Method of regulating the polymerization of cyclic polycarbonates

Abstract: A phenol or bisphenol has been found effective as a chain transfer agent in the polymerization of cyclic carbonates to make hydroxyl-terminated polycarbonate oligomer of varying molecular weight.

Description: BACKGROUND OF THE INVENTION The present invention relates to a method for regulating the polymerization of cyclic polycarbonates using a polymerization initiator and a phenol or polyphenol as a chain-transfer agent. More particularly, the present invention relates to a method for making hydroxyl-terminated polycarbonate oligomers of a predetermined molecular weight. As used hereafter, the term cyclic polycarbonate, polycarbonate, or cyclic polycarbonate oligomer means cyclics or polymers made from the reaction of bisphenols, such as bisphenol-A with phosgene. Prior to the present invention, one method of regulating the molecular weight of polycarbonates involved the employment of a diarylcarbonate as a chain-transfer agent. Although diarylcarbonate has been found to be an effective chain-transfer agent, the polycarbonate chains made by this procedure are capped with arylcarbonate end-groups. It would be desirable, therefore, to provide a method for polymerizing cyclic carbonate with a chain-transfer agent which would result in hydroxyl-terminated polycarbonate oligomers as well as offer greater potential for making copolymers, as well as provide cross-linking of polycarbonates during polymerization. The present invention is based on the discovery that phenols, including polyhydric phenols, can be used effectively as chain-transfer agents for the polymerization of cyclic carbonate if used in combination with an effective amount of a polymerization initiator. There can be obtained hydroxyl-terminated polycarbonate oligomer having a predetermined block size which can be made under solution blending or melt polymerization conditions. There is provided by the present invention, a method for producing hydroxy-terminated polycarbonate oligomer having a number average molecular weight of 6,279 to 18,165, comprising polymerizing a cyclic polycarbonate of the formula wherein R is independently a divalent aliphatic alicyclic or aromatic radical, each Y¹ is independently oxygen or sulfur and n has a value of 2 to 30, comprising heating said cyclic polycarbonate in the presence of, relative to the mols of carbonate repeating units in the cyclic carbonate, 0.001 to 1.0 mol % of tetrabutylammonium tetraphenylborate and from 1 to 3 mol % of a chain transfer agent of the formula R(OH)₂, wherein R is a divalent aromatic radical having from 6 to 30 carbon atoms. Cyclic polycarbonate oligomers which can be used in the practice of the present invention are shown by Brunelle et al., U.S. Patent 4,644,053. The cyclic polycarbonate oligomers consist essentially of from 2 to about 30 intercondensed structural units of the formula, wherein each R is independently a divalent aliphatic, alicyclic or aromatic radical and each Y¹ is independently oxygen or sulfur. The dihydric phenol which can be used in the practice of the present invention for the regulation of molecular weights of polycarbonates prepared by means of ring opening polymerization of cyclic oligomeric carbonates as previously defined is, preferably bisphenol-A. Additional phenols which can be utilized are shown by the following formula, R(OH)₂ , (2) where R is a divalent aromatic organic radical having from about 6-30 carbon atoms. Some of the aromatic radicals included by R are, for example, phenylene, and where Q is a member selected from SO₂, -S-, and -(C) y (H₂) y , and where y is an integer equal to 1 to 5 inclusive. In the practice of the present invention, the polymerization of cyclic carbonate can be conducted under neat conditions or in the presence of an organic solvent. In instances where the polymerization is conducted in the presence of an organic solvent, temperatures in the range of from -10°C to 300°C can be employed. Suitable organic solvents which can be used are, for example, N,N-dimethylformamide, tetrahydrofuran, diethylether, ethylene glycol dimethylether, methylene chloride or o-dichlorobenzene. In instances where polymerization is conducted under neat conditions, temperatures in the range of from 200°C to 350°C can be used. The polymerization initiator which is employed to initiate the polymerization of the cyclic carbonate is tetrabutylammonium tetraphenylborate. Reference is made to