(226bs) Polymorphism of Precision Halogen Substituted Polyethylenes Studied By Thermal, Microcopy and Spectroscopic Techniques

Polyethylenes with halogen precisely substitution along the methylene backbone are unique models to study the effect of chain-defects on crystallization of polymers. Packing of the Chlorine units in the crystallites of polyethylene with Chlorine substitution on every 15^th backbone carbon was found to undergo a transition within one degree of undercooling. On crystallization with high undercooling the chains pack in an all-trans planar conformation (Form I). The crystals formed at higher temperatures pack in a non-planar herringbone-like structure (Form II). The FTIR spectra analysis in a broad range of crystallization temperatures is extended here to a series of polyethylenes with Cl substitution every 9^th, 19^th and 21^st carbons. The unique polymorphic transition found before, is also found in all members of the series. The polymorphic transition temperatures and temperature range of coexistence of both forms are analyzed as a function of Chlorine contents in the series.