WO2006109915A1

WO2006109915A1 - Prepolymer for preparing high molecular weight polyethylene terephthalate

Info

Publication number: WO2006109915A1
Application number: PCT/KR2005/003830
Authority: WO
Inventors: Hee Young Kim; Yong-Ki Park; Kyung Koo Yoon; Won Choon Choi; Jong Yeol Jeon; Ilhoon Cha; Jong In Lee; Hang Duk Roh
Original assignee: Korea Research Institute Of Chemical Technology; Sk Chemicals, Co., Ltd.
Priority date: 2005-04-11
Filing date: 2005-11-11
Publication date: 2006-10-19
Also published as: KR100616100B1; WO2006109915A9

Abstract

The present invention relates to a prepolymer for preparing high molecular weight polyethylene terephthalate (PET), more particularly to a polyethylene terephthalate prepolymer that reacts an ethyleneglycol-based compound and terephthalic acid by esterification and prepolymerization and specifies intrinsic viscosity, concentration of a carboxyl group, ratio of the prepolymer components composed of at least one diethyleneglycol unit to those composed of ethyleneglycol units only that are coupled with terephthalic acid and the prepolymer for preparing high molecular weight polyethylene terephthalate that enhances the reaction rate over the equivalent rate without applying a catalyst or only using a small amount of the catalyst used conventionally to increase the reaction rate during additional polymerization, using the same.

Description

PREPOLYMER FOR PREPARING HIGH MOLECULAR WEIGHT POLYETHYLENE TEREPHTHALATE

[i]

Technical Field

[2]

[3] This invention relates to a prepolymer used for preparing high molecular weight polyethylene terephthalate. More particularly, this invention relates to a polyethylene terephthalate prepolymer prepared by reacting an ethyleneglycol-based compound with terephthalic acid by esterification and prepolymerization, thereby obtaining predetermined values of intrinsic viscosity, concentration of a carboxyl group, ratio of the prepolymer components composed of at least one diethyleneglycol unit to those composed of ethyleneglycol units only wherein either unit is subject to coupling with terephthalic acid unit. The thus obtained prepolymer, which can be used for preparing a high molecular weight polyethylene terephthalate, allows the reaction rate of its subsequent polymerization steps to be equal or better even without applying a catalyst for enhancing the reaction rate, and reduces significantly the amount of catalyst when its application is required.

[4]

Background Art

[5]

[6] Polyethylene terephthalate (hereinafter, referred to as ¹PET') has been widely used in manufacturing textile goods, chemical products such as bottles, packing materials, films, and materials such as resins for molding. PET for commercial use is in general required to have relatively high molecular weight although it may vary greatly depending on its uses.

[7] The process for manufacturing high molecular weight PET is as follows.

[8] Monomers and oligomers are prepared first and then formed into a prepolymer by a subsequent prepolymerization. Then, the molecular weight of the resulting prepolymer is increased to a desired level by an additional polymerization in a melt and/or solid state.

[9] That is, oligomers are prepared by reacting terephthalic acid (hereinafter, referred to as 'TPA') with ethylene glycol (hereinafter, referred to as 'EG') through esterification or by reacting dimethyl terephthalate (hereinafter, referred to as 'DMT') with EG through ester exchange reaction. Then, a prepolymer is prepared by prepolymerization mainly composed of polycondensation of the oligomers in a stirred-type or column- type reactor to retain the degree of polymerization (hereinafter, referred to as ¹DP') of about 20 - 50.

[10] Then, melt polymerization is performed to increase the molecular weight of the prepolymer with its DP becoming greater than about 60, which corresponds to the intrinsic viscosity (hereinafter, referred to as IV) of greater than about 0.5 dl/g. In polymerization of the highly viscous melt, it is essential that the reactor maintain a relatively high vacuum condition inside for prompt removal of EG vapor generated as a byproduct of the polycondensation. For this purpose, the reactor is maintained at about 270 - 300 °C and this results in many problems such as high-temperature heating, degradation of polymers, discoloring, generation of byproducts such as ac- etaldehyde and decrease in catalyst activity for polycondensation.

[11] As an example, US Pat. No. 6,559,271 (2003) discloses a process for preparing high molecular weight PET of IV >0.63 dl/g by melt polymerization in which an inhibitor to prevent decrease in catalyst activity and a substance reacting with the ac- etaldehyde byproduct are added to the polymerization step.

[12] Practically, it is very difficult to increase the molecular weight of PET to IV > 0.65 dl/g, namely, DP > 80 only by melt polymerization, since the higher the molecular weight, the higher the viscosity.

[13] Therefore, a high molecular weight PET of IV > 0.7 dl/g, useful for manufacturing bottles, containers, films and the like, can be prepared by the solid-state polycondensation, i. e., the solid-state polymerization which follows the melt-state polymerization. On the contrary, the molecular weight of IV < 0.65 dl/g is sufficient for the PET to be used for manufacturing polyester textiles.

[14] The solid-state polymerization consists of several steps comprising: (1) the granulation step by which solid particles are formed from the highly viscous melt obtainable through the melt-state polycondensation under high vacuum; (2) the pre- treatment step including heat treatment and/or crystallization of the particles; and (3) the solid-state polymerization step in a reactor the type of which includes a packed bed, a moving bed or a fluidized bed.

[15] The solid-state polymerization is advantageous in that a high molecular weight

PET with low content of acetaldehyde can economically be obtainable because the reaction is executed at a relatively low temperature of about 200 - 230 ⁰C as compared to that of the melt-state polycondensation. However, it is disadvantageous in that its reaction rate is very low because the polycondensation reaction proceeds at a relatively low temperature within the solid particles.

