LIPASE-CATALYZED RING-OPENING POLYMERIZATION OF TRIMETHYLENE CARBONATE

Citation
Ks. Bisht et al., LIPASE-CATALYZED RING-OPENING POLYMERIZATION OF TRIMETHYLENE CARBONATE, Macromolecules, 30(25), 1997, pp. 7735-7742
Citations number
35
Categorie Soggetti
Polymer Sciences
Journal title
ISSN journal
00249297
Volume
30
Issue
25
Year of publication
1997
Pages
7735 - 7742
Database
ISI
SICI code
0024-9297(1997)30:25<7735:LRPOTC>2.0.ZU;2-3
Abstract
This work was directed at extending the use of lipase-catalyzed ring-o pening polymerizations to cyclic carbonate monomers. Of the seven lipa ses screened for bulk trimethylene carbonate (TMC) polymerization (70 degrees C, 120 h), Novozym-435 from Candida antarctica gave almost qua ntitative monomer conversion (97%) and poly(TMC) with a M-n = 15 000 ( M-w/M-n = 2.2) with no apparent decarboxylation during propagation. Th e lipases from Pseudomonas species (AK and PS-30) and porcine pancreas (PPL) also exhibited high monomer conversions (>80%, 120 h) but gave lower molecular weight polymers with broad polydispersity. Analyses by H-1-NMR spectroscopy suggested that poly(TMC) prepared by Novozym-435 -catalyzed polymerization had terminal -CH2OH functionalities at both chain ends. A monotonic increase in monomer conversion with time and t he rapid increase in M,, as a function of monomer conversion for Novoz ym-435-catalyzed TMC bulk polymerization at 70 degrees C suggest that the polymerization has chain-type propagation kinetics. An increase in conversion above 66% did not substantially change M-n. The percent co nversion was larger when the reaction temperature was increased from 4 5 to 55 degrees C. Further increase in the reaction temperature from 5 5 to 85 degrees C did not give higher percent conversion values. The m olecular weight decreased substantially as the reaction temperature wa s increased from 55 to 85 degrees C (M-n from 24 400 to 5 900). The hi ghest poly(TMC) molecular weight (M-n = 24 400) was obtained by conduc ting the polymerization at 55 degrees C. Monomer conversion and molecu lar weight as a function of the percent reaction water content (w/w) w ere investigated. Increasing the water content resulted in enhanced po lymerization rates and decreased molecular weights. Separation of the oligomeric products from polymerizations of TMC in dried dioxane and t oluene catalyzed by porcine pancreatic lipase led to the isolation of di- and triadducts of trimethylene carbonate. Based on the symmetrical structure of these products and the end-group structure of high molec ular weight chains, a mechanism for chain initiation and propagation f or lipase-catalyzed TMC polymerization was proposed.