Copolyesters of poly(butylene terephthalate), 1,4-naphthalene dicarboxylic acid, and hydroquinone diacetate: A simple rate model

Abstract

The kinetics of novel liquid crystalline copolyesters between poly(butylene terephthalate) (PBT), 1,4-naphthalene dicarboxylic acid (1,4 NDCA), and hydroquinone diacetate (HQDA) are examined by using the melt polymerization route. Three different copolyester compositions (i.e., PBT 70 mol % + 1,4 NDCA 15 mol % + HQDA 15 mol %, PBT 50 mol % + 1,4 NDCA 25 mol % + HQDA 25 mol %, and PBT 30 mol % + 1,4 NDCA 35 mol % + HQDA 35 mol %) were synthesized via the melt polymerization route. Sodium acetate and zinc acetate, 1.0 mol %, concentrations were tried as the polymerization catalysts. The reaction temperatures were 260, 270, and 280°C for PBT 70 and PBT 50 mol % compositions. PBT 30 mol % compositions were synthesized at 245, 255, and 265°C by using the above catalysts. Lower temperatures were employed for PBT 30 mol % reactions to avoid degradation reactions. The kinetics of complex systems are analyzed by methods analogous to solution kinetics. Few assumptions are proposed and tried to simplify the kinetics of this complex system and to make the kinetic analysis tractable. Two different models containing different rate constants, k1 and k2, are considered in this work. A key postulation is that the reaction originates between 1, 4 NDCA and HQDA to form a dimer. This dimer copolymerizes with the PBT chain with evolution of acetic acid (model 1) or without (model 2). The subsequent coupling of PBT segments reforms the PBT chain in the case of model 1 with random incorporation of 1, 4 NDCA–HQDA units; whereas blocks of PBT units and 1, 4 NDCA + HQDA units are formed in the case of model 2. The kinetic analysis reveals the implicit simplicity of complex systems. The number of moles of acetic acid, generated in both homopolyesterification and copolyesterfication channels, is monitored to follow the rate of the reaction and evaluate the individual rate constants. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2817–2832, 2004