed in an amount corresponding to between about
1 x 10"7 and about 1 x 10"3, preferably between about 1 x 10"6 and about 1 x 10"3 moles
of said beta catalyst per mole of dihydroxy compound.
Following the first reaction stage, the reaction mixture comprising the oligomeric
polycarbonate is further reacted, according to the method of the present invention, in a
second reaction stage under conditions which comprise heating at a temperature in a
range between about 250 and about 350°C, preferably between about 260 and about
310°C, and a pressure of between about 10,000 Pa and about 100 Pa, preferably
between about 2000 Pa and about 100 Pa, for a time period of between about 15
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WO 2007/024425 PCT/US2006/029976
minutes and about 3 hours, preferably between about 1 and about 2 hours. In addition
to temperature and pressure regimes which differ from the temperature and pressure
regimes employed in the first reaction stage, the second reaction stage comprises the
addition of an alkali metal salt or earth alkaline metal salt co-catalyst (alpha catalyst)
to the reaction mixture. The alpha co-catalyst is typically added at the beginning of
the second reaction stage, but may be added at any time during the second reaction
stage provided sufficient time remains during said second reaction stage for the
catalytic effect of the alpha co-catalyst to be manifested. The alpha co-catalyst is
added in any catalytically effective amount, however, it is advantageous to introduce
as little of the co-catalyst as possible since alpha co-catalysts are known to catalyze
the Fries rearrangement in polycarbonates. Typically, the alpha co-catalyst is
employed in an amount corresponding to between about 1 x 10"8 and about 1 xlO"4,
preferably between about 1 x 10"8 and about 1 xlO"5 moles alpha co-catalyst per mole
dihydroxy aromatic compound. A portion of the aryl alcohol (phenol) by-product
generated during the first reaction stage is present during the second reaction stage.
In addition, the polymerization reaction of the second reaction stage gives rise to
additional aryl alcohol (phenol) by-product. Thus, the second reaction stage
comprises distilling phenolic by-product from the reaction mixture in order to drive
the polymerization reaction toward completion. The polymerization reaction which
occurs during the second reaction stage provides a product polycarbonate comprising
structural units derived from the diaryl carbonate and dihydroxy compound employed,
and has a weight average molecular weight, Mw, of at least about 18,000, preferably at
least about 22,000, more preferably about 25,000 and most preferably about 27,000.
In one embodiment, the product polycarbonate prepared for use in the method of the
present invention comprises between about 200 and about 3000, preferably between
about 100 and about 2000 parts per million (ppm) Fries product, said Fries product
furnishing upon complete hydrolysis of the product polycarbonate, a carboxy
bisphenol having structure (10)
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wherein R1 is at each occurrence a halogen atom, nitro group, cyano group, C1-C20
alkyl group, C4-C20 cycloalkyl group, or C6-C20 aryl group; n and m are independently
0, 1, 2 or 3; W is a bond, an oxygen atom, a sulfur atom, a SO2 group, a CrC2o
aliphatic radical, a C6-C20 aromatic radical, a C6-C20 cycloaliphatic radical or the
group,

wherein R2 and R3 are independently a hydrogen atom, C1-C20 alkyl group, C4-C20
cycloalkyl group, or C4-C20 aryl group; or R2 and R3 together form a C4-C20
cycloaliphatic ring which is optionally substituted by one or more C1-C20 alkyl, C6-
C20 aryl, C5-C21 aralkyl, C5-C20 cycloalkyl groups or a combination thereof. Examples
of carboxy bisphenols having structure (10) include 2-(3-carboxy-4-hydroxyphenyl)-
2-(4-hydroxyphenyl)propane; 2-(3-carboxy-4-hydroxy-5-methylphenyl)-2-(4-
hydroxy-3-methylphenyl)propaneand2-(3-carboxy-4-hydroxy-6-methylphenyl)-2-(4-
hydroxy-2-methylphenyl)propane. The carboxy bisphenol designated 2-(3-carboxy-
4-hydroxyphenyl)-2-(4-hydroxyphenyl)propane is also referred to as carboxy
bisphenol A.
Generally, in the method of the present invention, the weight average molecular
weight of the melt polycarbonate can be from 22,000 to 36,000. In one embodiment
the weight average molecular weight is from 25,000 to 35,000. In another
embodiment the weight average molecular weight is from 27,000 to 31,000. The
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WO 2007/024425 PCT/US2006/029976
weight average molecular weights are measured by Gel Permeation Chromatography
and are expressed against polycarbonate standards.
