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

Abstract

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.

Comparison of Crystalline Phase Transitions in Fluorniated vs Nonfluorinated Parylene Thin Films

“…The upward shift in stress in the heating curve for PPX-N at the phase transition is likely caused by contraction of the crystal structure along the polymer chain ( c -axis) that occurs upon passing from the β 1 to β 2 crystalline form. , It has been speculated that this contraction is due to a kinked or helical chain conformation in the higher temperature crystalline form . Since the polymer chains in PPX-N thin films align preferentially parallel to the substrate, ,, such a chain contraction should result in an increase in the in-plane tensile stress. If this is the case, then the similar shift in PPX-F, which is more pronounced than that in PPX- N, may also be due to chain contraction accompanying a phase transition.…”

Effects of the film thickness on the morphology, structure, and crystal orientation behavior of poly(chloro‐p‐xylylene) films

“…Parylene polymers are semicrystalline thermoplastics and are often synthesized as thin films by the chemical vapor deposition (CVD) method. The deposition conditions (deposition temperature, pressure, substrate, and so on) consequently play crucial roles in the morphology, microstructure, and properties of the films . However, some other factors, such as the thermal history of the polymer films, can also severely influence the degree of crystallization, crystallite size, stress state, and thermal stability of the films .…”

Intermediates and monomers for vapor phase deposition and polybenzoxazoles

“…The solution immediately turned red with evolution of gas (H2) and was analyzed by NMR; 1H-NMR (DMSOd6): 6 7.84 (d, J = 6.5 Hz), 6 …”

“…The pyrolysis of [2.2]paracyclophane to give poly(p-xylylene) was first reported by Gorham in 1966 [3], although Szwarc had previously described the pyrolysis products of p-xylene to yield [2.2]paracylclophane and poly-(p-xylylene) [4,5]. Since then, there has been extensive work on improving the ringopening polymerization of [2.2]paracyclophane and other cyclophanes [6][7][8][9] [14], and 2,5-dimethylene-2,5-dihydrofuran [15]. The inherent ring strain in these cyclic structures leads to their high reactivity and makes them excellent monomers; however, the monomers are difficult to synthesize.…”