| Abstract: | The possibility of reinforcing polyethylene (PE) by blending it with a liquid crystalline polymer (LCP) rests on the successful improvement of phase compatibility and interfacial adhesion of these two structurally unlike polymers. The approach that is being considered in our laboratories consists of the synthesis of PE–LCP block or graft copolymers and of their use as compatibilizing agents for PE/LCP blends. In this work, the melt polycon-densation of sebacic acid (S), 4,4′-dihydroxybiphenyl (B), and 4-hydroxybenzoic acid (H) has been carried out at temperatures up to 280°C in the presence of an oxidized low molar mass PE sample containing free carboxylic groups (PEox), with the main scope of demonstrating that a PE-g-LCP copolymer may be synthesized by this route. The polycon-densation product has been fractionated by successive extractions with boiling toluene and xylene. The soluble fractions and the residues have been characterized by IR and NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TG, DTG), and scanning electron microscopy (SEM). The extractions and the analyses have been repeated on a PEox/LCP blend prepared by melt mixing PEox and preformed LCP (SBH 112, by Eniricerche). The results show that, whereas for the blend a fairly clean separation of PEox and SBH can be obtained by solvent extraction, this is not so for the polycondensation product. All analytical procedures concordantly show that a PEox-g-SBH copolymer has, in fact, been obtained. In effect, both PEox and SBH chain segments are present, with different relative ratios, in all fractions of the polycondensate. Moreover, a fairly quantitative esterification of the PEox carboxyl groups has been shown by IR analysis to take place in the adopted conditions. Preliminary morphological investigations carried out by SEM have shown that the addition of the synthesized graft copolymer into HDPE/SBH blends leads to an improvement of the interfacial adhesion. © 1996 John Wiley & Sons, Inc. |
