FORM 2
THE PATENT ACT 1970
(39 of 1970) & The Patents Rules, 2003

PROVISIONAL SPECIFICATION
(See section 10 and rulel3)
1. TITLE OF THE INVENTION:
2 APPLICANT
(a) NAME: Reliance Industries Limited
(b)NATIONALITY: Indian company incorporated under the Companies Act
1956
(c) ADDRESS : Reliance Technology Centre, B-4 MIDC Industrial Area,
Patalganga- 410220, Dist- Raigad, Maharashtra, India.
3. INVENTORS
(a) Name : Nadkarni Vikas Madhusudan
(b) Nationality : Indian
(c) Address : A18 Garden Estate, Off D P Road, Aundh, Pune -411007,
Maharashtra, India.
(a) Name : Wadekar Shreeram Ashok
(b)Nationality Indian
(c) Address : 204, Mohandeep Co-Op Housing Society Ltd.
Almeida Road, Chandanwadi, Panchpakhadi,Thane (W),400601
Maharashtra, India
(a)Name : Dubey Rajan
(b)Nationality : Indian
(c) Address : 201, Ambe Bhawan CHS, Plot No. 65 , Sector 12,Vashi,
Navi Mumbai-400703 Maharashtra, India
a)Name : Kesarwani Sanjay
(b)Nationality : Indian
(c) Address : 22D Katghar behind Shankar Garh House
Allahabad-211003, India
a)Name : Satpathy Anil Kumar
(b)Nationality : Indian
(c) Address : Village/Post Banasing Dist.Dhenkanal,
State Orrisa-759014, India
3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention :

TECHNICAL FILED OF THE INVENTION:
The invention relates to novel catalysts for producing polyester with increased rate of melt polymerization or/ and increased rate of solid state polymerization.
The invention also relates to the efficient processes for the production of polyester by adding the above catalyst in esterification or melt polymerization to increase rate of melt polymerization or / and rate of solid state polymerization.
The invention also relates to amorphous or crystalline low molecular weight prepolymers produced by the above processes.
The invention also relates to high molecular weight polyester resins produced from the low molecular weight prepolymers by the above processes.
BACKGROUND OF THE INVENTION:
Polyester resins such as polyethylene terephthalate (PET) are well known for making films, fibers and packaged container applications. A process for the production of high molecular weight polyesters comprises only melt polymerization optionally in combination with solid-state polymerization (SSP).
In the melt polymerization process for producing PET, base prepolymer of Intrinsic Viscosity (IV) of about 0.4 to 0.65 dl/g is produced. The base prepolymer is either in the form of cylindrical chip or spherical chip and is amorphous in nature. The base chips are then subjected to solid-state polymerization after crystallizing it in a crystallizer so as to avoid sintering or lump formation in the solid-state polymerization reactor. Depending upon the end application, polyester with different IV is produced by solid-state polymerization (ref: US 3,405,098, 3,544,525, 4,245,253, 4,238,593, and 5,408,035).
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Another polymerization process which is different than the conventional polymerization process is disclosed in US 5,510,454, 5,532,333, 5,540,868, 5,714,262, 5,830,982, and 6,451,966 which are incorporated herein as reference in their entirety.
In this polymerization process, a crystalline hemispherical prepolymer having IV of about 0.2 to 0.45 dl/g is formed using particle former process. Such low IV prepolymer particles can also be produced with other techniques that are well known in the art and can be subjected to solid-state polymerization for producing higher molecular weight polyesters. Examples of such particle formation processes are given in US patents namely; US 4123207 and US 7,008,203.
Prepolymer produced by these various techniques are then used as a precursor for solid-state polymerization process to increase the IV from about 0.5 dl/g to about 1.2 dl/g.
US patent 6,953,768 B2 describes antimony-free multi-component catalyst systems for the production of polyesters. The catalyst system comprises the element, Germanium and one more catalyst enhancers selected from aluminum, molybdenum, silicon, manganese, lithium or combinations thereof. The element is in the form of compounds, salts, compositions, oxides or organic complexes.
US patent 6,034,202 discloses non antimony containing polymerization catalysts for the condensation of polyesters. The catalyst is in the form of the form of a clear chlorine and/or bromine containing solution of a metal glycoxide and a metal glycolate having a pH in the range of from 0 to about 1.
