Physical properties and hydrolytic degradability of polyethylene-like polyacetals and polycarbonates†
Long-chain polyacetals and polycarbonates were prepared by polycondensation of α,ω-diols (C18, C19, C23) derived from fatty acids as a renewable feedstock with diethoxymethane and dimethyl carbonate, respectively, in one step. Studies of hydrolytic degradation of the solid polymers show a much higher stability compared to their shorter-chain counterparts. Long-chain polyacetals were found to degrade slowly under acidic conditions, while the long-chain polycarbonates also degraded in a basic environment. To rationalize the impact of acetal and carbonate groups on the thermal and crystalline properties of polyacetals and polycarbonates, additional model polymers with a further reduced and systematically varied functional group density were generated by ADMET copolymerization of the unfunctionalized undeca-1,10-diene with bis(undec-10-en-1-yloxy)methane or di(undec-10-en-1-yl) carbonate, respectively, followed by exhaustive hydrogenation. Long-chain polycarbonates possess polyethylene-like solid state structures. By comparison to polyesters, a given density of carbonate groups in the polymer chain reduces melting and crystallization temperatures significantly more strongly. By contrast, long-chain polyacetals possess more complex non-uniform crystal structures, and only adopt a polyethylene-like structure at very low densities of acetal groups. Also, acetal groups more strongly impact melting and crystallization temperatures vs. carbonates.