Generally during the rotation molding cycle the mold is filled with polymer at a low
temperature, heated up to the rotation molding temperature to allow the polymer to
soften and distribute itself and adopt the shape of the mold. After a period at the
rotation molding temperature, the mold temperature will be reduced to the starting
temperature to cool off the article so that it can be removed from the mold. The
rotation molding cycle time is to be understood as the time from the filling of the
mold at low temperature until the mold is ready to be filled again.
Generally the temperature of rotation molding (or rotation molding temperature) is
selected such that cycle time of the rotation molding cycle is minimized while
ensuring at the same time excellent mold filling and product appearance. The
temperature of rotation molding is to be understood as the maximum temperature
reached during the rotation molding cycle. Typically temperature of rotation molding
will be from about 3O5°C to about 360°C. In an embodiment the temperature will be
from about 315°C to about 340°C, or from about 320°C to about 335°C.
The method of the present invention will allow rotation molding of articles requiring a
substantially long cycle time. Generally during the rotation molding cycle the mold is
filled with polymer at a low temperature, heated up to the rotation molding
temperature to allow the polymer to soften, distribute itself and adopt the shape of the
mold. After a period at the rotation molding temperature, the mold temperature will
be reduced to the starting temperature to cool off the article so that it can be removed
from the mold. Articles with complex shapes and/or substantial wall thickness
consequently can be prepared by the method of the present invention while
maintaining excellent quality in terms of transparency, surface appearance and ease of
mold release. In one embodiment of the invention the cycle times may be greater than
25 minutes. In another embodiment the cycle time may be greater than 50 minutes.
In yet another embodiment the cycle time may be greater than 75 minutes. In another
embodiment the cycle time will be greater than 100 minutes.
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The composition can further comprise a UV absorbing additive. The UV absorbing
additive facilitates the preservation of the IR absorbing additive by increasing its
hydrolytic stability. Suitable non-limiting examples of UV absorbing additives are
benzophenones such as 2,4 dihydroxybenzophenone, 2-hydroxy-4-
methoxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone, 4-dodecyloxy-2
hydroxybenzophenone, 2-hydroxy-4-octadecyloxybenzophenone, 2,2' dihydroxy- 4
methoxybenzophenone, 2,2' dihydroxy-4,4'dimethoxybenzophenone, 2,2' dihydroxy-4
methoxybenzophenone, 2,2', 4,4' tetra hydroxybenzophenone, 2-hydroxy-4-methoxy-
5 sulfobenzophenone, 2-hydroxy-4-methoxy-2'-carboxybenzophenone, 2,2'dihydroxy-
4,4'dimethoxy-5 sulfobenzophenone, 2-hydroxy-4-(2-hydroxy-3-methylaryloxy)
propoxybenzophenone and 2-hydroxy-4 chlorobenzopheone; benzotriazoles such as
2-(2-hydroxy-5-tert-octylphenyl)-benzotriazole, 2-hydroxy-4-n-octoxy benzophenone
2-(2-hydroxy-5-methyl phenyl) benzotriazole, 2-(2-hydroxy-3',5'-di-tert-butyl phenyl)
benzotriazole, and 2-(2-hydroxy-X-tert, butyl-5'-methyl-phenyl) benzotriazole;
salicylates such as phenyl salicylate, carboxyphenyl salicylate, p-octylphenyl
salicylate, strontium salicylate, p-tert butylphenyl salicylate, methyl salicylate and
dodecyl salicylate; and also other ultraviolet absorbents such as resorcinol
monobenzoate, 2 ethyl hexyl-2-cyano, 3-phenylcinnamate, 2-ethyl-hexyl-2-cyano-
3,3-diphenyl acrylate, ethyl-2-cyano-3,3-diphenyl acrylate and 2-2'-thiobis(4-t-
octylphenolate)-l-n-butylamine, or combinations comprising at least one of the
foregoing UV absorbing additives. Preferred commercially available UV absorbers
are TINUVIN™ 234, TINUVIN™ 329, TINUVIN™ 350 and TINUVIN™ 360,
commercially available from Ciba Specialty Chemicals; CYASORB™ UV absorbers,
available from Cyanamide, such as 2- (2H-benzotriazol-2-yl)-4-(l,l,3,3-
tetramethylbutyl)-phenol (CYASORB™ 5411); 2-hydroxy-4-n-
octyloxybenzophenone (CYASORB™ 531); 2-[4,6-bis(2,4-dimetliylphenyl)-1,3,5-
triazin-2-yl]- 5-(octyloxy)-phenol (CYASORB™ 1164); 2,2'-(l,4- phenylene)bis(4H-
3,l-benzoxazin-4-one) (CYASORB™ UV- 3638); l,3-bis[(2-cyano-3,3-
diphenylacryloyl)oxy]-2,2-bis[[(2-cyano-3, 3-diphenylacryloyl)oxy]methyl]propane
(UVINUL 3030); 2,2'-(l,4-phenylene) bis(4H-3,l-benzoxazin-4-one); l,3-bis[(2-
cyano-3,3-diphenylacryloyl)oxy] -2,2-bis[[(2-cyano-3,3-
diphenylacryloyl)oxy]methyl]propane.
