| The objective of this research was to prepare nylon 6-b-aramid-b-nylon 6 copolymers. It was postulated that these materials would function as one-component molecular composites. The work was begun with the synthesis of an end-capping agent, i.e., 4-aminobenzoyl caprolactam. The agent was used to prepare aromatic amide oligomers terminated with N-acyllactam moieties. The oligomers were then used as difunctional activators in the anionic polymerization of {dollar}varepsilon{dollar}-caprolactam. Thus, a series of novel nylon 6-b-aramid-b-nylon 6 copolymers containing 5-15 wt% of an aromatic polyamide was synthesized. Several model compound studies showed that (1) no nylon 6 homopolymer is produced under the copolymerization conditions; (2) grafting of nylon 6 homopolymer onto the aromatic polyamide backbone does not occur; (3) the aromatic polyamide is not attacked by the caprolactam anion as the block copolymerization proceeds; and (4) nylon 6 chains only grow from the activator sites at the aromatic polyamide chain-ends. The block copolymers were tough, thermoplastic materials, which could be readily compression-molded. Their inherent viscosities ranged from 2.35 to 4.42 dl/g in m-cresol at 60.0 {dollar}pm{dollar} 0.1{dollar}spcirc{dollar}C. Compared to unmodified nylon 6, the copolymers had much higher yield strengths, tensile strengths, and moduli, but slightly shorter elongations to break. The mechanical properties of the block copolymers increased as the compatibility of the aromatic polyamide with the nylon 6 increased. The properties decreased as the aramid content was increased and as the calculated molecular weight of the aramid segment was increased above 12,000 g/mol. The copolymers also displayed higher glass transition temperatures, and improved moisture and chemical resistance compared to nylon 6. Scanning electron micrographs of the block copolymer films did not show any phase-separated domains. |
