Preparation And Application Of Bio-based Limonene Copolymer Microspheres

As a widely available bio-based monomer,limonene（LIM）has great potential to replace fossil-based monomers in the development of sustainable polymers.However,the efficient preparation of LIM-based polymers remains great challenge owing to the special allyl group of LIM.As a result,the monomer conversion and molecular weight of the resultant LIM-based copolymers were extremely low due to degradative chain transfer reaction to LIM.In this paper,heat resistant bio-based limonene copolymer microspheres with adjustable copolymer composition and controllable particle size were successfully prepared by self-stabilized precipitation polymerization（2SP）using LIM and N-phenylmaleimide（NPMI）as comonomers.Moreover,the copolymerization behavior of LIM-NPMI was systematically investigated and its application for the modification of cyanate ester（BADCY）resin was further investigated.The main research contents are as follows:1.Heat-resistant LIM-based copolymer（PML）microspheres were prepared by 2SP polymerization in a mixed solvent of butanone and n-heptane.The influence of solvent composition,monomer concentrations,monomer feed ratio,initiator type and dosage,and reaction time on the yield,particle size and copolymer composition of the as-prepared PML microspheres were explored systematically.Finally,PML microspheres with smooth surface,controllable particle size and adjustable copolymer composition were successfully obtained.After separation of the 2SP polymerization product,the supernatant was reused to further improve the monomer conversion of LIM.After four consecutive 2SP polymerization reusing cycles,NPMI and LIM conversion increased up to 92%and 46%,respectively.2.The reactivity ratio of LIM and NPMI were measured by Fineman-Ross（F-R）and Kelen-Tudos（K-T）methods to quantitatively characterize the copolymerization activity of both monomers.At a reaction temperature of 75°C,r_LIM=0.26,r_NPMI=2.53,which is a non-ideal and non-azeotropic copolymerization reaction.When the reaction temperature further increased to 145°C,r _LIM=0.88,r _NPMI=1.00,the polymerization evolves toward the ideal copolymerization direction.3.The side groups of PML contain high reactive double bond groups,which can effectively promote the cross-linking and curing reaction of cyanate groups in BADCY monomer.Therefore,the PML copolymer can be regarded as a curing modifier to significantly reduce the maximum curing temperature of BADCY resin,and BADCY/PML modified resin with good interfacial compatibility,excellent dielectric and mechanical properties were successfully obtained.The impact strength of BADCY/PML-10 wt%modified resin was up to 15.1 k J/m²,which is 86%higher than that of the pure BADCY resin（8.1k J/m²）.The dielectric constant（ε）and dielectric loss（tanδ）at 10⁶Hz were as low as 2.61 and 0.0032,respectively,which has good prospects for application as a high performance and low dielectric material.