[16] In efforts to solve the above problem, several methods have been attempted for the solid-state polymerization. US Pat. No. 4,876,326 (1989) discloses a process for improving the rate of solid-state polymerization by forming a prepolymer into porous particles. However, the porous particles are not advantageous in that they readily generate powders before and after particle formation and solid-state polymerization. In general, the prepolymer used for solid-state polymerization is prepared in the form of chip such as sphere, pellet and semi-spherical pastille without pores. Therefore, for preparation of a high molecular weight PET by the solid-state polymerization of the prepolymer in a particle or chip form, it is important to find a method to optimize the kind and the amount of a catalyst to be added, which can also avoid side effects that may incur due to the use of the catalyst.

[17] In practice, oxides of metals including antimony (Sb), titanium (Ti), germanium

(Ge), iron (Fe), zinc (Zn), calcium (Ca), magnesium (Mg), cobalt (Co), cadmium (Cd), lead (Pb), manganese (Mn), niobium (Nb) or the like and their organic compounds are used as a catalyst to improve polymerization rate in preparing PET. But, this also has a few problems that the catalyst is very expensive, discolors the products, behaves like contaminants and deteriorates the physical properties of the PET products. Further, if a catalyst is used, its components remain in the final resin products. The catalyst residue then makes the PET resin products be susceptible to thermal degradation, thus deteriorates their stability under a thermal or hydrolytic condition. In this regard an additive may be used to inactivate the adverse functions of the catalyst by forming a complex with the catalyst residue, but this effort was revealed not to be effective. In fact, it has been found that antimony-based catalysts, most commonly used as a representative commercial catalyst, can be harmful to humans and environments, if overused. US Pat. No. 6,160,085 (2000) discloses that those catalysts, if applied for preparation of PET bottles, can deteriorate the physical properties of the products.

[18] Therefore, to prevent the side effects resulted from the use of a catalyst, it is preferable to exclude a catalyst in the process for preparing high molecular weight PET or to minimize its amount to be used. Generally, PET can hardly be prepared without applying a catalyst from the economical and technical aspects. Nevertheless, US Pat. No. 4,150,215 (1979) discloses a method for preparing PET without a catalyst. Precisely, it suggests that, being sonicated to minute particles with a size of less than 20 mesh, the prepolymer of 0.1 < IV(dl/g) < 0.4 can be polymerized to the high molecular weight PET of 0.942 dl/g by the solid-state polymerization at 240 - 250 °C in a fluidized bed or a packing bed without using a proper catalyst. In light of kinetics of solid-state polymerization, this is not a remarkable result because the polymerization rate increases as the size of particle becomes smaller and the reaction temperature becomes higher. Also, the method may cause a serious problem of agglomeration in particles because the solid-state polymerization is performed at a higher temperature, 20 - 40⁰C higher than the conventional temperature. Therefore, this method is not suitable for large-scale production of high molecular weight PET with reliable product quality.

[ 19] Besides, US Pat. No. 6, 180,756 (2001 ) discloses a method to reduce the catalyst content in preparing PET resin products made of high molecular weight PET. In this patent, a catalyst is added to prepolymer particles instantly during solid-state polymerization and immediately removed upon completion of the reaction to reduce the catalyst residue. However, it is noticeable that the addition and the removal of a catalyst should complicate the process of solid-state polymerization.

[20] Meanwhile, from the viewpoints of the efficiency and feasibility of the manufacturing process of high molecular weight PET, the low polymerization rate in a melt or solid state is still to be solved irrespective of the use of catalyst for preparation of the prepolymer. It is therefore very important for improving the polymerization rate how to adjust the respective molecular structures of various polymer components composing the PET prepolymer as well as their composition. In fact, it is preferred that the time required for the polymerization be reduced or the amount of a catalyst to be used be curtailed or excluded by optimizing the respective molecular structures of the polymer components composing the PET prepolymer as well as their composition.

[21] US Pat. No. 4,205, 157 (1980) discloses that a high molecular weight PET is obtainable if the prepolymer with IV of 0.15 dl/g and the carboxyl group content at the terminal ends of the polymer (hereinafter, referred to as '[-COOH] content') of less than 20% is prepared by applying a catalyst and then polymerized in a solid state (i.e., by solid-state polycondensation) using a fluidized bed reactor.

[22] On the contrary, US Pat. No. 4,238,593 (1980) discloses that a small [-COOH] content may not always give a good performance, and rather, an appropriate [-COOH] content of about 18 - 40% improves the rate of solid-state polymerization. More specifically, it is illustrated that the prepolymer having a considerable [-COOH] content in the range of 0.4<iV(dl/g)<0.62 can lead to the manufacture of a high molecular weight PET of IV>0.7 dl/g with the rate of solid-state polymerization being increased by 25 - 75%.

[23] In the meantime, US Pat. No. 5,663,281 (1997) discloses that it is advantageous in terms of the rate of solid-state polymerization to prepare a prepolymer with 0.1 <IV(dl/g ) <0.3 and [-COOH] content of less than 15% by use of a catalyst and a chemical composition which contains greater than a 1% stoichiometric excess of a glycol feed above the amount required.

[24] As described above with regard to the characteristics of prepolymers, conventional techniques have not been sufficient to improve the rate of solid-state polymerization but they are rather contradictory to each another. Further, conventional techniques do not teach much about the molecular structures of the polymer components and their composition. Thus there is limit in practical application of them for industrial purpose of preparing high molecular weight PET.

