Preparation, Characterization, and Microstructure of Poly(epsilon-caprolactone-co-2,2-dimethyltrimethylene carbonate) Using Metal-free Organocatalysts

摘要

We investigated the random copolymerization of epsilon-caprolactone and 2,2-dimethyltrimethylene carbonate [poly(CL-co-DTC)] promoted by various imidazolium-based carbenes, including 1-isopropyl-3-p-methoxyphenylimidazol-2-ylidene [Catalyst (1)], 1-isopropy-3-p-methylphenylimidazol-2-ylidene [Catalyst (2)], and 1-methyl-3-p-methoxyphenyl-imidazol-2-ylidene [Catalyst (3)], all of which are new types of unsymmetrical N-heterocyclic carbene catalysts. The reaction was carried out in the presence of benzyl alcohol (BnOH) as an initiator in tetrahydrofuran. By varying the experimental conditions and the monomer feed composition, poly(CL-co-DTC) with high yield and molecular weight was prepared using the binary system Catalyst (1)/BnOH as catalyst/initiator. H-1 NMR and differential scanning calorimetry (DSC) characterizations verified random structures of the polymer. GPC characterization further showed high molecular weights and narrow molecular weight distribution of the final product.