WO2002046270A1

WO2002046270A1 - High heat polycarbonates with improved toughness and method for making same

Info

Publication number: WO2002046270A1
Application number: PCT/US2001/031901
Authority: WO
Inventors: James Alan Mahood
Original assignee: General Electric Company
Priority date: 2000-12-08
Filing date: 2001-10-10
Publication date: 2002-06-13
Also published as: AU2002216623A1

Abstract

Copolymers of BPA, BPT-1 and BPT-2 have both elevated glass transition temperatures while retaining good clarity ductility, and resistance to edge-cracking. Thus, polycarbonate is made by copolymerizing BPA with BPT-1 and BPT-2. The resulting polycarbonate is a terpolymer of BPA/BPT-1/BPT-2, where the BPA preferably makes up at least 20 mol % of the polymer. This terpolymer suitably contains BPT-1 and BPT-2 in a ratio, BPT-1/BPT-2, in the range of 70/30 to 10/90, preferably less than or equal to 50/50, for example around 30/70.

Description

HIGH HEAT POLYCARBONATES WITH IMPROVED TOUGHNESS AND METHOD FOR MAKING SAME

This application claims the benefit of US Provisional Application No. 60/254,357, filed December 8, 2000, which application is incorporated herein by reference.

This application is related to US Provisional Patent Applications Serial Nos. 60/254,359 and 60/254,397 both filed December 8, 2000, and to US

Patent Applications claiming the benefit therefrom and filed concurrently herewith, all of which are incorporated herein by reference.

FIELD OF THE INVENTION

This application relates to high heat polycarbonates, and to methods and compositions useful in making same.

Polycarbonates are a well known class of high impact resistant thermoplastic resins characterized by optical clarity, high ductility as well as other advantageous properties. They are frequently employed as lenses and windows as a result of their transparency.

Bisphenol A (BPA) polycarbonate is the predominant commercially available resin of this type. It is derived from 2,2-bis(4- hydroxyphenyl)propane and ordinarily has a glass transition temperature of about 150 °C.

It is of increasing interest to prepare polycarbonates which, while retaining the ductility of BPA, have higher glass transition temperatures and are therefore more resistant to softening when heated. Polycarbonates possessing increased glass transition temperatures are very desirable, for instance, in the automotive and aircraft industries. Particularly, they may be used in the preparation of automotive headlamp lenses which are becoming smaller in size and characterized by closer proximity of the lenses to the heat- generating light source.

Current approaches to high heat polycarbonate involve polymerizing BPA with a monomer with that increases the copolymer glass transition temperature (Tg). This improvement usually comes at the expense of other polymer properties. For example, Bayer has commercialized a family of copolymers based on Bisphenol I, which provide higher Tg at the expense of reduced ductility. Bayer APEC DP9-9340 resin gives a Tg of 177 °C and a 23°C notched izod impact of 6 ft-lb/in, as compared to a Tg of 150 °C and a

23° notched izod impact of 14-16 ft-lbs/in for BPA homopolymer.

US Patent No. 5,480,959 disclosed substantially pure bisphenols; in particular, 4-[l-[3-(4-hydroxyphenyl)-4-methylcyclohexyl]-l- methyl ethyl ]ph en ol (hereinafter referred to as BPT-1) and 4,4'-[l-methyl-4-(l- methy]ethyl)-l,3-cyclohexandiyl]bisphenol (hereinafter referred to as BPT-2).

These materials can be used to make homopolycarbonates that possess increased glass transition temperatures on the order of about 198 °C. when employing BPT-1 and about 249 °C. when employing BPT-2. A copolymer of BPT-1 and BPA (35:65 mol %) was reported to have a glass transition temperature of 171 °C and a 23 °C notched Izod impact strength of about 3.8 ft-lbs/in.

