Zhaohua Zeng

Photoinitiated copolymerization of acrylamide and styrene in oil-in-water microemulsion

This article describes the copolymerization of acrylamide with styrene in oil-in-water microemulsion, using dodecyl betaine as emulsifier and a-hydroxy-a,a- dimethyl acetophenone or a,a-dimethoxy-phenyl acetophenone as photoinitiator. Re- sults indicated that the photoinitiation of polymerization occurs at the interface be- tween the oil phase and the water phase and that the polymerization occurs in the microemulsion droplet. Particle size increased with increasing polymerization time. The copolymer chain consisted of isolated acrylamide units randomly distributed among styrene groups. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2543-2549, 1997

Monodisperse highly cross-linked “living” microspheres prepared via photoinitiated RAFT dispersion polymerization

Cross-linked PMMA microspheres have been synthesized by photoinitiated RAFT dispersion polymerization with dipropylene glycol diacrylate (DPGDA) or trimethylolpropane triacrylate (TMPTA) as the cross-linker. Monodisperse microspheres were obtained in the presence of 0.5 wt% S,S′-bis(α,α′-dimethyl-α′′-acetic acid) trithiocarbonate (BDMAT, a RAFT agent) with DPGDA concentration up to 5 wt% or TMPTA concentration up to 2 wt%. The particle formation process was investigated, and the results reveal that the cross-linking reaction was retarded to a certain extent by the RAFT process, which is crucial for the formation of uniform particles under high cross-linker concentrations. The phase diagrams for the methodology have been built up, and show that the procedure could only give polydisperse microspheres at a low DPGDA concentration or coagulum at a high DPGDA concentration in the absence of a RAFT agent, and monodisperse microspheres were obtained at DPGDA concentration up to 5 wt% when the RAFT agent concentration reached an appropriately high level, e.g. 0.5 wt% BDMAT or 0.75 wt% DDMAT. By adjusting the reaction conditions, we have prepared monodisperse cross-linked PMMA microspheres with 10 wt% DPGDA added at the beginning of the reaction. Furthermore, we have functionalized the cross-linked microspheres by adding a functional comonomer to the system at the beginning of polymerization, or by surface-initiated RAFT polymerization via the RAFT groups attached on the particle surface.

Fast and facile one-step synthesis of monodisperse thermo-responsive core–shell microspheres and applications

Highly monodisperse PMMA microspheres covered with a thermo-responsive shell were synthesized in a single step by means of photoinitiated RAFT dispersion polymerization at room temperature. Thermo-responsive macro-RAFT agents (P(mPEGA-co-MEA)-TTCs) with different lower critical solution temperatures (LCST) were used as stabilizers in the process. Particle yields of over 95% were achieved within 45 min of UV irradiation, showing a fast process. The microspheres obtained were well-dispersed in water at a temperature below the LCST, and precipitated from the aqueous dispersion at a temperature above the LCST, exhibiting reversible thermo-responsive properties. The particle size can be precisely controlled by adding a monomer to the reaction in batches, and the microspheres maintained their high uniformities during the reaction. The thermo-responsive PMMA microspheres can be effectively conjugated to proteins via the carboxyl groups on the macro-RAFT chains. A thermo-responsive PMMA/ZIF-8 core–shell structure was also synthesized by using P(mPEGA-co-MEA)-b-PAA stabilized PMMA microspheres as the template, and exhibited good adsorption properties for methylene blue.

N-Phthaloyltranexamic acid ammonium salt derivatives as photocaged superbase for redox free radical photopolymerization

N-Phthaloyltranexamic acid ammonium salt derivatives integrating with peroxides can invoke redox photopolymerization and propagating polymerization. A series of N-phthaloyltranexamic acid ammonium salt derivatives based on benzophenone, thioxanthen, and naphtha chromophores as novel photocaged bases were synthesized and characterized. In combination with a benzoyl peroxide initiator, these structures were able to initiate the amine-mediated redox photopolymerization of acrylates. In particular, the covalent binding of N-phthalimidoamino acid and type II chromophores (thioxanthone, benzophenone) improved remarkably the photoreactivity of photocaged bases (thioxanthen-DBU and benzophenone-DBU) compared to the parent compound. Furthermore, naphthal-DBU matches well the emission spectra of the mercury lamp with a dominant emission wavelength at 365 nm. More importantly, phthal-DBU & BPO as a new photocaged redox combination can invoke controlled redox polymerization within an irradiation time of 3 min. Finally, due to the persistent interaction of the produced longeval amine with peroxides, remarkable post conversion after irradiation, which is significant for preparation of photo-screened materials, was thus initially achieved in the redox photopolymerization.

Spectroscopic studies of the anomalous viscosity‐temperature relationship of sulfonated EPDM ionomer solution

FTIR and ESR studies of sulfonated EPDM ionomers in xylene/alcohol show that alcohol solvation of SO3M occurs and the extent of solvation relates to the species and concentration of the metallic ions and the molar concentration of OH from the cosolvent (alcohol) and temperature. The relationship between these factors and the viscometric behaviors of the ionomer solution were investigated. The results of these two studies are quite consistent with each other. At the molecular level the solvation of the metallic ion with the cosolvent plays a key role in the anomalous viscosity-temperature behavior of ionomer solutions.

A study on hybrid oligomeric type II photoinitiator

Abstract Preparing tailor-made hybrid photoinitiator (PI) for specific applications continues to gain momentum. The hybrid PIs comprising both H-abstraction chromophore and coinitiator moiety are the candidate materials with energy-saving and environment-protection in the photo-curing field. So two oligomeric photoinitiators (OMKs) containing benzophenone (BP) and aliphatic tert-amines chromophore in the main-chain (OMK-2) or side-chain (OMK-1) were synthesized and characterized respectively. Photophysical investigation showed that the absorption maxima of OMKs were around 340 nm, red shifted about 5-10 nm compared to BP. Their initiation efficiencies were found to be higher than that of BP and 4,4’-bis(dimethylamino)benzophenone(MK) respectively. The reaction proceeds via a simple electron-transfer/proton-transfer mechanism. Dynamic NMR data reveal that H-abstraction reacts predominantly via alpha H of aliphatic tertamines, as might be expected on the basis of the lower ionization potential and bond dissociation energy of aliphatic amines compared to aromatic amines. The reaction mechanism of H-abstraction was confirmed by using radical scavenger 2,2,6,6-tetramethylpiperidin-1-oxy(TEMPO), which acts as a probe under photolysis reaction conditions. The volatility and migration were tested under simulated conditions, the result show that OMKs exhibited very low volatility and significantly reduced migration compared to the low molecular analogs. Results showed that the OMKs are the promising candidate as higher efficient PIs with low volatile organic compounds (VOCs) emission and reduced migration. They are suitable for environmental-friendly formulations.