Characterization of a PE-g-LCP compatibilizer, prepared by reactive blending of acrylic acid grafted polyethylene (PE) and a semiflexible liquid crystalline polymer (LCP)

Abstract

Novel graft copolymers (PE-g-LCP) consisting of polyethylene (PE) backbones and liquid crystalline polymer (LCP) branches, synthesized via reactive blending of acrylic acid functionalized PE (Escor 5000 and Escor 5001 by Exxon) with a semiflexible LCP (SBH by Eniricerche S.p.A.; mole ratio sebacic acid (S): 4,4'-dihydroxybiphenyl (B): 4-hydroxybenzoic acid (H) = 1:1:2) have been characterized by differential scanning calorimetry (DSC), optical microscopy and X-ray diffraction. The isothermal crystallization, the morphology, and the crystalline structure of the crude reactive blending products (COPLE and COPHE) and of their fractions soluble in boiling toluene and xylene and of the residue have been investigated. It has been shown that the isothermal crystallization rate of PE segments of the copolymers decreases from toluene fractions to xylene insoluble fractions, however, these segments preserve their crystallizability even in SBH-rich copolymers. LCP does not lose its mesophase behaviour when bonded to the PE backbone and the morphology of the copolymers is not homogeneous. It is characterized by two types of structure typical of both copolymer segments. There are no interactions in the crystal phase or co-crystallization between the copolymer segments, forming separate crystalline phases. The results have been interpreted by a sufficient length of crystallizable segments of PE and SBH grafts and by a random distribution of SBH grafts along the PE backbone. The latter effect is more pronounced for PE-g-SBH copolymers based on higher molar mass functionalized PE (Escor 5001). It has been assumed that the compatibilization activity of these copolymers towards polyethylene/SBH blends is due not only to the identical chemical structure of the copolymer segments and the corresponding blend components but also to the similarity of their crystalline structure, crystallization behaviour, and morphology.