Synthesis of nylon 6-poly(oxytetramethylene)-nylon 6 triblock copolymers

Abstract

Prepolymeric isocyanate-terminated poly(oxytetramethylene) was synthesized and used as an initiator for the anionic polymerization of ε-caprolactam. The polymeric initiators of various molecular weight, 2,000, 2,020, 3,000, 3,720, 7,475 and 16,030 were prepared by the reaction of hexamethylene diisocyanate with poly(oxytetramethylene) in benzene or toluene. To find the optimum conditions the preparative reaction was carried out under various conditions. The best result was obtained by carrying out the reaction at the temperature 80℃ with (diisocyanate)/(diol) ratio around 2.0 (2.0 to 2.1) The anionic polymerization of ε-caprolactam initiated by an polymeric initiator was achieved by allowing them to react in bulk or in solution system at the temperature range of 80˚ - 220℃ for more than 3 hours. Then sodium metal or sodium hydride was used as a catalyst and in solution system Benzene, toluene and decalin were used as solvents. The effect of reaction condition, i.e., polymerization time, temperature, polymeric initiator concentration, catalyst/polymeric initiator ratio and molecular weight of polymeric initiator, on the composition and molecular weight of the resulting copolymers was examined. The conversion and the viscosity of the block copolymer increased with polymerization time for the initial stage of polymerization and resulted in the highest conversion of caprolactam at 180˚ to 200℃. And the change in catalyst/polymeric initiator ratio, above 2 did not exhibit any significant effect. The results of various analyses including infrared spectra, differential scanning calorimetry and thermogravimetry for the products confirmed that the ABA block copolymer was synthesized, where A and B represent nylon 6 and poly (oxytetramethylene) blocks, respectively. All those copolymers showed similarly two melting transitions at 13˚-21℃ and 215˚-224℃ representing the blocks. The tensile strength and elongation increased slightly with the increase of number average mole...