Effect of copolycondensation temperature on the reactivity ratios of bis(4-hydroxybutyl) terephthalate and bis(2-hydroxyethyl) terephthalate

The effect of copolycondensation temperature on the monomer reactivity rati os of bis(4-hydroxybutyl) terephthalate (BHBT) and bis(2-hydroxyethyl) tere phthalate (BHET) was investigated at 260, 270, and 280 degrees C, in the pr esence of titanium tetrabutoxide as a catalyst. Adopting 2nd order kinetics to polycondensation, the rate constants of polycondensation of BHBT and BH ET, k(11) and k(22), were calculated to be 2.58, 1.30; 3.87, 2.24; and 5.29 , 4.06 min(-1). In addition, the rate constants k(12) and k(21) of cross re actions could be determined as 0.91, 3.00; 1.49, 4.42; and 2.13, 5.85 min(- 1) from a proton nuclear magnetic resonance spectroscopic analysis. The mon omer reactivity ratios of BHBT were much larger than those of BHET, indicat ing the block nature of the copolycondensation, but the differences between monomer reactivity ratios were decreased with increasing polycondensation temperature, indicating that a probability of randomization was increased.