Polymerization from the vapor phase. I. Poly(p-phenyleneterephthalamide) gas barrier coatings

An atmospheric‐pressure, vapor‐phase polymerization technique was used to deposit thin(1–10 μm) poly(p‐phenyleneterephthalamide) coatings onto polyester film and other sheet substrates. A minimum deposition temperature of 170°C, was found to be critical. When substrate temperatures were below 170°C, coatings were loosely adhered, powdery, and of low molecular weight; above 170°C, coherent, well‐adhered, high molecular weight coatings were obtained. These vapor‐deposited coatings exhibited exceptionally good oxygen barrier properties and were found to consist of fused 0.1‐μm particulates. Scanning electron microscopy (SEM) of the top surfaces of these coatings clearly revealed their particulate origin. Similar evidence was also obtained from SEM examination of fracture surfaces and transmission electron microscopy of microtomed sections. The coalescence of these coatings was demonstrated by SEM of plasma‐etched surfaces and oxygen permeability information. The uniplanar orientation of the polymer crystals in these multiparticulate coatings was strong evidence for the epitaxial growth of the crystals.