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WO 2007/024425 PCT/US2006/029976
The composition can further comprise thermal stabilizers. Suitable thermal stabilizers
include phosphites, phosphonites, phosphines, hindered amines, hydroxyl amines,
phenols, acryloyl modified phenols, hydroperoxide decomposers and benzofuranone
derivatives, or combinations comprising at least two of the foregoing thermal
stabilizers. Suitable thermal stabilizers that are commercially available are phosphites
such as IRGAPHOS 168, DOVERPHOS S-9228, ULTRANOX 641 and ALKANOX
240. If desirable, an optional co-stabilizer such as a aliphatic epoxy or a hindered
phenol anti-oxidant such as IRGANOX 1076 or IRGANOX 1010, both from Ciba
Specialty chemicals may also be added to improve thermal stability of the
composition. The typical thermal stabilizers are phosphites.
It is generally desirable to add the thermal stabilizer in an amount of about 0.001 to
about 3 wt%, based on the total weight of the composition. In one embodiment, the
thermal stabilizer may be added in amounts of about 0.002 to about 0.5 wt%, based on
the total weight of the composition. In another embodiment, the thermal stabilizer
may be added in amounts of about 0.005 to about 0.2 wt%, based on the total weight
of the composition. In yet another embodiment, the thermal stabilizer may be added
in amounts of about 0.01 to about 0.1 wt%, based on the total weight of the
composition. If a co-stabilizer is added, it is generally desirable to add it in an amount
of about 0.001 to about 2 wt%, based on the total weight of the composition.
The composition can further comprise flame retardant salts. Non-limiting examples of
suitable flame retardant salts include alkali metal or earth alkaline metal salts of alkyl
sulphonates; alkali metal or earth alkaline metal salts of perfluoro alkyl sulphonates
and alkali aryl sulphon sulphonates. Commercial flame retardant salts that are readily
available are Rimar® Salt (potassium perfluoro butyl sulphonate) and KSS
(potassium diphenylsulphon-3-sulphonate).
In one embodiment it is desirable to produce light diffusive opal parts. An example is
a decorative light fixture where the opal effect allows for diffuse lighting by shielding
the light source, e.g. a clear incandescent light bulb or halogen light, from direct
viewing by the viewer. In order to obtain light diffusive opal parts, a light diffusive
agent like barium sulfate or cross-linked PMMA beads is commonly added to the
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WO 2007/024425 PCT/US2006/029976
composition. In combination with pigments like titanium dioxide and optional dyes
the desired light diffusive opal effect can be obtained. However the use of barium
sulfate containing polycarbonate composition in a rotation molding process can result
in significant yellowing and polymer degradation due to limited stability of the
polycarbonate composition. Similarly the cross-linked PMMA beads tend to
decompose at temperatures above 300°C and thereby generate volatile components
during the rotation molding process. Volatile components may cause irregular surface
appearance and unacceptable article aesthetics. The present inventors have found that
when instead of barium sulfate or cross-linked PMMA a polyalkyl silsesquioxane
light diffusive agent is used, an excellent light diffusive opal effect can be obtained
with good article aesthetics. An example of a commercially available suitable
polyalkyl silsesquioxane light diffusive agent is Tospearl™ 120, available from GE
Toshiba Silicones. This opal effect has been disclosed in U.S. Patent No. 6,773,787 to
Maas et al, titled "Light Diffusing Articles And Methods To Manufacture Thereof.
The method of the invention and the articles formed by rotational molding are further
illustrated by the following non-limiting examples, which were prepared from the
components set forth in Table 1.
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Table 1

Compositions of polycarbonate as listed in table 2 were extruded at 300°C in a twin
screw extruder and chopped into granulate. The granulate was subsequently ground
into powder.
