Copolyester composition

Abstract: An amorphous copolyester is prepared by contacting, under polymerization conditions an aromatic dicarboxylic acid or ester or anhydride thereof, a 2,2,4,4-tetraalkyl-1,3-cyclobutanediol and 1,3-propanediol or 1, 4-butanediol.

Description: This invention relates to cyclobutanediol copolyesters having superior impact resistance and transparency. According to the invention, amorphous copolyesters are prepared by contacting, under polymerization conditions and in the presence of a polycondensation catalyst, the folowoing monomers:- a) an aromatic dicarboxylic acid or ester or anhydride thereof; (b) a 2,2,4,4-tetraalkyl-1,3-cyclobutanediol; and c) 1, 3-propanediol and/or 1,4-butanediol. The monomers a) are preferably aromatic C 8-22 dicarboxylic acids, including terephthalic acid, isophthalic acid, phthalic acid and 2,6-naphthalene dicarboxylic acid; alkyl diesters thereof such as dimethyl, diethyl and dipropyl diesters; and anhydrides thereof such as phthalic anhydride. Terephthalic species such as dimethyl terephthalate and terephthalic acid are preferred. The monomers b) are preferably 2,2,4,4-tetraalkyl-1,3-cyclobutanediols in which the alkyl groups are independently C 1-8 , preferably methyl or ethyl, most preferably in which each alkyl is methyl. The resulting copolyesters are random copolymers, are amorphous as molded, and have a yellowness index less than about 50. The preferred terephthalate copolyesters can be represented structurally as in which R is 1,3-trimethylene or 1,4-tetramethylene and x:y is within the range of 40:60 to 90:10. The preferred compositions, because of the good combination of thermal and impact properties achieved, are those in which the molar ratio of cyclobutanediol to 1,3-propanediol and/or 1,4-butanediol is between 45:55 and 85:15. For the desired amorphous copolyesters, the ratio of cis/trans isomers in the cyclobutyl ring of monomer b) based on the relative positions of the hydroxyl groups, is suitably within the range of 33:67 to 67:33, preferably 40:60 to 60:40; most preferably 45:55 to 55:45. The copolyesters of the invention can be prepared by condensation polymerization which can be carried out by (a) transesterification polycondensation in which the diol is reacted with a dicarboxylate diester in the presence of a catalyst, or (b) dehydrative polycondensation in which the diol is reacted with a dicarboxylic acid, optionally in the presence of a catalyst. There are many suitable catalysts for the polycondensation reaction, including compounds and salts of alkali and alkaline earth metals such as sodium and calcium, of first row transition metals such as titanium, manganese, cobalt and zinc, and of Group IIA-VA elements such as antimony, tin, lead and germanium, and also including inorganic and organic acid catalysts such as phosphoric acid and toluene sulfonic acid. The preferred catalysts for preparation of the invention copolyesters are compounds of tin, manganese, zinc, cobalt and titanium. Tin catalysts, alone or in combination with a cocatalyst, are particularly preferred because of the faster reaction rate with the cyclobutanediol and formation of low-color copolymers with 1,3-propanediol or 1,4-butanediol. Examples of tin catalysts include dibutyltin oxide, tin acetate, tin oxalate, dibutyltin dimethoxide, tin isopropoxide, tributyltin acetate, dioctyltin oxide, dimethyltin dichloride, triphenyltin acetate, tin amyloxide, dibutyltin bis(2-ethylhexanoate), dibutyltin dilaurate, tin chloride, potassium tin oxide, tin oxide, bis(tributyltin oxide) and the like. Transesterification copolycondensation can be carried out by heating excess diols with dicarboxylate diester and catalyst at a temperature sufficient to distill off the alcohol derived from the ester, usually methanol, ethanol or phenol, and then applying sufficient vacuum and heat to distill off the excess diol. In the case of the cyclobutanediol copolyesters of this invention, we have found that temperatures of about 180 to about 250°C are suitable for the first stage in which about 70% or more of the corresponding alcohol is removed and for the second (vacuum) stage temperatures above about 250°C are preferred once the vacuum is reduced to below about 1mm Hg and preferably to below about 0.5mm Hg. An especially preferred embodiment is given in present claim 6. The copolymerization may be carried out batchwise in a conventional reactor or continuously as in an extruder. It is common to further advance the polymer molecular weight in a separate, additional step referred