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

Limonene (LIM), a bio-based cyclic monoterpene, has receivedextensiveattention due to it abundance, environment-friendliness, and sustainability.However, the efficient preparation of LIM-based polymers remains agreat challenge owing to severe steric hindrance of endocyclic doublebonds and the significant self-inhibition effect of the exocyclicallyl group. Herein, we developed a facile and efficient method forthe preparation of heat-resistant poly(N-phenylmaleimide-co-limonene) [poly(NPMI-co-LIM)] microspheresbearing endocyclic vinyl groups through self-stabilized precipitationpolymerization. The influence of the solvent composition, monomerconcentration, and monomer feed ratio on the yield and size of poly(NPMI-co-LIM) microspheres were systematically studied. Monodispersepoly(NPMI-co-LIM) microspheres with tunable sizesand copolymer compositions were facilely obtained in butanone/n-heptane (4/6, v/v) through simple adjustment of the monomerfeed ratio and monomer concentration. As the total monomer concentrationincreased from 0.1 to 0.8 mol/L ([NPMI]/[LIM] = 1/1), the number-averageparticle size increased gradually from 0.42 to 1.23 & mu;m. Moreimportantly, the as-prepared poly(NPMI-co-LIM) microspherescan be simply separated, and the supernatant containing unreactedmonomers can be directly reused, which is conducive to improving monomerconversion. After four consecutive reusing cycles, the overall conversionof 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.