Reactive compatibilization of blends containing liquid crystalline polymers

This paper describes the reactive compatibilization of blends of a wholly aromatic thermotropic copolyester liquid crystalline polymer (TLCP) with random copolymers of ethylene and acrylic acid (EAA) and their salts. Two different TLCPs were used: one was a copolymer of hydroxybenzoic acid and hydroxynaphthanoic acid and the other also contained terephthalic acid and hydroquinone monomers. The EAA ionomers contained either 15 or 20 wt% acrylic acid, and the salts considered included Na+, Zn2+, Li+ and K+. Blends were prepared by melt-mixing in an intensive mixer, and the formation of a graft copolymer due to acidolysis between the TLCP and the acrylic acid group of the ionomer (none of the ionomers were fully neutralized) was evaluated. Chemical reaction was assessed by torque measurements during melt-mixing, thermal analysis and microscopy of the blends. The Na-salt of the EAA ionomers was especially effective at inducing a grafting reaction. The free-acid derivative and Ether salts either did not react or were much less effective at promoting an interpolymer reaction. The extent of reaction depended not only on the cation, but also on the composition of the ionomer, the reaction temperature and time. The reaction between the ionomer and the TLCP during mixing, effectively compatibilized the blend. Also the addition of a minor amount of the Na-salt of EAA compatibilized a TLCP-high density polyethylene blend. (C) 2000 Elsevier Science Ltd. All rights reserved.