Mesomorphic-monoclinic Phase Transition in Isotactic Polypropylene: A Study of Processing Effects

摘要

Isotactic polypropylene (i-PP) has been shown to crystallize predominately in the α-monoclinic form under slow cooling or isothermal crystallization or during melt spinning of filaments. The β- hexagonal or γ-triclinic polymorphs may be obtained while crystallizing from the melt at high undercoolings or pressures or with the addition of nucleating agents. An intermediate polymorph, which has been described as smectic, paracrystalline, and mesomorphic but is not considered an imperfect crystal, has also been identified for very high rates of cooling from the melt, isothermal crystallization between 0 and 40°C 12 and in fiber spinning.