CA1162347A - Copolyesters, method of making same and packaging materials - Google Patents

Abstract

COPOLYESTERS, METHOD OF MAKING
SAME AND PACKAGING MATERIALS.

ABSTRACT

Disclosed are copolyesters based on terephthalic acid, ethylene glycol and bis (4-.beta.-hydroxyethoxyphenyl) sulfone made by solid state polycondensation of a lower molecular weight polymer thereof, a process for making same, and containers, packages and packaging materials made therefrom. The copolyester have low acetaldehyde content.

Description

~162347 i I Poly~ethylene terephthalate) resins are excellent j molding compounds ~or making packages and packaging materials.
In one important application such packaging materials and packages, such as bottles or packaging film are used to package : comestibles intendea for human consumption, wherein the resin comes in direct contact with the food or be~erage produ.ct packaged~ In recent years it has become increasingly appaxen~
that a disaavantage of usi~ such resins in the packaging of co~estibles is that in forml~hg the packaging materials or packages, such as film or a container or bottle, some thermal ¦ degradation o~ the product takes place, resulting in some cases ! in discoloration. More importantly, it has become apparent ¦ that an important product of such decomposition are aldehydes Il , ,~ I

~;1623'~7 such as acetaldehyde which affects the flavor of some food products such as beverages and, moreover, because of the presence of acetaldehyde therein, such beverages or foodstuffs may be considered to be unfit for human consumption by govern-mental regulatory bodies. The foregoing is recognized in U.S.
patent 4,064,112.
Various methods have been proposed to regulate the polymerization process and the handling of the resulting resins to minimize the formation and presence of acetaldehyde in the final packaging material or container. For instance, in the aforementioned U.S. patent it is stated that it is known to produce the high viscosity pol~esters by solid state poly-cond~nsation under an inert gas blanket or vacuum, and it is implied that this aids in minimizing the decomposition and the formation of aldehydes.
Presellt commercial methods for producing poly(ethylene terephthalate) resins of a suitable viscosity for molding produces polymers that are low enough in acetaldehyde content to satisfy standards for packaging of beverages in large bottles. However, improvement in the acetaldehyde content of such polymers is desired for making beverage bottles of smaller size such as 6-1/2 and 8 oz. sizes, since the ratio of surface area of the bottle walls to the volume of the bottle is much larger than in large bottles, such asri~or instance quart bottles. Improvement is desired also in other applications of such packaging resins for packaging foodstuffs and beverages and other comestibles.
It would be desirable to provide containers and packaging materials for packaging comestibles such as food-stuffs and liquid beverages made of polyesters based on tere-phthalic acid wherein the decomposition products, spec-fically 1;1623~

acetaldehyde, can be controlled to a lower value than in packaging materials and containers made from poly(ethylene terephthalate).
Objects, as well as aspects and advantages, of the invention will ~ecome apparent from a study of this specification.
According to one aspect of the invention there is provided a thermoplastic copolyester, having an inherent vis-cosity of over 0.65 dl/gm, a Tg of at least 82 C. and a melting point peak of at least 220C, which is the solid state polycondensation reaction product of a thermoplastic ~o-polyester which is the polymeric reaction product of reactants consisting essentially of IA) reactant(s) selected from terephthalic acid andits Cl to C4 alkyl esters, with (B) reactants, bis(4-~-hydroxyethoxyphenyl) sulfone and ethylene glycol, wherein the amount of said bis(4-~-hydroxyethoxyphenyl) sulfone is 2-12 mol percent of the amount A of reactantls), the combined amount of B reactants is about 110 to 300 mol percent of the amount of A reactant(s), prepared by melt polymerization to yield a copolyester having a lower inherent viscosity which is in the range 0.2 to 0.7 dl/gm., said solid state copolyester being more resistant to decomposition in the molten state to fo~rm acetaldehyde than (1) the same copolyester of the same or lower inherent viscosity but made entirely by polymerization and condensation in the molten state or (2) polylethylene terephthalate)made by solid state polycondensation or by melt polymerization.
In another important aspect of the present invention there are provided plastic containers made by melt forming the described improved copolyesters of the present invention.
It has been discovered that the new copolyesters made B

with 2-12 percent charged bis(4-~-hydroxyethoxyphenyl) sulfone (herein called BSE) can be made having a crystalline melting point of at least 220 C, or 221C, and that such polymers can be crystallized to contain sufficient crystallinity to permit solid state reaction to a higher molecular weight, while higher percentages of BSE yield polymers of lower crystallinity and lower melting point, or with no tendency to crystallize. As a consequence, no practical method can be devised to produce copolyesters by solid state polycondensation where such co-polyesters contain much over 12 percent BSE. Thus, the polymer cannot be maintained in particulate form during polycondensation because it cannot adequately be crystallized. Therefore, if a nonparticulate mass is heated for polycondensation the reaction would scarcely proceed because of the inability of the ethylene glycol to diffuse to the surface of the mass to be withdrawn from the reaction zone.
It has further been discovered that copolyesters having the percentages of BSE recited herein are intrinsically very much more thermally stable at working temperatures above their DSC melting points when solid stated according to the present invention than (1) when made by melt polymerization alone or

