One-Shot Block Copolymerization of a Functional Seven-Membered Cyclic Carbonate Derived from l-Tartaric Acid with ε-Caprolactone

Block copolymerization of a seven-membered cyclic carbonate (5 S,6 S )-dimethyl-5,6-isopropylidene-1,3-dioxepin-2-one (ITC) with ε-caprolactone in “one-shot feeding” is reported. The cyclic carbonate monomer ITC was synthesized from naturally occurring l -tartaric acid in three steps. Three catalysts—stannous octanoate, Sn(Oct) 2, triisopropoxide aluminum, Al(O i Pr) 3, and diethylzinc monohydrate, ZnEt 2 −H 2 O—were tested for the homopolymerization of ITC monomer at 120 °C for 12 h in bulk. The results show that Sn(Oct) 2 was the most effective catalyst to carry out the polymerization ( M n = 24 000 g/mol; PDI = 1.6; [α] D 20 = +77.8). The copolymerization of ITC with ε-caprolactone (CL) in various feed ratios was also investigated. The detailed spectral and thermal analysis of the copolymers catalyzed by Sn(Oct) 2 revealed formation of the block copolymer (poly[44%ITC- block -56%CL], M n = 24 000 g/mol; PDI = 1.6; [α] D 20 = +33.8). Two glass transition temperatures ( T g ) were observed for poly(44%ITC)- block -poly(56% ε-CL) at −59.1 and −37.2 °C for the poly(CL) and the poly(ITC) block, respectively, confirming the diblock nature of the copolymer. It is the first report of “one-shot” block copolymerization of ε-caprolactone with a cyclic carbonate monomer. The deprotection of the ketal groups resulted in copolymers containing free hydroxy groups in the polymer backbone.