Tailored rigid-flexible block copolymers, 4. Synthesis and properties of diblocks of poly(p-benzamide) and poly(m-benzamide)

✍ Scribed by Piero Cavalleri; Alberto Ciferri; Carlo Dell'Erba; Antonella Gabellini; Marino Novi

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 759 KB
• Volume: 199
• Category: Article
• ISSN: 1022-1352
• DOI: 10.1002/(sici)1521-3935(19981001)199:10<2087::aid-macp2087>3.0.co;2-y

✦ Synopsis

Copolymers were prepared by the condensation of rigid benzoyl-terminated poly@-benzamide) and flexible anilino-terminated poly(m-benzamide) prepolymers. The use of two monomers of the AB type and of end-capped prepolymers resulted in the formation of diblock molecules uncontaminated by triblock or multiblock sequences. Moreover, selective extraction techniques in N,N-dimethylacetamide (DMAc) with varying amounts of LiCl resulted in the complete elimination of unreacted prepolymers, as evidenced from material balance and 'H NMR data. The above extraction technique also allowed a fractionation of the copolymers in terms of their rigidflexible compositional distribution ratio. The molecular weight-intrinsic viscosity dependence of poly(y-benzamide) determined in a nonaggregating solvent using light scattering yielded a persistence length of 8 A, suggesting a relatively large chain flexibility. A tailored copolymer with a fraction B of flexible residues = 0.70 was fractionated, determining the solubility, the viscosity, and the critical composition for mesophase formation in DMAcLiCl and in 96% H2S04 solutions. The results, in line with those previously reported for a related system, reveal that the addition of the flexible segment has a little effect on the critical concentration of poly@-benzamide), whereas the biphasic gap is strongly reduced. Moreover, the solubility of the copolymer is substantially increased over that of the rigid homopolymer. The net result is an unexpected widening of the range of stability of the pure mesophase, with significant implications from both a fundamental and an applied standpoint. a