The formation of curved polymer crystals: Polyoxymethylene

An opti cal and electron microsco pi cal study is PJese nte d of th e habits exhibited by chainfolded polyoxymethylene crys tals grow n from hot 0.02 percent solutions of th e polymer in orthodi chlorobe nzene when th ese solutions are cooled to temperatures (Te) between 140 and 80 C inclus ive . In co ntras t with the lam ellar crystals formed in the Te= 140 and 120 C preparations, whi ch crystals were six-sectored and nearly planar, the crystals formed below Tc= 120 C exhibited multisectored dendriti c habits and were all the more pronouncedly curved the lower the temperature at whic h they grew. The most pronouncedly c urved crystals which were observed were hollow bow! shaped dendrites having a radiu s of c urvature of -2 /-tm which were formed in th e 80 C preparations. The possible origins of why the lam ellar crys tals of polyoxymethylene were all the more pronouncedly curved th e lower the cryst allization temperature are co nside red in th e light of conjectures which hav e been previously advanced concerning th e formation of curved crystals of poly(4-methylpente ne-l). Among the features which are di sc ussed is th e role played by th e bulkiness of the chain folds.