US patent 5,242,645 discloses use of antimony and germanium catalyst combination for the production of polyester for fiber applications.
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US 6,699,545 discloses a method for increasing the polymerization rate of polyester polymers in the solid state by adding a catalytic amount of zinc p-toluenesulfonate to a polyester polymer melt, before solid state polymerization. Further the catalyst used is essentially free of antimony and germanium. This patent also doesn't disclose the use of group IV metal salts of Lewis acids such as tin methane sulfonate and tin para-toluene sulfonate for increasing the rate of melt polymerization and increasing the rate of solid-state polymerization.
US patent 6,180,756 discloses the addition of treatment agents based on sulfonic acids prior or during solid-state polymerization process for increasing solid-state polymerization rate. This patent also doesn't deal with use of group IV metal salts of Lewis acids such as tin methane sulfonate and tin para-toluene sulfonate for increasing the rate of melt polymerization and solid-state polymerization.
US patent 20020193555 discloses the use of titanium compounds for increasing reactivity of polyester polymerization
US patent 20020032300 relates to synergistic combinations of titanium containing catalysts and catalyst enhancers of carboxylic acid or oxalic acid or their Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba and ammonium salts and optionally containing a metallic catalyst such as antimony that are useful for manufacturing polyesters.
US patent 20030083191 discloses polyester polymerization catalyst comprising an aluminum compound and a phosphorus compound having a specific structure.
None of the above patents deal with the group IV metal salts of Lewis acids such as sulfonic acid catalyts for increasing the rate of melt polymerization as well as increasing the rate of solid-state polymerization.
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The basic process comprising particle former process and solid-state polymerization is disclosed in US 5,510,454 (herein after referred as '454 patent), US 5,532,333, US 5,540,868, US 5,714,262, US 5,830,982, and US 6,451,966. However, none of these patents disclose the use of catalyst such as group IV metal salts of Lewis acids like sulfonic acid particularly tin methanesulfonate or tin para-toluene sulfonate for increasing the rate of melt polymerization or /and increasing the rate of solid-state polymerization.
OBJECTS OF THE INVENTION:
An object of the invention is to provide novel catalysts such as group IV metal salts of Lewis acid like sulfonic acid for increasing the rate of melt polymerization or/ and increasing the rate of solid-state polymerization of polyester thereby increasing productivity.
Another object of the invention is to provide novel catalysts such as group IV metal salts of Lewis acid like sulfonic acid for increasing the rate of melt polymerization or/ and increasing the rate of solid state polymerization of polyester thereby reducing duration.
Another object of the invention is to provide an efficient process for production of high molecular weight polyester having IV of about 0.7 dl/g to 1.2 dl/g from the low molecular weight polyester prepolymer having IV of about 0.4 to about 0.65 dl/g by adding the above catalyst at any stage during esterification or melt polymerization but before the solid state polymerization thereby increasing the rate of melt polymerization or/and increasing the rate of solid state polymerization thereby increasing the productivity.
Another object of the invention is to provide an efficient process for production of high molecular weight polyester having IV of about 0.7 dl/g to 1.2 dl/g from the low molecular weight polyester prepolymer having IV of about 0.4 to about 0.65
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dl/g by adding the above catalyst at any stage during esterification or melt polymerization but before the solid state polymerization thereby increasing rate of melt polymerization or/and increasing the rate of solid state polymerization thereby reducing the duration.
Another object of the invention is to provide an efficient process for production of high molecular weight polyester having IV of about 0.5 dl/g to 1.2 dl/g from the low molecular weight crystalline polyester prepolymer of IV of about 0.2 to about 0.45 dl/g by adding the above catalyst at any stage during esterification or melt polymerization but before the particle former process thereby increasing rate of melt polymerization or/and increasing the rate of solid state polymerization thereby increasing the productivity.
Another object of the invention is to provide an efficient process for production of high molecular weight polyester having IV of about 0.5 dl/g to 1.2 dl/g from the low molecular weight crystalline polyester prepolymer of IV of about 0.2 to about 0.45 dl/g by adding the above catalyst at any stage during esterification or melt polymerization but before the particle former process thereby increasing rate of melt polymerization or/and increasing the rate of solid state polymerization thereby reducing the duration.
