NANOCOMPOSITES OF RIGID POLYAMIDE DISPERSED IN FLEXIBLE VINYL POLYMER

Polymer composites consisting of a rigid poly(p-benzamide) (PBA) and a flexible poly(vinyl chloride-co-vinyl acetate-co-2-hydroxypropyl acry late) (PVVH) were prepared by a two-step method. A nanoscale level of mixing in the solid state was achieved. In the first step, a turbid, v iscous PBA dispersion was obtained by the direct polycondensation of p -aminobenzoic acid in N,N'-dimethylacetamide (DMAc) under mild reactio n conditions. In the second step, the PBA dispersion was mixed with a solution of PVVH in DMAc. A clear and homogeneous solution, which may be under certain conditions thermodynamically stable, was thus obtaine d, from which the polymer composite was recovered by precipitation in methanol. The composites could be re-dissolved in DMAc, generating sli ghtly turbid solutions. The thin films prepared via casting exhibited rather good transparency. FTi.r. revealed the presence of hydrogen bon ding between the two polymers. Scanning electron microscopy revealed t he presence of uniformly dispersed PBA particles with sizes between 50 and 70 nm. The yield and tensile strengths and Young's modulus increa sed two- to three-fold, while the elongation decreased, when the PBA c ontent increased from 0 to 25 wt%. Within the scanning range, a single T-g was identified in the composites by differential scanning calorim etry, which increased with increasing PBA content during the first the rmal scanning; only the T-g of the PVVH was detected during the second scanning. The chemical resistance of PBA/PVVH composites was signific antly enhanced compared to that of PVVH. The strong interactions betwe en PBA and PVVH, which act as physical cross-linkers, are responsible for the behaviour of these composites. (C) 1997 Elsevier Science Ltd.