- 2 -
CROSSLINKED NANOSTRUCTURED CAST SHEETS
The present invention relates to the field of the
impact strengthening of cast acrylic sheets.
5
Polymethyl methacrylate (PMMA) is a material valued for
its excellent optical properties (in particular the
gloss and a high transparency with a transmission of at
least 90% of visible light) . However, it is also a
10 brittle impact-sensitive thermoplastic material. This
characteristic is related to the fact that the glass
transition temperature of PMMA is approximately 110°C,
so that, in this material, the polymer chains are not
capable of readily moving at ambient temperature. For
15 some applications, it is therefore necessary to improve
the impact strength of the PMMA while retaining its
transparency.
The impact strengthening of PMMA is generally improved
20 by virtue of the introduction into the acrylic resin of
an impact additive, known as core-shell additive, which
is provided in the form of multilayer spherical
particles. These particles are prepared by emulsion
polymerization and are recovered in the powder form by
25 atomization. They generally comprise a sequence of
"hard" and "soft" layers. It is thus possible to find
two-layer (soft-hard) or three-layer (hard-soft-hard)
particles. In the case of cast acrylic sheets, obtained
by polymerization of the mixture of monomers in a mold,
30 the impact additive is dispersed beforehand in the
mixture of monomers. In the case of extruded acrylic
sheets, the impact additive is compounded in the
extruder with the acrylic resin. In both cases, it is
necessary for the impact additive to be well dispersed
35 within the acrylic resin in order to maintain an
unchanging and homogeneous level of impact strength.
- 3 -
[Prior art]
International application WO 99/29772 describes the
impact strengthening of semicrystalline thermoplastic
5 resins using block copolymers of SBM type (styrenebutadiene-
methyl methacrylate block copolymers).
International application WO 02/055573 of the Applicant
Company describes the impact strengthening of a
10 methacrylate homo- or copolymer using a block copolymer
of ABA type in which B denotes a block obtained from a
diene, for example an SBM.
International application WO 03/062293 of the Applicant
15 Company describes a process of the impact strengthening
of a thermoplastic matrix using a B(-A)n block copolymer
composed of a block B and of n branches A and prepared
using the controlled radical polymerization technique.
This process applies to the strengthening of numerous
20 thermoplastics (PS, PC, PVDF, and the like) and in
particular to the manufacture of cast PMMA sheets.
The process of WO 03/062293 applied to the manufacture
of cast sheets is not capable of being transferred to
25 the industrial scale. This is because it exhibits the
disadvantage of requiring a stage of removal of
solvent, followed by a stage of redissolution of the
copolymer. First, these two unit operations, by
increasing the overall cycle time, affect the yield of
30 the process. Secondly, the stage of removal of solvent
is also capable of resulting in the formation of gels
in the B(-A)n copolymer, which affects its redissolution
in the mixture of monomers and, consequently, can
damage the transparency of the cast sheet.
35
Furthermore, according to the process described, in
particular in the examples, it is preferable, during j
the 2nd stage, to initiate the formation of the
i
- 4 -
branches A at the same time as that of the matrix. For
this, the monomer A is brought into contact with two
types of initiators, the conventional radical initiator
and the reactivatable block B. The monomer A is thus
5 consumed at the same time according to two competing
radical polymerization mechanisms, each exhibiting its
own kinetics. The control of this 2nd stage is highly
problematic as it implies matching the rates of
formation of the blocks A and the matrix. This implies
10 that it is necessary to adjust the nature of the
radical initiator to the block B and thus also to
carefully adjust the temperature cycle. In practice,
contradictory requirements are encountered and the
possible compromises generally result:
15
- in a premature separation during polymerization
of the copolymer B(-A)n, which migrates to the
interface of the sheet and mold. In this case,
sheets are obtained which are impossible to remove
20 from the mold and/or which are partially or
completely opaque;
- in unacceptable contents of residual methyl
methacrylate, which it is impossible to remove
once the sheet is complete.
25
An improvement is introduced in patent EP 1 858 939.
The cycle time of the process of this patent is
improved with respect to that described in WO 03/062293
as it does not require any stage of removal of
30 solvent/redissolution.
However, the mechanical properties of the materials
obtained with the processes described above are not
entirely satisfactory and an improvement in the
35 properties, such as impact strength and the flexural
modulus, is desired.
The Applicant Company has now -discovered that major
improvements in the impact strength and in the flexural
- 5 -
modulus are observed when some compositions comprise
crosslinking agents.
While the abovementioned documents often mention the
possible use of crosslinking agent, none gives examples
5 of or describes the properties of compositions
comprising them, in particular the advantage presented
by the use of crosslinking agent with a view to a
combined increase in the flexural modulus and the
impact strength.
10
[Brief description of the invention]
The present invention relates to a transparent and
impact-resistant crosslinked acrylic composition
15 consisting of a brittle matrix (I) having a glass
transition temperature of greater than 0°C and of
elastomeric domains having a characteristic dimension
of less than 100 nm consisting of macromolecular
sequences (II) having a flexible nature with a glass
20 transition temperature of less than 0°C, characterized
by a number-average molecular weight of between 30 000
and 500 000 g/mol.
