Isothermal crystallization of blends containing two thermotropic liquid crystalline polymers

Abstract

The intention of this work is to determine how the isothermal crystallization behavior of a thermotropic liquid crystalline polymer (TLCP) can be adjusted by blending it with a pure TLCP of lower melting point. One TLCP (Tm ∼350°C) used is a copolyester synthesized from terephthalic acid, 4-hydroxybenzoic acid, hydroquinone and hydroquinone derivatives. The other TLCP (Tm ∼280°C) is a copolyesteramide of 60mol% hydroxynaphthoic acid, 20mol% terephthalic acid and 20mol% 4-aminophenol. As the content of the low melting TLCP increases in the blends, the temperature at which isothermal crystallization occurs decreases. Comparing with pure TLCPs, the blend of 75% low melting TLCP crystallizes at a lower temperature than the pure matrix, and the blend remains as a stable super-cooled fluid in the temperature range from 220 to 280°C for 1200s. Because of the low energy released during the phase transition, small amplitude oscillatory shear (SAOS) is more sensitive to detecting the onset of isothermal crystallization than differential scanning calorimetry (DSC).