Lipase-catalyzed ring-opening polymerizations: Polyesters, polycarbonates and block copolymers

In the first part of this dissertation, lipase Novozym 435 (immobilized form of lipase B from Candida antarctica) was used as the catalyst for the ring-opening bulk polymerization of {dollar}varepsilon{dollar}-caprolacone ({dollar}varepsilon{dollar}-CL) and trimethylene carbonate (TMC). The effects of variation in the monomer to catalyst ratio on the polymerization mechanism(s) and propagation kinetics were studied. Lipase amount and catalyst concentration had a profound affect on monomer conversion rate and product molecular weight. Increasing the (catalyst) in both systems increased the initial rates of monomer conversion. Reactions conducted with 9.8 mg of catalyst per mmole of {dollar}varepsilon{dollar}-CL reached 78 mole % monomer conversion in just 4 hours. In contrast, with 1.8 mg of catalyst per mmole of {dollar}varepsilon{dollar}-CL, 48 hours was needed to reach a similar level of conversion. On the other hand, at the same level of monomer conversion, the number-average molecular weight M{dollar}rmsb{lcub}n{rcub}{dollar} decreased with increasing catalyst concentration. The polymerization propagation kinetics was studied using the diagnostic tools for living polymerizations. For the {dollar}varepsilon{dollar}-CL system, a linear relationship exists between M{dollar}rmsb{lcub}n{rcub}{dollar} and monomer conversion suggesting that chain transfer does not occur. A linear relationship between the natural log plot of monomer conversion versus reaction time was observed for {dollar}varepsilon{dollar}-CL polymerization. Thus, it was concluded that the rate of polymerization {dollar}(rm Rsb{lcub}p{rcub}){dollar} is first order in monomer consumption and that chain termination does not occur in this system. Similarly, increasing the Novozym 435 concentration from 8.3 to 23.6 mg/mmol-TMC increased the rate of monomer conversion. However, more amount of catalyst is needed to reach the same monomer conversion level. Nonlinear behaviors for both the natural log plot of {dollar}rm Ln{lcub}lbrack Mrbrack sb0/lbrack Mrbracksb{lcub}t{rcub}{rcub}{dollar} versus reaction time and M{dollar}rmsb{lcub}n{rcub}{dollar} with monomer conversion were observed. Comparison of the results obtained by using lipase Novozym 435 to catalyze {dollar}varepsilon{dollar}-CL and TMC polymerizations suggests that other factors such as enzyme-substrate specificity in addition to total number of chains in the system may govern the R{dollar}rmsb{lcub}p{rcub}.{dollar}; In the second part of this dissertation, a one-pot biocatalytic synthesis of novel amphiphilic products consisting of an ethylglucopyranoside (EGP) head group and a hydrophobic polyester chain is described. The porcine pancreatic lipase (PPL) catalyzed ring-opening polymerization of {dollar}varepsilon{dollar}-caprolactone ({dollar}varepsilon{dollar}-CL) by the multifunctional initiator EGP was carried out in bulk. Products of variable oligo({dollar}varepsilon{dollar}-CL) chain length (M{dollar}rmsb{lcub}n{rcub}{dollar} = 450, 2200 g/mol) were formed by variation of the {dollar}varepsilon{dollar}-CL/EGP ratio. Structural analysis showed that the reactions were highly regiospecific. The resulted EGP polyester conjugates were found to be surface active and the surface activity of the conjugates were related to their molecular weights.; The EGP oligo({dollar}varepsilon{dollar}-CL) conjugate was also used as a macromonomer to prepare a novel multiarm block copolymer of PCL and PLA with a well-defined spatial architecture. For this purpose, 1-ethyl 6-oligo({dollar}varepsilon{dollar}-CL) glucopyranoside (EGP) with M{dollar}rmsb{lcub}n{rcub}{dollar} = 1,120 g/mol {dollar}rm (Msb{lcub}w{rcub}/Msb{lcub}n{rcub}{dollar} = 2.16) was first regioselectively end-capped through a transesterification reaction catalyzed by lipase PS30 (from Pseudomonas cepacia). Vinyl acetate was used as an irreversible capping agent. The resulted block copolymer was found to consist of three...