A novel concept for the metal-free synthesis of block copolymers combining enzymatic ring-opening polymerization and nitroxide-mediated living free-radical polymerization from a bifunctional initiator is presented. Block copolymers comprising a poly(styrene) and poly(caprolactone) block were obtained in two consecutive polymerization steps (macroinitiation) and in a one-pot cascade approach without intermediate transformation or work up step. By optimization of the reaction conditions a high selectivity of both transformations could be realized in the cascade polymerization, resulting in high block copolymer yields. The same concept was successfully applied to enzymatic resolution polymerization of racemic 4-methyl-ε-caprolactone combined with the living free-radical polymerization of styrene yielding block copolymers with high enantiomeric excess in the 4-methyl-ε-caprolactone block.

The effect of chain structure (supramolecular random copolymer vs supramolecular segmented copolymer) on material properties of supramolecular polymers was studied, using polyesters, end-functionalized with quadruple hydrogen-bonding ureidopyrimidinone (UPy) units. Mixing of miscible UPy homopolymers led to supramolecular segmented copolymers while functionalized random copolymer diols resulted in supramolecular random copolymers. The (co)polymers were prepared by (co)polymerization of -CL and δ-VL using Novozym 435, followed by end functionalization with UPy. Thermal analysis of the functionalized (co)polymers showed two melting transitions. With variable temperature IR, the lower transition was attributed to the melting of the polyester part, while the higher transition corresponded to melting of UPy moieties. The materials can therefore be considered as supramolecular thermoplastic elastomers with a hard phase of microphase separated UPy dimers, giving mechanical strength to the material. Mixing of UPy functionalized homopolymers gave better control over the mechanical properties than UPy functionalized copolymers as a correlation was found between the Young modulus and the fraction of δ-VL polymer in the material.

Novozym 435-catalyzed ring-opening of a range of omega-methylated lactones demonstrates fascinating differences in rate of reaction and enantioselectivity. A switch from S- to R-selectivity was observed upon going from small (ring sizes or=8). This was attributed to the transition from a cisoid to a transoid conformational preference of the ester bond on going from small to large lactones. The S-selectivity of the ring-opening of the small, cisoid lactones was low to moderate, while the R-selectivity of the ring-opening of the large transoid lactones was surprisingly high. The S-selectivity of the ring-opening of the small, cisoid lactones combined with the established R-selectivity of the transesterification of (aliphatic) secondary alcohols prevented polymerization from taking place. Ring-opening of the large, transoid lactones was R-selective with high enantioselectivity. As a result, these lactones could be polymerized, without exception, by straightforward kinetic resolution polymerization, yielding the enantiopure R-polyester with excellent enantiomeric excess (>99%).

Iterative tandem catalysis is presented as a flexible tool for obtaining chiral macromolecules from racemic or prochiral monomers. Here, we combine lipase-catalyzed ring-opening of omega-substituted lactones with ruthenium-catalyzed racemization. In a two-pot system, enantioenriched oligomers of 6-methyl-epsilon-caprolactone were synthesized, which could not have been obtained by enzymatic ring-opening alone. A one-pot experiment proved highly promising in developing a novel route toward enantiopure polyesters.