[Detailed description]
25
The term "crosslink" is understood to mean a polymer or
copolymer, some of its chains of which are connected to
one another via covalent bonds or chemical or physical
interactions. These chains, connected to one another,
30 are for the most part distributed in the 3 dimensions
of the space.
As regards the matrix (I), this exhibits an overall Tg
of greater than 0°C, measured by DSC, and is compatible
35 with the methyl methacrylate homo- or copolymer.
The matrix (I) is prepared from methyl methacrylate and
optionally one or more monomer(s) chosen from:
I
- 6 -
I
I " • acrylic monomers of formula CH2=CH-C (=0) -O-Ri,
where R± denotes a hydrogen atom or a linear,
cyclic or branched C1-C40 alkyl group optionally
substituted by a halogen atom or a hydroxyl,
5 alkoxy, cyano, amino or epoxy group, such as, for
example, acrylic acid, methyl acrylate, ethyl
acrylate, propyl acrylate, n-butyl acrylate,
isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl
acrylate, glycidyl acrylate, hydroxyalkyl
10 acrylates or acrylonitrile;
• methacrylic monomers of formula 1
CH2=C(CH3) -C(=0)-O-R2, where R2 denotes a hydrogen I
atom or a linear, cyclic or branched C1-C40 alkyl
group optionally substituted by a halogen atom or
15 a hydroxyl, alkoxy, cyano, amino or epoxy group,
such as, for example, methacrylic acid, methyl
methacrylate, ethyl methacrylate, propyl
methacrylate, n-butyl methacrylate, isobutyl
methacrylate, tert-butyl methacrylate, 2-ethyl-
20 hexyl methacrylate, glycidyl methacrylate,
hydroxyalkyl methacrylates or methacrylonitrile;
• vinylaromatic monomers, such as, for example,
styrene or substituted styrenes, such as a-methylstyrene,
monochlorostyrene or tert-butylstyrene.
25
Methyl methacrylate is predominant. The matrix (I) thus
I includes a proportion of methyl methacrylate of between
i
I 50 and 100%, preferably between 75 and 100% and
! advantageously between 90 and 100%.
j 30
! As regards the macromolecular sequences (II) having a
I flexible nature, these exhibit a glass transition
! temperature of less than 0°C (denoted Tg and measured
i by DSC) . Furthermore, the number-average weight of the
! 35 macromolecular sequences (II) having a flexible nature
i with a glass transition temperature of less than 0°C is
greater than 30 000 g/mol, preferably greater than
60 000 g/mol and advantageously greater than
1
- 7 -
120 000 g/mol, but less than 500 000 g/mol. The
polydispersity is between 1.5 and 2.5.
The macromolecular sequences (II) are prepared from one
5 or more monomer(s) chosen from:
• acrylic monomers of formula CH2=CH-C (=0) -O-Ri,
where Ri denotes a hydrogen atom or a linear,
cyclic or branched Ci-C40 alkyl group optionally
substituted by a halogen atom or a hydroxyl,
10 alkoxy, cyano, amino or epoxy group, such as, for
example, acrylic acid, methyl acrylate, ethyl
acrylate, propyl acrylate, n-butyl acrylate,
isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl
acrylate, glycidyl acrylate, hydroxyalkyl
15 acrylates or acrylonitrile;
• methacrylic monomers of formula
CH2=C(CH3)-C(=0)-0-R2, where R2 denotes a hydrogen
atom or a linear, cyclic or branched Ci-C40 alkyl
group optionally substituted by a halogen atom or
20 a hydroxyl, alkoxy, cyano, amino or epoxy group,
such as, for example, methacrylic acid, methyl
methacrylate, ethyl methacrylate, propyl
methacrylate, n-butyl methacrylate, isobutyl
methacrylate, tert-butyl methacrylate, 2-ethyl-
25 hexyl methacrylate, glycidyl methacrylate,
hydroxyalkyl methacrylates or methacrylonitrile;
• vinylaromatic monomers, such as, for example,
styrene or substituted styrenes, a-methylstyrene,
monochlorostyrene or tert-butylstyrene.
30
The macromolecular sequences (II) are not prepared from
a diene. A person skilled in the art knows how to
j combine these monomers so as to adjust:
the overall Tg of the block B. In order to
35 obtain a block B with a Tg of less than 0°C, it
is necessary to use at least one monomer
I exhibiting a Tg of less than 0°C, for example
1 butyl acrylate or 2-ethylhexyl acrylate;
- 8 -
the refractive index of the block B, which has
to be as close as possible to that of the
matrix (I) in order to provide the best
possible transparency when the transparency is
5 required for the targeted application.
The macromolecular sequences (II) can be composed
solely of a monomer exhibiting a Tg of less than 0°C,
for example butyl acrylate or 2-ethylhexyl acrylate.
10 The macromolecular sequences (II) can also be composed
of at least one alkyl acrylate and of a vinylaromatic
monomer. Advantageously, the macromolecular sequences
(II) are composed of butyl acrylate and styrene in the
butyl acrylate/styrene ratio by weight of between 70/30
15 and 90/10, preferably between 75/25 and 85/15.
