Weiqu Liu

Cycloaliphatic epoxy resin modified by two kinds of oligo-fluorosiloxanes for potential application in light-emitting diode (LED) encapsulation

Oligo-fluorosiloxane (DFOS) and epoxy-containing oligo-fluorosiloxane (DFEHOS) were synthesized by the hydrolytic condensation reaction to modify 3, 4-epoxycyclohexylmethyl-3, 4-epoxycyclohexanecarboxylate (ERL-4221) for potential application in LED packaging. The chemical structures of DFOS and DFEHOS were characterized by Fourier transform infrared (FT-IR), 29Si nuclear magnetic resonance (29Si NMR), and gel permeation chromatography (GPC). The thermal behavior, mechanical properties, morphologies of impact fracture surfaces, surface wettability and absorbency of the modified epoxy resins were examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile and impact testing, scanning electron microscopy (SEM), and contact angle measurement, respectively. The experimental results indicated that the contact angles, surface energies and water absorption ratios of the modified epoxy resins were effectively improved by the introduction of oligo-fluorosiloxanes. Compared to neat epoxy resin, the thermal stabilities of DFEHOS-modified epoxy resins were basically kept, and that of DFOS-modified epoxy resins were slightly depressed with the increasing content of modifiers. As the additive quantity of modifiers was about 5pph to 15pph relative to ERL-4221, good thermal stability, fracture toughness and surface hydrophobicity of the modified epoxy resin was exhibited, and the cured DFEHOS-10 that embraced the relatively optimum comprehensive property was possible for LED encapsulation. Moreover, the reactable groups formed during hydrolytic condensation in DFOS and DFEHOS made good compatibilities between the modifiers and the epoxy matrix.

Studies on the Thermal Properties of Epoxy Resins Modified with Two Kinds of Silanes

Dimethyldiethoxysilane (DMDES) and diphenyldimethoxysilane (DPDMS)-containing epoxy resins were synthesized by dehydration polycondensation. The chemical structures were determined by FT-IR, 1H NMR, and 13C NMR. The cured samples, with 4, 4′-diaminodiphenylmethane (DDM) as curing agent, were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and tensile and impact testing. Results showed that DMDES and DPDMS-modified epoxy resins possess higher glass transition temperatures, better thermal stability, and better fracture toughness than the neat epoxy resin.

Waterborne UV-curable comb-shaped (meth)acrylate graft copolymer containing long fluorinated and/or polysiloxane side chains

A series of waterborne UV-curable comb-shaped (meth)acrylate graft copolymers containing long fluorinated and/or siloxane side chains were synthesized by conventional radical copolymerization of a novel mono-methacryloyloxy terminated fluorinated macromonomer (PHFA-GMA) and/or polysiloxane macromonomer (SiOHMAC) with (meth)acrylate monomers. The separate effects of PHFA-GMA and SiOHMAC, as well as the synergic effect of these two components, on the properties, especially the surface properties were investigated in detail. A hydrophobic surface could be obtained with extremely low content of PHFA-GMA and/or SiOHMAC due to the strong tendency of the macromonomers to migrate towards the outmost layer, resulting in abundant enrichment of fluorine and silicon atoms on the surface. XPS (X-ray photoelectron spectroscopy) results revealed that for a given weight of the two macromonomers, Si atomic concentration of the copolymer modified by SiOHMAC is higher than F atomic concentration of the copolymer modified by PHFA-GMA. AFM (atomic force microscopy) images showed that surface of the copolymer modified by SiOHMAC is rougher than that modified by PHFA-GMA. Compared to PHFA-GMA, SiOHMAC had higher efficiency and effectiveness in creating hydrophobic surfaces. In addition, the influence of PHFA-GMA and/or SiOHMAC on the physical properties, such as water dispersion particle size, water absorption, pencil hardness, adhesion, mechanical properties and thermal properties were also investigated. The novel comb-shaped copolymers prepared via conventional radical polymerization not only had excellent properties but also have potential applications in large scale industrialization.

