Thermally Depolymerizable Polycarbonates. 2. Synthesis of Novel Linear Tertiary Copolycarbonates by Phase-Transfer Catalysis

The first synthesis of copolycarbonates containing a tertiary diol structure has been achieved by using a solid-liquid phase-transfer-catalyzed polycondensation of the bis(carbonylimidazolide) of 2,5-dimethyl-2,5-hexanediol with various other diols in the presence of powdered potassium carbonate. The solubility and physical properties of the copolycarbonates are affected by the nature of the diol used in the polycondensation. Higher melting polymers are obtained when the diol structure incorporates an aromatic ring while increased solubility results from increased steric crowding or the incorporation of less symmetrical or aliphatic structures in the diol component. The copolycarbonates decompose cleanly upon heating to approximately 200 °C with liberation of volatile materials, leaving no solid residue. For example, the copolycarbonate of 2,5-dimethyl-2,5-hexanediol and p-benzenedimethanol is stable to 200 °C, and then undergoes rapid thermolysis with formation of carbon dioxide, p-benzenedimethanol, and a mixture of three dienes corresponding to all the possible dehydration products of 2,5-dimethyl-2,5-hexanediol. The thermal lability of the polycarbonates allows their analysis by gas chromatography-mass spectroscopy using direct solid sample injection.