Another object of the invention is to provide low molecular weight polyester prepolymer having IV of about 0.4 to about 0.65 dl/g comprising, among other things, group IV metal salts of Lewis acids such as sulfonic acid.
Yet another object of the invention is to provide low molecular weight polyester prepolymer having IV of about 0.2 to about 0.45 dl/g comprising, among other things, group IV metal salts of Lewis acids such as sulfonic acid.
Yet another object of the invention is to provide high molecular weight polyester resins having IV of 0.7 dl/g to 1.2 dl/g from the low molecular weight polyester
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prepolymer having IV of about 0.4 to about 0.65 dl/g comprising, among other things, group IV metal salts of Lewis acids such as sulfonic acid.
Yet another object of the invention is to provide high molecular weight polyester resins of IV of 0.5 dl/g to 1.2 dl/g from the low molecular weight crystalline polyester prepolymer of IV of about 0.2 to about 0.45 dl/g comprising, among other things, group IV metal salts of Lewis acids such as sulfonic acid.
Yet another object of the invention is to provide high molecular weight polyester resins of IV of about 0.7 dl/g to 1.2 dl/g produced from a low molecular weight polyester prepolymer of IV of about 0.4 to about 0.65 dl/g comprising, among other things, group IV metal salts of Lewis acids such as sulfonic acid for the production of various packaging products such as performs, containers, films, sheets, fibre, filament or technical yarns.
Yet another object of the invention is to provide a high molecular weight polyester resins of IV of about 0.5 dl/g to 1.2 dl/g produced from a low molecular weight crystalline polyester prepolymer of IV of about 0.2 to about 0.45 dl/g comprising, among other things, group IV metal salts of Lewis acids such as sulfonic acid for the production of various packaging products such as performs, containers, films, sheets, fibre, filament or technical yarns.
Detailed Description of the invention:
According to the invention there is provided novel catalysts for the production of polyester with increased rate of melt polymerization or / and increased rate of solid state polymerization; the catalyst comprising group IV metal salts of Lewis acid such as sulfonic acid.
The group IV metal salts of Lewis acid are selected from tin methane sulfonate or tin para-toluene sulfonate. Group IV metal salts of Lewis acid used in the
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production of polyester is in the range of 10 ppm to 1000 ppm as a metal by weight of polyester, preferably 10 ppm to 150 ppm as a metal by weight of polyester. Tin methanesulfonate or tin para-toluene sulfonate is added in the range of about 10ppm to 1000ppm as metallic tin by weight of polyester, preferably about 10 ppm to 150 ppm.
According to the invention there is provided an efficient process for the
production of high molecular weight polyester from low molecular weight
polyester prepolymer with increased rate of melt polymerization or/ and
increased rate of solid state polymerization;
the process comprising :
esterifying at least one dicarboxylic acid or mono-ester thereof or di-ester thereof
or anhydrides thereof and at least one polyol to obtain an esterified mixture;
melt polymerizing the esterified mixture to obtain low molecular weight polyester
prepolymer;
adding the catalyst such as group IV metal salts of Lewis acid such as sulfonic
acid at any stage during the esterification or melt polymerization and
solid state polymerizing the polyester prepolymer to obtain high molecular weight
polyester.
The process further comprises particle former process after melt polymerization but before solid state polymerization. The process comprises addition of catalyst such as group IV metal salts of Lewis acid such as sulfonic acid at any stage during the esterification or melt polymerization but before particle former process. The group IV metal salts of Lewis acid are selected from tin methane sulfonate or tin para-toluene sulfonate. Group IV metal salts of Lewis acid used in the production of polyester is in the range of 10 ppm to 1000 ppm as a metal by weight of polyester, preferably 50 ppm to 200 ppm. Tin methanesulfonate or tin para-toluene sulfonate is added in the range of about 10ppm to 1000ppm as metallic tin by weight of polyester, preferably about 10 ppm to about 150 ppm.
