Copolymers of Depolymerized Cellulose Triacetate and Diisocyanates Submitted by: S. Kim, V. T. Stannett, and R. D. Gilbert1 Checked by: R. R. Mercier and W. H. Daly2 1. Procedure a. Depolymerization of Cellulose Triacetate (CTA) In a 500 mL, three-necked flask fitted with a stirrer, a dropping funnel, and a nitrogen inlet tube, CTA [40 g [ç] = 1.77 dL/g (Note 1), acetyl content 43.9%] is dissolved in 400 mL of glacial acetic acid at 80o. Acetic anhydride, 6.6 mL (Note 2), and 2 mL of conc. sulfuric acid are added (Note 3); 2 min later 2.4 mL of water is added (Note 4). The clear solution is agitated at 80o for 6 h, cooled to 35o, and the catalyst is neutralized by adding a 21% aqueous solution of manganese acetate (30 g). The solution is poured into petroleum ether (Note 5) with agitation. The agitation is continued overnight and then the liquid is decanted. The redisual solvent is removed under reduced pressure at 60o to near dryness. The solid is washed with 95% ethanol, agitated overnight in ethanol, and then washed with water on a filter until no acid is detected in the filtrate. The depolymerized CTA is dried overnight under high vacuum at 60o; yield 36 g (93%); [ç] 0.16 dL/g; acetyl content 45.4%; very strong OH stretching absorption at 3500 cm-1; mp range 220 - 240o (on differential scanning calorimetry at a scan rate of 0.1o/min). 1 2 Macromolecular Syntheses, Collective Volume 2 b. Block Copolymers of Depolymerized CTA and Diisocyanates In a 250 mL, two-necked flask equipped with a liquid seal agitator, a distillation adapter, and a condenser, is added 10 g of depolymerized CTA (0.002 mol) dissolved in a mixture of 50 mL of methylene dichloride and 15 mL of ethylene dichloride. The solution is heated under nitrogen to collect 25 mL of distillate. The adapter and condenser are replaced with a dropping funnel. Diphenylmethane diisocyanate (MDI, 0.002 mol, Caution! Note 6), dissolved in 10 mL of a 2:1 mixture of methylene dichloride and ethylene dichloride is introduced. After solution is complete 0.15 mL of triethylamine is added. The mixture is agitated at 70o for 7 h, dry ethylene dichloride (50 mL) is added, and agitation is continued overnight at room temperature. The mixture is filtered through a coarse sintered glass filter (Note 7) and the filtrate evaporated under reduced pressure to near dryness. The resulting solid is washed with ethanol, soaked in a 2:1 mixture of ethanol and acetone for 4 h, filtered, and then soaked in the same solvent mixture for another 4 h. The copolymer is recovered by filtration and dried at 60o under high vacuum. The yield is 70%; [ç] 0.37 dL/g; softening range 180 - 240o. This procedure is repeated except that m-tolylene diisocyanate (TDI, 0.002 mol) is substituted for MDI. The yield is 90%; [ç] 0.41 dL/g; softening range 245 - 260o. c. Terpolymers of Depolymerized CTA, Diisocyanates, and Polypropylene Glycol (PPG) In a 250 mL, two-necked, flask equipped with a liquid seal agitator and a Dean-Stark trap, is added 10 g of depolymerized CTA (0.002 mol) dissolved in a mixture of 50 mL of methylene dichloride with 25 mL of ethylene dichloride. The mixture is azeotropically distilled to collect 25 mL of distillate. In another 250 mL three-necked flask equipped with a liquid seal agitator, thermometer, nitrogen inlet, Dean-Stark trap with condenser, and attached drying tube, are charged polypropylene glycol (molecular weight ca 1007, 0.002 mole) and ethylene dichloride (7mL). The solution is azeotropically distilled and 4 mL of distillate is collected. Under a stream of dry nitrogen MDI (0.003 mol) dissolved in 10 mL of a 2:1 mixture of methylene dichloride and ethylene dichloride is added. The reaction mixture is agitated, heated at 105o for 3 h, cooled to 50o, and the dry, depolymerized CTA solution added. The agitation is continued until mixing is complete (2-3 min); triethylamine (0.15 mL) is added and the mixture