As regards the compounds which make the crosslinking
possible (the crosslinking agent), they are preferably
polyfunctional acrylic monomers, such as, for example,
20 polyol polyacrylates, alkylene glycol polyacrylates or
allyl acrylate, ethylene glycol diacrylate,
1,3-butylene glycol diacrylate or 1,4-butylene glycol
diacrylate, polyfunctional methacrylic monomers, such
as polyol polymethacrylates, alkylene glycol
25 polymethacrylates or allyl methacrylate, ethylene
glycol dimethacrylate, 1,3-butylene glycol
dimethacrylate or 1,4-butylene glycol dimethacrylate,
divinylbenzene or trivinylbenzene. Preferably, it is
1,4-butylene glycol dimethacrylate (BDMA). The content
30 of crosslinking agent is between 0.1 and 2% by weight,
with respect to the crosslinked polymer materials which
are a subject matter of the invention.
Preferably, the content of crosslinking agent is
between 0.4 and 2% by weight, with respect to the
35 crosslinked polymer materials which are a subject
matter of the invention, and more preferably still
between 0.6 and 0.8% by weight, with respect to the
- 9 -
crosslinked polymer materials which are a subject
matter of the invention.
According to a first embodiment of the invention, the
preparation of cast sheets made of methyl methacrylate
5 homo- or copolymer which are impact-reinforced using
the macromolecular sequences (II) comprises the
following stages:
1. preparing the macromolecular sequences (II) by
mixing, with the monomer(s) intended to form the I
10 macromolecular sequences (II), an alkoxyamine of 1
general formula Z(-T)n, in which Z denotes a polyvalent I
group, T denotes a nitroxide and n is an integer i
greater than or equal to 2;
2. mixing the macromolecular sequences (II) of
15 stage 1 with methyl methacrylate, the crosslinking
agent, optionally at least one comonomer M and at least
one radical initiator;
3. casting the mixture obtained in stage 2 in a
mold and then heating it according to a temperature
20 cycle in order to obtain a cast sheet.
The content of block B (the macromolecular sequences
(II) ) in the sheet is between 5 and 20% by weight,
preferably between 5 and 15% by weight, with respect to
25 the crosslinked polymer material which is a subject
matter of the invention.
According to a second embodiment of the invention, the
preparation of cast sheets made of crosslinked methyl
30 methacrylate copolymer which are impact-reinforced
using a block copolymer B(-A)n consisting of a block B
(the macromolecular sequences (II)) and of n branches A
(n being an integer between 1 and 3) comprises the
following stages:
35 1. preparing the block B by mixing, with the
monomer(s) intended to form the block B, an alkoxyamine
of general formula Z(-T)n, in which Z denotes a
I
- 10 -
polyvalent group, T denotes a nitroxide and n is an
integer greater than or equal to 2;
2. preparing the block copolymer B(-A)n by mixing
the block B obtained in stage 1 with the monomer (s)
5 intended to form the branches A; the monomers intended
to form the branches A are identical to those of the
matrix 1, that is to say methyl methacrylate, and
optionally at least one comonomer M, in the absence of
the crosslinking agent;
10 3. mixing the block copolymer B(-A)n of stage 2
with methyl methacrylate, the crosslinking agent,
optionally at least one comonomer M and at least one
radical initiator;
4. casting the mixture obtained in stage 3 in a
15 mold and then heating it according to a temperature
cycle in order to obtain a cast sheet.
The content of block B (the macromolecular sequences
(II)) in the sheet is between 5 and 20% by weight,
20 preferably between 5 and 15% by weight, with respect to
the crosslinked polymer material which is a subject
matter of the invention.
| As regards the block copolymer B(-A)n, the latter is
I 2 5 composed of several polymer blocks connected to one
j another via covalent bonds (see Kirk-Othmer 1
Encyclopedia of Chemical Technology, 3rd ed., Vol. 6, I
p. 798) . The block B is the core of the copolymer and
the blocks A represent the branches attached to the
j 30 block B. The block copolymer B(-A)n is thus composed of
I a block B and of n branches, n denoting an integer of
j greater than or equal to 2, preferably of between 2 and
! 10 and advantageously of between 2 and 8. The block
j copolymer B(-A)n, although possessing a block B, has
I 35 nothing to do with the impact-strengthening agents
| commonly referred to as core-shell agents, which are
composed of substantially spherical particles obtained
by emulsion polymerization.
(
j
1
I
! - 1 1 -
s
] In the context of the invention, it can be a triblock
j
| copolymer with, in this case, n = 2 (a central block
and 2 branches). Examples of triblock copolymer can be:
i 5 PMMA-b-poly(n-butyl acrylate)-b-PMMA
I PMMA-b-poly(n-butyl acrylate-co-styrene)-b-PMMA
PMMA-b-poly(isobutyl acrylate-co-styrene)-b-PMMA
poly(methyl methacrylate-co-n-butyl acrylate)-b-poly(nbutyl
acrylate-co-styrene)-b-poly(methyl methacrylate-
| 10 co-n-butyl acrylate)
j (b: symbol used to denote a block copolymer, co: symbol 1
\ used to denote a random copolymer).
| In the case where n > 2, the copolymer is said to be a
| 15 star copolymer.
j The block copolymer B(-A)n is prepared as was described
| above using an alkoxyamine Z(-T)n and monomers which
j make it possible to obtain the block B and the branches
20 A. Preferably, the copolymer B(-A)n is obtained using
| the alkoxyamine Z(-T)n and the controlled radical
I polymerization technique. By this technique, the
j branches A are terminated by a nitroxide, all or in
\ part according to the control of the polymerization.