It would be desirable to have a method for modifying the thermal characteristics of polycarbonate to increase the glass transition temperature, that does not result in the a significant degradation of the impact properties of the polymer. SUMMARY OF THE INVENTION

It has now been determined that copolymers of BPA, BPT-1 and BPT-2 have both elevated glass transition temperatures while retaining good clarity ductility, and resistance to edge-cracking. Thus, the invention provides a method for making polycarbonate comprising copolymerizing BPA with BPT- 1 and BPT-2. The resulting polycarbonate is thus a terpolymer of BPA/BPT- l/BPT-2, where the BPA preferably makes up at least 20 mol% of the polymer. The BPT-1 and BPT-2 are suitably added to the BPA during the reaction as a mixture. This teipolymer suitably contains BPT-1 and BPT-2 in a ratio, BPT-l/BPT-2, in the range of 70/30 to 10/90, preferably less than or equal to 50/50, for example around 30/70.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows the structure of a type of phenol useful in making polycarbonates in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides polycarbonate copolymers having increased glass transition temperatures, a method for making such copolymers, and a mixture which can be used in the method.

The polycarbonate copolymers of the invention comprise copolymerized residues of BPA, BPT-1 and BPT-2. The BPA is suitably present in amounts in excess of 20 mol %, for example 20-75 mol%, preferably 35 to 50 mol %. In one embodiment, the balance of the polycarbonate is BPT- 1 and BPT-2 residues. The ratio of BPT-l/BPT-2 is in the range of 70/30 to

10/90, preferably less than or equal to 50/50, for example around 30/70. (It should be noted that BPT-1 and BPT-2 are isomers and that they therefore have the same molecular weight. Thus, the ratio of BPT-1 to BPT-2 is the same, whether it is on a molar or weight basis).

The polycarbonate of the invention may also include residues of additional dihydric phenol comonomers known for use in the production of polycarbonates, including but not limited to those phenols which can be employed in the synthesis of polycarbonates having the general formula as shown in Fig. 1, where R15 is selected independently from the group consisting of H and C]-C₃ alkyl, and R₁₆ and R17 are independently O-Cβ alkyl or aryl. In general, these additional comonomers will be limited to amounts of less than 20% by weight.

The polycarbonate copolymers of the invention can be prepared by an interfacial process in which the BPA, BPT-1 and BPT-2 are solubilized in a solvent system and then exposed to phosgene in the presence of a base. The resulting polymer is recovered from the brine layer, washed with acid, and may then be further recovered by conventional methods such as steam precipitation and drying. The polycarbonate copolymers of the invention can also be prepared using the indicated comonomers by other techniques known in the art including melt polymerizations (transesterification) for example as described in U.S. Patents Nos. 4,948,871, 5,204,377 and 5,214,073 and bischloroformate/oligomerization reactions for example as described in US

Patent No. 5,580,951.

It is convenient for practicing the method of the invention using a mixture consisting essentially of BPT-1 and BPT-2 and to add this mixture to the reactor. A mixture of this type (with a 30/70 ratio) is available commercially under the tradename YP-90 from Yahuhara Chemical,

Hiroshima, Japan. Alternatively, one could prepare a mixture from purified isomers by melting the isomers or dissolving the isomers in a solvent. One could also use a purified (or partially purified) isomer to adjust the composition of an iso er mixture by adding an additional amount of the isomer whose concentration is to be increased. Formation of such a mixture prior to the polymerization reaction enhances the uniformity of the product polycarbonate.

The invention will now be further described with reference to the following, non-limiting example.

Example 3

Bisphenol A (5396g, 23.6 mol) and a 30/70 mixture of BPT1/BPT2 (3602g, 11.1 mol) were charged to a 100L agitated reactor along with methylene chloride (39L), water (19L), triethylamine (48 ml) and p- cumylphenol (221 g). Phosgene (4020 g, 40.6 mol) was added at 150 g/min rate while the pH was held at 10.0-10.50 by controlled addition of a 50% caustic solution. The resulting polymer solution was separated from the brine layer, washed with dilute HCl solution, and then washed with water until the level of titratable chloride was less than 3 ppm. The polymer was precipitated with steam and dried. The resulting resin was a molecular weight of 30,400 by GPC, a Tg of 177 °C and a 23 °C notched izod impact strength of 11.8 ft- lb/in.