[25] It is well known that diethyleneglycol (hereinafter, referred to as ¹DEG') is generated as a byproduct in the process of manufacturing PET and is essentially included in both the prepolymer and high molecular weight PET. Also, it is known that the DEG byproduct is mostly generated during a direct esterification using TPA and EG as feed materials. The thus generated DEG molecules can exist either as a polymer-composing DEG-unit composing the molecular structures of the polymer components in the form of the DEG-unit (-CH CH OCH CH - segment) coupled with the TPA-unit (-OOC-C H -COO- segment) or as a DEG residue remaining inde-

6 4 pendently within the PET polymer in the form of a single molecule regardless of the structures of the polymer components.

[26] It has been widely known that, as the DEG content contained in the PET polymer increases by 1%, melting point (T ) of PET decreases by about 4 - 5 ⁰C. Further the m

PET resin with a high DEG content can hardly be applied to the manufacture of film- or foil-type products due to its low thermal stability. In addition, the PET having a high DEG content may result in side effects in the spinning process of textile products. Therefore, many researchers have attempted to reduce DEG content to within about 1 - 2 wt% in the industrial process for preparing PET.

[27] As an example, US Pat. No. 5,644,019 (1997) discloses a method by which the generation of DEG is suppressed as much as possible by using several different catalysts together to prepare a high molecular weight PET for textile use. Besides, US Pat. No. 4,204,070 (1980) illustrates the reduction of DEG content in the PET polymer according to the minimum use of EG feed by supplying TPA feed after dissolving in bis (2-hydroxyethyl) terephthalate (BHET), the intermediate product of the esterification .

[28] The DEG can be included in PET in the form of either a polymer-composing DEG- unit coupled with the TPA-unit or a DEG residue in a separate molecular form. However, their respective negative contributions to the physical properties of PET such as melting point and to forming processes have not been elucidated.

[29] It is acknowledgeable that the DEG residue existing around the polymer components as a independent molecular impurity tends to induce troubles in PET forming processes such as spinning process. However, it is still controversial whether the polymer-composing DEG-units greatly influence the physical properties or PET forming processes or not [G. W. Miller, Thermochimica Acta, 8, pp 129-140 (1974)].

[30] The above-mentioned prior literatures have not described the molecular structures of the polymer components composing the PET prepolymer in terms of its respective values of DP yet. For example, the difference in the contents of the EG-units (-CH CH -) and the DEG-units (-CH CH OCH CH -) among the glycol units coupled with the TPA-units for a certain value of DP and the effect of the differences in molecular structure upon the polymerization rate are not yet clearly understood. Further, various requirements to enhance the polymerization rate in a melt and/or solid state in relation with the content of the DEG-units and the composition of the polymer components have not been clearly explained yet.

[31] In order to solve the above-mentioned problems and ultimately to prepare high molecular weight PET without a catalyst or by using it only a minimal amount , t he present inventors have examined the molecular structures of the polymer components composing the prepolymer for preparing PET and the effect of the differences in molecular structure on polymerization rate .

[32] As a consequence, the present inventors found that the PET prepolymer satisfying some conditions as described hereinafter is able to enhance the polymerization rate over the equivalent rate even without applying a catalyst in a traditional manner, with high molecular weight PET being obtainable effectively . According to the conditions required, the PET prepolymer needs to have (i) intrinsic viscosity of 0.25 - 0.55 dl/g; (ii) concentration of the carboxyl group [-COOH] of less than 50 equivalents/10 g; and (iii) the prepolymer components having the structure of Formula 1, wherein P n

(DEG)/P (EG) ³ 1 for the cases when DP ³ 10, i.e., n (= m + k) ³ 10 , with P (DEG)ZP n n n

(EG) being the ratio of the number of the prepolymer components [P (DEG); n > k > n

1], in which the TPA-units are coupled with at least one diethyleneglycol unit (-CH CH OCH CH -; DEG-unit), to the number of the prepolymer components [P (EG); k

2 2 2 n

= 0 and n = m], in which the TPA-units are coupled only with ethyleneglycol units (-CH CH OCH CH -: EG-unit).

2 2 2 2

[33] The object of the present invention is to provide a PET prepolymer specified in the physical properties that can be used for preparing a remarkably high molecular weight PET even without a catalyst or only using a minute amount of the catalyst applied for enhancing the reaction rate.

[34]

Disclosure

[35]

[36] The present invention provides a PET prepolymer prepared by esterification between an ethyleneglycol-based compound and a terephthalic acid compound and by a subsequent prepolymerization, which has (i) intrinsic viscosity of 0.25 - 0.55 dl/g; (ii) concentration of the carboxyl group [-COOH] of less than 50 equivalents/10 g; and (iii) the prepolymer components having the structure of Formula 1, wherein P n

(DEG)ZP (EG) ³ 1 for the cases when n ³ IO, with P (DEG)ZP (EG) being the ratio of n n n the number of the prepolymer components [P (DEG); n > k > 1], in which the TPA- n units are coupled with at least one diethyleneglycol unit (-CH CH OCH CH -; DEG- unit), to the number of the prepolymer components [P (EG); k = 0 and n = m], in which the TPA-units are coupled only with ethyleneglycol units (-CH CH OCH CH -:

EG-unit).

[37] <Formula 1>

[38]

0 0 0

- - O-C-: O)-C-O-CH₂CH₂ ^■oc ©---<* CH₂CH₂OCH₂CH₂ ^k »

[39] wherein the positive integer n is the degree of polymerization representing the number of terephthalic acid units ( -OOC-C H -COO-; TPA-unit) repeated in the

6 4 respective prepolymer component, n = m + k ; k and m are in the range of O < k < n and O < m < n, respectively; k and m are integers but they are not zero simultaneously. [40] In addition, the present invention provides a PET polymer prepared by further polymerizing the prepolymer including the compound of Formula 1, wherein (a) concentration of the carboxyl group [-COOH] is less than 30 equivalents/10 g; (b) IV is 0.55 - 1.6 dl/g; and (c) melting point (T ) is 240 - 260 ⁰C. m

[41] Hereinafter, the present invention will be described more clearly as follows.