(2) poly ~et~ylene terephthalate).
While the prior art has melt polymerized, crystallized poly(ehtylene terephthalate) while flushing with nitrogen, then the crystalline prepolymer is heated to effect polycondensation in the solid state below its melting temperature such polymers are intrinsically less stable at working temperatures above their melting points and contain more acetaldehyde after ex-trusion to form film, sheet or containers.
Furthermore, I have discovered that inclusion of 2-12 percent BSE lowers the-melting point and this further minimizes ~162347 the decomposition products, such as acetaldehyde, in containers and packaging materials such as film and sheet because a lower extrusion temperature can be employed since the melting point is lower than poly(ethylene terephthalate) having no such additive.

, . 15080 !' ' t . ;. l i ,` llfi23~7 1 ` !
.

i. ~ccording to another aspect of the present invention ~ there is provided a process for making a thermoplastic copolyester ! which is intxinsicall~ more stable than poly(ethylene terephtha-il late) toward decomposition to form unwanted proaucts such as ! acetaldeh~de, which comprises (1) melt polymerizing reactants consisting essentially ~' . (A) reactant(s) selected from terephthalic acid and its C1 to CL~ alkyl esters with j (B) reactants, bis(4-~-hydroxyethoxyphenyll i~ sulfone and ethylene glycol, wherein the amount of said bis(4-~-hydroxyethoxyphenyl) sulfone I' is 2-12 mol percen~ of the amount ~ of reactant(s), and the ¦ combined amount of B reactants is about 110 to 3~0 mol percent j, of the amount of A ~eactant(s), u~il the polymeric reaction lS ¦, product has an inherent viscosity of 0.~ to 0.7 dl¢gm., i (21 cooliny the copolyester from step (1) to a solid Il state, reducing it to particulate form and heat crystalliæing .
¦', the particulate copolyester, and . (3) effec~ing solid state reaction of said particulate i copolyester by polycondensation thereof, in a temperature range from 180~C to just below the temperature of the onset of melting as indica~ed by a thermogram d ~ermined using a differential scanning calorimeter, to a higher inherent ~iscosity than the ! product of step (1), said higher viscosity being at least 0 . 65 i dl/gm.
In the crystallization step the particulate copolyester i is typically flushed with a dry gas such as nitrogen during il this step, as is customary.
1l, !

30 j~
.1, i ~ 2347 , 15080 i ~, In the solid state polymeri~ation step the flushing ' gas can be nitrogen, CO2, or other inert gases, or a vacuum ; can be used. If desired, a partial vacuum can be used in , conjunction with a flow of one of the foregoing purge i, gases.
!~ In the foregoing process of my invention the highest ~, temperature employed in the melt polymerization step is usually ¦ not over 280C,, preferably not over 275C., but is usually at ~', least 260C, j The crystallization step is usually effected mainly in l~ the temperature range 120 to 180C, If the temperature is ~oo il low, the crystallization rate will be impracticably slow; if ¦¦ too high trouble with sticking and ayglomeration is encountered, ¦¦ However, during the latter stages of crystallization the crys-tal ! lization temperature can be above 180C~ without sticking I because as crystallization proceeds the sticking temperature ¦ becomes higher with the increasing proportion of crystalline polymer contained in the product. Some routine experimentation ¦
may be re~uired in a given case if one wants to ef*ect the latter sta~es of crystallization at the highest possible temperature `
without encoun~ering sticking, The lowest temperature for any practicably rapid rate of reaction in the polycondensa~ n step of the present process ¦ is about 180C. This limits the amount of BSE that can be ¦ included since much over 12 percent results in a polymer that has so few crystals tha~ it simply sticks and agglomerates when ¦
¦ attempting the solid state polycondensation at this temperature.j See Example 11. The lower limit of BS~ is governed by the ~act ¦
~ that lower amounts do not form a polymer much more s~able than I PET. Compare the acetaldehyae amounts ~ormed at temperatures , above the melting point peak for Examples ~ (2%BSE), 6 (1%BSE) ¦ and 7 (PET). ii ~ 47 ' 15~80 , j~ The solid stat,~ polycondensation step of the invention ,, can be e~fected from 180~C., as stated, up to the temperature ! Of the onset o~ melting as indicated by the DSC thermogram.
' This is the temperature at which the curve first rises slightly , above the horizontal toward the melting peak of the thermogram.
Reference is made to a typical or schematic thermogram sho~n in U. S. patent 3,822,332. The onset of melting for ~he present li products ranges from about 197C. for 12 percent BSE (Example 5 ¦l up to about 224C. for 2% BS~ (Example ~). Onset of melting is ¦~ 205C. for 7 percent BSE (Example 2). Usually, the maximum temperature during the solid state reaction step is no more than 5C. below the onset of melting temperature; this is in order to avoid any ~uestion of incipient ætickiness leading to a~glomeration of the particulate pol~mer. Thus, the solid state 1, polycondensation temperature is always below about 224UC., ¦ preferably below about 219C., based on the 2 percent BSE
copolyester, ha~ing the highest meiting point peak temperature.
From the foregoing discussion of temperature, it will I also be apparent that polycondensation can begin auring the 20 j latter stages of the crystallization step. In other words, the two steps can overlap to a certain extent in a given case.
The foregoing process of the present in~ention has numerous advantages. Thus, not only is a more stable, impxoYed copolyester produced than in the case of poly(ethylene terephtha-late) but several process aavantages result. Thus, for a given temperature I have discovered that the rate of increase in molecular weightr as reflected in relati~e increase in inherent ¦ viscosity, is more rapid than in the case o the solid state I polymexization (polycondensation) of poly(ethylene terephthalate) 30 ~ This is surprising since the rate of inherent viscosity increase i , -8-'f`
~ ~ ' 150~0 1` 116i2347 of poly(ethylene terephthalate) and ~he present copolyester in '~ the molten state are about the same. ~or instance, compare ¦I Examples 12 and 13.
¦ This more rapid reaction in ~he present system usin~
~ the co-reactant, BSE, allows the use of lo~er solid state J~ polymexization temperatures, thus saving in heat energy.
', Furthermore, use of such lower temperatures helps minimize ¦' thexmal decomposition, thus minimizing the formation of unwanted I decomposition products, such as acetaldehyde in particular.
j Finally, of course, the present solid statin~ polycondensation ~ pxocess produces polymers inherently more stable at tempera~ures ¦~ exceeding the polymer meltin~ points. Thus, the initial step ¦' in ~orming containers, such as bottles, or packaging materials, such as film or sheet, is a melt ~orming step wherein the molten copolyester is melt formed by extrusion to make a parison or preform, as the initial step in making a bottle or container, or film or sheet is extruded directly.
~hen it is stated herein that the reactants "consist I essentially of" certain reactants, this means that such re-20 ¦ actants are essential, but that the usual other ingredients can be included, such as colorants, inert fillers, pol~merization catalysts, cross-linking ayents to improve melt strength (see my Belgian paten-t 872,792 having an e~fective date under 35 U.S.C. 102~a) and (b) of March 30, 1979, whereln from 0.1 to 0.7 mol percent of trimellitic acid anhydride is included ¦ to increase melt strength). Such other ingredicnts can be included if they do not deleteriously affect the basic and novel characteristics of the products o~ my invention or of l the process o~ the present inven-tion, as they are described 1, herein.