Example 2

The procedure of Example 1 was repeated except that BPA was added at a level of 75 mol% instead of 68 mol %. The resulting polymer had a molecular weight of 30,100 by GC, a Tg of 169 °C and a 23 °C notched izod impact of 12.9 ft-lb/in. Comparative Example

US Patent No. 5,480,959 describes the preparation of BPT-1 and BPT-2 in substantially pure form, but presents data only for copolymers of BPT-1 and BPA. To evaluate the properties of copolymers of BPT-2 and BPA, a substantially pure preparation of BPT-2 was made and copolymerized with

BPA at various concentrations from 30 to 50 mol % and end-cap levels. The measured values for Tg ranged from 169 to 195 °C and for 23 °C notched izod impact energy ranged from 5.8 to 10.1 ft-lbs/in. Thus, in all cases the notched izod impact energy of the copolymers made with BPT-2 was less than the values observed using the combination of BPT-1 and BPT-2 in accordance with the invention. Indeed, in compositions having molecular weights of 30,000 ± 1,000 g/mol, the highest observed notched izod value was 8.8 ft- lbs/in, a value which is substantially below that observed for the compositions of examples 1 and 2.

Claims

WHAT IS CLAIMED IS:

1. A polvcarbonate resin comprising polymerized residues of

(a) bisphenol A;

(b) 4-[l-[3-(4-hydroxyphenyl)-4-methylcyclohexyl]-]- methylethyljphenol (hereinafter referred to as BPT-1) and

(c) 4,4'-|l-methyl-4-(l-methylethyl)-l,3- cyclohexandiyljbisphenol (hereinafter referred to as BPT-2), wherein BPT-1 and BPT-2 residues are present in the polycarbonate in a ratio, BPT-l/BPT-2, of 70/30 to 10/90.

2. The resin of claim 1, wherein the ratio, BPT-l/BPT-2 is less than 1/1.

3. The resin of claim 1, wherein the resin comprises 20 to 75 mol % bisphenol A residues, and 80 to 25 mol% of BPT-1 and BPT-2 residues combined.

4. The resin of claim 3, wherein the resin comprises from 35 to 50 mol% bisphenol A residues.

5. A method for making a polycarbonate resin having a glass transition temperature of 165 °C or higher, comprising copolymerizing bisphenol A under interfacial conditions with 4-[l-[3-(4-hydroxyphenyl)-4- methylcyclohexyl]-l-methy]ethyl]phenol (hereinafter referred to as BPT-1) and 4,4'-[l-methyl-4-(l-methylethy])-l,3-cyclohexandiyl] bisphenol

(hereinafter referred to as BPT-2), wherein BPT-1 and BPT-2 residues are present in the polycarbonate in a ratio, BPT-l/BPT-2, of 70/30 to 10/90.

6. The method of claim 5, wherein the ratio, BPT-1 /BPT-2 is less than 1/1. 7 The method of claim 1, wherein 20 to 75 mol % bisphenol A, and

80 to 25 mol% of BPT-1 and BPT-2, combined, are copolymerized.

S. The method of claim 7, wherein the resin comprises from 35 to 50 mol% bisphenol A residues.

9. The method of claim 5, wherein the BPT-1 and BPT-2 are formulated as a mixture and then added to the bisphenol A for copolym eriza ti on .

10. The method of claim 9, wherein the ratio, BPT-l/BPT-2 is less than 1/1.

11. The method of claim 9, wherein 20 to 75 mol % bisphenol A, and

80 to 25 mol% of BPT-1 and BPT-2, combined, are copolymerized.

12. The method of claim 11, wherein the resin comprises from 35 to 50 mol% bisphenol A residues.