1 25 The branches can be terminated in part by a nitroxide
j when, for example, there occurs a transfer reaction
! between a nitroxide and an alkyl methacrylate, as shown
! in the reaction below:
i \ „. I \ I "
N—O + CH2=C—C—OR2 *- N—OH+ CH2=C—C—OR2
30 O O
The block copolymer A(-B)n exhibits a number-average
molecular weight of between 40 000 and 1 000 000 g/mol,
preferably between 100 000 and 1 000 000 g/mol. The
} 35 polydispersity index is between 1.5 and 3.0, preferably
- 12 -
between 1.8 and 2.7 and more preferably between 1.9 and
2.7.
As regards the alkoxyamine, the latter is described by
5 the general formula Z(-T)n, in which Z denotes a
polyvalent group, T denotes a nitroxide and n denotes
an integer greater than 2, preferably between 2 and 10,
advantageously between 2 and 8.
10 n represents the functionality of the alkoxyamine, that
is to say the number of nitroxide radicals T which can
be released by the alkoxyamine according to the
mechanism:
| Z(-T)n^r=^ Z + nT
j 15 This reaction is activated by the temperature. In the
! presence of monomer(s), the activated alkoxyamine
| initiates a polymerization. The preparation of a
I copolymer polyM2-polyMl-polyM2 based on an alkoxyamine
j for which n = 2 is illustrated in the scheme below. The
j
I 20 monomer Ml is first polymerized after activation of the
| alkoxyamine and then, once the block polyMl is
i
| complete, the monomer M2 is subsequently polymerized:
|
I
| T-Z-T -ML*. T-CMxJ.-Z-CMxJ.-T
i I
| -^-+ T-(M2)jr-(M1)IS-Z-(M1)lt-(M2)y-T
| polyM2 polyMi polyM2
j 25 The principle of the preparation of block copolymers
| remains valid for n > 2.
i Z denotes a polyvalent group, that is to say a group
capable of releasing, after activation, several radical
I sites. The activation in question takes place by
i 30 cleavage of the covalent bond Z-T.
- 13 -
By way of example, Z can be chosen from the following
groups (I) to (VIII) :
«
in which R3 and R4, which are identical or different,
5 represent a linear or branched alkyl radical having a
number of carbon atoms ranging from 1 to 10, phenyl or
thienyl radicals optionally substituted by a halogen
atom, such as F, CI or Br, or else by a linear or I
branched alkyl radical having a number of carbon atoms
10 ranging from 1 to 4, or else again by nitro, alkoxy,
aryloxy, carbonyl or carboxyl radicals; a benzyl
radical, a cycloalkyl radical having a number of carbon
atoms ranging from 3 to 12, a radical comprising one or
more unsaturations; B represents a linear or branched
15 alkylene radical having a number of carbon atoms
ranging from 1 to 20; m is an integer ranging from 1 to
10;
R5-cJHCH2-0-C-(D)p-C-0-CH2iH-R6 (n)
0 0
in which R5 and R6, which are identical or different,
20 represent aryl, pyridyl, furyl or thienyl radicals
optionally substituted by a halogen atom, such as F, CI
or Br, or else by a linear or branched alkyl radical
having a number of carbon atoms ranging from 1 to 4, or
else again by nitro, alkoxy, aryloxy, carbonyl or
25 carboxyl radicals; D represents a linear or branched
alkylene radical having a number of carbon atoms
ranging from 1 to 6, a phenylene radical or a cycloalkylene
radical; p is an integer ranging from 1 to 10;
1
j
j
j
! - 1 4 -
i
i •
0
I II X II I
R7-CH-C-0-(CH2)q—N - ^ ^ N -(CH^-O-C-CH-Rg
1 (III)
I I I
(CH,)3-0-C-CH-Rg I
" II
O I
j in which R7, R$ and R9, which are identical or
j different, have the same meanings as R3 and R4 of the
1 formula (I) and q, r and s are integers ranging from 1
j 5 to 10;
j [T^ic.O.(CH2)t-CH-Rj (IV)
! in which Rio has the same meaning as R5 and R6 of the
j formula (II), t is an integer ranging from 1 to 4 and u
! is an integer between 2 and 6 (the aromatic group is
10 substituted);
j in which Rn has the same meaning as the radical Rio of
i
j the formula (IV) and v is an integer between 2 and 6;
! 1
] 0-CH2-CH-R13
I [W]w=P-0-CH2-(pH-R13 (VI)
0-CH2_CH-Rj4
I
j 15 in which R12, R13 and R14, which are identical or
different, represent a phenyl radical optionally
i substituted by a halogen atom, such as CI or Br, or
i else by a linear or branched alkyl radical having a
j number of carbon atoms ranging from 1 to 10, W
I 20 represents an oxygen, sulfur or selenium atom and w is
equal to 0 or 1;
I
i
i
! - 15 -
I
i
Q
R15-CH-C-0-CH2-CH-R16 (VII)
| in which Rj.5 has the same meaning as R3 of the 1
formula (I) and Ri6 has the same meaning as R5 or R6 of I
the formula (II);
JW
R22 Y R24
R-23
J 5
! in which R19, R20, R21/ R22/ R23 and R24 denote:
linear or branched C1-C20? preferably C1-C10,
alkyl groups, such as methyl, ethyl, propyl,
butyl, isopropyl, isobutyl, tert-butyl or
10 neopentyl, which are substituted or
I unsubstituted,
I - substituted or unsubstituted C6-C3o aryl groups,
; such as benzyl or aryl(phenyl),
saturated C1-C30 cyclic groups,
j 15 and in which the R19 and R22 groups can form part of an
j optionally substituted cyclic structure R19-CNC-R22 which
can be chosen from:
0 0 Q '^Q
in which x denotes an integer of between 1 and 12.
