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Crosslink network and phenyl content on the optical, hardness, and thermal aging of PDMS LED encapsulant
摘要： This work aims to synthesize new series of polysiloxane copolymer through hydrosilylation reaction based on different level of crosslink densities and phenyl content. The results revealed that polysiloxanes resins with phenyl rings increased viscosity up to 3800 cps while displaying a relatively high refractive index of 1.531. The asymmetric phenyl substitution onto chain backbone led to formation of densely packed structure resulting in reduced water absorption and gas permeability of PDMS resins. High level of crosslinking contributed to a high shore A hardness and adhesion strength. It displayed transparency of 97% whose percentage reduction was 1.6% under thermal and 0.6% UV aging. No obvious discoloration was observed during accelerated thermal aging up to 210 min at 80 (cid:1)C. These results are key attributes that make the synthesized polysiloxane series as ideal candidate for high brightness LED encapsulant. ? 2019 Wiley Periodicals, Inc. ? 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47895.
关键词： copolymers,thermal properties,ring-opening polymerization,optical properties,synthesis and processing techniques
更新于2025-11-19 16:56:42
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Thiol–ene click reaction-induced fluorescence enhancement by altering the radiative rate for assaying butyrylcholinesterase activity
摘要： Bis‐ligated, homoleptic magnesium complexes 1–3 were synthesized through the reaction of 1 equiv. dibutyl magnesium with 2 equiv. β‐ketiminato ligands bearing different substituents on the nitrogen atom and 8 position on benzocyclohexanone. All of the complexes were identified by nuclear magnetic resonance (NMR) and X‐ray crystallography. Complexes 2 and 3 adopted distorted tetrahedral geometry around Mg, by chelating of two ancillary ligands, while complex 1 adopted a dimeric structure with penta‐coordination around Mg. These complexes can be used as efficient catalysts for ring‐opening polymerization of L‐lactide, ε‐caprolactone, δ‐valerolactone (δ‐VL) and trimethylene carbonate in the presence of alcohol as a co‐initiator. With the increasing steric bulk of the ancillary ligands, the catalytic activity of Mg complexes was improved significantly. Particularly, complex 3 having the largest steric hindrance showed excellent catalytic performance for the polymerization of δ‐VL. It could polymerize 800 equiv. δ‐VL in 10 min, and produce polyvalerolactone with narrow molecular weight distributions (Mw/Mn < 1.2) at 35°C or higher temperature. No transesterification side reaction was observed. Moreover, complex 3 exhibited good tolerance to excessive alcohol and an immortal polymerization characteristic. The mechanism studies by in situ NMR demonstrated a coordination‐insertion process. Besides, it revealed that the steric bulky substituents in the active species derived from the complex and alcohol prevented the metal center from deactivation.
关键词： ring‐opening polymerization,magnesium complex,polyester,δ‐valerolactone,bis‐ligated
更新于2025-09-19 17:15:36
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<i>ipso</i> -Arylative Ring-Opening Polymerization as a Route to Electron-Deficient Conjugated Polymers
摘要： ipso-Arylative ring-opening polymerization of 2-bromo-8-aryl-8H-indeno[2,1-b]thiophen-8-ol monomers proceeds to Mn up to 9 kg mol(cid:2)1 with conversion of the monomer diarylcarbinol groups to pendent conjugated aroylphenyl side chains (2-benzoylphenyl or 2-(4-hexylbenzoyl)phenyl), which influence the optical and electronic properties of the resulting polythiophenes. Poly(3-(2-(4-hexylbenzoyl)phenyl)thiophene) was found to have lower frontier orbital energy levels (HOMO/LUMO = (cid:2)5.9/(cid:2)4.0 eV) than poly(3-hexylthiophene) owing to the electron-withdrawing ability of the aryl ketone side chains. The electron mobility (ca. 2 (cid:2) 10(cid:2)3 cm2 V(cid:2)1 s(cid:2)1) for poly(3-(2-(4-hexylbenzoyl)phenyl)thiophene) was found to be significantly higher than the hole mobility (ca. 8 (cid:2) 10(cid:2)6 cm2 V(cid:2)1 s(cid:2)1), which suggests such polymers are candidates for n-type organic semiconductors. Density functional theory calculations suggest that backbone distortion resulting from side-chain steric interactions could be a key factor influencing charge mobilities.
关键词： ipso-arylative polymerization,ring-opening polymerization,conducting materials,cross-coupling,palladium
更新于2025-09-10 09:29:36
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Visible light 3D printing with epoxidized vegetable oils
摘要： Stereolithography is a 3D printing technique in which a liquid monomer is photopolymerized to produce a solid object. The most widely used materials usually belong to the family of acrylate monomers, and photopolymerization occurs through a radical pathway. Photoinitiators can absorb UV or (less often) visible light, producing radicals for direct decomposition or hydrogen abstraction. Due to the toxicity of acrylates, vegetable oil-derived monomers were used in this study. In fact, vegetable oils contain unsaturations, and thus, they can be exploited as monomers. In particular, linseed oil, tung oil or edible oils (soybean, sunflower or corn) could be good candidates as raw materials. Unfortunately, the photoinduced radical polymerization of these oils either does not occur or is too slow for 3D printing applications. For this reason, the oils were modified as epoxides. Epoxides are monomers that are more reactive than natural oils, and they can be polymerized via a cationic mechanism. The aim of this work was to exploit visible light generated by a common digital projector (like those used in classrooms) as a light source. Since the tested photoacid generators working under visible light are ineffective for the polymerization of epoxidized oils, a multi-component photo-initiating mixture was used.
关键词： Green resins,Photoinduced cationic polymerization,Ring opening polymerization,Visible light stereolithography,Vegetable oil epoxides
更新于2025-09-10 09:29:36