Influence of Catalyst and Polymerization Conditions on the Properties of 1,3‐Trimethylene Carbonate and ε‐Caprolactone Copolymers

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Abstract
The influence of the catalyst/initiator system and polymerization conditions on the microstructure and physical properties of copolymers of equimolar amounts of 1,3‐trimethylene carbonate (TMC) and ε‐caprolactone (CL) was studied. Statistical copolymers were prepared in the presence of stannous octoate (SnOct2) in the bulk at 80 °C (14 and 28 d) and 130 °C (1 and 3 d). The copolymerization of TMC and CL initiated by yttrium isopropoxide (Y5(μ‐O)(OiPr)13) was performed in solution at room temperature (5 min) and in the bulk at 80 °C (2 min). Block copolymers, used as reference materials, were also prepared by sequential polymerization of the monomers in solution at room temperature with yttrium isopropoxide. Both SnOct2 and yttrium isopropoxide yielded polymers with shorter average monomer sequence lengths at higher reaction temperatures. For the polymerizations with SnOct2 a similar effect was observed when the reactions were allowed to proceed for longer periods of time. Independent of the catalyst/initiator system, the statistical copolymers prepared in the bulk at 80 or 130 °C were amorphous, with average monomer sequence lengths shorter than 3. The copolymer prepared in solution at room temperature with yttrium isopropoxide was more blocky, with CL sequences long enough to crystallize ($\overline {\rm L} _{{\rm CL}} = 3.93$ ). The former copolymers are highly flexible but show low tensile strengths, in agreement with their amorphous structure and low glass transition temperature. The latter copolymer is also flexible but much tougher and stiffer, as it is semi‐crystalline. Its properties are characteristic of phase‐separated block copolymers. Expanded regions of carbonyl carbon atoms in 13C NMR (75.5 MHz) spectra of TMC–CL copolymer prepared at 80 °C in the bulk in the presence of yttrium isopropoxide. magnified image Expanded regions of carbonyl carbon atoms in 13C NMR (75.5 MHz) spectra of TMC–CL copolymer prepared at 80 °C in the bulk in the presence of yttrium isopropoxide.

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