the drawing showing a curve illustrating the inverse relationship between oligomer molecular weight and mol percent phenol chain-transfer agent. The hydroxy-terminated oligomers made in accordance with the practice of the present invention can be used to make block copolymers, such as silicone block copolymers as shown in copending application EP-A-0329953 filed concurrently herewith. In order that those skilled in the art will be better able to practice the present invention, the following examples are given by way of illustration All parts are by weight. EXAMPLE 1 Premixtures were prepared of 3 grams of cyclic polycarbonate, 0.0033 gram of tetrabutylammonium tetraphenylborate initiator, and 30 mL of dry methylene chloride. To one of the mixtures there was added 0.0704 gram (2 mole %) of dicumylcarbonate relative to carbonate repeat units in the cyclic carbonate. To the remaining mixture there was added 0.059 gram (2 mole %) of a bisphenol-A relative to carbonate repeat units. The solvent was removed by rotoevaporation of the mixtures and the samples dried for two hours before polymerization was attempted. 0.05 gram of each of the mixtures was then heated to 250°C for 30 minutes under nitrogen. Molecular weights of the resulting polycarbonates were then determined by gel permeation chromatography (relative to polystyrene standards). The following results were obtained, where CTA is chain-transfer agent: CTA Mw Mn 1.* None 90,745 18,419 2. Dicumylcarbonate 33,323 11,852 3. Bisphenol-A 25,092 6,097 The above results show that bisphenol-A is an effective molecular weight regulator for the polymerization of the cyclic carbonate. EXAMPLE 2 The procedure of Example 1 was repeated, except that 0.0322 gram (2 mole %) of mesitol was used as a chain-transfer agent compared to the same mole % of bisphenol-A in the cyclic mixture. The following results were obtained: CTA Mw Mn 1. Control 90,745 18,419 2. Mesitol 24,554 8,401 3. BPA 23,367 5,089 EXAMPLE 3 The procedure of Example 1 was repeated employing mixtures of 1 gram cyclic carbonate, 0.0008 gram or (0.05 mole) of tetramethylammonium tetraphenylborate as a polymerization initiator. In one of the mixtures, there was used 0.0107 gram of mesitol while 0.0180 gram of bisphenol-A was used in another mixture. A mixture also was prepared having 0.0235 gram of dicumyl carbonate. The various mixtures were polymerized at 250°C for 0.50 hour. The resulting products were then dissolved in methylene chloride and precipitated into methanol and thereafter collected by filtration. After drying, the products were then reprecipitated in acetone. The samples were then examined by Fourier Transform infrared spectroscopy. A determination of hydroxyl end-group content was made by examining the samples in the hydroxy overtone region of the spectrum and comparing the peak areas to a standard calibration. The following results were obtained: Hydroxyl Wt % Mw Mn 1. Dicumylcarbonate 0.024 79,423 26,442 2. Mesitol 0.070 47,673 22,838 3. Bisphenol-A 0.134 44,215 18,115 The above results show that the use of bisphenol-A doubles the hydroxyl content in the final polycarbonate oligomer as compared with mesitol. Although the above examples are directed to only a few of the many variables which can be used in the practice of the method of the present invention, it should be understood that the method of the present invention can use a much broader variety of cyclic carbonate, and dihydric phenol as shown in the description preceding these examples.

Claims: A method for producing hydroxy-terminated polycarbonate oligomer having a number average molecular weight of 6,279 to 18,165, comprising polymerizing a cyclic polycarbonate of the formula wherein R is independently a divalent aliphatic, alicyclic or aromatic radical, each Y¹ is independently oxygen or sulfur and n has a value of 2 to 30, comprising heating said cyclic polycarbonate in the presence of, relative to the mols of carbonate repeating units in the cyclic carbonate, 0.001 to 1.0 mol % of tetrabutylammonium tetraphenylborate and from 1 to 3 mol % of a chain transfer agent of the formula R(OH)₂, wherein R is a divalent aromatic radical having from 6 to 30 carbon atoms. A method in accordance with Claim 1, wherein the chain transfer agent is bisphenol-A.

Inventors: EVANS THOMAS LANE, WASSERMAN CAROL BARBARA, EVANS, THOMAS LANE, WASSERMAN, CAROL BARBARA
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1989
Main classification: C08G64
IPC codes: C08G64