to as solid state advancement by heating the polymer, often in the form of particles or powder, under vacuum and/or a flow of inert gas. For the amorphous copolymers of the invention, such solid state post-treatment may be used, particularly if the temperature during this treatment does not exceed the glass transition temperature of the copolymer by more than about 20°C and preferably is kept at or below the copolymer glass transition temperature. If desired, the post-treatment can be carried out in the melt at temperatures at least about 20°C above the Tg of the copolymer, as in an extruder. The transesterification copolycondensation (using, for example, the diols and a dicarboxylate diester) can be carried out in various ways, including first reacting the cyclobutanediol and diester with tin catalyst, then adding 1,3-propanediol and/or 1,4-butanediol and an optional catalyst such as titanium butoxide followed by the vacuum step; and reacting cyclobutanediol, 1,3-propanediol and/or 1,4-butanediol and diester with a tin catalyst or a tin/titanium catalyst followed by the vacuum step. The desired molar ratio of cyclobutanediol to 1,3-propanediol and/or 1,4-butanediol in the polymer can be obtained by adjusting the initial monomer charge. This CBDO/diol molar ratio in the polymer has been found to closely match the CBDO/diol molar ratio charged to the reactor. Excess diol (cyclobutanediol plus 1,3-propanediol and/or 1,4-butanediol) is desirable in the initial stages of the polymerization. The excess of diols to diester is generally within the range of 5 to 150% or more, preferably from 10 to 100%, most preferably 20 to 30% moles per mole diester. Excess diols are removed at the later stages of the process to obtain high molecular weight polymers. For dehydrative polycondensation, the reaction temperature is generally above 200°C, preferably above 250°C. It is often desirable to conduct at least the initial stages of the reaction under pressure so as to avoid loss of monomers. Generally, an excess of diols of about 2 to about 30 mole% is preferred. During the polymerization reaction, stabilizers and other additives may be present during the reaction or added to the polymer. By "amorphous" is meant that the invention copolymers do not exhibit a distinct melting point (by differential scanning calorimetry at 10°C/min.) after being molded under typical molding conditions. Furthermore, the invention copolyesters are soluble at room temperature in chlorohydrocarbon solvents such as methylene chloride and chloroform. By contrast, the homopolyesters of 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 1,3-propanediol and 1,4-butanediol and certain crystalline CBDO/PDO and CBDO/BDO copolymers are generally not soluble to an appreciable degree in these solvents. The amorphous polymers of the invention are generally transparent or slightly opaque glasses, while crystalline or crystallizable polymers are generally noticeably opaque. A benefit of the cyclobutanediol copolyesters containing 1,3-propanediol or 1,4-butanediol monomers is relatively low color, as compared with ethylene glycol-containing cyclobutanediol copolyesters, which tend to test high on the yellowness index (ASTM D-1925) as measured on 3 mm disks (see Table 2 of Example 3). The invention copolymers preferably exhibit yellowness indexes less than about 50, most preferably less than about 20. The preferred copolyesters have high molecular weights, most preferably reflected in an intrinsic viscosity (IV) (in hexafluoroisopropanol at room temperature) of at least about 0.5 preferably about 0.6 to about 1.0. Preferred copolyesters have notched izod impacts (3 mm thickness) of greater than 2.7, most preferably greater than 4 Joules per 25.4 mm notch, and glass transition temperatures greater than about 80°C, most preferably greater than about 100°C. The copolyesters of the invention can be used in applications in which clarity, low shrinkage during molding, weatherability and toughness are desired in the preparation of molded articles such as lenses, glazing, packaging and compact disks. The invention copolyesters can also be blended with other polymers such as ABS, polycarbonates, poly(ethylene terephthalate) and poly(trimethylene terephthalate). Referential Example 1 (Not part of the invention) Catalyst Reactivity A 250-mL three-neck reaction flask fitted with a mechanical stirrer, graduated Dean-Stark trap and water-cooled condenser was charged with dimethyl terephthalate (0.10 moles, 19.4g), 2,2,4,4-tetramethyl-1,3-cyclobutanediol (0.12 mol, 