Control of crystalline modifications of poly(p-xylylene) by copolymerization

Poly(p-xylylene) (PPX), phenylethyl-substituted PPX (PEPPX) and copolymers of both were synthesized by base-induced dehydrohalogenation of correspondi ng 4-chloromethyltoluenes. Analysis of the crystal structure of PEPPX by X- ray diffractometry reveals close resemblance of its unit cell with the unit cell of PPX in its alpha-modification. The crystalline morphology of as-po lymerized PPX can be described as a mixed modification consisting of alpha- and beta-crystals. However, copolymers of PPX and PEPPX show predominantly the alpha-crystals, even at very low ratio of PEPPX moieties in the copoly mer. Conversion of the alpha-modification to the beta-modification cannot b e accomplished by annealing of copolymers above 200 degrees C, which is in contrast to PPX homopolymers.