Crystallization during polymerization of poly‐p‐xylylene. III. Crystal structure and molecular orientation as a function of temperature

Polymerization of p‐xylylene was carried out from the gas phase with monomer produced by the pyrolysis of [2,2]‐p‐cyclophane. The crystalline form and preferred orientation of as‐polymerized polymer deposited at various temperatures (−196 to 80°C) were investigated by x‐ray diffraction methods. The melting behavior and other thermal transitions were studied by DSC. At 80°C the polymer film deposit is a mixture of the α and β forms, while between 60 and 0°C the deposit is of the α form. At lower temperature the polymer deposit is mainly of the β form, which shows diffuse reflections. At liquid nitrogen temperature it is of the β form with sharp reflections, contaminated with a small amount of oligomer. It was also found that at low temperatures, fibrillar crystals grow from the substrate in a direction 45° against the gas flow, and at even lower temperature, well‐oriented filmlike crystals grow perpendicular to the substrate surface.