il _9_ ~ 1 ` 105~0 !
, In the following examples the various properties were ¦ determined as follows:
i The inherent viscosities were measured at 25C., using 1 a solution of 0.25 gms. of polymer dissolved in 100 milliliters of a mixture of 3 weight parts phenol wi~h 2 weight parts 1,1, 1 2,2 tetrachloro-ethane. All polymers of the invention have il inherent viscosities of over 0.65 deciliters per gram measured ~ in this manner.
j, The glass transition temperature, Tg, the melting point ¦ temperature, Tm and the crystallization temperature, ~c were ¦~ determined using a Perkin-Elmer differential scanning calorimeter model DSC-2, in a manner similax to that described in U. S.
patent 3,822,332 issued July 2, 1974, using a heating rate of Il 10C./minute~ As is well-known these values are all essentially !! the same for the prepolymer, the product of the melt polymeri-¦¦ zation stepl as for the inal, higher viscosity product of thesolid state polyconaensation- This is illustrated by comparing ! the ~alues for Example 4 herein with Example 8 of my Belgian i patent 872,792.
Examples 1-5 are examples of copolyesters and processes within the scope of the invention and each has the combination of properties set forth hereinbefore for copolyester compositions and processes of the invention.
I The determination of acetaldehyde generated by the 25 ¦ pol~mers gi~en in the e~amples and in Table 1 was effected as follows:
A 100 mg ground p~lymer samp~e, about 10-40 mesh size, was weighed into a glass test tube. The size of the test tube I was 1.1 cm inside diameter and 10 cm long. The content of the glass tube was flushed with nitrogen gas and sealed with a ¦ rubber stopper. Then the sealed tube was transfered into a heating block that was ~aintained at the re~uired temperature l , 10580 ;Z347 , (given in the examples). After 5 or 10 minutes~ a 1 cc head-, space gas sample was taken out from the glass tube and injected il, i a gas chromatograph and analyzed therein. The gas chromato-graph was equippe~ with a Poropak QS column, 1/8" O. D. x 5' ~, long. The injection port temperature was at 200C~, column ¦, temperature at 165C. and detector temperature at 220C~
The residual acetaldehyde in some of ~he polymers was li similarly determined but using a temperature for heating the j, sampling tube that would de-gas the polymer but would not I generate further acet`aldehyde. A 300 mg ground polymer sample, about 20 mesh size, was weighed into a glass test tube. The siæe of the test tube was 1.1 cm inside diameter and 10 cm long.
The glass tube was sealed with a rubber stopper. Then the I sealed tube was transferred into a heating block that was main-' tained at 150C. After 30 minutes, a 1 cc headspace gas sample ' il was taken out from the glass tube and injected into a gas chroma-¦ tograph and analyzed therein. ~he gas chroma~ograph ~7as eguipped j w~th a Porapak QS column, 1/8" O.D. x 5' long. The injection ¦ port temperature was at 200~C., column temperature at 165~C. and i ¦ detector temperature at 220C.
Examples ~-5 are eæamples of copolyesters and processes ~ within the scope of the inven~ion and each has the combination ¦ of properties set forth hereinbefore for copolyester compositions and processes of the invention.
The crystallization temperature peak, Tc, o~ copolyeste~
products of the invention ranges from a fe~7 degrees above the Ij 135C. crystallization temperature of PET ~Example 7) for 2 per-¦, cent (Example 4) of the sulfone monomer (BSE) to 184~C. for 10 1¦ percent BSE (Example 3) and a few degrees higher fox the 12 ~ 08~ .
;2~47 .
i~
percent BSE copolyester. The cr~stallization temper~ture peak ' for the copolyesters having 7 percent BSE charged in the co- !
¦, polyester reaction mixture ~Examples 1 and 2) is about 155C.
.' Table 1 summarizes in tabular form some of the results of some of the examples which follow.
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1 ~6234~ ' ¦I EXAMPLE 1 (~ BSE) i' Into a l-liter s~ainliess ste~l reactor equipped with a i stirrer, nitroyen gas inlet port and a condenser, the ~ollowing ¦ were added:
5 , 388.4 g dimethyl terephthalate (DMT) 248.0 g ethylene ~lycol 47.35 ~ bis(4-iB-hydroxyethoxyphenyl)sulfone(BSE) O.7685 g trimellitic acid anhyaride(TMA) 0.1225 g ~(OAc)2 4H20 10 ~ The reaction mixture was heated, under a nitrogen 'i atmosphere (continuously flushing with N2), at 200C for 2 3/4 ¦l, hours. Methanoi was continuously distilled out during this period. Then ~.1458g of Sb203 and a. 082g of H3RO3 were added I to the reactive mixture. The reaction temperature was increased ' to 250DC. After 1 hour and 35 minutes, the nitrogen gas flow I
was stopped, and the reaction was continued at 270C for 3 1/4 ! hours, under less than 0.5r~n Hg vacuum. The copolyester product had an inherent viscosity of 0.64 dl/gm. Its differential I scanning calorimeter (DSC) meltin~ peak, Tm was at 236C, the ' crystallization tempexature peak, Tc, was 155bC! and its glass transition temperature was 90C.
i The product was ground to 10-40 mesh (U. S. Standard Sieve Series) in a Wiley mill. It was then crystallized at 180C
¦ while fiushing with dxy nitrogen gas. The crystallized copoly-I ester was subjected to solid state polycondensation at 200C for ¦ 7 hours xesidence time under a continuous flow of 700 cc/min of dry nitrogen gas. After the 7 hours reaction time, the product was cooled down to room temperature and it was removed from ~he 1~ solid state xeactor~ The particulate solid ~tated copolyester l product had an inherent viscosity of 1.13, and a residual acetal-ldehyde content of 0.18 pprn (wei~ht acetaldehyde/weight polymer).

