| The broad objective of my thesis was to better understand the factors that govern step-growth kinetics, molecular weight distribution and chain end-group structure for enzyme catalyzed direct condensation reactions between linear aliphatic diols and diacids.; Bulk condensation polymerization of adipic acid and octane diol, catalyzed by Candida antartica Lipase B (CALB), was investigated. Comparison of polymerizations conducted using Accurel and Lewatit as supports gave similar products after 8 and 24 h polymerizations (e.g., Mn at 24 h ≈ 15 000). Non-immobilized CALB was active for the polymerization but gave slower chain growth (Mn ≈ 10 000 by 48 h). For all three catalyst systems at degree of polymerization (DP) ≥ 20, dispersity (Mw/Mn) was ≤1.5. Molecular weight build up and distribution with time were assessed. Unexpectedly, an increase in the concentration of CALB on Lewatit from 0.1 to 1% by wt. protein resulted in only a small increase in M n. (e.g., at 24 h, 14 500 versus 17 800). However, decrease in the %-protein to 0.5 had a much larger detrimental effect. The polymerization showed little dependence on the temperature between 65 and 90°C.; It was seen that systems with longer chain length of diacids (sebacic and adipic acid) and diols (1,8-octane and 1,6-hexane diol) give higher reactivity than systems with shorter chain length of diacids (succinic and glutaric) and diol (1,4-butane). The condensation polymerization of adipic acid and 1,8-octanediol in diphenyl ether gave the highest molecular weight (42,400 g/mol) in 3 days at 70°C. No specific trend of end group structure development with time was observed. At 70°C the catalyst activity with time, and diol and diacid chain length were analyzed in bulk and diphenyl ether.; Novozyme-435 catalyzed bulk polyesterifications of linear aliphatic hydroxyl acids, were investigated. The effect of substrates, enzyme concentration, removal of water on enzyme activity and molecular weight build up and distribution with time were assessed. The relative reactivity of hydroxy acids as a function of chain length is as follows: 16-hydroxyhexadecanoic acid ≈ 12-hydroxydodecanoic acid ≈ 10-hydroxydecanoic acid (DPavg ≅ 120, M w/Mn ≤ 1.5,48 hr, 90°C) > 6-hydroxyhexanoic acid (DPavg ≅ 80, M w/Mn ≤ 1.5, 48 hr, 90°C). (Abstract shortened by UMI.)... |
