Studies on Comonomer Compositional Distribution of Poly(propylene carbonate-propylene oxide) Copolymer and Its Effect on the Thermal, Mechanical and Oxygen Barrier Properties of Fractions

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Poly(propylene carbonate) (PPC) was synthesized by the alternating copolymerization of carbon dioxide and propylene oxide (PO). However, during the polymerization, two by-products tended to produce cyclic propylene carbonate (CPC) and a polyether (PE) segment. The excess PO repeat units (PE segment) can easily insert into the PPC backbone and eventually produce the PPC–PO copolymer. The production of CPC and PE segments affected the increase of polymer chain length. In order to investigate the effects of the existence of PE segments, CPC, and molecular weight of fractions on the physical properties of PPC–PO copolymer, a series of fractions with narrow molecular weight distribution were obtained by repeated fractionation. Based on a solvent/non-solvent (chloroform/n-heptane) mixture, an original PPC–PO sample was fractionated into nine fractions with number–average molecular weights (Mn) from 0.34 × 105 to 5.56 × 105 and PE content from 0.4 to 15 mol%. The Mn of PPC–PO fractions decreased with the increase of PE content in the PPC–PO backbone, and the thermal and mechanical properties of the PPC–PO copolymers were affected by their Mn and PE contents. Furthermore, the lower the PE content, the higher the Mn value. Higher Mn means better tensile and lower oxygen permeability of PPC–PO copolymer.