Reactive blending of a functionalized polyethylene with a semiflexible liquid crystalline copolyester

Abstract

Reactive blends (50/50 w/w) of a low molar mass polyethylene containing free carboxylic groups (PEox) and a semiflexible liquid crystalline polyester (SBH 1 : 1 : 2, by Eniricerche) have been prepared at 240 degrees C in a Brabender mixer, in the presence of Ti(OBu)(4) catalyst, for different mixing times (15, 60, and 120 min). In order to prove the formation of a PE-g-SBH copolymer, the blends have been fractionated by successive extractions with boiling toluene and xylene. The soluble fractions and the residues have been analyzed by Fourier transform infrared (FTIR) spectroscopy, thermogravimetry (TG and DTG), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). All analytical procedures concordantly show that PE-g-SBH copolymers with different compositions, arising from differences of either the number of PEox carboxylic groups entering the transesterification or the length of grafted SBH branches, are formed as a result of blending. Depending on the relative content of PE and SBH segments, the copolymers dissolve in the solvents, together with any unreacted PEox, or remain in the residues, together with neat SBH. Qualitative IR analyses and quantitative TG measurements have shown that the amount of copolymers increases strongly with the mixing time. Preliminary SEM observations indicate that the unfractionated products of the reactive blending carried out with long (120 min) mixing times lead to improved interfacial adhesion and phase dispersion when added to PE/SBH blends.