Modification of Epoxy Resin with Cycloaliphatic-Epoxy Oligosiloxane for Light-Emitting Diode (LED) Encapsulation Application

A novel cycloaliphatic-epoxy oligosiloxane (EHDM) was incorporated into 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (ERL-4221) for use as a light-emitting diode (LED) encapsulant. EHDM, with reactable epoxy groups and flexible Si-O-Si chains, was obtained by the hydrolytic condensation reaction between 2-(3,4-epoxycyclo-hexyl)ethyl-trimethoxysilane (EHETMS) and dimethyldiethoxylsilane (DMDES). The results of Fourier transform infrared spectroscopy, 29Si nuclear magnetic resonance, and gel permeation chromatography indicated that EHDM had a narrow molecular weight distribution and high epoxy graft degree. The thermal and mechanical properties, morphologies, and light transmittance of the cured neat epoxy resin and EHDM-modified epoxy were investigated by differential scanning calorimetry, thermogravimetric analysis, tensile and impact testing, scanning electron microscopy, and ultraviolet-visible spectrophotometry. The experimental results demonstrated that the cured EHDM-10 hybrimer with 10 pph of EHDM relative to ERL-4221 maintained the neat ERL-4221 epoxy transmittance of 85% at 450 nm. With respect to the corresponding properties of the neat epoxy resin, EHDM-10 hybrimer possessed a higher glass transition temperature, better thermal stability, better fracture toughness, and lower water absorption ratio, indicating EHDM effectively improved the properties of ERL-4221 for LED packaging applications.

Synthesis and characterization of UV-curable acrylate films modified by functional methacrylate terminated polysiloxane hybrid oligomers

A series of novel methacrylate terminated polysiloxane hybrid oligomers and functional acrylate oligomers were synthesized and characterized by GPC, FT-IR and NMR. The functional polysiloxane oligomers were introduced into the acrylate UV-curing system to improve its surface and thermal properties. With increasing the organosiloxane content, the contact angles of the UV-cured films increased, suggesting that the organosiloxane segments migrated to the top surface. The SEM and EDS results demonstrated the migration of the organosiloxane segments. The refractive index results showed that the optical performance did not decrease after the organosiloxane segments were incorporated. According the TGA curves, the decomposition temperatures of the polysiloxane/acrylate composite UV-cured films were higher than that of the pure acrylate UV-cured film, which demonstrated that the organosiloxane groups enhanced the thermal properties of the acrylate film due to the high energy of the Si–C bond. The observation of the fractured-surface morphology showed that the organosiloxane segments floated on the surface of the UV-cured films.

Synthesis and properties of triblock copolymers containing PDMS via AGET ATRP

The bromo-terminated macroinitiator was prepared by direct addition reaction of difunctional poly(dimethylsiloxane) (PDMS) containing methyl methacrylate end groups with hydrobromic acid in acetic acid under mild conditions, and well-defined triblock copolymers of poly(methyl methacrylate-b-dimethylsiloxane-b-methyl methacrylate) (MMA-b-DMS-b-MMA) were synthesized via activators generated by election transfer atom transfer radical polymerization (AGET ATRP). The gel permeation chromatography data obtained verified the polymerization and showed the well controlling of the reaction. FTIR and 1H NMR measured the structure of the macroinitiator and copolymers. The contact angle measurement indicated that the water contact angles decreased gradually with the increasing of PMMA block content. The self-assembly behaviors of the triblock polymer were studied by transmission electron micrograph, scanning electron microscopy, and dynamic light scattering measurement. The results indicated that the polymers could self-assemble into various complex morphologies in different solvents and the morphologies depended on the properties of solvents. The possible molecular packing models for self-assembly behaviors of the ABA triblock polymers were proposed.

Synthesis and properties of cross-linkable block copolymer end-capped with 2, 2, 3, 4, 4, 4-hexafluorobutyl methacrylate

A series of novel cross-linkable copolymers 2, 2, 3, 4, 4, 4-hexafluorobutyl methacrylate-poly (isobutyl methacrylate)-b-poly[3-(trimethoxysilyl)propyl methacrylate] (HFMA-PIBMA-b-PTMSPMA) were synthesized via atom transfer radical polymerization (ATRP). The synthesis and structure of the polymers were characterized by gel permeation chromatography (GPC), Fourier transform infrartd (FTIR) and 1H nuclear magnetic resonance (NMR). The properties of HFMA-PIBMA-b-PTMSPMA and the corresponding copolymers end-capped with nonfluorinated acrylate were comparatively studied by contact angle, transmission electron micrograph (TEM), and dynamic light scattering (DLS) measurement. The results indicated that the surface properties and self-assembly behaviors of HFMA-PIBMA-b-PTMSPMA were changed greatly by the introducing of only one fluorinated acrylate. Finally, the transparent solid materials with a slightly blue color were obtained based on the cross-linked behaviors of HFMA-PIBMA-b-PTMSPMA and fracture surfaces of the materials were exhibited by scanning electron microscopy (SEM).

