Yanmei Yao

Preparation and properties of thermally conductive polyimide/boron nitride composites

Polyimide (PI) has been widely used as a preferred packaging matrix material due to its low dielectricity, outstanding insulation and excellent thermal stability. Hexagonal boron nitride (h-BN) microparticles were functionalized with a silane coupling agent, 3-glycidyloxypropyltrimethoxy silane (γ-MPS), to improve the interface action with the PI matrix. The modified h-BN (m-BN) particles were used to fabricate the PI/m-BN composites with enhanced thermal conductivity by in situ polymerization. The Fourier transform infrared (FTIR) spectra, thermo-gravimetric analysis (TGA), transmission electron microscopy (TEM) and contact angle test proved that γ-MPS coupling agent molecules had been chemically grafted onto the h-BN surface. In addition, the effects of the m-BN content on the thermal conductivity of PI/m-BN composites were investigated. The composite obtained with 40 wt% m-BN particle loading presented a thermal conductivity of 0.748 W m−1 K−1, 4.6 times higher than that of pure PI. Meanwhile, the fabricated PI/m-BN composites retained excellent electrical insulation and thermal stability. The glass transition temperature values of the PI/m-BN composites decreased slightly while the storage modulus improved with the increase of the m-BN content. These results showed that PI/m-BN composites may offer new applications in the microelectronic industry because future substrate materials require effective heat dissipation.

Flame retarding epoxy composites with poly(phosphazene-co-bisphenol A)-coated boron nitride to improve thermal conductivity and thermal stability

Based on the template-induced self-assembly characteristic of cyclomatrix polyphosphazene micro–nanometer materials, novel poly(cyclotriphosphazene-co-bisphenol A)-coated boron nitride (PCB-BN) was designed and synthesized by in situ condensation polymerization on the surfaces of boron nitride (BN) particles using the reaction of hexachlorocyclotriphosphazene (HCCP) with bisphenol A (BPA). It was found that the incorporation of PCB-BN particles in the epoxy matrix significantly enhanced thermal conductivity of the epoxy composites. With 20 wt% PCB-BN loading, the thermal conductivity of the EP/PCB-BN composites was 0.708 W m−1 K−1, which was 3.7 times higher than that of the neat epoxy. Meanwhile, the EP/PCB-BN composites possessed good electrical insulation and thermal stability simultaneously. The composites fabricated also exhibited improved flame retardation and superior dimensional stability during combustion.

Power feed synthesis of pressure-sensitive latex adhesives

Abstract Latex particles with the same core composition of poly(MMA-co-ALMA) and different shell compositions of poly(BA-co-AA) were prepared by semibatch emulsion polymerization using ‘power feed’ monomer and chain transfer agent addition methods in the shell layers. The seed stage involved formation of seed particles of 111 nm in diameter with a batch process. After that, two growth stages formed the final particle diameter, dz = 300 nm measured by dynamic light scattering. The gel content and the molecular parameters of the polymer were determined. The adhesive properties including loop tack, peel force and shear resistance were measured according to the FINAT test methods No. 9, 1 and 8. An evaluation was also made for the relationship between pressure-sensitive properties and molecular parameters. Introducing power feed to semibatch emulsion polymerization had no significant effect on the latex preparations and could improve the final conversion and the colloidal stability. The observed particles were grown without significant secondary nucleation. The power feed methods had no effect on the glass transfer temperature (Tg) of the shell layer also. Emulsion polymerization conducted by positive power feed resulted in the formation of longer primary polymer chains at the beginning than that conducted by negative power feed and standard uniform feed, which caused a very high gel fraction. As pressure-sensitive adhesives prepared by using the positive power feed had the highest gel content and strongest core–shell interaction, they exhibited the highest shear resistance, but the lowest tack and peel force.

Super-tough Poly(butylene terephthalate) Materials: Blending with CSSP Nanoparticles

Core-shell structured polyacrylic (CSSP) impact modifiers, consisting of a rubbery poly(n-butyl acrylate) core and a rigid poly(methyl methacrylate) shell, were synthesized by seed emulsion polymerization. The CSSP modifier with core-shell weight ratio 75/25 was used to modify the toughness of poly(butylene terephthalate) (PBT) by melt blending. The CSSP morphology was confirmed by TEM and SEM. Dynamic mechanical analyses of PBT/CSSP blends showed two merged transition peaks of PBT matrix. Increasing CSSP content increased elongation at break and impact strength, but decreased tensile strength. The notch impact strength of PBT/CSSP blends with weight ratio 85/15 was eight times greater than pure PBT.