Biodegradable polymers are designed to degrade upon disposal by the action of living organisms. Extraordinary progress has been made in the development of practical processes and products from polymers such as starch, cellulose, and lactic acid. The need to create alternative biodegradable water-soluble polymers for down-the-drain products such as detergents and cosmetics has taken on increasing importance. Consumers have, however, thus far attached little or no added value to the property of biodegradability, forcing industry to compete head-to-head on a cost-performance basis with existing familiar products. In addition, no suitable infrastructure for the disposal of biodegradable materials exists as yet.

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In this paper, Novozyme-435-catalyzed ω-pentadecalactone and ω-pentadecalactone/ε-caprolactone polymerizations were investigated. Novozyme-435-catalyzed ω-pentadecalactone polymerizations were studied in bulk and at ω-pentadecalactone-to-toluene ratios from 1:1 to 1:10 (wt/vol). By carrying out polymerizations with ω-pentadecalactone to toluene 1:1 wt/vol instead of in bulk, the monomer conversion (32 to 90%) and product M n (22 × 103 to 86 × 103 g/mol) increased. Effects of reaction temperature on monomer conversion and product molecular weights also were studied. ω-Pentadecalactone polymerization at 90 °C in toluene (1:2 ω-pentadecalactone to toluene wt/vol) resulted in the fastest kinetics thus far reported for lipase-catalyzed polyester production. However, reduction of the polymerization temperature from 90 to 55 °C gave polypentadecalactone with increased M n (66 × 103 to 81 × 103 g/mol). Novozyme-435-catalyzed ω-pentadecalactone/ε-caprolactone copolymerizations conducted at 70 °C in toluene occurred at unexpectedly rapid rates. Studies of monomer coreactivity ratios (r 1 = 1.742 and r 2 = 0.135) showed that ω-pentadecalactone reacted 13 times faster than ε-caprolactone. 13C NMR studies showed that copolymers with random repeat unit sequence distributions were formed after 10 min at monomer conversions ≥44%). We believe that Novozyme-435 actively promotes interchain transesterification reactions that tend to randomize the repeat unit sequence distribution.

The effects of substrates and solvent on polymer formation, number-average molecular weight (M(n)), polydispersity, and end-group structure for lipase-catalyzed polycondensations were investigated. Diphenyl ether was found to be the preferred solvent for the polyesterification of adipic acid and 1,8-octanediol giving a M(n) of 28 500 (48 h, 70 degrees C). The effect of varying the alkylene chain length of diols and diacids on the molecular weight distribution and the polymer end-group structure was assessed. A series of diacids (succinic, glutaric, adipic, and sebacic acid) and diols (1,4-butanediol, 1,6-hexanediol, and 1,8-octanediol) were polymerized in solution and in bulk. It was found that reactions involving monomers having longer alkylene chain lengths of diacids (sebacic and adipic acid) and diols (1,8-octanediol and 1,6-hexanediol) give a higher reactivity than reactions of shorter chain-length diacids (succinic and glutaric acid) and 1,4-butanediol. The bulk lipase-catalyzed condensation reactions were feasible, but the use of diphenyl ether gave higher M(n) values (42,400 g/mol in 3 days at 70 degrees C). The polydispersity varied little over the conditions studied giving values

Random copolymers were prepared by Candida antarctica lipase B (Novozyme-435) catalyzed copolymerization of omega-pentadecalactone (PDL) with epsilon-caprolactone (CL). Over the whole composition range PDL-CL copolymers are highly crystalline (melting enthalpy by differential scanning calorimetry, above 100 J/g; crystallinity degree by wide-angle X-ray scattering, WAXS, 60-70%). The copolymers melt at temperatures that linearly decrease with composition from that of poly(omega-pentadecalactone) (PPDL; 97 degrees C) to that of poly(epsilon-caprolactone) (PCL; 59 degrees C). The WAXS profiles of PCL and PPDL homopolymers are very similar, except for the presence in PPDL of the (001) reflection at 2theta = 4.58 degrees that corresponds to a 19.3 angstroms periodicity in the chain direction. In PDL-CL copolymers the intensity of this reflection decreases with increasing content of CL units and vanishes at 50 mol % CL, as a result of randomization of the ester group alignment and loss of chain periodicity. PDL-CL copolymers crystallize in a lattice that gradually changes from that of one homopolymer to that of the other, owing to comonomer isomorphous substitution. Cocrystallization of comonomer units is also shown by a random PDL-CL copolymer obtained in a polymerization/transesterification reaction catalyzed by C. antarctica lipase B (Novozyme-435) starting from preformed PCL and PDL monomer.

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Bulk condensation polymerizations of adipic acid and octanediol, catalyzed by Candida antartica Lipase B (CALB), were investigated. The polymers formed by 8 and 24 h polymerizations using CALB immobilized on Accurel and Lewatit had similar molecular weights (e.g., M n at 24 h ≈15 000). CALB "free" of the immobilization resin was also active for the polymerization but, relative to its immobilized forms, gave slower chain growth (M n ≈ 10 000 by 48 h). For all three catalyst systems at degree of polymerization (DP) g 20, dispersity (Mw/Mn) was e1.5. Since random processes of step-growth condensation polymerizations give dispersity values g 2, the dispersity of products obtained using CALB as the catalyst is believed to result from the unique chain length or mass selectivity of the lipase. Gel permeation chromatograms showed that between 15 min and 4 h chain growth occurred rapidly so that the fraction of product with M p values > 2910 increased from 28 to 78%. At 70°C the catalyst activity at 4 h remained unchanged but decreased by 15 and 21% at 24 and 48 h. Unexpectedly, an increase in the concentration of CALB on Lewatit from 0.1 to 1 wt % protein resulted in only a small increase in M n (e.g., at 24 h, 14 500 vs 17 800). However, decrease in the percent protein to 0.5% had a large detrimental effect. Between 65 and 90°C the polymerizations occurred with little dependence on the reaction temperature.

This paper reports the free radical polymerization of methyl methacrylate (MMA) catalyzed by horseradish peroxidase (HRP). A novel method was developed whereby MMA polymerization can be carried out at ambient temperatures in the presence of low concentrations of hydrogen peroxide and 2,4-pentanedione in a mixture of water and a water-miscible solvent. Polymers of MMA formed were highly stereoregular with predominantly syndiotactic sequences (syn-dyad fractions from 0.82 to 0.87). Analyses of the chloroform-soluble fraction of syndio-PMMA products by GPC showed that they have number-average molecular weights, Mn, that range from 7500 to 75,000. By using 25% v/v of the cosolvents dioxane, tetrahydrofuran, acetone, and dimethylformamide, 85, 45, 7 and 2% product yields, respectively, resulted after 24 h. Increasing the proportion of dioxane to water from 1:3 to 1:1 and 3:1 resulted in a decrease in polymer yield from 45 to 38 and 7%, respectively. Increase in the enzyme concentration from 70 to 80 and 90 mg/mL resulted in increased reaction kinetics. By adjustment of the molar ratio of 2,4-pentanedione to hydrogen peroxide between 1.30:1.0 and 1.45:1.0, the product yields and Mn values were increased. On the basis of the catalytic properties of HRP and studies herein, we believe that the keto-enoxy radicals from 2,4-pentanedione are the first radical species generated. Then, initiation may take place through this radical or by the radical transfer to another molecule.