is continuously stirred at 70o for 45 h. The resulting almost clear, viscous dope is diluted with ethylene chloride (50 mL, filtered through a coarse sintered glass filter, and most of the solvent removed under reduced pressure. The solid is washed with 95% ethanol, and the polymer is separated by centrifugation (Note 8). The yield is 85%; [ç] 0.33 dL/g; softening range 300 - 310o. This procedure is repeated except that TDI is substituted for MDI. The yield is 89%; [ç] 0.64 dL/g; softening range 315 - 330o. d. Deacetylation of the Block Copolymers (Note 9) In a 500 mL, three-necked flask, equipped with a nitrogen inlet and outlet tube and an agitator, sodium (1.2 g) is added to 300 mL of anhydrous methanol. After solution is complete 10 g of the copolymer is introduced under a blanket of nitrogen. The heterogeneous mixture is stirred continuously at room temperature for 3 h. With the CTA-MDI and CTA-TDI copolymers, the solid deacetylated product is collected by filtration, and washed with methanol, methanol-acetic acid (95:5), and again with methanol. In the case of the terpolymers, the reaction mixture is neutralized with acetic acid and the product is recovered by centrifuging. The solid is washed with methanol 3 times, with centrifuging each time to remove solvent. The polymers are dried at 60o under high vacuum. Cellulose Triacetate Polyurethanes 3 2. Characterization The polymers have the following intrinsic viscosities and acetyl values: Copolymer [ç]a Acetyl Contentb CTA-MDI 0.35 9.0 CTA-TDI 0.36 9.8 PPG-MDI-CTA 0.43 10.7 PPG-TDI-CTA 0.52 10.7 aIn DMSO at 30o. Gel removed by filtration through a fine, sintered glass filter (Note 10). bAverage of two determinations. An acetyl content of 10% corresponds to a D.S. of 0.42. 3 3.Notes 1. All intrinsic viscosities of the acetylated polymers are measured in a mixture of 90% (wt.) methylene dichloride with 10% methanol at 25o. 2. Acetic anhydride reacts with water in cellulose triacetate, glacial acetic acid, and catalyst. 3. Sulfuric acid catalyzes the depolymerization. 4. Steinman4 showed that acetic acid containing 0.6% water is the optimum composition for depolymerizing cellulose triacetate at 80o in an acetic acid-water medium. When no or little water is present, the chain ends are acetylated as they are cleaved. 5. Because of the long stirring time, a high boiling fraction of petroleum ether should be used. 6. All procedures involving the isocyanates should be carried out in a well-ventilated hood, and the isocyanates should be handled with caution. Provision should be made to avoid contact of the isocyanates with the skin. The manufacturer's directions for handling MDI and TDI should be carefully followed. Aromatic diisocyanates have a marked tendency to dimerize at room temperature, and contain dimers as received from most suppliers. Such dimers alter the solubility of the diisocyanates and, more importantly, upsets the stoichiometry of the reaction. The diisocyanates should be distilled under reduced pressure prior to use. 7. Depending on the degree of deacetylation that occurs during the depolymerization of the CTA, some gel may be retained on the filter. 8. On addition of the ethanol a colloidal solution tends to form. 9. A modification of Vink's5 procedure is employed. 10. Some gel is formed during the deacetylation step, probably because of reaction of terminal isocyanate groups with the freed hydroxyl groups. 4. References 1. College of Engineering, North Carolina State University, P. O. Box 5335, Raleigh, NC 27695-7905. Taken in part from the doctoral thesis of S. Kim. 2. Department of Chemistry, Louisiana State University, Baton Rouge, LA 70843. 3. Tanghe, L. J.; Genung, L. B.; Mench, J. W.; Whistler, R. L. in Methods in Carbonhydrate Chemistry, Academic Press: New York, 1962; Vol. 3, p 201. 4. Steinmann, H. W. Polym. Preprints, 1970, 11, 285. 5. Vink, H. Arkiv Kemi, 1958, 13(21), 193..