[42] The present invention relates to a PET prepolymer prepared by esterification of the ethylene glycol-based compound and the terephthalic acid compound to have a specific molecular structure and to a high molecular weight PET prepared by an additional polymerization of the prepolymer. As described above, the present invention relates to the PET with a high molecular weight (hereinafter, referred to as 'high MW PET') that is prepared by using a specified PET prepolymer (hereinafter, referred to as 'prepolymer') without a catalyst or only using a small amount of the catalyst, more rapidly than the conventional process.

[43] That is, the present invention has a technical feature to establish optimal conditions for preparing high MW PET. For this, the molecular structure of the prepolymer, the influence of contents of the EG-units (-CH CH -) and the DEG-units (-CH CH OCH

2 2 2 2 2

CH -), the correlation of reaction rate with those parameters are considered to improve the reaction rate over the equivalent rate of a conventional process even without applying a catalyst for enhancing the rate. It is natural that the optimal condition be not attained simply by those skilled in the art and any has not attempted to establish the above-mentioned conditions of a reaction. It is also understood that the effect of the present invention can be attained by optimizing all the requirements. Accordingly, the present invention has the technical feature to select and exploit the specified prepolymer for preparing the high MW PET. [44] Additional advantages, objects and features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.

[45] It is natural that other objects and advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof.

[46]

Best Mode

[47]

[48] Hereinafter, the PET prepolymer of the present invention will be described more clearly as follows.

[49] In the present invention, the PET prepolymer used to prepare a PET has (i) intrinsic viscosity of 0.25 - 0.55 dl/g; (ii) concentration of the carboxyl group [-COOH] of less than 50 equivalents/10 g; and (iii) the prepolymer components having the structure of Formula 1, wherein P (DEG)/P (EG) ³ 1 for the cases when n ³ 10, with P (DEG)/P n n n n

1], in which the TPA-units are coupled with at least one diethyleneglycol unit (-CH CH OCH CH -; DEG-unit), to the number of the prepolymer components [P (EG); k = 0 and n = m], in which the TPA-units are coupled only with ethyleneglycol units (-CH CH OCH CH -: EG-unit).

2 2 2 2

[50] In general, the high MW PET refers to the polyester with FV greater than about

0.55 dl/g, representing an average molecular weight, and to the polymer used for preparing high MW PET resin products and polyester fiber products. The prepolymer refers to the polymer which has IV of 0.25 - 0.55 dl/g of and is smaller in the average molecular weight than the high MW PET, but can be formed into the high MW PET rapidly by an additional polymerization in a melt state (liquid phase) and/or in a solid state. If the prepolymer has an IV less than 0.25 dl/g, it is difficult to prepare the high MW PET by additional polymerization due to small molecular weight. In contrast, if the prepolymer has IV greater than 0.55 dl/g, it reduces the rate of additional polymerization due to large molecular weight. Preferably, the range of IV mentioned above is maintained to prepare high MW PET. PET can be prepared by reacting terephthalic acid (TPA), as a terephthalic acid compound, and ethyleneglycol (EG) and/or diethyleneglycol (DEG), as an ethyleneglycol-based compound, through direct ester- ification and polycondensation. The esterification can be performed at about 230 - 260⁰C. The reaction product prepared by the esterification can include not only monomer components such as bis (2-hydroxyethyl) terephthalate (BHET), but also oligomers having various kinds of molecular structures by coupling the terephthalic acid unit (hereinafter, referred to as 'TPA-unit') (-OOC-C H -COO-) with the

6 4 ethyleneglycol unit (hereinafter, referred to as ^TEG-unit') or with the diethyleneglycol unit (hereinafter, referred to as 'DEG-unit') (-CH CH OCH CH -). Then, the temperature of the subsequent polycondensation is preferably selected within the range of 270 - 300°C.

[51] In the present invention, the prepolymer or high MW PET has the molecular structure coupling the TPA-unit with an EG-unit or a DEG-unit and comprises prepolymer components varying in their molecular weights. The DEG-units appears inevitably in the process for preparing PET to make the above-mentioned structure.

[52] That is, the polymer components composing PET can be grouped into three types of molecular structures as follows: (1) a PET homopolymer comprising the repeating units of [TPA-EG] coupling all the TPA-units only with the EG-units in the form of [-OOC-C H -COO-CH CH -] structure; (2) a polydiethylene terephthalate ho-

6 4 2 2 mopolymer comprising the repeating units of [TPA-DEG] coupling all the TPA-units only with the DEG-units in the form of [-OOC-C H -COO-CH CH OCH CH -]

^J 6 4 2 2 2 2 structure; and (3) a copolymer comprising two kinds of repeating units where the TPA- units can couple with the EG-unit as well as with the DEG unit.

[53] In order to quantitatively describe the requirements of a prepolymer for preparing the high MW PET, the molecular structures of the prepolymer components composing the prepolymer will be illustrated more clearly as follows.

[54] In each prepolymer component for a certain value of DP, the value of DP corresponds to the integer number, n, of the terephthalic acid units ( -OOC-C H -

6 4

COO-; TPA-unit) repeated in the respective prepolymer component; m indicates the number of [TPA-EG] repeating units; and k indicates the number of [TPA-DEG] repeating units . Then, each polymer component can be represented by -[TPA-EG-] -

[TPA-DEG] - of the general structure depicted in Formula 1. k

[55]

O O O

- O-C-:_vθ)-C-0-CH_£CH₂ ^■o-c <0>J-o-^, CH₂CH₂OCH₂CH₂ ^k «

[56] In the above Formula 1, k and m are respectively in the range of O < k < n and O < m < n; n is a positive integer; k and m are integers but they are not zero simultaneously. Then the value of (k + m) represents DP (= n); i.e., DP = n = (k + m).

