CHEMICAL-KINETICS OF A 2-COMPONENT PHASE SEGREGATED SYSTEM - A SIMPLERATE MODEL

Considerable research has been performed on polymeric systems that exh ibit liquid crystalline or mesomorphic behavior. The principal reason for this effort was that these materials might be developed as ultrahi gh strength materials. Jackson and Kuhfuss from Tennessee Eastman demo nstrated that liquid crystalline behavior existed in copolymers based on poly(ethylene terephthalate) (PET) and para-hydroxy benzoic acid (A BA). However, intricate details pertaining to the polyesterification k inetics have remained unexamined. Structural elucidations have generat ed conflicting data for the system. The C-13 NMR(16) and high-temperat ure X-ray diffraction indicate a random behavior of PET and oxybenzoat e. Thermal analyses have implied an inclination towards nonrandom asse mbly. Similarly, optical and electron microscopy examinations, coupled with data from X-ray and conventional electron microscopy endorse the existence of ordered domains of lamellar 4-oxybenzoate blocks in the PET/80 ABA copolyester. The cooling of a biphasic melt is known to tri gger a biphasic structure [4]. Transesterification reactions between p oly(ethylene terephthalate) PET, and acetoxybenzoic acid (ABA) were co nducted using the melt polymerization technique to understand the tran sesterification kinetics of a phase segregated system. The transesteri fication kinetics of two compositions PET 20/80 (ABA) and PET 10/90 (A BA) have been studied at 260, 275, 290 and 305 degrees C using dibutyl tinoxide (0.1 mole percent) as a catalyst. Then the homopolymerizatio n of acetoxy benzoic acid was studied at similar temperatures and cata lyst concentration. Few assumptions were made to simplify the kinetic analysis. (1) ABA homopolymerises to form acetic acid and higher oligo mers. The oligomers add on to a PET chain to give a copolymer or PET/A BA, the product of interest. (2) The reaction between PET and ABA proc eeds in a heterogeneous two-phase system consisting of a ABA rich and poor phase. The reaction sequence would be: (i) ABA reacts with itself to form oligomers of varying chain length and (ii) The subsequent add ition of the oligomers onto the PET chain. The reaction sequence is as sumed to be valid for ABA rich and poor phase. Both the reactions are assumed to be second order with respect to the reactants. Moles of ace tic acid found experimentally are computed using a standard procedure. The rate constant k is determined. The role of the catalyst is also e valuated.