Polyhydroxymethylene Films via Poly(vinylene carbonate)

Submitted by: J. R. Schaefgen and N. D. Field 1 Checked by: J. B. Clements 2

A. Poly(vinylene carbonate) 1. Procedure Chloroethylene Carbonate. (Note 1, 500 g, 5.7 mol) and 1 l carbon tetrachloride are added to a 2 l, three-necked, standard taper flask equipped with an ultraviolet lamp in a quartz jacket immersed in the flask, a gas inlet tube, and an efficient condenser (Note 2). The two-phase system is heated with a heating mantle to reflux. Heating is then stopped, the ultraviolet lamp is turned on, and chlorine from a cylinder is introduced at a rate sufficient to maintain vigorous refluxing (Note 2). The ethylene carbonate-rich phase gradually disappears and a homogeneous solution forms. Chlorination is continued beyond this point until the total weight of chlorine added is about 600 g (8.5 mol). This requires 3-5 h (Note 3). The product is isolated by fractional distillation through an efficient column (Note 4). After removal of the solvent and a low-boiling solid o 25 impurity (Note 5), 1,2-dichloroethylene carbonate, 114 g (13%, bp 91 /30 torr, nD 1.4606), and o 25 chloroethylene carbonate (420-475 g, 60-68%, bp 102 /8 torr, nD 1.4525) are isolated. Vinylene Carbonate. The chloroethylene carbonate from the preceding step (450 g, 3.65 mol), 450 ml of anhydrous ether (Note 6), and 4 g of di-t-butyl-p-cresol (Note 7) are added to a 2 l, three- necked, standard taper flask equipped with a precision-ground stirrer, dropping funnel, and reflux condenser to which a drying tube filled with Dririte is attached. (560 ml, 4.1 mol) is added slowly over about 4 h to the stirred, refluxing solution (Note 8). Gentle refluxing is maintained for 2 days. A copious precipitate of amine salt forms, and the color of the solution becomes dark brown. The precipitate is collected and washed four times with 400 ml of a mixture of 50/50 vol % of benzene and ether. The second and third washings are carried out by slurrying the solid precipitate with the solvent mixture in a beaker. The filtrate and washings are combined, and most of the ether and some of the benzene are removed by simple distillation. Distillation of the remainder of the solution at reduced pressure through an efficient column (Note 4) yields 200- 230 g (63-73%) of vinylene carbonate, bp 74o/30 torr. This material rapidly turns brown on

81 82 Macromolecular Syntheses, Collective Volume 1 standing. It is further purified by refluxing for 1 h over 1.5% by weight and then distilling (Note 9). A second treatment with sodium borohydride is recommended to obtain a color- 25 o o stable, purer product; nD 1.4185, mp 20.5 ; d 1.35 g/mL at 27 .

Polymerization. A thick-walled test tube is narrowed near the top and 0.01 g of 2,2'- azobis(isobutyronitrile) (AIBN, Note 10) is introduced. By use of a syringe, 5 ml of the sodium borohydride-treated vinylene carbonate is added. The tube is cooled in ice water to freeze the monomer and then evacuated through a stopcock to 1 torr. The stopcock is closed and the monomer is then degassed by melting and refreezing. The evacuation and degassing procedure is then repeated, after which the system is sealed under reduced pressure (Note 11). The sealed tube is placed in a bath thermostated at 60-65o. Polymerization takes place slowly to give a clear solid resin in 18-72 h. The tube is broken, and the tough plug of is dissolved in 50 ml of N,N- (DMF) at room temperature (Note 12) and reprecipitated as a white fibrous solid by adding this solution slowly with stirring to 200 ml of . The polymer is collected by filtration and washed repeatedly by slurrying with methanol until the filtrate is nearly clear. The yield of polymer is 3.7-5.6 g (57-87%). The inherent viscosity at 30o of a 0.5% solution of polymer in DMF is 2.0-3.5 dl/g (Note 13).

B. Polyhydroxymethylene 2. Procedure Poly(vinylene carbonate) is dissolved in DMF to form a 10% solution. This is cast as a 10-mil film on a glass plate by use of a doctor knife. After drying overnight at room temperature, the clear film is removed from the plate and hydrolyzed. To accomplish this, the film is suspended in a 1% sodium methylate (Note 14) solution in methanol in a covered beaker. Hydrolysis to clear but crinkled films of polyhydroxymethylene is complete after 24 h at 50-60o or after 3-5 days at room temperature. The progress of hydrolysis may be followed conveniently by noting the disappearance of the carbonyl bond at 5.5 ì in the infrared spectrum. The films of polyhydroxymethylene (Note 15) are stiff and brittle when thoroughly dry but become tough and flexible in moist air. They are insoluble even in boiling water and retain moderate strength when wet. The wet film can be cut into narrow strips (about 5 mm wide), and these can be oriented by drawing them (Note 16) over a rod heated to 200o. Such films are quite strong [>6 g/denier (g.p.d.)] and very stiff (-300 g.p.d. initial modulus). Although measurements of inherent viscosity or molecular weight are precluded by polymer insolubility, retention of good mechanical properties indicates high molecular weight.

