Enzyme-catalyzed polymerizations of epsilon-caprolactone: Effects of initiator on product structure, propagation kinetics, and mechanism

被引:120
作者
Henderson, LA
Svirkin, YY
Gross, RA
Kaplan, DL
Swift, G
机构
[1] UNIV LOWELL,DEPT CHEM,LOWELL,MA 01854
[2] USA,NATICK RES DEV & ENGN CTR,DIV BIOTECHNOL,STRNC,YM,NATICK,MA 01760
[3] ROHM & HAAS CO,SPRING HOUSE,PA 19477
关键词
D O I
10.1021/ma960821h
中图分类号
O63 [高分子化学(高聚物)];
学科分类号
070305 ; 080501 ; 081704 ;
摘要
Studies were undertaken to gain mechanistic information on lactone ring-opening polymerization reactions using porcine pancreatic lipase (PPL) as the catalyst and epsilon-caprolactone (epsilon-CL) as the monomer. Polymerizations were carried out at low water levels (0.13 mmol) and supplemented with either butanol or butylamine. Rates of monomer conversion, product molecular weight, total chain number, and chain end structure were determined by H-1 NMR. In the presence of water alone, a maximum M(n) of 7600 g/mol was obtained at 85% conversion, which decreased to 4200 g/mol as the reaction continued to 98% conversion. Reactions with butanol and butylamine at 100% conversion gave polymers with M, values of 1900 and 1200 g/mol, respectively. For these three polymerizations, the total number of polymer chains increased with conversion due to a simultaneous increase in carboxylic acid chain ends. Within 4 h (similar to 26% monomer conversion), butylamine was completely consumed but only 37% of butanol reacted. Reactions with butylamine occurred predominantly by an enzyme-mediated route to form N-butyl-6-hydroxyhexanamide. This step was rapid relative to subsequent chain growth. In addition, the living or immortal nature of the polymerizations was assessed from plots of log{[M](0)/[M](t)} versus time and M(n) Versus conversion. These results indicate that termination and chain transfer did not occur, and we described the system as providing ''controlled'' polymerizations. Furthermore, an expression for the rate of propagation was derived from the experimental data which is consistent with that derived from the proposed enzyme-catalyzed polymerization mechanism. The absence of termination in conjunction with the relationship between molecular weight and the total concentration of multiple initiators suggests that E-CL polymerization by PPL catalysis shares many features of immortal polymerizations.
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页码:7759 / 7766
页数:8
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