--1 ~-- .
l .

234. ` i, 1 ,` The high molecular weight copolyester was heated at 210C, 230C
and 250C for 5 minutes and 10 minutes, and the amount of acetaldehyde gas given off (per weight of polymex) was measured ' in a gas chromatograph. The results were as follows:
S j Temperature Timeppm of acetaldehyde !~ 210C 5 min0.16 230C 5 min0.32 i 250C 5 min0.76 !~ 210C 10 min0.28 10 j~ 230C 10 min ` 0.50 ¦l 250C lQ min 2.12 ¦ Eight ounce narxow necked beverage bottles are made from solid stated product made under the conditions of this ~l example by free extrusion of a tubular parison and blow molding 15~ the parison. The bottle walls contain less acetaldehyde than , bottles made fxom PET prepared according to Example 7 herein.

i EXAMPLE 2 ~7% BSE) Into a l-liter stainless steel reactor equipped with a stirrer, nitrogen gas inlet port ana a condenser, the following I were aaded:
t 388.4 g dimethyl terephthalate ~ 248.0 g ethylene glycol ¦ 47.35 g bis(4-~-hydroxyethoxyphenyl)sulfone 0.1225 g Mn~OAc2 4H20 25 i The reaction mixture was heated, undex nitrogen atmosphere, at 200C for 2 1/4 hours. Methanol was continuously distilled off during this pexiod. Then 0.1458 g of Sb203 and 0.082 g of H3PO3 were added to the re~ction mixture. The ¦ reaction temperature was increased to 240C. After 50 minutes, I the nitrogen gas flow was stopped, and the reaction was continued I at 262C for 3 hours, under less than 0.5mm Hg vacuum. The co-¦¦ polyester product had an inheren~ viscosi~y of 0.5~. Tm was !! 236C, Tc was 155C, and Tg was 90C.