[57] The terminal group of the prepolymer component can be -OOC-C H -COO-CH

CH OH, -OOC-C H -COO-CH CH OCH CH OH or the like. However, since the

2 6 4 2 2 2 2 conversion of the terephthalic acid, used as a starting feed material for preparing the prepolymer, the unreacted terephthalic acid itself or a fraction of polymer components are terminated as the carboxylic group [-COOH]. In the PET polymer, concentration of the terminal group [-COOH], i.e., [-COOH] content, can be measured by a well- established method of the wet chemical analysis when estimating the equivalents number (eq/10⁶ g) of the terminal group [-COOH] contained in 10⁶ g of the polymer.

[58] In general, it is preferable that [-COOH] content be lower than 50 eq/10 g, and more preferably, be maintained in the range of 5 - 40 eq/10⁶ g. If the concentration is below 5 eq/10 g, it takes an excessively long time to prepare the prepolymer. In contrast, if it is over 50 eq/10 g, the carboxylic group may give a negative effect on the subsequent additional polymerization.

[59] The physical properties of the prepolymer are determined according to the composition of the prepolymer components and their molecular structures. Briefly, the composition of the prepolymer can be largely grouped into two kinds of polymer components: the prepolymer components P (DEG) wherein each component contains at least one DEG-unit as represented by Formula 1 with k ³ 1 ; and the prepolymer components P (EG) wherein all the TPA-units are coupled only with EG-units. Here, in the prepolymer components, where n is DP representing the total number of TPA- units composing the respective component, the total number of the prepolymer components comprising only [TPA-EG] repeating units can be expressed as P (EG) with k = 0 and m = n. On the contrary, the total number of the prepolymer components, which respectively comprises at least one [TPA-DEG] repeating unit in addition to the [TPA-EG] repeating unit (m> 0), can be expressed as P (DEG) with k > 1 and DP = n. n

That is, the total number of the prepolymer components for each value of n is represented by [P (EG)+P (DEG)]. Then, the total number of the prepolymer n n components included in a whole prepolymer is expressed as the following Equation

(1): [60]

Ktotaύ ^ P'iE® + P'(DBG) ~ £ [P_n(EG) + P ,(DEG)]

^{*w l} (i)

[61] Theoretically, the value of P (EG) or P (DEG) can be zero. Practically, however, n n both P (EG) and P (DEG) cannot be zero if the basic units of the prepolymer is n n estimated based on its weight or volume. It is thus evident that P n (EG)>1 and P n

(DEG)>1 simultaneously.

[62] Based on these parameters, the composition of the prepolymer components having various molecular structures even at the case of the same DP (= n) can be represented by the ratio, P (DEG)/P (EG). Then the value of P (DEG)/P (EG) can behave as a rep- n n n n resentative factor for comparing the effects of the content of the DEG-units upon the reactivity of the prepolymer.

[63] In the present invention, the composition of the prepolymer to be used for efficiently preparing the high MW PET preferably satisfies the condition that , in case of the prepolymer components with DP(= n = m + k) ³ 10 representing the number of the terephthalic acid unit (TPA-unit) repeated in the respective prepolymer component, the respective component should have the molecular structure including the repeating [TPA-DEG] unit with P (DEG)/P (EG) ³ 1.0 , more preferably within the range of n n

1.0-10 . [64] If P (DEG)/P (EG) is less than 1 an additional polymerization of the prepolymer n n would not give any advantages with regard to PET production. In contrast, if P n

(DEG)/P (EG) is greater than 10 with P (DEG) becoming excessive, the physical n n properties of PET may be reduced. In case DP ³ 15, where DP (= n) represents the number of the terephthalic acid unit repeated in a prepolymer component, it is preferable that P (DEG)/P (EG) ³ 2, and more preferably, it should be maintained in n n the range of 2 - 40 to obtain a high rate of polymerization reaction. [65] The requirement of the prepolymer component associated with its molecular structure can change with DP, but P (DEG)ZP (EG) generally increases as DP (= n) of n n the prepolymer component increases.

[66] Concerning the molecular structure of each prepolymer component with DP (= n) ³

10, the respective numbers of the EG-units and the DEG-units coupled with TPA-units and P (DEG)/P (EG) can be measured by using the MALDI-TOF/MS (Matrix- Assisted n n

Laser Desorption Ionization-Time of Flight Mass Spectrometry) such as the Voyager System 4095 (Perseptive Biosystems Co. Ltd., USA).

[67] In addition to the requirement to improve the reaction rate of additional polymerization for preparing the high MW PET, the thermal property of a prepolymer may depend on the molecular structure and the composition of the prepolymer components. Preferably, melting point (T ) of the prepolymer should be maintained in the range of m

238 - 250 ⁰C in the present invention. [68] As described above, P (DEG)/P (EG) representing the composition of the n n prepolymer components in terms of DP (= n) can be used as a key parameter. Meanwhile , the content of DEG-units contained in the whole prepolymer composed of various kinds of prepolymer components can also be used to express the overall composition of the prepolymer.

[69] Preferably, the content of DEG-units can be expressed by the relative mole number of DEG-units per 1 mole of total TPA-units contained in the prepolymer. The content of DEG-units can be measured by the wet chemical analysis or by the H Nuclear Magnetic Resonance Spectroscopy. By conventional wet chemical analysis, the content of DEG-units composing the prepolymer and the content of the DEG residue remaining in the prepolymer as a mono-molecule independently from the prepolymer components are measured together and thus they cannot be discriminated. In contrast, by using the NMR, the content of DEG-units composing the prepolymer and the content of the DEG residue can be discriminated and be measured respectively. Pr eferably, the average content of DEG-units contained in the prepolymer can be calculated quantitatively by using the H NMR.

