Effects of elongation on the photochemistry of poly(ethylene- co-carbon monoxide).

Films of poly(ethylene-co-carbon monoxide), P(E/CO), were cold- drawn to various extensions. IR dichroism measurements showed that the molecular chains in the amorphous region were oriented along the direction of drawing. After UV irradiation (lambda > 290 nm, 30C, nitrogen atmosphere), the present crystallinity and average crystallite size, as determined by X-ray diffractometry, increased for both undrawn and drawn samples. Also, the orthorhombic form in drawn samples increased at the expense of monoclinic form during UV exposure. The formation of vinyl end groups increased with exposure and with extent of elongation as determined by IR spectroscopy, while the formation of acetyl end groups was strongly suppressed by orientation as determined by NMR spectroscopy. Molecular chain tension increased the overall scission rate slightly and shifted the reaction mechanism from mostly Norrish Type II scission in unoriented P(E/CO) to predominantly Norrish Type I scission in oriented samples.