6Z3~

The product was subjected to,solid state polyconden-sation according to Example 1. The soiid stated copolyester product had an inherent viscosity of 0.87, and a residual acetal-dehyde content of 0.24 ppm. The high molecular weight copoly- ¦
ester was heated at 230C, 250C, 270C for 5 minutes and 10 minutes, and the amount of acetaldehyde gas given off was measure~
in a gas chromatograph. The results were as follows: ¦

Temperature Time ppm of acetaldehyde !' ' - 230C 5 min 0.36 , 250C 5 min 0.64 ! 270C 5 min 1.65 ! 230C 10 min 0.72 250C 10 min 1.45 -270C 10 min 5.95 . .
I EXAMPLE 3 (10~ BSE) Xnto a l-~lter ~tainless steel reactor equipped with l! a stirrer, nitrogen gas inlet port and a condenser~ the following ! were added:
~ 388.4 g dimethyl terephthalate 20 , 248.0 g ethylene glycol 67.64 g bis(4~ hydroxyethoxyph~nyl)sulfone 0.7685 g trimellitic acid anhyari~e j 0.1225 g Mn(~Ac)2 4H20 I ~ The reaction mixture was heated, under nitrogen atmos-~j phere, at 200C for 3 hours. Methanol was continuously distillea out during this period. The 0.1458g of Sb203 and 0.082g H3PO3 ! were added to the reaction mixture. The reaction temperature was increased to 250C. After one hour, the nitrogen gas flow was ' stopped, and the reaction was continued at 270~C ~or 3 1/4 hours, 1 undex less than 0.5 mm Hg vacuum. The copolyester product had an !~ inherent viscosity o 0.61. Its DSC melting peak was at 2~8~C, " its crystallization peak was 184C, and its glass transition tem-perature was 90C.

Ii ' ' i ~;234~7``

1 '` The product was subjected to,solid state pol~conden-I sation accoxding to E~ample 1. The solia stated copolyester ! product had an inherent viscosity of 1.04, and a residual acetal-¦ dehyde content of 0.09 ppm. The high molecular weight copoly-ll ester was heated at 210C, 230C, 250C for 5 minutes and 10 ! minutes, and the amount of acetaldehyde gas that was gi~en off was measured in a gas chromatograph~ The results were as follows:
! Temperature Time ppm of Acetaldehyde 1 210C 5 min 0.14 - 10 ~, 230C 5 min 0.25 j 250C 5 min 0.66 210C 10 min 0.23 230C 10 min 0.060 250C 10 min 1.90 ii, ' , 1~, EXA~PLE 4 ~2~ BSE) jl Xnto a l-liter stainless steel reactor equipped with a stirrer, nitrogen gas inlet port and a condenser, the following were added: `
! 388.4 g dimethyl terephthalate 1 272.8 g ethylene glycol ! 13.53 g bis~4-~-hydroxyethox~phenyl)sulfone ¦ 0.7685 y trimellitic acid anhydride ¦ ~ 0.1225 g ~(OAc)2~4H20 , 0.1458 g Sb203 25 ! The reaction mixture was heated, under nitrogen atmos-¦ phere, at 200C for 3 1/2 hours. Methanol was continuously dis-tilled out during this period. ~hen 0.082 g H3PO3 was added to ¦ the reaction mlxture~ The reaction temperature was raised to 1 220C. After 1/2 hour, the nitrogen gas flow was stopped, and 'i the reaction was continued at 265C for 3 hours, under less than ¦l 0.5 mm Hg vacuum. The copol~ester product had an inherent vis-¦I cosity of 0.52. Its DSC melting peak was at 2~4C and i~s glass l! transition temperature was 84C.

i~ A~ `
1 i The product was ground and solid s-tated in the s~me manner as in ~xample 1. The solid stated copolymer product had ' an inherent viscosity of 0.73, and a residual acetaldehyde content ~' of 0.12 ppm. The high molecular weight copolyester was heate~ at ¦ 230C, 250C and 270C for 5 minutes and 10 minutes, and the , amount of acetaldehyde gas that was given off was measured in a ~ gas chromatograph. The results were as follows:
¦ Temperature Time ppm of Acetaldehyae 1 230C 5 min 0.26 i 250~C 5 min 1.20 !i 270C 5 min 3.45 !' 230C 10 min 0.48 ¦ 250C 10 min 4.85 270C 1~ min 8.55 1i ' ,. I
~ EX~MPL~ 5 ~1~% BSE~
j Into a 1-liter stainless steel reactor equipped with ¦l a stirrer, nitrogen gas inlet port and a condenser, the following were added:
1 388.4 g ~imethyl terephthalate 20 ¦! 248.0 g ethylene glycol 81.18 g bis(4-~-hydroxyethyoxyphenyl)sulfone , 0.1225 g Mn(OAc)2 4H20 0.1458 g Sb203 The reaction mixture was heated, under nitrogen atmos phere, at 200C for 2 hours and 20 minutes. Methanol was con-tinuousl~ distilled off during this period. Then 0.082 g ~13PO3 was added to the reaction mixtur~. The reaction temperatur~ .
was raised to 240C~ After 1 hour ~5 minutes, the nitrogen gas flow was stopped, and the reaction was continued at 262C for 2 1/2 hours, under less than 0.5 m~llg vacuurn. The copolyes~er product had an inherent viscosi-ty of 0.51. Its DSC melting peak was at 221C and a glass transition tempera-ture of 92C.