[70] In the present invention, the average content of total DEG-units that are coupled with total TPA-units contained in the prepolymer to be used for easy preparation of the high MW PET is preferable to be in the range of about 0.06 - 0.20 M per 1 mole of total TPA-units. If the content of the DEG-units is below 0.06 M, the additional polymerization for preparing high molecular PET cannot be executed effectively. In contrast, if the content of the DEG-units is over 0.2 M, the physical properties of the PET product may be deteriorated.

[71] As stated above, the prepolymer of the present invention is prepared by a process comprising steps of: (1) performing direct esterification (hereinafter, referred to as 'ES reaction') of a feed material in the form of slurry, a mixture of TPA and EG, to prepare an ES reaction intermediate (hereinafter, referred to as 'ES product'); and (2) performing prepolymerization focused on the polycondensation reaction of the monomers and oligomers composing the ES product. Preferably, the feed material in the form of slurry comprising TPA and EG can be prepared by the pure mixture of TPA and EG or by mixing EG and TPA together with a fraction of the ES product prepared in advance.

[72] In the present invention, to obtain the ES product to be used for preparing the prepolymer having a predetermined content of DEG-units, it is preferable that the mole ratio of EG moles per 1 M of DEG be greater than 1 (EG/TPA > 1), more preferably, in the range of 1.1 - 2.0 of mole ratio. If the mole ratio is below 1.1, the content of the DEG-unit can be limited in the ES product obtained by the esterification step. In contrast, if the mole ratio is greater than 2.0, unreacted EG will remain unnecessarily too much within the ES product.

[73] Concerning the glycol-based feed compound required for the ES reaction, EG may be used alone or used in the form of mixture by adding DEG feed to the EG feed. Preferably, the DEG feed is added to the feed mixture in the range of 0 - 0.08 M of DEG per 1 M of EG. If the DEG addition is over 0.08 M per 1 M of EG, the physical properties of the prepolymer will be deteriorated.

[74] The thus obtained prepolymer has IV of 0.25 - 0.55 dl/g. However, through an additional polymerization in a liquid and/or solid state, the prepolymer can easily be polymerized to the high MW PET with IV greater than 0.7 dl/g and melting point (T ) m of 240 - 260 ⁰C. The prepolymer according to the invention can be further polymerized by conventional methods in this art such as melt-state polymerization. Therefore, the high MW PET can be directly prepared from the prepolymer by utilizing a proper polymerization reactor or by applying appropriate reaction methods both of which are available at present.

[75] The high MW PET satisfying the requirements of the present invention can also be prepared by the solid-state polymerization, after the granulation step for forming the prepolymer in the form of particles and the heat treatment step. The solid-state polymerization can be performed by applying traditional processes using a fixed bed, fluidized bed or moving bed reactor or by applying the supercritical-fluid method.

[76] By performing both the melt-state polymerization and the solid-state polymerization in series, it is also possible to polymerize further the prepolymer to the high MW PET with IV of greater than 0.7 dl/g.

[77] It is natural that the present invention be not limited to the preparation of the very high MW PET having the high value of IV and can also be applied to the preparation of the high MW PET having lower IV than the above-mentioned PET. Precisely, the present invention can be applied to preparation of not only a high MW PET with IV of greater than 0.7 dl/g for manufacturing of PET resin products such as PET container or film but also a high MW PET with IV of 0.55 - 0.7 dl/g by curtailing the additional polymerization and is used for manufacturing polyester fiber products.

[78] As described hereinabove, the high MW PET prepared by additional polymerization, in a melt state and/or in a solid state, of the prepolymer according to the present invention has IV of 0.55 - 1.60 dl/g, [-COOH] concentration of 30 equivalents/ 10⁶ g, and melting point (T ) of 240 - 260⁰C.

[79] In order to reduce the reaction time required for the additional polymerization, in a melt state and/or in a solid state, for increasing the molecular weight of the prepolymer to a desired level, a conventional catalyst for polymerization may be used. However, according to the present invention, the catalyst can be used or its usage can be excluded. If the same kind of catalyst is used for the present prepolymer as for a conventionally prepared prepolymer, an equivalent effect of increase in reaction rate can still be achieved even with less than about 1/2 - 1/4 of the conventional dosage. For reference, when a lot of catalyst is required to prepare a high MW PET, the catalyst causes the problem of chemical instability during PET manufacturing and molding process of PET-applied products. In this case, for preserving stability, a stabilizer such as an organic phosphoric acid compound has been added the polymer in proportion to the amount of the catalyst used. Further, the addition of the stabilizer increases manufacturing cost, and the problems arising by the stabilizer itself often restricts the application range of such a stabilizer-including high MW PET. Therefore, it is another advantage of the present invention that addition of such undesirable compound is excluded in application of the prepolymer. [80]

Mode for Invention

[81]

[82] Practical and presently preferred embodiments of the present invention are illustrated as shown in the following Examples.

[83] However, it will be appreciated that those skilled in the art, in consideration of this disclosure, may make modifications and improvements within the spirit and scope of the present invention.

[84] <Example 1>

[85] For a c arboxylic acid compound, 4,486 g of terephthalic acid and for glycol-based compounds, 2,596 g of ethyleneglycol and 108 g of diethyleneglycol were used as feed materials and reacted by direct esterification to prepare an ES product sample in a reactor installed with a stirrer and heated through the wall. The esterification was proceeded at 230 - 255 ⁰C under about 2 - 2.5 bar, while removing the byproduct H O.

