Preparation and properties of hybrid organic-inorganic composites prepared from poly(phenylene terephthalamide) and titania

Abstract

The sol—gel process was used to prepare a class of composites in which a high-temperature polymer, poly(phenylene terephthalamide), was reinforced with varying amounts of in-situ generated titania. The polymer was synthesized by reacting a mixture of p- and m-phenylene diamines with terephthaloyl chloride in dimethylacetamide, using stoichiometry yielding chains with carbonyl chloride end groups. These chain ends were then replaced with methoxy groups using aminophenyltrimethoxysilane, and a titania network generated which should be chemically bonded to the polymer matrix through the hydrolysis of appropriate proportions of tetrapropylorthotitanate and water. The resulting composite films had amounts of titania ranging from 2.5 to 40 wt%, and were characterized with regard to their mechanical and thermal properties. The films containing relatively small amounts of titania were transparent and tough, and had tensile strengths the order of 193 MPa (relative to the 147 MPa of the pure copolymer). Thermal decomposition temperatures were in the range 350–450°C, and the weights of the samples remaining after heating to 800°C were found to be roughly proportional to the titania contents. Water absorption of the films consisting of pure Aramid was rather high (12.8 wt%), but decreased with increased amounts of titania. Dynamic mechanical thermal analysis showed a systematic increase in the glass transition temperature with increase in titania content. Increased amounts of titania also caused the tan δ peaks to shift to higher temperatures and to became broader and weaker, indicating the extent to which the mobility of the polymer chains was diminished by the titania phase.