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In one of the embodiments of the invention, there is provided an efficient process for the production of high molecular weight polyester resin having IV of about 0.7 dl/g to about 1.2 dl/g produced from low molecular weight prepolymer having IV of about 0.4 dl/g to about 0.65 dl/g with increased rate of melt polymerization or/ and increased rate of solid state polymerization; the process comprising
a) esterifying at least one dicarboxylic acid or mono-esters thereof or di-ester thereof or anhydrides thereof and at least one polyol at temperature in the range of 250°C to 290°C to obtain an esterified mixture;
b) melt polymerizing the esterified mixture at temperature in the range of 260°C to 300°C to obtain amorphous polyester prepolymer having IV of about 0.4 to about 0.65 dl/g;
c) adding the catalyst such as group IV metal salts of Lewis acids such as sulfonic acid at any stage during the esterification or melt polymerization process;
d) crystallizing the amorphous polyester prepolymer at temperature in the range of 100 -200°C to obtain crystalline prepolymer;
e) solid state polymerizing the crystalline prepolymer to obtain high molecular weight polyester resin having IV of about 0.7 dl/g to about 1.2 dl/g.
In another embodiment of the invention, there is provided an efficient process for
the production of high molecular weight polyester resin having IV of about 0.5
dl/g to about 1.2 dl/g produced from low molecular weight crystalline prepolymer
having IV of about 0.2 dl/g to about 0.45 dl/g with increased rate of melt
polymerization or/and increased rate of solid state polymerization;
the process comprising
a) esterifying at least one dicarboxylic acid or mono-esters thereof or di-ester
thereof thereof and at least one polyol at temperature in the range of
250°C to 290°C to obtain an esterified mixture;
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b) melt polymerizing the esterified mixture at temperature in the range of 260°C to 300°C to. obtain polyester prepolymer having IV of about 0.2 to about 0.45 dl/g;
c) producing crystalline prepolymer of polyesters by a particle former process at a temperature in the range of 110 to 160°C;
d) adding the catalyst such as group IV metal salts of Lewis acids like sulfonic acid at any steps during the esterification or melt polymerization but before particle former process;
e) solid state polymerizing the solid prepolymer particles to obtain a high molecular weight polyester resin having IV of about 0.5 dl/g to about 1.2 dl/g.
The term "polyester" as used herein means polyethylene terephthalate (PET), which intends to cover homopolymers and /or copolymers of polyethylene terephthalate.
Group IV metal salts of Lewis acid such as sulfonic acid are selected from Tin methane sulfonate or tin para toluene sulfonate. The group IV metal salts of Lewis acid such as sulfonic acid as catalyst is added in the range of about 10 ppm to 1000 ppm as a metal by weight of polyester, preferably 50 ppm to 200 ppm. Tin methanesulfonate or tin para toluene sulfonate is added in the range of about 10ppm to 1000ppm as tin by weight of polyester, preferably about 50 ppm to about 200 ppm. Tin methanesulfonate / tin para-toluene sulfonate as catalyst is added as liquid or slurry in ethylene glycol at any stage of esterification or melt polymerization. The dicarboxylic acid or its mono-esters thereof or di-esters thereof is selected from terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid or 4,4'-biphenyl dicarboxylic or any suitable dicarboxylic acids or mono-esters thereof or di-esters thereof, preferably isophthalic acid. The term polyol is intended to cover any suitable alcohol containing two or more hydroxyl groups known to those skilled in the art. The monoalcohol, diol or polyol is selected from monoethylene glycol, diethylene glycol, triethylene glycol,
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propylene glycol, dipropylene glycol, butylenes glycol or 1,4-cyclohexane diol or any suitable polyol. The process is a continuous or batch process.
According to the present invention there is provided low molecular weight polyester prepolymer having IV of about 0.4 to about 0.65 dl/g, the prepolymer comprising at least one dicarboxylic acid or mono-esters thereof or di-esters thereof or anhydrides, at least one polyol and group IV metals salts of Lewis acid such as sulfonic acid. The base polyester chips produced by the above process are amorphous in nature. These amorphous prepolymer chips are crystallized and subsequently used as a precursor for solid-state polymerization for increasing the IV.
According to the invention there is provided high molecular weight polyester resin having IV of about 0.7 dl/g to about 1.2 dl/g prepared from low molecular weight prepolymer having IV of about 0.4 to about 0.65 dl/g; the resin comprising at least one dicarboxylic acid or mono-esters thereof or di-esters thereof or anhydrides, at least one polyol and group IV metal salts of Lewis acid such as sulfonic acid. The high molecular weight polyester resin may also comprise any suitable additives for the improvement of performance of polyester article.