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All articles were produced using a rotation molding process as follows:
The inner wall of the mold in the rotation molding apparatus was coated with a
silicone release agent and inerted with nitrogen. Then the granulate polycarbonate
powder was transferred into the rotating spherical mold. Via a heating mantle the
mold is heated from 40°C up to 33O°C over a period of 15 up to 20 minutes under
multi-axial rotation until a uniformly dispersed melt is obtained. The temperature is
kept at 330°C for about 3 minutes after which the temperature is brought down to
40°C over a period of about 15 minutes. After cooling down the obtained globe is
taken out of the mold and inspected with respect to aesthetics. Particular attention is
paid to crater-like surface defects resembling 'orange skin'. Also the ease of release
from the mold is noted. The rotation molding process of one part takes about 50
minutes time. According to this process two types of globes were molded. Both have
a wall thickness between 3 and 2.5 mm. The weight of the smallest globe was 1545
grams (circumference 128 cm). The second globe type was 2150 grams
(circumference 143.5 cm).
EXAMPLES 1-6
These experiments were undertaken to demonstrate that excellent articles are
produced with the method of the present invention. Globes were produced using PC-
1 (Ex. 1), PC-2 (Ex. 2) and mixtures of PC-1 and PC-2 (Ex. 3-6). Formulations and
results are shown in Table 2 below.
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Table 2

EXAMPLES 7-11:
These examples were undertaken to demonstrate that light diffusing articles can be
made with compositions according to the invention. In order to test whether
formulations are suitable for rotation molding they are submitted to a melt stability
test. Rotation molding uses long cycle times and therefore good melt stability is
important to obtain consistent results and good surface appearance. Melt stability is
tested by measuring the Melt Stability Index defined as the percentage increase in
Melt Viscosity Rate (MVR, according ISO 1133, 300°C, 1.2 kg load) at 2 different
residence times in the MVR equipment. For this test the Melt Stability Index is
defined as the increase in Melt Viscosity Rate measured at residence times of 4 and
12 minutes. The increase in MVR value obtained after 12 minutes dwell time
compared to 4 minutes dwell time can be observed as an indication of melt stability.
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In general it is desirable that the increase in Melt Stability Index value is as low as
possible. In one embodiment the increase in Melt Stability index value is less than
8%, preferably less than 6%, more preferably less than 5% when measured at 4 and
12 minutes dwell time respectively. The formulations and results are listed in Table
3.
26
Table 3


WO 2007/024425 PCT/US2006/029976
** MAKROLON® 3103-020046 is a trade name of a polycarbonate material made
via an interfacial process and supplied by Bayer AG. Analysis of this material
suggests it contains 2.5% BaSO4 (Light Diffuser 2) and 0.1% TiO2 (Colorant).
From the results in Table 3 it can be concluded that the composition with Tospearl®
120 (Light Diffuser 1) is clearly superior in melt stability and therefore more suitable
for rotation molding than the compositions with BaSO4 (Light Diffuser 2) and TiC>2
(Colorant).
EXAMPLES 12-21:
These examples were undertaken to show that light diffusive compositions with
Tospearl® 120 and the polycarbonate of the present invention have superior color
stability at high temperatures and longer residence times than compositions with other
light diffusers and therefore are more suitable for rotation molding. Formulations as
listed in Table 4 were injection molded at a nominal melt temperature of 330°C.
Based on barrel dimensions and shot volume, machine residence time was calculated.
Produced plaques (thickness: 2.5 mm) resemble the performance expected with a
rotation molding process in which polycarbonate is submitted to an extensive period
of time to elevated temperatures. Light transmission (T) and haze (ASTM D1003) are
measured on plaques produced after 0.5 min and 24.5 min residence time. The
increase in yellowing (delta YI) is measured (ASTM E313-73) for plaques with a
machine residence time of 24.5 minutes compared to plaques with a machine
residence time of 0.5 minutes. Results can be found in Table 4.
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WO 2007/024425 PCT/US2006/029976
Table 4

Formulations containing Tospearl® 120 again show less yellowing with increased
residence time at 330°C than formulations containing barium sulfate, which indicates
better suitability for use in rotation molding.
