Zhenlong Yan

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.

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.

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.

Synthesis and Characterization of Fluorinated Acrylic Polymer and the Properties of Epoxy Thermosets Modified With It

A novel fluorinated acrylic polymer poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)-r-poly(glycidyl methacrylate) (PHFMA-r-PGMA) was synthesized and used to modify the general performances of epoxy resin. Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance spectroscopy (1H-NMR) successfully verified the synthesis of PHFMA-r-PGMA. In order to study the effect of epoxy groups in PHFMA-r-PGMA on the properties of modified epoxy resin, corresponding fluoropolymer without epoxy group (PHFMA) was also prepared, and the properties of epoxy thermosets modified by two kinds of fluoropolymers were comparatively studied. The contact angle measurements indicated that the PHFMA-r-PGMA and PHFMA modified thermosets both showed considerable hydrophobicity and lipophobicity. For further comparison, it was also found that the thermosets modified by PHFMA-r-PGMA had a little worse hydrophobicity and lipophobicity but better surface stability than which modified by PHFMA because the epoxy groups in PHFMA-r-PGMA “locked” more fluoropolymers in the bulk matrix of the thermosets, but PHFMA was more freely able to migrate to the surface of the thermosets. SEM images of the fracture surface of PHFMA-r-PGMA and PHFMA modified epoxy thermosets displayed “irregular ripples” or “protuberant island” structures, which suggesting both of these two copolymers could significantly toughen epoxy resin. The results of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the thermosets modified by PHFMA-r-PGMA had better thermal stability than which modified by PHFMA due to the higher crosslinking density between PHFMA-r-PGMA and epoxy resin because of the epoxy groups in PHFMA-r-PGMA. The mechanical properties were investigated by tensile testing and impact testing. Although the tensile strength of the PHFMA-r-PGMA and PHFMA modified epoxy thermosets both declined slightly with growing the content of fluoropolymers, the elongation at break and impact strength both increased first and then decreased in the meantime, which indicated that the two kinds of modified thermosets had better toughness than pure epoxy resin. It may be because the macro-phase separation between the long fluorine carbon chain segments and epoxy resin during curing could absorb the impact energy effectively.

Controlled Synthesis, Characterization and Application of Novel Functional Fluorinated Polymer By Metal-Free Anionic Polymerization

A well-defined block polymer, di-n-butyl ester terminated poly(2,2,3,4,4,4-hexafluorobutyl methacrylate (BTHFMA), was synthesized by the metal-free anionic polymerization. The tetrabutylammonium salt of di-n-butyl malonate was served as functional carbanionic initiator for the anionic polymerization of 2,2,3,4,4,4-hexafluorobutyl methacrylate in a controlled ‘living’ manner for the first time at ambient temperature. The chemical structure of this product was characterized by FT-IR, 1H-NMR, and 13C-NMR. Gel permeation chromatography (GPC) results showed that the molecular weight of BTHFMA ranged from 1025 to 6582 and the molecular weight distributions were fairly narrow (Mw/Mn = 1.12–1.16). By blending the poly(methyl methacrylate-co-butyl acrylate) [P(MMA-co-BA)] with BTHFMA, we minimized the amount of the BTHFMA used while achieving a hydrophobic surface. The surface properties and compositions of the [P(MMA-co-BA)]/BTHFMA blend films were studied by contact angle and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the 5 wt% blends of BTHFMA could obviously increase hydrophobic ability of the blend with a high water contact angle (98.2o) and low surface energy (24.2mN/m). XPS results indicated the fluorine mass content of the surface of the 5 wt% blend was up to 26.6%, which suggested BTHFMA enriched on the surface of the blend.

Synthesis and Properties of Polyurethanes Graft Modified by Long Polydimethylsiloxane Side Chain

Long side chain polyurethane oligomers were synthesized from tolylene diisocyanate (TDI), polyether triol (N330) and monohydroxy terminated polydimethylsiloxane (M-PDMS, ), and the structures were characterized by FT-IR spectrum. Subsequently, they were mixed with polyurethane oligomers synthesized from TDI and polyether triol (N220) to obtain M-PDMS graft modified polyurethanes (M-PDMS-PUs). Dihydroxy terminated polydimethylsiloxane modified polyurethanes (D-PDMS-PUs) were also prepared for the study in contrasts with M-PDMS-PUs. The influence of concentration and length of PDMS on the surface, thermal and mechanical properties was investigated by contact angle measurement, thermo-gravimetric analysis (TGA), different scanning calorimeter (DSC) and mechanical testing. Water contact angles showed the M-PDMS-PUs had higher contact angles than that of D-PDMS-PUs. Added with low amount of PDMS (2.6 wt%), the water contact angle of M-PDMS-PU was 95.5°C while that of D-PDMS-PU was 88.0o. TGA data showed that M-PDMS-PU (Tmax = 368.0°C) had better thermal stability than that of D-PDMS-PU (Tmax = 362.2°C) at low PDMS concentration (2.6 wt%). DSC data revealed that the incorporation of PDMS into PU resulted in a decrease in Tg values and the Tg values of D-PDMS-PUs decreased more drastically than those of M-PDMS-PUs. Mechanical testing indicated that the tensile strength, elongation at break and Shore A hardness of the PDMS modified polyurethanes decreased with the increase of the PDMS content. The morphologies of the fracture surfaces of the copolymers showed that microphase separation between PU and PDMS was formed in both types of PDMS modified polyurethanes and the size of the polysilicone phase became larger with increasing the PDMS content.