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

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journal contribution
posted on 14.04.2009, 00:00 by Ruizhi Wu, Talal F. AL-Azemi, Kirpal S. Bisht
Block copolymerization of a seven-membered cyclic carbonate (5S,6S)-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(OiPr)3, and diethylzinc monohydrate, ZnEt2−H2O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 (Mn = 24 000 g/mol; PDI = 1.6; [α]D20 = +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], Mn = 24 000 g/mol; PDI = 1.6; [α]D20 = +33.8). Two glass transition temperatures (Tg) 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.