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CLAIMS:
1. A method for making a polycarbonate article comprising the steps of:
1) producing an aromatic polycarbonate by a melt reaction process comprising the
steps of:
a) transesterifying a diaryl carbonate and a dihydroxy compound in the presence of a
catalyst system to form an intermediate aromatic polycarbonate, wherein said catalyst
system comprises
(i) an alpha catalyst selected from the group consisting of alkali metal salts and
alkaline earth metal salts; and
(ii) a beta catalyst selected from the group consisting of quaternary ammonium
compounds and quaternary phosphonium compounds;
b) adding to said intermediate aromatic polycarbonate a catalyst quencher; and
2) rotation molding the polycarbonate into an article at a rotation molding temperature
from about 305°C to about 360°C.
2. The method of claim 1 wherein the aromatic polycarbonate is subjected to a
grinding step before rotation molding said polycarbonate into an article
3. The method of claim 1 wherein said aromatic polycarbonate has a molecular
weight from 25,000 up to about 36,000.
4. The method of claim 1 wherein the rotation molding process has a total
residence time of from 25 to 100 minutes.
5. The method of claim 1 wherein the aromatic polycarbonate further comprises
from about 0.01 to about 5% by weight of the total composition of a polyalkyl
silsesquioxane based diffusing agent, and from about 0 to 0.5% weight of the total
composition of a stabilizer.
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6. The method of claim 1 wherein the diaryl carbonate is diphenyl carbonate and
the dihydroxy compound is bisphenol A.
7. The method of claim 5 wherein the diaryl carbonate is diphenyl carbonate and
the dihydroxy compound is bisphenol A.
8. The method of claim 1 wherein the alpha catalyst is selected from the group
consisting of NaOH, KOH, and LiOH and combinations thereof, and wherein the beta
catalyst is selected from the group consisting of tetramethyl ammonium hydroxide,
tetramethyl ammonium acetate, tetrabutyl phosphonium hydroxide and tetrabutyl
phosphonium acetate and combinations thereof.
9. The method of claim 1 wherein the quencher is a sulphonic acid or a sulphonic
acid ester.
10. The method of claim 9 wherein the quencher is butyl tosylate.
11. The method of claim 1 wherein the aromatic polycarbonate has a Fries level of
less than 2000 ppm.
12. An aromatic polycarbonate article, wherein said the aromatic polycarbonate
has been produced by a melt transesterification process and the polycarbonate has a
weight average molecular weight between 25,000 and about 36,000 and wherein the
article has been produced by rotation molding.
13. The article of claim 12 wherein the aromatic polycarbonate has been produced
by a transesterification reaction using an alpha, beta catalyst system.
14. The article of claim 12 wherein the polycarbonate has a Melt Stability Index
of less than 8%, wherein Melt Stability Index is defined as the percentage increase in
MVR (ISO 1133, 300°C, 1.2 kg load) when measured at 4 minutes and 12 minutes
dwell time.
15. The article of claim 14 wherein the Melt Stability Index is less than 5%.
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16. The article of claim 12 wherein the aromatic polycarbonate has a Fries level of
less than 2000 ppm.
17. An aromatic polycarbonate article made from an aromatic polycarbonate
composition comprising
a. an aromatic polycarbonate;
b. 0.01 to 5% by weight of the total composition of a polyalkyl silsesquioxane based
diffusing agent; and
c. 0 to 0.5% by weight of the total composition of a stabilizer
wherein the article is produced by rotation molding.
18. The article of claim 17 wherein the aromatic polycarbonate has been produced
by a transesterification reaction using an alpha, beta catalyst system.
19. The article of claim 18 wherein the aromatic polycarbonate has a weight
average molecular weight between 25,000 and about 36,000.
20. The article of claim 17 wherein the polycarbonate has a Melt Stability Index
of less than 8%, wherein Melt Stability Index is defined as the percentage increase in
MVR (ISO 1133, 300°C, 1.2 kg load) when measured at 4 minutes and 12 minutes
dwell time.

A method for making a polycarbonate article is described wherein the article is made by
rotation molding a melt polycarbonate having a weight average molecular weight from
25,000 to about 36,000. The melt polycarbonate is produced by transesterifying a diaryl
carbonate and a dihydroxy compound in the presence of a catalyst system to form an
intermediate aromatic polycarbonate, wherein the catalyst system comprises a first
catalyst selected from the group consisting of alkali metal salts and alkaline earth metal
salts; and a second catalyst selected from the group consisting of quaternary
ammonium compounds and quaternary phosphonium compounds; adding to said
intermediate aromatic polycarbonate a catalysts quencher, and rotation molding the
aromatic polycarbonate at a temperature from about 305°C to about 360°C. Also
disclosed are polycarbonate light diffusive articles produced by rotation molding.