17.06g), catalyst (see Table 1) and 0.035g Irganox 1098 free radical stabilizer. The mixture was degassed four times with argon and then heated in an oil bath to 240°C (bath temperature) at atmospheric pressure. The amount of methanol collected in the trap was measured at various times. The theoretical yield of methanol is 8.1 mL. Methanol yield for various catalysts is shown in Table 1. The results show the tin catalyst to be the most active for polymerizations using cyclobutanediol monomer. Cobalt, manganese and zinc catalyst are somewhat less reactive. However, catalysts with low activity toward cyclobutanediol such as titanium tetrabutoxide can be used in combination with the more active catalysts. Referential Example 2 (Not part of the invention) Copolyesters with Ethylene Glycol To the reaction described above with cobalt acetate catalyst was added ethylene glycol (1.86g, 0.03 mol), and the reaction was heated in the 240°C bath at atmospheric pressure. After three hours, an additional 2.6 mL of methanol had distilled. The reaction was then heated at 260°C under vacuum. After about 5 hours, some thickening was noted but the mixture was a stirrable liquid, indicating a relatively low molecular weight product. Titanium tetrabutoxide (0.0069g) was added and no appreciable increase in viscosity was apparent after three hours. The final polymer had a bluish cast and IV of 0.18. Similarly, to the reaction above with zinc acetate catalyst was added ethylene glycol (1.86g, 0.03 mol). After four hours at 240°C, an additional 2.5 mL of methanol was collected. Subsequent heating under vacuum at 260°C for a total of about 12 hours gave a yellow polymer having IV 0.22. Similarly, to the reaction above with manganese acetate catalyst was added ethylene glycol (1.86g, 0.03 mol); after four hours at 240°C an additional 2.9 mL methanol was collected and the reaction mixture had turned brownish yellow. Subsequent heating under vacuum at 260°C for about 4 hours gave a dark amber polymer with IV 0.13. The results show the poor quality, in terms of color and molecular weight, of the copolymers prepared with ethylene glycol comonomer. The tin catalyst was better in terms of the final copolymer molecular weight but produced very yellow copolymer (see Table 2) Example 3 Preparation of Copolyesters A 1-L, three-neck reaction flask fitted with a mechanical stirrer and distillation head was charged with dimethyl terephthalate (DMT:155.36g, 0.80 mol, 99%), 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO:91.01g, 0.64 mol, cis:trans about 48:52), Irganox 1098 stabilizer (0.2555g) and dibutyltin oxide (0.127g, 0.485mmol), degassed with argon and heated in an oil bath at about 235-250°C for about 5.5 hours to distill out methanol (about 35g) and then the reaction was cooled to room temperature. 1,3-Propanediol (P:27.43g, 0.36 mol, distilled) and titanium tetrabutoxide (0.535g, 0.154mmol, 99%) were added to the reaction mixture, the flask and contents were degassed with argon, and the contents were heated at about 230-250°C for about 6 hours to distill out methanol (about 13.9g). The reaction mixture was cooled to room temperature. The distillation head was replaced by a short path vacuum distillation adaptor with a collection flask cooled in dry ice. The reaction mixture was heated in the oil bath to about 260°C. The pressure was gradually reduced to less than about 1mm Hg over about 15 minutes and the reaction mixture was then heated under full vacuum for about 7 hours to give a viscous transparent polymer. The polymer was recovered by cutting it into pieces, dissolving it in methylene chloride, filtering, coagulating into methanol (containing a small amount of 2,6-di-t-butyl-4-methylphenol stabilizer) in a blender, washing the polymer twice with methanol and drying in a vacuum oven with N 2 bleed. The intrinsic viscosity of the polymer (in hexafluoroisopropanol solution) was 0.78. Nuclear magnetic resonance analysis showed that the final polymer contained CBDO/PDO units in a molar ratio of 64:36, which is essentially the same molar ratio as for the monomers charged to the reactor. Additional invention polymerizations and comparative polymerizations are shown in Table 2. Runs 4, 6-8, 10-13, 15 and 18 exhibited high impact resistance as expressed in notched Izod values. Example 4 1,4-Butanediol Copolyester Copolymer was prepared essentially as described in Example 3 using CBDO and 1,4-butanediol (BDO) in a monomer ratio of 78/22 to produce polymer with a 78/22 CBDO/BDO mol ratio, about 49/51 cis/trans and an IV of about 0.7. The