-18~

i 1 , The product was ~round and crystallized in the same manner as in Example 1. The solid state polycondensation reaction ., ` ¦, was conducted at 190C or 7 hours with nitrogen flow of 700 1,, cc/min. The solid stated copolyester product had an inheren~

1 viscosity of 0.68 and a residual acetaldehyde content of 0.20 ppm.

The high molecular`weight copolyester was heated at 230C, 250C,¦

270C for 5 minutes and 10 minutes, a~d the amount of acetalde- ¦

hyde gas that was given off was measured in a gas chromatograph.

~ The results were as follows:

TemperatureTime ppm Acetaldeh~de 1 230C 5 min 0.44 !, 250C 5 min 0.58 270C 5 min 1.35 i, 230C - 10 min 1.05 ¦l 250C 10 min 1.45 1 270C 10 min 4.85 I ` !
I EXhMPLE 6 (1% BSE) i Into a l-liter stainless steel reactor equipped wi~h I a stirrer, ni~rogen gas i~let port and a condenser, the following ¦ were added:

3~8.4 g dimethyl terephthalate t 260.4 g ethylene glycol 6.76 g bis(4-~-hydrox~ethyoxyphenyl)sulfone , 0.7685 g trimellitic acid anhydride 1 0.1225 g Mn(OAc)2 4H20 l 0.1458 y Sb203 i The reaction mixture was heated, under nitrogen atmos-phere, at 200C for 3 1/~ hours. Methanol was continuously distilled off during this period. Th~n 0.~82 g H3PO3 ~7as added I to the reaction mixture. The reaction temperature was raised to !
250C. ~fter 1 hour 15 minutes, the nitxogen ~as glow was stopped, and the reaction ~7as continued a~ 270C for 2 hours 1, . Ii 1, -19 - , ~ ~ i ` . I
li62347 1 1 35 millutes, under less than 0.5 mm Hg ~acuum. The copolyester product had an inherent viscosity of 0.56. Its DSC melting j peak was at 250C.
j The product was ground, crystallized and subjected to solid state polycondensation reaction as described in Example 1.
The solid stated copolyester product had an inherent viscosity ! f 0.83, and a residual acetaldehyde content of Q.06 ppm. The i high molecular weight copolyester was heated at 230C, 250C, 270C for 5 minutes and 10 minutes, an~ the amount of acetaldehyd~
1I gas that was given off was measured in a gas chromatograph. The ¦I results were as follows:

i Temperature Time ppm of Acetaldehyde 230C5 min 0.20 1 250C5 min 1.8 270C5 min 9.9 ~ 230C10 min 0.~7 j 250C10 min 16.
270C10 min 23.
Il ' ' .
Ii EX~MPLE 7 (PET) I
20 I Into a l-liter stainless steel reactor equipped with a stirrer, nitrogen gas inlet port and a condenser, the following were added:
388.4 g dimethyl terephthalate 310.0 g ethylene glycol 25 1 0.1225 g I~n(OAc)2 4H20 ¦ 0.1458 g Sb203 ~ he reaction mixture was heated under nitrogen atmos-phere, at 200~C for 3 houxs. Methanol was continuously distilled i off during this period. Then 0.082 g of H3PO3 ~7as added to th~

! xeaction mixture. The reaction temperature was raised to 245C.
~ ' i~234~ I
1 ~fter 1 hour 15 minutes, the nitrogen gas flow was stopped, and the reaction was continued at 270C ~ox 2 hours ~5 minutes under less than 0.5 mm Hg ~acuum. The poly(ethylene terephthalate) ~PET) product had an inherent viscosity of 0.57. Its DSC melting peak was at 252C.
The polyester material was ground, crystallized and subjected to solid state polycondensation reaction as described in Example 1. The reaction temperature was 200~C and the xeaction time was 7 hours. The solid state product had an inherent vis-, cosity of 0.78, and a residual acetaldehyde content of 0.10 ppm.
! This polyester was heated at 230C, 250C, 270C for 5 minutesand 10 minutes, and the amount of acetaldehyde gas that was given off was measured in a gas chromatograph. The results were as Ii follows:
15 ;, Temperature Time ppm of Acetaldehyde ' 230C 5 min 0.22 ii 250C 5 min - 1.58 270C 5 min 7.95 j, 230C 10 min 0.59 , 250C 10 min 12.7 i~ 270C 10 min 24.0 !' ~XAMPLE 8 Using the same apparatus used in Example 1, the follow-I ing were added:
25 ~! 2gl. 3 g dimethyl terephthalate 232.8 g ethylene glycol 47.5 g ethoxylated Bisphenol A
0.4078 g pentaerythritol 0.0919 g Mn~O~c)2 4H20 Il , ' ~' -2~-i'. I