[86] After the esterification, unreacted glycol components and H O as byproduct were mostly removed from reactants inside the reactor at an ambient pressure and under vacuum and then, the prepolymer was prepared by polymerizing the ES product in a melt state under vacuum at 280 - 290 ⁰C. The resulting prepolymer was extruded to cooling water and solid-state chips with 1.4 + 0.1 mm of thickness were obtained.

[87] Concerning the molecular structure of each prepolymer component composing the prepolymer, the numbers of EG-units and DEG-units coupled with repeated TPA-units and P (DEG)/P (EG) were measured by using MALDI-TOF/MS (Voyager System n n

4095) and the average content of the DEG-units included in the prepolymer was calculated by using ¹H NMR as illustrated in Table 1.

[88] The polymerization characteristics of the prepolymer samples comprising various compositions and molecular structures were examined by an additional polycon- densation. In the present Example, the characteristics of the prepolymer samples were examined and compared with each other by performing the solid-state polymerization of the samples at the same conditions as a representative additional polymerization step, considering that the solid-state polymerization reveals more explicitly differences in reaction rates of the prepolymer samples compared with the melt-state polymerization whose results are very sensitive to operational conditions. As a result, the characteristics of the prepolymer samples were compared effectively.

[89] In order to perform the solid-state polymerization, the prepolymer samples were cut to have the average weight of 0.014 ± 0.002 g per one sample ship,. Two grams of the sample chips were packed in a quartz glass tube reactor (10 mm of inner diameter) installed in the heating box of a gas chromatography where temperature can be controlled constant. The reactor packed with the prepolymer samples was operated with nitrogen flowing constantly at the flow rate of 1.2 L/min, and was maintained at 210 ⁰C for 24 hours for the solid-state polymerization to prepare a polymer product, i.e., the high MW PET.

[90] Then, values of IV and melting temperature of the polymer product were measured and illustrated in Table 1.

[91] <Example 2>

[92] As described in Example 1, for carboxylic acid compound, 4,486 g of terephthalic acid and for glycol-based compounds, 2,388 g of ethyleneglycol and 216 g of di- ethyleneglycol were used as feed materials and reacted by direct esterification to prepare the ES product sample. The other procedures are the same as those described in Example 1. As a result, prepolymer samples that are different in [-COOH] content , intrinsic viscosity (FV) and P (DEG)/P (EG) value were prepared, respectively. n n

[93] Then, the IV and the melting temperature of the polymerized product, i.e., the high

MW PET sample, prepared by the procedure as described in Example 1, were measured and illustrated in Table 1.

[94] <Examples 3 - 4>

[95] Differently from the Examples 1 and 2, the stirred-type reactor was heated by using microwave. The other procedures are the same as those described in Examples 1 and 2. In order to prepare the prepolymer with relatively high IV, a catalyst solution, obtained by dissolving antimony oxide (Sb O ) in EG to 1.6 wt%, was applied to the polymerization step for preparing the PET prepolymer with Sb O concentration being adjusted to be 36 ppm (weight basis) within the prepolymer sample.

[96] As illustrated in Table 1, the prepolymer samples that are different in values of

[-COOH] content , IV and P (DEG)/P (EG) were prepared respectively. n n

[97] Then, IV and melting temperature of the polymerized product, i.e., the high MW

PET sample, prepared by the procedure as described in Example 1, were measured and illustrated in Table 1.

[98] <Comparative Examples 1 - 4>

[99] The experimental procedures were the same as those described in Examples 1 to 4.

As illustrated in Table 1, the various prepolymer samples were prepared by adjusting the composition of feed materials, the heating rate of the reactor and the concentration of catalyst so that the prepolymer samples could reveal different characteristics in the values of [-COOH] content , IV)and P (DEG)/P (EG). Among the samples obtained n n thereby, the prepolymer samples with IV of 0.25 - 0.55 dl/g were selected as comparative samples corresponding to the prepolymer samples of those Examples and the data are illustrated in Table 1. Then, IV and melting temperature of the polymerized product, i.e., the high MW PET sample, prepared by the procedure as described in Example 1, were measured and illustrated in Table 1.

[100] <Measurement of physical properties> [101] 1. Intrinsic viscosity (TV, dl/g): Measurement was executed according to ASTM D4603-96 [the Standard Test Method for Determining Inherent Viscosity of Poly(Ethylene Terephthalate) by Glass Capillary Viscometer] using the 60/40 wt% mixture of phenol and 1,1,2,2-tetrachloroethane as the solvent.

[102] 2. Melting temperature ( ⁰ C): Thermal analysis apparatus such as Differential Scanning Calorimeter (DSC) was used for measurement of melting temperature.

[103]

[104] As illustrated in Table 1, it was found that even if the prepolymer samples of Examples 1 and 2 were prepared without catalyst and relatively low in IV less than about 0.3 dl/g, the polymer products obtained by the additional solid-state poly- merization can yield the high MW PET. Especially, the prepolymer of Example 2 was more advantageous in respect of reaction rate for additional polycondensation to yield the polymer product with higher IV, since it has a higher value of P (DEG)/P (EG) n n than that of the prepolymer in Example 1.

[105] In addition, it is clarified that the prepolymer samples of Examples 3 and 4 were prepared by applying a catalyst for prepolymerization at a relatively lower concentration, 36 ppm, for a relatively high IV of about 0.4 dl/g, and can be further polymerized by the solid-state polymerization to the high MW PET with IV of 0.9 dl/g. Especially, the prepolymer of Example 4 was more advantageous in respect of reaction rate for the additional polycondensation to yield the polymer product higher in IV, since it has the higher value of P (DEG)/P (EG) than that of the prepolymer in n n

Example 3. [106] Besides, it was shown that the characteristic of P (DEG)/P (EG) in the n n prepolymer should influence melting point of the polymer product also.

