Synthesis and chemical recycling of biobased poly(acetal-ester)s with a non-cyclic acetal unit

Abstract

There is a high demand to design and develop recyclable biobased polymers using eco-friendly synthetic approaches. In this work, we present the facile synthesis of two dicarboxylate monomers with a central non-cyclic acetal unit (dimethyl 4,4′-(methylenebis(oxy))dibenzoate and dimethyl 4,4′-(methylenebis(oxy))bis(3-methoxybenzoate)), using potentially bio-sourced methyl paraben and methyl vanillate. The synthetic parameters were evaluated by a cradle to gate life cycle greenhouse gas emissions aiming to understand the environmental impacts. The two monomers were subjected to melt polycondensation with three linear aliphatic diols (ethylene glycol, 1,4-butanediol, and 1,6-hexanediol) with varied lengths and flexibility to yield six polyesters with molecular weights (M_n) ranging from 10–19 kDa, tunable glass transition (T_g ∼ 41–83 °C), and relatively high thermal stability. Most of the obtained biobased polyesters were amorphous, except for the polymer derived from butanediol and methyl paraben, which showed slow crystallization according to differential scanning calorimetry results. We discovered that the non-cyclic acetal bonds in the poly(acetal-ester)s could be selectively hydrolyzed under mild temperature (70 °C) by varying the acid concentration, offering a potential strategy for chemical recycling.