REACTIVE BLENDING OF A FUNCTIONALIZED POLYETHYLENE WITH A SEMIFLEXIBLE LIQUID-CRYSTALLINE COPOLYESTER

Reactive blends (50/50 w/w) of a low molar mass polyethylene containin g free carboxylic groups (PEox) and a semiflexible liquid crystalline polyester (SBH 1 : 1 : 2, by Eniricerche) have been prepared at 240 de grees 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 th e formation of a PE-g-SBH copolymer, the blends have been fractionated by successive extractions with boiling toluene and xylene. The solubl e fractions and the residues have been analyzed by Fourier transform i nfrared (FTIR) spectroscopy, thermogravimetry (TG and DTG), differenti al 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 nu mber of PEox carboxylic groups entering the transesterification or the length of grafted SBH branches, are formed as a result of blending. D epending on the relative content of PE and SBH segments, the copolymer s dissolve in the solvents, together with any unreacted PEox, or remai n 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 ca rried out with long (120 min) mixing times lead to improved interfacia l adhesion and phase dispersion when added to PE/SBH blends. (C) 1996 John Wiley & Sons, Inc.