Yakai Feng, Jens Knüfermann, D. Klee
Jun 1, 1999
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0
Influential Citations
26
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Journal
Macromolecular Chemistry and Physics
Abstract
Lipase-catalyzed ring-opening bulk polymerizations of 3(S)-isopropylmorpholine-2,5-dione (IPMD) were investigated. Selected commercial lipases were screened as catalysts for IPMD polymerization at 100°C. Polymerizations catalyzed with lipases PPL, PS, and CR result in IPMD conversions of about 50%, and in molecular weights of the products ranging from 3500 to 17500. Poly(3-isopropylmorpholine-2,5-dione) has a carboxylic acid group at one end and a hydroxyl group at the other end. During the polymerization, racemization of the valine residue takes place. Lipase PPL was selected for further studies. The apparent rate of polymerization increases with PPL concentration and polymerization time. When the PPL concentration is 5 wt.-% and 10 wt.-% with respect to the monomer, a conversion of about 70% is reached after 5 d and 7 d, respectively, while for PPL concentrations of 1 wt.-% and 0.5 wt.-% the conversion is less than 15% even after 11 d. High concentrations of PPL (10 wt.-%) result in high M n values (<4 d); with decreasing concentration of PPL, poly(IPMD) of lower molecular weight is obtained. The highest molecular weight poly(IPMD), M n = 30000, resulted from a polymerization conducted at 130°C. Increasing polymerization time (and conversion) leads for high PPL concentration (10 wt.-%) first to an increase in M n and later to a decrease. The general trends observed by variation of the polymerization temperature are the following: (i) increasing monomer conversion and M n increase with increasing reaction temperature from 100 to 130°C, (ii) increasing reaction temperature leads to a bimodal molecular weight distribution. Water is an important factor that controls not only the conversion but also the molecular weight. With increasing water content, enhanced polymerization rates are achieved while the molecular weight of poly(IPMD) decreases.