Synthesis of graft copolymers by the combination of ATRP and Enzymatic ROP in scC02

A simple strategy is reported for the synthesis of well-defined graft copolymers of poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) P(MMA-co-HEMA) with poly(ε-caprolactone) (PCL) grafted chains. Using scCO2 as the only solvent, a one-step synthetic approach is adopted to prepare copolymer backbones via atom transfer radical polymerization (ATRP), and grafted chains are added via enzymatic ring-opening polymerization (eROP). Exhaustive study of the enzymatic grafting efficiency showed that only the hydroxyl groups in the backbone initiated the polymerization of ε-CL, resulting in an exceptional polymer architecture which is not accessible by conventional chemical polymerization methodology. The lower grafting density obtained (ca. 30−40%) with the enzymatic polymerization of ε-CL indicates that the system is likely limited by steric hindrance

Simultaneous Dynamic Kinetic Resolution in Combination with Enzymatic Ring-Opening Polymerization

We report the simultaneous dynamic kinetic resolution (DKR) of a secondary alcohol in combination with lipase-catalyzed ring-opening polymerization (ROP) of ε-caprolactone (ε-CL). (R,S)-1-Phenylethanol (PhE) was used as a model secondary alcohol and incorporated into poly(ε-caprolactone) (PCL) under DKR conditions. A total of 75% of the PhE was incorporated as (R)-PhE-PCL with over 99% enantio excess (ee) in 23 h. This methodology could provide a simple one-step approach to prepare enantiopure sustained release polymeric formulations of chiral species such as drugs or drug precursors bearing a secondary hydroxyl group

Kinetics of Enzymatic Ring-Opening Polymerization of ε-Caprolactone in Supercritical Carbon Dioxide

The kinetics of enzymatic ring-opening polymerization (eROP) of ε-caprolactone in supercritical carbon dioxide (scCO2) was investigated using a new, high-pressure sampling autoclave. The polymerization was performed using Candida antarctica lipase B (CALB) as catalyst and was found to be approximately first order with respect to monomer up to 80% conversion. For the first time we have been able to present kinetic results on the eROP of caprolactone in scCO2. These results show that high molecular weight polymer could be obtained (up to 50 kDa) with polydispersities in the range of 2. The relatively poor molecular weight control was attributed to the large degree of enzyme-catalyzed transesterification that forms both cyclic species (intramolecular transesterification) and linear polymer (intermolecular transesterification). This effect has also been observed for eROP of ε-caprolactone in conventional solvents. The formation of cyclic oligomers of poly(caprolactone) (PCL) was investigated as a function of conversion, and comparisons were made to similar studies undertaken in conventional solvents

Dispersion Atom Transfer Radical Polymerization of vinyl monomers in supercritical carbon dioxide

Controlled dispersion atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out in supercritical carbon dioxide in the presence of aminated fluoropolymers. These materials played the dual role of macroligand for the copper bromide and also steric stabilizer to support formation of polymer microspheres. The livingness of the PMMA beads was confirmed by the one-pot two-step PMMA chain extension and the synthesis of poly(methyl methacrylate)-b-poly(2,2,2-trifluoroethyl methacrylate) (PMMA-b-PFMA) diblock copolymer in scCO2. Successful activator generated by electron transfer (AGET) for ATRP of MMA, using tin ethylhexanoate as a reducing agent, is also discussed, and the concept of dispersion ATRP of MMA was successfully extended to the controlled dispersion polymerization of styrene by ATRP leading to the formation of PS microparticles. Finally, due to the high solubility of the catalyst in scCO2, the purification of PMMA was investigated by supercritical fluid extraction, leading to the preparation of PMMA beads with low residual catalyst traces