According to the present invention there is provided low molecular weight crystalline polyester prepolymer having IV of about 0.2 to about 0.45 dl/g comprising at least one dicarboxylic acid or mono-esters thereof or di-esters thereof or anhydrides, at least one polyol and group IV metal salts of Lewis acid such as sulfonic acid The base polyester chips produced by the above process are either cylindrical, or spherical or hemispherical or any other suitable shape. These crystalline prepolymer chips are used as a precursor for solid-state polymerization for increasing the IV.
According to the invention there is provided high molecular weight polyester resin having IV of about 0.5 dl/g to about 1.2 dl/g prepared from low molecular weight
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prepolymer having IV of about 0.2 to about 0.45 dl/g; the resin comprising at least one dicarboxylic acid or mono-esters thereof or di-esters thereof or anhydrides, at least one polyol and group IV metal salts of Lewis acid such as sulfonic acid. The high molecular weight polyester resin may also comprise any suitable additives for the improvement of performance of polyester article.
The polyester may be a linear or branched and may be a homo-polyester or contain comonomers upto 10 wt%.
Group IV metal salts of Lewis acid such as sulfonic acid are selected from Tin methane sulfonate or tin para toluene sulfonate. The group IV metal salts of Lewis acid such as sulfonic acid is added as catalyst in the range of about 10 ppm to 1000 ppm as a metal by weight of polyester, preferably 10 ppm to 150 ppm. Tin methanesulfonate or tin para toluene sulfonate is added in the range of about 10ppm to 1000ppm as tin by weight of polyester, preferably about 10 ppm to about 150 ppm.
According to the present invention there is provided use of resin for the production of polyester articles such as preforms, containers, fibers or filaments, films or sheets or technical yarn.
According to the invention the use of catalyst namely group IV metals salts of
Lewis acid such as sulfonic acid increases the rate of melt polymerization and
also increases the rate of solid-state of polymerization thereby increasing the
productivity of the polyester plant and it also reduces the duration of the reaction
and hence above processes are cost effective.
The present invention is further exemplified by the following non-limiting
examples.
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Example 1:
PET prepolymer having IV of 0.6 dl/g prepared by melt-phase polymerization process.
Purified terephthalic acid and monoethylene glycol (MEG) were charged in 1:2 molar ratio. To the above reaction mixture, 2 wt % Isophthalic acid, 290 ppm of Antimony trioxide catalyst based on antimony and 25 ppm NaOH were added. The esterification reaction was carried out at 256°C. Tin methanesulfonate based on 50 ppm as metallic tin was added at the end of esterification reaction. The oligomer obtained was then subjected to polycondensation in the presence pf 25 ppm of cobalt as Cobalt acetate and 25 ppm of phosphorous as phosphoric acid at temperature of 285°C to obtain a prepolymer having IV up to 0.6 dl/g. After achieving the desired prepolymer IV, it was drained and cut in a granular form for further processing. The granulated prepolymer was amorphous in nature.
Example 2:
PET prepolymer particles having IV of 0.26 dl/g prepared by melt-phase polymerization followed by particle former process.
Purified terephthalic acid and monoethylene glycol (MEG) were charged in 1:2 molar ratio. To the above reaction mixture, 2 wt % Isophthalic acid and 1.5 wt % diethylene glycol (DEG) were added. The esterification reaction was carried out at 280°C. The oligomer obtained was further polymerized at 290°C to raise the IV up to 0.26 di/g. Tin methanesulfonate having 50ppm as metallic tin was added during the melt polymerization. About 290ppm of antimony was added as a catalyst and 15 ppm P was added as a thermal stabilizer. A static mixer was put after every injection nozzle for adding any suitable additive, co-monomer for better dispersion. The low IV prepolymer melt was then passed through the 1.5 mm diameter orifice to form droplets on a continuous moving steel belt of particle former. These droplets were then crystallized on the particle former maintained at a temperature between 110 to 160°C and then collected for carrying out solid-state polymerization.
Example 3:
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Comparative for Example 1
PET prepolymer having IV of 0.6 dl/g prepared by melt-phase polymerization process.
