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Aliphatic polycarbonates (APC) are a class of biodegradable polymers that are attracting great interest of materials engineers because of their good biocompatibility and degradation to less acidic products. There are many types of APC consisting of different alkanediol units. Those consisting of diols of middle carbon-chain length (C5 C8) are used as soft segments having low Tg, while those consisting of alicyclic building blocks can be applied as hard segments. The commercially available poly(hexamethylene carbonate) (PHMC) diol and poly(hexamethylene/ pentamethylene carbonate) (PHPC) diol, having low molecular weight and bis-hydroxyl terminals, are used as soft segments of polyurethane. Recently their environmental friendliness is highlighted because they are synthesized from ethylene carbonate (EC) manufactured by the use of carbon dioxide as feedstock. With this nature in mind, we have demonstrated that PHMC diol can be used as a macroinitiator of the ring-opening polymerization (ROP) of Llactide to prepare tri-block copolymers comprising polyL-lactide (PLLA) and PHMC (PLLA-PHMC-PLLA) that have both biobased and CO2-originated characters. Since PHMC is crystalline at ambient temperature, the properties of the PLLA-PHMC-PLLA copolymers may be significantly influenced by the temperature change. In the present study, therefore, we use amorphous PHPC diol as the macro-initiator to obtain similar PLLA-APC block copolymers, and for which the elastomeric properties are evaluated. Here, we first analyze the microstructure of the PHPC oligomer that is industrially produced by the reaction of an alkanediol mixture and EC. Since the synthetic procedure using EC as the starting carbonate source is different from the ordinary polycondensation of diphenyl carbonate (DPC) and diols, the resultant polycarbonate is known to involve minor units different from the diol units. The well-characterized PHPC oligomer is then chain-extended with DPC as chain extender to obtain high molecular weight polymers, and which were used as the macroinitiators of the ROP of Llactide to prepare PLLA-PHPC-PLLA tri-block copolymers (Scheme 1). The PLLA-PHPC-PLLA block copolymers obtained are finally characterized in detail to Preparation of Chain-Extended Poly(hexamethylene/pentamethylene carbonate)s and Their Block Copolymerization with Poly-L-lactide into Partly Biobased Thermoplastic Elastomers

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Preparation of Chain-Extended Poly(hexamethylene/pentamethylene carbonate)s and Their Block Copolymerization with Poly-L-lactide into Partly Biobased Thermoplastic Elastomers