Influence of polymorphism and the new trigonal modification on the mechanical response of isotactic poly(propylene-co-1-pentene-co-1-hexene) terpolymers

Abstract

The mechanical response and crystalline structure have been analyzed in several propylene-co-1-pentene-co-1-hexene terpolymers. Different polymorphs are developed in these terpolymers depending on global comonomer content, 1-pentene:1-hexene ratio and thermal history. The trigonal δ crystal modification is observed in addition to monoclinic and orthorhombic crystallites and mesomorphic entities. For the terpolymers with higher comonomers contents, the mesophase and even the totally amorphous samples can be readily obtained at easily accessible cooling rates. Intensity and location of relaxation processes, values for storage and indentation modulus and hardness as well are found to be related to the type of crystallites and to the crystallinity. The variation of crystallinity upon the comonomer content is rather unusual when trigonal lattice is able to be developed if compared with that exhibited by other copolymers/terpolymers based on propylene. Because of the important effect of this variable on mechanical response and mobility within amorphous regions, relationships found in other mechanical parameters and in the relaxation associated with glass transition (location and intensity) are also uncommon. The presence of trigonal polymorph exerts a key role in those atypical dependences.