3. Notes 1. Material obtained from the Jefferson Chemical Company is sufficiently pure to use as received. It was found convenient to add this chemical to the reaction flask as a liquid (m.p. 36o). 2. Two Liebig condensers, one on top of the other, were found convenient. The top of the upper condenser should be connected to a scrubber to trap evolved HCl, excess chlorine, and any carbon tetrachloride which fails to condense. The rate at which chlorine can be added depends on the efficiency of the condenser system. The checker found that an external sun lamp (G. E. RS type) was also satisfactory, but reaction time was longer, i.e., 9 h. 3. Near the end of the reaction, the solution turns green and this color change may be used as an indication of completion of the reaction if it is not convenient to weigh the chlorine cylinder. 4. A 3 ft spinning band column in which the spinning element is a tungsten wire supporting a platinum gauze was used by the submitter. The checker found that a 30 cm Vigreux column gave sufficiently pure chloroethylene carbonate for dehydrohalogenation. Polyhydroxymethylene 83 5. This impurity was not identified. If the take-off head clogs, an infrared lamp may be used to maintain fluidity. It may also be necessary to clean the column before collecting the pure 1,2- dichloroethylene carbonate. 6. The commercial purified product is suitable. 7. This is added to prevent polymerization of the monomer by adventitious impurities during reaction and distillation. 8. A water bath should be used to avoid overheating the reaction. If convenient, a thermometer should be used in the flask, and a temperature of about 45o should be maintained. 9. A simple Vigreux column allows nearly all the product to be recovered. 10. DuPont Vazo vinyl initiator is convenient. 11. An alternative procedure3 is to repeatedly (5 or 6 times) alternately evacuate to about 30 torr pressure and flush with purified nitrogen, and then seal the tube under reduced pressure. 12. Hot DMF degrades the polymer.3 Solution requires about 8-16 h (i.e., overnight) with occasional shaking by hand. 13. The rate of polymerization is quite low, necessitating long polymerization times. The inherent viscosity of the polymer is a function of the initiator to monomer ratio, but it is greater than 2 even at five times the ratio used in the example. The preparation also has been carried out at five times the scale indicated here with corresponding yields of polymer with the designated range of inherent viscosity. 14. Commercially available sodium methylate may be used. The reaction probably involves hydrolysis by small amounts of water present in the methanol rather than by alcoholysis because a white precipitate (presumably sodium carbonate) forms. The presence of a few percent of water does not cause difficulty. 15. The checker was able to make 12% solutions of polyhydroxymethylene in dimethylsulfoxide from which 5-mil films were cast. The submitter was not able to obtain gel-free solutions of high molecular weight polymer in this solvent. 16. The films must be cut when wet because the dry films are brittle and may shatter. Practice is required to orient the films uniformly without breaking them. The films may be drawn 600- 800% when the technique is perfected. Such films are smooth and oriented, as shown by wide angle x-ray diffraction patterns. Alternatively, the films can be stretched to a lower degree of orientation in warm water (60o). The great difference in stiffness of dry and wet films is intriguing.

4. Methods of Preparation This preparation is based on the article by Field and Schaefgen.3 Other authors have used similar methods to prepare vinylene carbonate4 but have used more involved and less effective purification methods.5 The hydrolysis of poly(vinylene carbonate6) has usually been carried out in aqueous solution. In aqueous hydrolysis, polyhydroxymethylene precipitates as a completely intractable white powder.

5. References 1. Pioneering Research Division, Textile Fibers Department, E. I. DuPont de Nemours & Co., Inc., WIlmington, DE 19898; current address Field - International Playtex Co., 215 College Rd., Paramus, NJ 07652. 2. Chemstrand Research Center, Inc., Durham, NC 27709. 3. Field, N. D.; Schaefgen, J. R. J. Polym. Sci. 1962, 58, 533. 4. Newman, M. S.; Addor, R. W. J. Am. Chem. Soc. 1953, 75, 1263; 1955, 77, 3789. 5. Thomas, R. M. U.S. Patent 2,873,230, 1959. 6. Haas, H. C.; Schuler, N. W. J. Polym. Sci. 1958, 31, 237; also see Ref. 4.