; 20
Use may be made, as examples, of the following
nitroxides:
j
I
i
i
I - 17 -
Tyv TyV ^ V
TEMPO OXO-TEMPO
j Particularly preferably, the nitroxides of formula (X)
i are used in the context of the invention:
j R* N — o * (X)
I RL
1 5 Ra and Rb denoting identical or different alkyl
| groups having from 1 to 40 carbon atoms which are
j optionally connected to one another, so as to form a
I ring, and which are optionally substituted by hydroxyl,
| alkoxy or amino groups,
j 10 RL denoting a monovalent group having a molar mass
i of greater than 16 g/mol, preferably of greater than
i 30 g/mol. The RL group can, for example, have a molar I
! mass of between 40 and 450 g/mol. It is preferably a J
phosphorus group of general formula (XI): J
x > " - «
i i5
in which X and Y, which can be identical or different,
]
i can be chosen from alkyl, cycloalkyl, alkoxyl,
aryloxyl, aryl, aralkyloxyl, perfluoroalkyl or aralkyl
; radicals and can comprise from 1 to 2 0 carbon atoms; X 1
20 and/or Y can also be a halogen atom, such as a j
' chlorine, bromine or fluorine atom. 1
Advantageously, RL is a phosphonate group of formula: 1
i
1
!
!
1
!
|
J
j - 18 -
0
y— (xii)
Rd—O
| in which Rc and Rd are two identical or different alkyl
! groups which are optionally connected, so as to form a
i ring comprising from 1 to 40 carbon atoms, and which
5 are optionally substituted or unsubstituted.
j The group RL can also comprise at least one aromatic
! ring, such as the phenyl radical or the naphthyl
| radical, for example substituted by one or more alkyl
| 10 radical(s) comprising from 1 to 10 carbon atoms.
I The nitroxides of formula (X) are preferred as they
I make it possible to attain good control of the radical
j polymerization of (meth)acrylic monomers, as is taught
| 15 in WO 03/062293. The alkoxyamines of formula (XIII),
I having a nitroxide of formula (X), are thus preferred:
! / Rh H / «\ (XIII)
! RL U—| Z
I \ la.
j in which:
Z denotes a polyvalent group and n is an integer
20 greater than or equal to 1;
I Ra and Rb denote identical or different alkyl
groups having from 1 to 40 carbon atoms which are
j optionally connected to one another, so as to form a
ring, and which are optionally substituted by hydroxyl,
I 25 alkoxy or amino groups,
RL denotes a monovalent group having a molar mass
of greater than 16 g/mol, preferably of greater than
30 g/mol. The RL group can, for example, have a molar
! mass of between 40 and 450 g/mol. It is preferably a
! 30 phosphorus group of general formula (XI):
I
!
|
i
- 19 -
) p — (XI)
j in which X and Y, which can be identical or different,
I can be chosen from alkyl, cycloalkyl, alkoxyl,
j aryloxyl, aryl, aralkyloxyl, perfluoroalkyl or aralkyl
5 radicals and can comprise from 1 to 2 0 carbon atoms; X
i and/or Y can also be a halogen atom, such as a
| chlorine, bromine or fluorine atom.
i
j Advantageously, RL is a phosphonate group of formula:
i Rc — o ||
y— (xii)
I Rd—O
| 10
I in which Rc and Rd are two identical or different alkyl
I groups which are optionally connected, so as to form a
ring comprising from 1 to 4 0 carbon atoms, and which
are optionally substituted or unsubstituted.
! 15
The group RL can also comprise at least one aromatic
ring, such as the phenyl radical or the naphthyl
; radical, for example substituted by one or more alkyl j
| radical(s) comprising from 1 to 10 carbon atoms.
