Crystallography of Poly-p-Xylylene

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 Å, 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 Å and c=6.581±0.020 Å, having a theoretical density at 23°C equal to 1.153±0.005 g·cm−3. The fiber repeat distance consists of one chemical repeat unit in a fully extended configuration for both modifications. The high positive birefringence, particularly for the beta modification, reveals that the planes of benzene rings in neighboring molecules are steeply inclined to one another.

Multipotent Polymer Coatings Based on Chemical Vapor Deposition Copolymerization

“…[23] This approach takes advantage of the fact that poly(pxylylenes) are often semicrystalline polymers with characteristic features in the XRD spectra. [24,25] phous in the as-deposited state. [26] However, after annealing for 14 h at 120°C, the trifluoroacetyl-functionalized polymer 4 showed characteristic diffraction patterns, which likely correspond to (020) and (110) planes, and a d-spacing greater than that reported for the monoclinic poly(p-xylylene).…”

On the reversibility of the crystalline phase transitions of poly(p‐xylylene)

“…This process yields a more highly crystalline polymer which clearly shows a third polymorph initially described as a smectic mesopmorph of the fl phase. 3 The p state was then renamed p1 and the highertemperature polymorph was designated as &. Thus the crystalline phase transformations were described as follows with the approximate transition temperatures: a -pl fl, -melt (followed by decomposition)…”

Structure and optical properties of thin poly(p-xylylene) – Silver nanocomposite films prepared by low-temperature vapor deposition polymerization

“…[36,28] Interestingly, the planar texture of the films is retained during the a to b 1 phase transition. The a to b 1 phase transition was first observed by Niegisch, who suggested that this transition is irreversible [37]. However, it was shown in Refs.…”