1 ~6~4~ I

,~ The reaction mixture was heated at 190C for 2 hours under N atmosphere. Methanol was continuously distilled off i during this period. Then the following compounds were ad~ed to I the mixture in the reactor:
¦~ 0.1093 g Sb23 0.225 g triphenyl phosphite 0.0894 g tetrakis[2,4-ditert-butylphenyl3 ~,4' biphenylenediphosphonite ~ The reaction temperature was increased to 260C and li maintained for 50 minutes under nitrogen atmosphere. Then the 1~ nitrogen gas flow was stopped and a vacuum of less than 0.4 mm ¦~ Hg was applied. The reaction was continued at 270C for 3 hours j 50 minutes under vacuum. The copolyester has an inherent vis-11 cosity o 0.69. The ~SC melting peak was at 225C and its glass ¦
¦i transition temperature was 76C.
¦l The copol~ester was subjected to solid state poly- ¦
condensation reaction as described in hxample 1. The copolyester l~, solid state proauct turned light brown in color. The inherent ¦¦ viscosity of the product was not measured because a large amount ¦ of insoluble gel was formed. The residual acetaldehyde content I was 0.18 ppm.
i . '' ¦ E~ PLE 9 (7~ BSE) The melt pol~merized copolyester of ~xample 1 was crystallized inside a vacuum oven at 135C for 12 hours. The residual acetaldehyde content was 0.44 ppm. This copolyestex was not subjected to solid state polycondensation. It was heated at 230C, 250C, 270C for 5 minutes and 10 minutes, and the amount of acetaldehyde gas that was given of was measured in a gas ch~omatograph. The results were as Jollows: ¦

-22~
.

;2$4~ I
.
Temperature Time p, pm ~f Acetalaehyde , 230~C 5 min 2.35 . l' 250C 5 min 2.10 270~C 5 min 4,45 5 ~ Z30C 10 min - 4.85 ' 250C lO min 5.10 . 270C 10 min 9.00 ''; ' ' ' I
. EXAMPLE 10 (CO~RCIAL PET) , I
li A solid state PET sample that was obtained from Zi~mer , ;; !
ll A.G. had an inherent viscosity of 0.78 and a residual acetalde-,~ hyde content of 0.14 ppm. This sample was heated at 210C, , 230~C, 250C and 270C for 5 rninutes and 10 minutes, and the ' acetaldehyde gas that was given off was measured in a gas chromato-graph. The results were as follows:
15 1 TemperatureTime ppm of Acetaldehyde ¦' 210~C5 min 0.26 230CS min 0.54 250C5 min 0.30 . J 270C5 min 10.1 20 i 210C10 min 0.44 230C10 min 1.45 1 250C10 min 6.40 li 270C10 min 19.0 Il XAMPLE 11 ~15% BSE~
25 ¦Using the same apparatus as described in Example 1, the .
f~llowing were added:
. 1 291.3 g dimethyl ~erephthalate 233.4 g ethylene glycol ¦ 76.1 g bis(~- ~hydroxyethyoxyphenyl)sulfone 30 ¦¦ 0.0919 g Mn(OAc)2 4H20 ll 0.2882 g trimellitic acid anhydride il I
i! I

11 ii . i 1 The reaction mixture was hea~ed at 19~0C fvr 2 hours and at 210C for 2 hours under nitrogen atmosphere. Methanol was continuously'distilled out during this period. Then the ' following compounds were added to the mixture in the reactor:
5 , 0.1093 g Sb203 ' -', 0.225 g triphenylphosphite 0.0894 g tetrakis[2,4-ditertbutylphenyll " 4,4' biphenylenediphosphonite The reaction temperature was increased to 260C and ,, maintained for 1/2 hour under nitrogen atmosphexe. Then the i! nitrogen gas flow was stopped and a vacuum of less than 0.4 mm ',I Hg was applied. This reaction was continued at 275C under ,' vacuum,for 4 hours and 10 minutes. The copolyester had an in- I
i~l herent ~iscosit~ of 0,77. The DSC melting peak was at 215C.
~ t was crystallized in the vacuum oven at 125C for 12 hours.
¦jThe thermogxam from the differential scanning calorimeter showed that there was only slight crystallization. As a result, the , copolyester was partially melted when "solid state" polyconden-',sation reaction was attempted under the conditions described in I,Example 1, but at only 180C.
' .

