Synthesis of H-shaped carbon-dioxide-derived poly(propylene carbonate) for topology-based reduction of the glass transition temperature

Abstract

H-shaped poly(propylene carbonate) (PPC) was synthesized from a tetrafunctional linear PPC. First, a linear α,ω-dihydroxy PPC (1) was synthesized via the alternating copolymerization of carbon dioxide (CO₂) and propylene oxide (PO) catalysed by a cobalt porphyrin complex and DMAP system. A subsequent chain-end functionalization with 1,3,5-benzenetricarbonyl trichloride afforded a tetrafunctional linear PPC (2) with dicarboxylic acid groups at both chain ends. H-shaped PPC (3) was synthesized from 2, as the macromolecular chain-transfer agent, by further alternating copolymerization of CO₂ and PO. Moreover, the thermal properties of 3, as determined by DSC, indicated that the glass transition temperature (T_g) of 3 (T_g = 21 °C) is significantly lower than that of linear PPC (T_g = 30 °C). This attribute of the H-shaped topology (lowering of T_g) was then applied to a new self-assembly system. Thus, a PPC with two thymine groups at both chain ends (4) and a PPC with a 2,6-diaminopyridine group at the centre of the main chain (5) were synthesized and self-assembled simply by mixing at a 1 : 2 ratio. Interestingly, the T_g of the self-assembled product (from 4 and 5) was comparable to that of 3, indicating the formation of an H-shaped topology through complementary hydrogen-bonding interactions.