Exploring ε-Caprolactone Polymerization using N-Heterocyclic Carbene-Carbodiimide Adducts
Poly(ε-caprolactone), a flexible polymer with a low glass-transition temperature, is compatible with conditions inside the body as well as being permeable, which makes it ideal for biomedical applications such as drug-delivery beads and medical sutures.1 It can also be combined with other biopolymers such as starches to make degradable plastics. The corresponding monomer, ε-caprolactone, can undergo ring-opening polymerization catalyzed by N-heterocyclic carbenes (NHCs). NHCs can form adducts with carbodiimides (CDIs), which offer a way to control the release of the free carbene without changing the structure of the NHC. Herein, we describe a synthesis of the NHC 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, which has been reported by Kamber et al. to efficiently catalyze the ring-opening polymerization of ε-caprolactone in high yield and with low polydispersity index. Future work will involve determining the temperature at which the free carbene is released as a function of the substituents on the CDI, and subsequently gaining precise control over the properties of the polymer through NHC-CDI catalysis.