I 20
! Mention may be made, as examples of nitroxide of
formula (X) which can be carried by the alkoxyamine
j (XIII), of:
- N-(tert-butyl)-l-phenyl-2-methylpropyl nitroxide,
j 25 - N-(2-hydroxymethylpropyl)-l-phenyl-2-methylpropyl
nitroxide,
- N-(tert-butyl)-l-dibenzylphosphono-2, 2-dimethyl-
! propyl nitroxide,
- N-(tert-butyl)-1-di(2,2,2-trifluoroethyl)-
30 phosphono-2,2-dimethylpropyl nitroxide,
- N-(tert-butyl)-l-diethylphosphono-2-methylpropyl
nitroxide,
I - 20 -
- N-(1-methylethyl)-1-cyclohexyl-l-diethylphosphono
nitroxide,
«
- N-(1-phenylbenzyl)-1-diethylphosphono-l-methyl-
I ethyl nitroxide,
5 - N-phenyl-l-diethylphosphono-2,2-dimethylpropyl
nitroxide,
! - N-phenyl-1-diethylphosphono-l-methylethyl
| nitroxide,
- N-(l-phenyl-2-methylpropyl)-1-diethylphosphono-
! 10 methylethyl nitroxide,
I - or also the nitroxide of formula ,
J The nitroxide of formula (XIV) is particularly
15 preferred:
DCH2CH3
! Q=P
DCHoCH3
CH^ ^H3
CH3—C —CH—N—C—-CH3 (XIV)
CH3 ^ CH3
It is N-(tert-butyl)-l-diethylphosphono-2,2-dimethyl- i
propyl nitroxide, commonly referred to as SGI for
simplicity.
j 20
The alkoxyamine (I) and in particular alkoxyamine
(XIII) can be prepared by recipes described, for 1
example, in US 5910549 or in FR99.04405. One method
which can be used consists in carrying out the coupling
25 of a carbon-based radical with a nitroxide. The
; coupling can be carried out starting from a halogenated
derivative in the presence of an organometallic system,
j such as CuX/ligand (X = CI or Br) , according to a
reaction of ATRA (Atom Transfer Radical Addition) type
- 21 -
such as described by D. Greszta et al. in
I Macromolecules, 1996, 29, 7661-7670.
i •
+ nCuJ01iguid
Z(-X)n+nT ; +* Z(-T)n
N /a solvent
- nCuXj/ligand
The alkoxyamines which can be used in the context of
5 the invention are represented below:
/ v SG1 0 0
SGI
TRIAMINS HOv f ° //—( SG/ V-COOH
HOOC— 5 the reactants. i
I
\ On conclusion of this 1st stage, the block B, i
« optionally mixed with the unconsumed monomer(s), is I
;
obtained. They can be removed by distillation under j
j 10 reduced pressure at a temperature of less than 80°C. In
the context of the first embodiment of the invention,
the block B constituting the macromolecular sequences
(II) is mixed with methyl methacrylate, the
crosslinking agent, optionally at least one comonomer M
15 and at least one radical initiator and is then cast in
a mold, which is subsequently subjected to a
temperature cycle in order to obtain a cast sheet. The
; thermal cycle comprises a first stationary phase with a
temperature of between 60 and 120 °C for a time which
20 can vary from 2 to 6 hours, followed by a second
stationary phase with a temperature of between 100 and j
I 150°C for a time which can vary from 1 to 4 hours. According to the second embodiment of the invention,
the block B, optionally mixed with the unconsumed
2 5 monomer (s) from the 1st stage, is subjected to a 2nd
stage of polymerization in the presence of the
monomer (s) intended to form the branches A, with the
exclusion of the crosslinking agent.
This stage can be carried out in the same reactor as j
30 the reactor employed in the 1st stage or in another
reactor. Preferably, the reactor is the same closed
reactor.
; If the conversion of the 1st stage is less than 100%,
35 the not completely polymerized monomer(s) from the 1st
stage may be found in the mixture. The mixture thus
I comprises the block B, the monomer(s) intended to form
I the block A which has/have been added and possibly the
i
- 26 -
* monomer(s) not completely polymerized in the 1st stage.
The proportion of block B in this mixture is between 1
and 20%, preferably between 5 and 15%.
5 The branches A are formed at a temperature of between
80 and 150°C, preferably between 80 and 130°C. The
duration of the polymerization can vary between
30 minutes and 8 hours, preferably between 1 and 1
4 hours, advantageously between 1 and 2 hours. As j
! 10 during stage 1, it is preferable to avoid the presence 1
of oxygen. To do this, the reaction mixture is I
generally degassed under reduced pressure and the
reactor is rendered inert by flushing with nitrogen or j
with argon after introducing the reactants. It is also '
i 15 possible to envisage adding nitroxide during this
! stage, it being possible for this nitroxide to be
different from that carried by the alkoxyamine. The
proportion of nitroxide added at this stage is between
0 and 20 mol%, with respect to the alkoxyamine,
20 preferably between 0 and 10 mol%.
During the 2nd stage, the conversion can vary between
10 and 100%. However, in order not to obtain an
excessively viscous mixture, it is preferable to limit I
25 the conversion to between 5 and 50%, preferably between
5 and 30%, so that the mixture obtained on conclusion
of this 2nd stage comprises the block copolymer B(-A)n
mixed with the unconverted monomer(s). This mixture is
commonly referred to as "syrup". I
30 !
!
•• !