Copol~ester prepared from dimethyl terephthalate, ethylene glycol and bis(4-~-h~droxyethoxyphenyl)sulfone by melt ¦~polymerization.
¦¦ 291.3 g of dimethyl-terephtha:late, 233.4 g of ethylene ¦gl~col and 0.0919 g of Mn(OAc)2 4H20 were charged into a l-liter stainless steel reactor equipped with a stirrer, nitrogen gas ! inlet port and a condenser. The xeaction mixture was heated to ~190C for 2 hours, 210C for 2 hours under nitrogen atmosphere I
i' -2~-I' `i 2~47 1 Methanol was continuously distilled out'during this period. Then ; 76.1 g of bis(~-~~hydroxyethoxyphenyl) sulfone, 0.1093 g of ji Sb203, 0.255 g of (PhO)3P (i.e., triphenyl phosphite) and ~ 0.0894 g of tetrakis [2,4-di-tertiarybutylphenyl] 4,4t-biphenyl-~, enediphosphonite were added into the reactor. The reaction , temperature was raised to 260C ànd maintained ~or 45 minutes.
The nitrogen gas flow was turned of and a vacuum of less than , O.4 mm Hg was applied. The reaction was continued at 275C for

4 1/4 hours. The inherent viscosity of the copolyester was 0.77 .1, .
j EXAMPLE 13 Poly[ethylene terephthalate) was prepared by melt poly-li merization as follows:
I Into a 500 ml 3~necked round bottom flask, e~uipped ¦I with a nitrogen gas inlet tube, stirrer and a condenser, the ¦~ following compounds were added:
- ji 46.5 g dimethyl terephthalate ~i 35.4 y ethylene glycol j 0.0263 g zinc acetate dihydrate ! o. 01398g antimony trioxide 20 1I The contents of the flask was heated at 200C under I nitrogen atmosphere for 3 hours. During ~his time, methanol I was distilled off. Then the reaction temperature was raised ¦ to 280C, nitrogen flow was stopped and vacuum was gradually 1 ~pplied until less than 0.5 ~ Hg. Exces5 ethylene glycol was I continuously distilled of. The reaction was stopped after 4 hours. The inherent viscosity was O.g3, the glass transition temperature was 72C, ana the melting point was 252C.

_~5_ . 15~80 ~2a~

' ~s will be evident to those skilled in the axt, various I
!- modifications of this invention can be made or followed in the ht of the foregoing aisclosure and discussion without depart-ing fxom ~he spirit and scope of the disclosure or from the scope of the La~ms.

Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A thermoplastic copolyester, having an inherent viscosity of over 0.65 dl/gm, a Tg of at least 82°C. and a melting point peak of at least 220°C, which is the solid state polycondensation reaction product of a thermoplastic copolyester which is the polymeric reaction product of reactants consisting essentially of (A) reactant(s) selected from terephthalic acid and its C1 to C4 alkyl esters, with (B) reactants, bis(4-.beta.-hydroxyethoxyphenyl) sulfone and ethylene glycol, wherein the amount of said bis(4-.beta.-hydroxyethoxyphenyl) sulfone is 2-12 mol percent of the amount of A reactant(s), the combined amount of B reactants is about 110 to 300 mol percent of the amount of A reactant(s), prepared by melt polymerization to yield a copolyester having a lower inherent viscosity which is in the range 0.2 to 0.7 dl/gm., said solid state copolyester being more resistant to decomposition in the molten state to form acetaldehyde than (1) the same copolyester of the same or lower inherent viscosity but made entirely by polymerization and condensation in the molten state or (2) poly(ethylene terephthalate) made by solid state polycondensation or by melt polymerization.

2. A plastic container made by melt forming a copoly-ester of claim 1.

3. A copolyester according to claim 1 that is crystallized.

4. A copolyester according to claim 1 that has a crystalline melting point peak of at least 220°C.

5. A process for making a thermoplastic copolyester which is intrinsically more stable than poly(ethylene terephtha-late) toward decomposition to from unwanted products such as acetaldehyde, which comprises (1) melt polymerizing reactants consisting essentially of (A) reactant(s) selected from terephthalic acid and its C1 to C4 alkyl esters with (B) reactants, bis(4-.beta.-hydroxyethoxyphenyl) sulfone and ethylene glycol, wherein the amount of said bis(4-.beta.-hydroxyethoxyphenyl) sulfone is 2-12 mol percent of the amount A of reactant(s), and the combined amount of B reactants is about 110 to 300 mol percent of the amount of A reactant(s), until the polymeric reaction product has an inherent viscosity of 0.2 to 0.7 dl/gm., (2) cooling the copolyester from step (1) to a solid state, reducing it to particular form and heat crystallizing the particulate copolyester, and (3) effecting solid state reaction of said particulate copolyester by polycondensation thereof, in a temperature range from 180°C. to just below the temperature of the onset of melting as indicated by a thermogram determined using a dif-ferential scanning calorimeter, to a higher inherent viscosity than the product of step(1) said higher viscosity being at least 0.65 dl/gm.

6. A product of the process of claim 5 in particulate crystalline form.

7. A process of claim 5, wherein the highest tempera-ture in step (1) is from 260 to 280°C.

8. A process of claim 5 or claim 7 wherein step (3) is effected in the temperature range from 180°C. to a higher temperature below the temperature of the onset of melting or below 224°C., whichever is lower.

9. A process of claim 5 or claim 7 wherein step (3) is effected in the temperature range from 180°C to a higher temperature at least 5°C. below the temperature of the onset of melting or below 219°C., whichever is lower.