Organic microcomposites via reactive processing

Abstract

The in-situ formation of dispersed polyaramide whiskers during melt processing of polymers represents a new route to thermoplastic and elastomeric organic microcomposites. When N-(p-amino-benzoyl)-caprolactam (PAC) is injected into melts of high molecular weight polyamide-6 or dihydroxy-terminated poly(oxytetramethylene) liquid rubber, stable dispersions of polymeric whiskers are formed. At temperatures around 200°C, PAC polymerization takes place exclusively through attack of the PAC amine group at the exocyclic carbonyl group, thus eliminating caprolactam and forming whiskers being composed of highly crystalline poly(p-phenylenebenzamide). With increasing polymerization temperature, the elimination reaction is accompanied by the competing attack of the amine group at the endocyclic carbonyl group of the caprolactam ring system. This side-reaction causes ring-opening, thus incorporating 6-aminocaproic structural units into the polyaramide backbone. Moreover, the condensation reaction of PAC and N-acyl-caprolactam-functional whisker surfaces with hydroxy- or amine-endgroups affords steric stabilization of the dispersions and excellent interfacial adhesion of the microcomposites. This covalent bond formation between matrix polymer and dispersed in-situ formed polyaramide whiskers is the key to unusual property synergisms of such organic microcomposites. In most cases, small amounts of PAC as additives during processing are sufficient to improve stiffness and strength without sacrificing toughness. Morphologies, mechanical properties, and the basic structure/property relationships of in-situ formed polyaramide-reinforced polyamide-6 and of polyurethanes elastomers prepared from novel anisotropic polymer polyol dispersions and diisocyanates are reported as a function of the PAC content and polymerization conditions