During the 3rd stage, still according to the second
embodiment of the invention, methyl methacrylate, the
crosslinking agent, optionally at least one other
monomer M, at least one radical initiator and
35 optionally a chain-limiting agent are added to the
mixture obtained in the 2nd stage.
| This stage, carried out at ambient temperature, can be
I I
1 i
- 27 -
* carried out in another reactor or preferably in the
same reactor as that used in the 2nd stage.
Advantageously, the same closed reactor is used for the
three stages which have just been described.
5
During the 4th stage, the mixture from the 3rd stage is i
— i
cast in a mold and then heated. This final stage is j
very similar to that which may be encountered in the j
case of the processes for the manufacture of acrylic i
i
10 sheets already known. The mold is formed of two glass
sheets separated by a seal made of PVC, for example.
I The heating can, for example, consist in using a vessel
filled with water or a ventilated oven in which the i
! |
molds with their mixture are placed in a row and which
15 has a temperature which is modified.
According to the invention, the heating can be carried
I out at a constant temperature (isotherm) or else it can
j follow a very precise temperature program. The
20 temperature program generally comprises a first
i stationary phase at a temperature of the order of 70°C,
! followed by a second stationary phase at a temperature
of the order of 120°C. After cooling, the sheet
obtained is removed from the mold.
25
The process of the present invention is applicable to
\ the production of industrial acrylic sheets of various
thicknesses. A person skilled in the art knows how to
i adapt the manufacturing process, in particular as I
30 regards the 3rd stage (choice of the radical initiator j
and of the temperature program), according to the
thickness of the acrylic sheet.
As regards the cast sheet, the latter comprises a
35 crosslinked methyl methacrylate copolymer which
constitutes the matrix in which the macromolecular I
sequences (II) are homogeneously dispersed. The |
j macromolecular sequences (II) have a tendency to settle
i
- 28 -
down inside the matrix to give homogeneously
distributed domains. The matrix thus constitutes a
continuous phase of crosslinked methyl methacrylate
copolymer. The domains, visible using electron
5 microscopy or an atomic force microscope, exist in the
form of nodules having a size of less than 100 nm. The
size of the domains is estimated from the atomic force
microscope analyses. I
10 The sheets manufactured according to the present
invention can be used as windows, noise-reducing walls,
flat screens, and the like, or else can be converted to
various articles by thermoforming, cutting out,
polishing, adhesive bonding or folding. These sheets
15 can be used in particular to manufacture bathroom
fittings (baths, sinks, shower trays, and the like).
For this, the sheets are thermoformed in a way known to
a person skilled in the art.
20 The molecular weights are determined by steric
exclusion chromatography (SEC) or gel permeation
chromatography (GPC). The polymers are dissolved at
1 g/1 in THF stabilized with BHT. The calibration is
carried out using monodisperse polystyrene standards. I
25
Differential Scanning Calorimetry (DSC), in order to
estimate the glass transition temperature Tg, is
carried out according to Standard ISO 11357-2.
30 EXAMPLES
1st stage: Preparation of a block B based on butyl
acrylate and on styrene
The following are introduced into a 2 liter metal
reactor equipped with a propeller mixer, with a jacket
35 for heating by circulation of oil and with a
vacuum/nitrogen line:
• 616 g of butyl acrylate
• 84 g of styrene
- 29 -
" • 2.4 g of dialkoxyamine DIAMS (purity of 94% and
free SGI of 0.35%), i.e. 2.3 g of pure DIAMS
• 0.09 g of SGI with a purity of 85% (i.e., 0.077 g
of pure SGI), which represents a 5 mol% excess per
5 alkoxy functional group carried by the DIAMS,
taking into account the 0.35% of free SGI already
present in the DIAMS.
After introduction of the reactants, the reaction
10 mixture is degassed three times under vacuum/nitrogen.
The reactor is then closed and then stirring
(50 rev/min) and heating (set temperature: 125°C) are
begun. The temperature of the reaction mixture is 113°C
in approximately 30 min. The pressure stabilizes at
15 approximately 1.5 bar. The temperature of the reactor
is kept stationary at 115°C for 522 min. After cooling,
608 g of a mixture with a solids content of 67% are
recovered. The excess butyl acrylate is subsequently
removed by evaporation at 70°C under reduced pressure
20 for 3 h and replaced with 700 g of MMA. 1110 g of a 37%
solution in MMA of a "stripped" macroradical (freed
from its excess butyl acrylate) are thus recovered. The
butyl acrylate:styrene ratio by weight of the
macroradical obtained is 83:17. The GPC analysis of the
25 block B gives the following results: Mn: 120 000 g/mol;
Mw: 252 000 g/mol; polydispersity: 2.1.
Stage 2
The sheets are produced from a mixture of 10% by weight
30 of a poly(butyl acrylate-co-styrene) macroinitiator
macromolecular sequence prepared in stage 1, of methyl
methacrylate, of 1,4-butylene glycol dimethacrylate
(BDMA, in amounts which can vary according to the test
under consideration) and of 800 ppm of 1,1-di(t-amyl-
35 peroxy)cyclohexane. The mixture is subsequently cast in
a mold. The mold is first heated at a temperature of
approximately 90°C for approximately 3 hours.
