Preparation Of Bismaleimide-Based Polymer Microspheres By Self-Stabilized Precipitation Polymerization And Their Applications

As a kind of high-performance thermosetting resin matrix,bismaleimide（BMI）resin has been widely used in microelectronic packaging,aerospace,electronics and other fields due to its advantages of excellent heat resistance,good electrical insulation,high wave-transparent property and outstanding radiation resistance.However,the inherent disadvantages of pure BMI resin including poor processability,low fracture toughness and high brittleness limit its application to some extent.In recent years,the design and preparation of high-performance BMI-based nanocomposites,self-healing smart materials and other functional polymers have gradually become hot spots in the field of BMI.In particular,BMI-based functional polymers could be customized on-demand by taking advantages of BMI monomers,including high reactivity,the ability to undergo multiple chemical reactions and the highly designable molecular structure.However,the synthesis of functional nano/micro-particles of BMI-based polymers with controlled morphology and size still remains a big challenge due to the poor solubility of BMI monomers.Herein,a series of BMI-based polymer microspheres with various structures（solid,hollow and porous architectures）,controllable particle size and morphology,adjustable chemical composition and versatile surface functional groups were specially designed and prepared through self-stabilized precipitation polymerization（2SP）of BMI and other monomers.Based on an in-depth understanding of the structure and properties of these BMI-based polymer microspheres,their applications in low-k materials,catalysis and energy storage were explored.The present work opens up new horizons for the facile and high-efficient construction of BMI-based polymer microspheres with different chemical compositions,morphologies,sizes and surface functionalization,and greatly broadens the application scope of BMI resin.The main contents are as follows:1.Novel bismaleimide（BMI）based heat-resistant microspheres（BMPs）were synthesized by 2SP copolymerization of styrene（St）and2,2’-bis[4-（4-maleimidophenoxy）phenyl]propane（BMIP）in N-methyl pyrrolidone/isopentyl acetate mixed solvent.The effects of solvent composition,initiator concentration,monomer feed ratio and monomer concentration on the particle size and morphology of the resultant BMPs,as well as the formation and growth process of BMPs were systematically investigated and the formation mechanism was then clearly elucidated.Due to the presence of rigid imide rings and highly crosslinking density,the BMPs exhibited excellent thermal stability with an initial decomposition temperature up to 440°C,and the residual carbon rate remained above 30%at 750°C.Furthermore,the highly reactive maleimide groups on the surface of the BMPs can effectively react with cyanate ester（CE）monomer,and BMPs could serve as a modifier to effectively lower the curing temperature of CE resins.2.A novel type of BMI-based hollow polymer microspheres（BMI-HPPs）with controllable particle size and shell thickness were designed and synthesized using template method through precipitation copolymerization of divinylbenzene（DVB）and BMIP.There were unreacted vinyl and maleimide groups in the shell layer of the BMI-HPPs,which can serve as an effective modifier to prepare high performance CE resins.On the one hand,BMI-HPPs can effectively react with CE monomer to lower the curing temperature and obtain better interfacial compatibility.Furthermore,the hollow voids introduced by BMI-HPPs could significantly reduce dielectric constant（ε）and dielectric constant（tanδ）values of the modified CE resins and simultaneously improve their toughness.The resultant BMI-HPPs/CE resin showed a maximum impact strength of 18.8 k J/m² at 5 wt%loading of BMI-HPPs,while the BMI-HPPs/CE resin with 7.5 wt%BMI-HPPs exhibited minimum values ofεand tanδof 2.69 and 0.006 at 10⁷ Hz.Furthermore,the BMI-HPPs/CE resins also possessed excellent low-k properties（εand tanδvalues of 2.46,0.006 at 16 GHz,respectively）and excellent wave transmittance performance at Ku-band（the transmittance values up to93.8%-97.1%at 15-18 GHz）.3.Octavinyloctasilasesquioxane（Ovl-POSS）with cage framework can be used as an ideal building block for low-k materials.Novel porous polymer microspheres（BMI-MCPs）with reactive surface vinyl and maleimide groups were prepared by 2SP terpolymerization of Ovl-POSS/BMIP/DVB.The pore architecture,specific surface area and chemical composition of the obtained microspheres could be effectively adjusted by changing the monomer feed ratio,and BMI-MCPs with large specific surface area（647.99 m²/g）and high pore volume（0.68 cm³/g）were successfully prepared.The modification of CE resins by BMI-MCPs was investigated,and it was found that the reactive groups on the surface of the microspheres can significantly reduce the curing temperature of CE resins and improved the interfacial compatibility.Compared to BMPs and BMI-HPPs,the BMI-MCPs with nanoscale pore structure and larger pore volume provided more abundant nanopores.Therefore,the BMI-MCPs modified CE resins exhibited minimumεand tanδvalues of 2.51 and 0.005 at 10⁷ Hz,respectively.And the BMI-MCPs/CE resins also possessed outstanding low-k properties（εand tanδvalues of 2.33,0.015 at 16 GHz,respectively）and excellent wave transmittance performance at Ku-band（the transmittance values up to 96.4%-98.6%at 15-18 GHz）,while the impact strength increased up to 17.8 k J/m² simultaneously.4.A series of highly cross-linked porous polymer microspheres（BMPMs）with uniform particle size,hierarchical pore structure and high specific surface area were designed and prepared directly by 2SP copolymerization of BMIP and DVB.The effects of reaction factors such as monomer feed ratio and solvent composition on the chemical composition,particle size,porous structure and specific surface area of BMPMs were systematically investigated.Under optimized reaction conditions,monodispersed BMPMs microspheres with an average particle size of 1.37μm,large specific surface area（556.25m²/g）and high pore volume（0.48 cm³/g）were obtained.The BMPMs microspheres could be used as an ideal catalyst carrier due to the high specific surface area and well-developed hierarchical pore structure（meso-micropores）,and an efficient heterogeneous catalyst BMPMs@Pd was prepared by effective loading of Pd nanoparticles through in-situ reduction reaction.The catalyst exhibited extraordinarily high catalytic activity(967.92 h^-1)and excellent cycling stability for the hydrogenation reaction of 4-nitrophenol.5.Monodispersed porous BMPMs microspheres can serve as precursors for porous carbon materials,and the corresponding N-doped porous carbon microspheres（BMCMs）with well-preserved spherical morphology and higher specific surface area could be produced by carbonization and KOH activation process.The BMCMs prepared under a KOH/carbon microspheres mass ratio of 2 exhibited large specific surface area（1567.15 m²/g）and high pore volume（0.63 cm³/g）.The resultant BMCMs were used as electrode materials for supercapacitors and exhibited good rate performance,high capacitance（338F/g at 0.5 A/g）and excellent electrochemical cycling stability.The BMCMs based symmetric supercapacitors displayed a high energy density（8.4 Wh/kg）at a power density of 250 W/kg.The capacity retention rate remained above99%after 5000 galvanostatic charge-discharge cycles at 5 A/g,indicating great practical values of BMCMs for high-performance supercapacitors.