Synthesis of α-methylene-δ-valerolactone and its selective polymerization from a product mixture for concurrent separation and polymer production†

Abstract

We report the continuous, gas-phase synthesis of α-methylene-δ-valerolactone (MVL) from δ-valerolactone (DVL) and formaldehyde (FA) over alkaline earth oxide catalysts. MgO, CaO, and BaO supported on silica (∼5 wt%) were active for MVL production (613 K, 0.4 kPa DVL, 1.2 kPa FA, 101 kPa total pressure). CaO and BaO showed 90% and 83% selectivity to MVL at ∼60% DVL conversion, respectively. Decreasing contact times improved MVL selectivity for all three catalysts, achieving near quantitative selectivity at DVL conversions <40% with CaO. Further studies with CaO indicated that increasing the FA partial pressure for a given DVL partial pressure negligibly changed conversion while maintaining high selectivity; however, increasing the reaction temperature generally resulted in lower MVL selectivity. Deactivation and carbon loss were attributed to non-volatile compound formation from series and parallel reactions that consume MVL and DVL and poison the catalyst surface. These side reactions were more pronounced at high temperatures and higher contact times. While slow deactivation poses a challenge, the catalyst could be fully regenerated by calcining at 773 K for 4 h under flowing air. As the product mixture of MVL and DVL is difficult to separate, we developed a selective polymerization strategy to convert either one or both monomers into valuable polymeric materials, thereby achieving efficient separation and concurrent polymer production. Using a model mixture of 30 wt% of MVL in DVL, vinyl-addition polymerization converted MVL to the corresponding vinyl polymer (PMVL)_VAP in 98% yield, while DVL was recovered in 96% yield by distillation. Alternatively, ring-opening polymerization of the same mixture resulted in a DVL/MVL copolyester and separatable vinyl homopolymer P(MVL)_VAP.