Facile and Efficient Synthesis of Heat-Resistant Poly(N-phenylmaleimide-co-limonene) Microspheres Bearing Endocyclic Vinyl Groups Based on Bio-Based Limonene

Abstract

Limonene (LIM), a bio-based cyclic monoterpene, has received extensive attention due to it abundance, environmentfriendliness, and sustainability. However, the efficient preparation of LIM-based polymers remains a great challenge owing to severe steric hindrance of endocyclic double bonds and the significant selfinhibition effect of the exocyclic allyl group. Herein, we developed a facile and efficient method for the preparation of heat-resistant poly(N-phenylmaleimide-co-limonene) [poly(NPMI-co-LIM)] microspheres bearing endocyclic vinyl groups through self-stabilized precipitation polymerization. The influence of the solvent composition, monomer concentration, and monomer feed ratio on the yield and size of poly(NPMI-co-LIM) microspheres were systematically studied. Monodisperse poly(NPMI-co-LIM) microspheres with tunable sizes and copolymer compositions were facilely obtained in butanone/n-heptane (4/6, v/v) through simple adjustment of the monomer feed ratio and monomer concentration. As the total monomer concentration increased from 0.1 to 0.8 mol/L ([NPMI]/[LIM] = 1/1), the number-average particle size increased gradually from 0.42 to 1.23 μm. More importantly, the as-prepared poly(NPMI-co-LIM) microspheres can be simply separated, and the supernatant containing unreacted monomers can be directly reused, which is conducive to improving monomer conversion. After four consecutive reusing cycles, the overall conversion of LIM and NPMI increased up to 46 and 92%, respectively. Furthermore, the unreacted endocyclic double bonds in the side group of poly(NPMI-co-LIM) provide a versatile platform for chemical modification.