dried polymer (about 370g) was injection molded (temperature 250-272°C, 7000 kPa injection pressure, 400 rpm, 50C mold temperature) to provide transparent, slightly yellow test bars for physical property measurements. Physical properties are shown in Table 3. Example 5 Copolymer was prepared essentially as described in Example 3 in several batches using an initial charge of diols such that the CBDO (about 47:53 cis:trans) to 1,3-propanediol mole ratio was about 77:23 and with about 1.25 mole diols per mole dimethyl terephthalate. Dibutyltin oxide catalyst was used. The polymers were recovered by coagulation of methylene chloride solutions into methanol to give 1.4 kg polymer fluff. Intrinsic viscosities of the batches ranged from 0.55 to 1.11 and were blended. The prime fraction (0.6 kg) had an IV of 0.96 and yellowness index of 18. Most of the prime material was converted to chips from 3 mm compression molded plaques. The dried copolymer fluff and chips were injection molded (barrel temperatures 300-330°C and mold temperature 80°C for chips) to produce transparent test samples. Physical properties are given in Table 3. Example 6 Weathering Comparisons The CBDO copolyester of Example 5 having a CBDO:PDO mole ratio of 78:22 was injection molded in 3 mm thick bars and disks. Disks were used to measure haze, gloss and transmission. Yellowness index (ASTM D-1925) was measured on two compression-molded disks of the same composition. Comparisons were made with unstabilized commercial-grade bisphenol-A-based polycarbonate molded on the same injection molding machine in accordance with the recommended molding conditions. Sample panels were placed in an accelerated weathering tester and exposed to UVA-340 lamps at the ambient temperature (∼50°C). Panels were rotated twice a week, and lamp positions were changed every 400 hours. Data on optical and impact properties were obtained at intervals over the 2500-hour trial. Results are summarized in Table 4. In comparison with the unstabilized polycarbonate, the unstabilized copolyester exhibited less yellowing upon exposure to ultraviolet light and better retention of notched Izod impact resistance. Initial Final Change Yellowness index ASTM D-1925 CBDO copolymer 17 67 +50 +294% Polycarbonate 3 87 +84 +2800% Haze (%) ASTM D-1003 CBDO copolymer 19 29 +10 +53% Polycarbonate 3 17 +14 +470% Transmission (%) ASTM D-1003 CBDO copolymer 70 63 -7 -10% Polycarbonate 87 72 -15 -17% Gloss 45 ASTM D-523 CBDO copolymer 68 62 -6 -9% Polycarbonate 93 63 -30 -32% Gloss 60° ASTM D-523 CBDO copolymer 108 72 -36 -33% Polycarbonate 150 102 -48 -32% Notched Izod impact (J/25.4 mm) CBDO copolymer 9.9 2.8 -7.1 -71% Polycarbonate 25.1 1.8 -23.3 -93% Dynatup plate impact (Joules; total energy) CBDO copolymer 10.4 4.9 -5.5 -53% Polycarbonate 80.3 13.4 -66.9 -83%

Claims: Process for preparing an amorphous copolyester which comprises contacting, under polycondensation reaction conditions and in the presence of a polycondensation catalyst, monomers comprising (a) at least one aromatic dicarboxylic acid or an alkyl ester or anhydride thereof; (b) at least one 2,2,4,4,-tetra-alkyl-1,3-cyclobutanediol; and (c) 1,3-propanediol and/or 1,4-butanediol. Process as claimed in claim 1 wherein the polycondensation catalyst is a tin compound. Process as claimed in claim 1 or 2 in which component (a) is dimethyl terephthalate, component (b) is 2,2,4,4-tetramethyl-1,3-cyclobutanediol, and component (c) is 1,3-propanediol. Process as claimed in claim 1, 2 or 3 in which component (b) has a cis:trans isomer ratio within the range of 33:67 to 67:33. Process as claimed in any one of the preceding claims, in which the molar ratio of component (b) to component (c) is within the range of 45:55 to 85:15. Process as claimed in any one of the preceding claims wherein the monomers are contacted at a temperature within the range of 180 to 250°C, for at least 1 hour, during which by-product alcohol is distilled off, and the reaction product is heated at a temperature greater than 200°C under reduced pressure for a time effective to remove excess 2,2,4,4-tetraalkyl-1,3-cyclobutanediol. An amorphous polyester composition of the structural formula in which x:y is within the range of 40:60 to 90:10 and R is 1,3-trimethylene or 1,4-tetramethylene. A blend of the amorphous polyester of claim 7 with poly(ethylene terephthalate) and/or poly(trimethylene terephthalate).

Inventors: KELSEY DONALD ROSS, KELSEY, DONALD ROSS
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1996
Main classification: C08G63
IPC codes: C08G63, C08L67