Purified terephthalic acid and monoethylene glycol (MEG) were charged in 1:2 molar ratio. To the above reaction mixture, 2 wt % Isophthalic acid, Antimony trioxide catalyst containing 290 ppm antimony and sodium hydroxide containing 25 ppm of sodium metal were added. The esterification reaction was carried out at 256°C. The oligomer obtained was then subjected to polycondensation in the presence of Cobalt acetate containing 25 ppm of cobalt and phosphoric acid containing 25 ppm of phosphorous at temperature of 285°C to obtained a prepolymer having IV up to 0.6 dl/g. This prepolymer was considered as "Control" for the prepolymer prepared according to Example 1. After achieving desired prepolymer IV, it was drained and cut in a granular form for further processing. The granulated prepolymer was amorphous in nature.
Example 4:
Comparative for Example 2
PET prepolymer particles having IV of 0.26 dl/g prepared by melt-phase polymerization process.
Purified terephthalic acid and monoethylene glycol were charged in 1:2 molar ratio. To the above reaction mixture, 1.5wt % Isophthalic acid and 1.5 wt % diethylene glycol were added. The esterification reaction was carried out at 280°C. The oligomer obtained was further polymerized at 290°C to raise the IV up to 0.26 dl/g. About 290ppm of antimony was added as a catalyst and 15 ppm Phosphorous was added as a thermal stabilizer. A static mixer was put after every injection nozzle for adding any suitable additive, co-monomer for better dispersion. The low IV prepolymer melt was then passed through the 1.5 mm diameter orifice to form droplets on a continuous moving steel belt of particle former. These droplets were then crystallized on the particle former maintained at
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a temperature between 110 to 160°C and then collected for carrying out solid-state polymerization. This prepolymer particles was considered as "Control" for the prepolymer particles prepared according to Example 2.
Example 5:
Solid state polymerization
Amorphous chips obtained in the example 1 & 3 were precrystallized in a tumbler dryer at a temperature of usually 100 to 200°C for a period of two hours. These precrystallized chips desirably have 20 to 40 % crystallinity. These chips were then used as a precurser of solid-state polymerization. 20kg Crystallized prepolymer chips were subjected to solid-state polymerization at nitrogen gas temperature of 210°C. Samples were drawn every hour to monitor IV rise for each recipe. After achieving desired IV, the reaction was terminated and polymer was drained and collected.
Example 6:
Solid state polymerization
Crystalline prepolymer having IV of 0.26 dl/g obtained in the example 2 and 4, was solid-state polymerized under inert atmosphere to raise the IV up to 0.76 dl/g. The solid-state polymerization reaction was carried out at 235°C of nitrogen gas temperature. After achieving desired IV, the reaction terminated and polymer drained and collected.
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Table 1 : Data related to melt polymerization

Trial Target IV (dl/g) Polycondensation time (min)
Example 1 0.6 64
Example 3 99
As seen from table 1, melt polymerization time was less with tin methane sulfonate than that of control sample (i.e. without catalyst).
Table 2 : Data related Solid state polymerization

Trial Prepolymerprepared according to Example No. SSP residence time (Hrs) IV achieved (dl/g)
Example 5 1 10 0.92
Example 5 3 12 0.842
As per the data given in Table 2, substantial improvement in solid-state polymerization rate was observed with Tin methane sulfonate.
Table 3: Data related to melt polymerization

Trial No. IV (dl/g) N2 gas temp in Column reactor (°C) N2 gas flow inColumn reactor (pph)
Example 2 0.26 291.0 7.8
Example 4 291.0 8.7
Table 3 shows reduction in nitrogen flow in column reactor to achieve desired IV of 0.26 dl/g by addition of tin methane sulfonate. This indicates increase in melt polymerization reactivity with these novel compounds.
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Table 4 : Data related Solid state polymerization

Trial No. Prepolymerprepared according to Example No. N2gas temp (°C) SSP residence time (Hrs) IV (dl/g)
Example 6 2 235 9 0.778
Example 6 4 16 0.764
As seen from the table - 4, substantial reduction in solid-state polymerization time was observed indicating faster reaction rate with the use of tin methanesulfonate.
According to the present invention, no adverse effect on the perform clarity was observed due to the addition of Tin methane sulfonate.
Bottles of 1.5 L volume were produced using SIDEL SB01 single cavity blow moulding machine. Performance of the bottles produced with Tin methane sulfonate was comparable to the bottles produced without Tin methane sulfonate.