W. D. Niegisch
Oct 1, 1966
Citations
0
Influential Citations
47
Citations
Journal
Journal of Applied Physics
Abstract
Poly‐p‐xylylene prepared by the vapor‐phase pyrolysis of di‐p‐xylylene affords a linear high‐purity polymer whose crystalline transitions were characterized by x‐ray and electron diffraction, mechanical creep studies, and differential thermal analysis (DTA). Two of the three endotherms observed by DTA correspond to the known alpha and beta polymorphs of poly‐p‐xylylene. The third, occurring at 270°C, is a reversible transition which is regarded as a smectic mesomorphic transition of the stable beta modification. Hence: α→ lim 220∘Cβ1⇋ lim 270∘Cβ2→Tm 420∘C (decomposition). Single crystals precipitated from alpha‐chloronaphthalene were instrumental in characterizing the alpha and beta unit cells. The alpha modification is best represented by an orthorhombic cell with a=21.3, b=33.6, c=6.58 A, for which the theoretical density is 1.141 g·cm−3 at 23°C. The beta modification is hexagonal, with a=20.52±0.05 A and c=6.581±0.020 A, having a theoretical density at 23°C equal to 1.153±0.005 g·cm−3. The fiber repeat...