[107] The samples of Comparative Examples not satisfying the physical properties required by the present invention will be described clearly as follows.

[108] The sample of Comparative Example 1 had a feature of the prepolymer with relatively high [-COOH] content and IV of 0.365 dl/g. The sample of Comparative Example 2 had a feature of the prepolymer with relatively low [-COOH] content and IV of 0.251 dl/g. The polymer products of Comparative Examples 1 and 2 were prepared by the additional solid-state polymerization of the respective prepolymer samples without catalyst under the same conditions as described in Example 1. However, it was found that the prepolymer samples of Comparative Examples did not show a sufficient increase in IV representing the increase of molecular weight.

[109] Especially, the prepolymer samples of Comparative Examples 1 and 2 were disadvantageous in terms of reaction rate for the additional polycondensation and inadequate for use in preparing polymer products with high IV, since the values of P n

(DEG)/P (EG) are relatively low compared with the prepolymer samples of Examples n

1 and 2. [110] It has already been predictable that the prepolymer samples of Comparative

Examples 3 and 4 reveal relatively high IV of 0.4 dl/g because they were prepared by using relatively very high concentration of catalyst compared with the cases for Examples 3 and 4. Thus the high MW PET with IV greater than 0.7 dl/g could unsur prisingly be obtained by the solid-state polymerization under the same conditions as described in Examples. However, it was confirmed that the prepolymer samples of Comparative Examples 3 and 4 are more disadvantageous in terms of reaction rate to produce the polymer products by the additional solid-state polymerization in spite of the large amount of catalyst applied, since their polymerization rate were revealed to be relatively lower than those of the prepolymer samples of Examples 3 and 4.

[Ill] Therefore, it is concluded that the prepolymer samples according to the present invention prepared in Examples 1 to 4 should be advantageous for manufacturing of the high MW PET, since they are polymerized rapidly even with a smaller amount of catalyst than the cases of conventional processes.

[112]

Industrial Applicability

[113]

[114] As described above, the prepolymer satisfying the requirements of the present invention allows the additional polymerization to be accomplished easily and rapidly without a catalyst or only using a small amount of the catalyst. The prepolymer can reduce the production cost in manufacturing of the high MW PET and effectively decrease or exclude the use of the conventionally applied catalysts which have been known to be toxic to human body and environment if included in PET products.

[115] Those skilled in the art will appreciate that the conceptions and specific embodiments disclosed in the foregoing description may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present invention.

[116] Those skilled in the art will also appreciate that such equivalent embodiments do not depart from the spirit and scope of the invention as set forth in the appended claims.

Claims

[1] A polyethylene terephthalate prepolymer prepared by esterification between an ethyleneglycol-based compound and a terephthalic acid compound and a subsequent prepolymerization, which has (i) intrinsic viscosity of 0.25 - 0.55 dl/g; (ii) concentration of the carboxyl group [-COOH] of less than 50 equivalents/10 g; and (iii) the prepolymer components having the structure of Formula 1, wherein P (DEG)/P (EG) ³ 1 for the cases when n ³ 10, with P (DEG)/P (EG) n n n n being the ratio of the number of the prepolymer components [P (DEG); n > k > n

1], in which the TPA-units are coupled with at least one diethyleneglycol unit (-CH CH OCH CH -; DEG-unit), to the number of the prepolymer components

[P (EG); k = 0 and n = m], in which the TPA-units are coupled only with n e tthhyylleenneeggllyyccooll units (-CH CH OCH CH -: EG-unit). <Formulal>

wherein the positive integer n is the degree of polymerization representing the number of terephthalic acid units ( -OOC-C H -COO-; TPA-unit) repeated in the

6 4 respective prepolymer component, n = m + k ; k and m are in the range of 0 < k < n and 0 < m < n, respectively; k and m are integers but they are not zero simultaneously.

[2] The polyethylene terephthalate prepolymer according to claim 1, wherein the ethyleneglycol-based compound is ethyleneglycol or a mixture of ethyleneglycol and diethyleneglycol.

[3] The polyethylene terephthalate prepolymer according to claim 1 or claim 2, wherein the ethyleneglycol-based compound is used in a ratio of 1.1 - 2.0 M per 1 M of the terephthalic acid compound.

[4] The polyethylene terephthalate prepolymer according to claim 2, wherein diethyleneglycol is used in the range of 0 - 0.08 M of diethyleneglycol per 1 M of ethyleneglycol when the ethyleneglycol-based compound is a mixture of ethyleneglycol and diethyleneglycol.

[5] The polyethylene terephthalate prepolymer according to claim 1, wherein P

(DEG)ZP (EG) ³ 2 for the cases of n ³ 15. n

[6] The polyethylene terephthalate prepolymer according to claim 1, wherein the melting point (Tm) of which is maintained in the range of 238 - 250 ⁰C.

[7] The polyethylene terephthalate prepolymer according to claim 1, wherein the average content of DEG-units coupled with the TPA-units in the prepolymer is in a ratio of about 0.06 - 0.20 M per 1 M of total TPA-units.

[8] The polyethylene terephthalate prepolymer according to claim 1, wherein the polyethylene terephthalate prepolymer is further polymerized to polyethylene terephthalate wherein (a) concentration of a carboxyl group ([-COOH]) is less than 30 equivalents/10⁶ g; (b) intrinsic viscosity is 0.55 - 1.6 dl/g; and (c) melting point (T ) is 240 - 260 ⁰C.