The sheet is subsequently subjected to a post-
30 -
* polymerization at a temperature of approximately 130°C
for approximately 2 hours.
I I • - —- 1 [ • » - • • • i. i - m
Unnotched
Flexural
Charpy
%BDMA modulus
impact
(MPa) . ,
TEST ; (kJ/»aE
1 1 2100 I : 65
2 0^8 2200 65
3 f^JS 2180 j 60
4 0JL4 1983 53
5 0.3 1700 ! 38
j
6 0.2 1300 ! 37
• ., , ,
7 (Kl 8_51 43
[ 8 | 0 1 900 1 ; 40 |
2500 -I r70
• •
S. 2000 - • *
f 4 -5 Q£
1 1500 u • ._4Q3
? • . . a
J 1000 . • Flexural modulus (Pa) --30 |
| * • UN Charpy (kJ/m2) --2o"l
% 50Q - |2
EI -10
0 -I 1 1 1 1 1 h0
0 0.2 0.4 0.6 0.8 1 1.2
Content of crosslinking agent (BDMA w%)
5
It is observed that the impact strength (toughness) and
the flexural modulus are an increasing function of the
content of crosslinking agent with a maximum in the
10 vicinity of 0.7%.
|
i

- 31 -
• We claim: v
1. A transparent and impact-resistant crosslinked
acrylic composition consisting of a brittle matrix
5 (I) having a glass transition temperature of
greater than 0°C and of elastomeric domains having
a characteristic dimension of less than 100 nm
consisting of macromolecular sequences (II) having
a flexible nature with a glass transition
10 temperature of less than 0°C, characterized by a
number-average molecular weight of between 30 000
and 500 000 g/mol, in which the content of
crosslinking agent is between 0.1 and 2% by
weight, with respect to the crosslinked polymer
15 material.
2. The composition as claimed in claim 1, in which
the content of macromolecular sequences (II) is
between 5 and 20% by weight.
20
3. The composition as claimed in claims 1 and 2, in
which the crosslinking agent is chosen from polyol
polyacrylates, alkylene glycol polyacrylates or
allyl acrylate, ethylene glycol diacrylate,
25 1,3-butylene glycol diacrylate or 1,4-butylene
glycol diacrylate, polyfunctional methacrylic
monomers, such as polyol polymethacrylates,
alkylene glycol polymethacrylates or allyl
methacrylate, ethylene glycol dimethacrylate, 1,3-
30 butylene glycol dimethacrylate or 1,4-butylene
glycol dimethacrylate, divinylbenzene or
trivinylbenzene.
4. The composition as claimed in claims 1 and 2, in
35 which the crosslinking agent is butylenes glycol
dimethacrylate.
- 32 -
5. The composition as claimed in claim 1, in which
the macromolecular sequences (II) are prepared
from monomers chosen from acrylic monomers of
formula CH2=CH-C (=0)-O-Ri, where Ri denotes a
5 hydrogen atom or a linear, cyclic or branched
C1-C40 alkyl group optionally substituted by a
halogen atom or a hydroxyl, alkoxy, cyano, amino
or epoxy group, such as, for example, acrylic
acid, methyl acrylate, ethyl acrylate, propyl
10 acrylate, n-butyl acrylate, isobutyl acrylate,
tert-butyl acrylate, 2-ethylhexyl acrylate,
glycidyl acrylate, hydroxyalkyl acrylates or
acrylonitrile, methacrylic monomers of formula
CH2=C(CH3)-C(=0)-0-R2, where R2 denotes a hydrogen
15 atom or a linear, cyclic or branched Ci-C40 alkyl
group optionally substituted by a halogen atom or
a hydroxyl, alkoxy, cyano, amino or epoxy group,
such as, for example, methacrylic acid, methyl
methacrylate, ethyl methacrylate, propyl
20 methacrylate, n-butyl methacrylate, isobutyl
methacrylate, tert-butyl methacrylate, 2-ethylhexyl
methacrylate, glycidyl methacrylate,
hydroxyalkyl methacrylates or methacrylonitrile,
or vinylaromatic monomers, such as, for example,
25 styrene or substituted styrenes, a-methylstyrene,
monochlorostyrene or tert-butylstyrene.
6. The composition as claimed in claim 1, in which
the macromolecular sequences (II) are prepared
30 from butyl acrylate and styrene in the butyl
acrylate/styrene ratio by weight of between 70/30
and 90/10.
7. The composition as claimed in claims 1 to 4, in
35 which the macromolecular sequences (II) are
prepared by mixing, with the monomer(s) intended
to form the macromolecular sequences (II), an
alkoxyamine of general formula Z(-T)n in which Z
- 33 -
«
denotes a polyvalent group, T denotes a nitroxide
and n is an integer greater than or equal to 2.
8. The composition as claimed in claim 7, in which
5 the alkoxyamine corresponds to the following
formula:
' N SG 1 0 0
SGI being N-(tert-butyl)-l-diethylphosphono-2, 2-
dimethylpropyl nitroxide.
10
9. The composition as claimed in claim 7, in which
the alkoxyamine corresponds to the following
formula:
SGI
HOOC—