Mechanical and Thermal Properties and Morphology of Epoxy Resins Modified by a Silicon Compound

A silicon compound (GAPSO) was synthesized to modify the diglycidyl ether of bisphenol-A (DGEBA). The chemical structure of GAPSO was confirmed using FT-IR, 29Si NMR and GPC. The mechanical and thermal properties and morphologies of the cured epoxy resins were investigated by impact testing, tensile testing, differential scanning calorimetry and environmental scanning electron microscopy. The impact strength and tensile strength were both increased by introducing GAPSO, meanwhile the glass transition temperature (Tg ) was not decreased and the morphologies of the fracture surfaces show that the compatibility of GAPSO with epoxy resin was very good and the toughening follows the pinning and crack tip bifurcation mechanism. The high functional groups in GAPSO can react during the curing process, and chemically participate in the crosslinking network. GAPSO is thus expected to improve the toughness of epoxy resin, meanwhile maintain the glass transition temperature.

Nano- and micro-structured random copolymer modified cycloaliphatic epoxy resins for use as light-emitting diode encapsulation

ABSTRACT Poly(2,2,3,4,4,4-Hexafluorobutylmethacrylate–random–glycidolmethacrylate) random copolymer (P(HFBMA-r-GMA)) was synthesized via free radical polymerization. The novel reactive random copolymer was incorporated to modify cycloaliphatic epoxy resins and obtain the nano- or micro- structured composites. The chemical structures of P(HFBMA-r-GMA) were confirmed by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The morphology and light transmittance of the cured epoxy resins were observed by scanning electron microscopy (SEM), transmission electron microscope (TEM) and ultraviolet-visible spectrophotometry (UV-vis), respectively. It is indicated that the optical transmittance of composites were basically kept although the microphase separation occurred in the curing process, which has a profound influence on the mechanical properties and refractive indexes. The thermal properties, surface dewettability and water absorbency of the cured epoxy resins were examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), contact angle measurement and immersion test respectively. The experimental results revealed that the values of glass transition temperatures (Tg), surface dewettability and water resistance were effectively improved by the high cross-linking density and the enrichment of the fluorinated random copolymer dispersing in the composites. With respect to the corresponding properties of the neat epoxy resin, P (HFBMA-r-GMA)-0.25 hybrimer embraced the relatively good comprehensive properties, making the modified epoxy resins as good candidates for LED encapsulation.

Curing Behavior and Thermal Properties of Autocatalytic Cycloaliphatic Epoxy

Cycloaliphatic epoxy resin containing hydroxyl group (DMTMP) was prepared by the transesterification between methyl-3,4-epoxycyclohexane carboxylate (MEC) and trimethylolpropane (TMP), which was then thermally cured with methylhexahydrophthalic anhydride (MHHPA). As comparison, a commercial available cycloaliphatic epoxy 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (ERL-4221) cured with the same curing agent was also investigated. The chemical structure was characterized by FT-IR and 1H-NMR. And the curing behavior and the thermal properties were studied by DSC and TGA. The DSC results showed that the DMTMP systems exhibited higher reactivity than the ERL-4221 systems due to the autocatalysis of hydroxyl group of DMTMP. While the glass temperature transitions (Tg s) of DMTMP systems were much lower than ERL-4221 systems, and the Tg s of DMTMP and ERL-4221 systems both reduced after introducing n-dodecyl trimethylammonium bromide (DTAB) as catalyst. The decomposition behavior from TGA shows that the DMTMP epoxy resins exhibited a relative slow weight decreasing tendency in comparison with ERL-4221 epoxy resins, but initial degradation temperatures of DMTMP systems were lower than ERL-4221 systems.