BPO和AIBN作引发剂对阳离子交换膜性能的影响

改进传统制备聚偏氟乙烯(PVDF)均相阳离子交换膜的方法,利用引发剂和浓硫酸磺化直接制备PVDF均相阳离子交换膜。通过溶剂蒸发法制备了含引发剂过氧化苯甲酰(BPO)和/或偶氮二异丁腈(AIBN)的PVDF阳离子交换膜,研究不同引发剂及其含量对膜结构和膜性能的影响。利用FE-SEM和FTIR分析了膜的形貌结构。结果表明:含有BPO的阳离子交换膜中PVDF与苯乙烯形成了半互穿网络结构,而含有AIBN的阳离子交换膜中苯乙烯接枝在线性PVDF链上并形成相分离结构。PVDF阳离子交换膜的结构和性能受膜制备时AIBN和BPO的添加量影响。当AIBN占PVDF5%(质量分数)、BPO占PVDF2%(质量分数)时,离子交换膜的膜电阻达最低值4.2Ω×cm~2,离子交换容量最高为1.59 meq/g;当AIBN占PVDF 3%(质量分数)、BPO占PVDF2%(质量分数)时,离子交换膜的迁移数为95.15%。最后通过循环伏安法和计时电位法进一步验证了引发剂对膜电阻和迁移数影响的实验结论。     

低温固化双马来酰亚胶树脂基体研究──引发剂的作用

本文以典型的ＸＵ２９２双马体系作为研究对象，选用引发剂加速树脂的固化反应，以期得到低温固化耐热的双马树脂体系。研究结果表明，引发剂能很有效地降低双马树脂的固化温度，低温固化阶段比高温固化阶段对树脂耐热性的影响更大。经１２０℃／８ｈ＋１４０℃／２ｈ＋１６０℃／２ｈ固化树脂的热变形温度为２６６℃，再经１８０℃／８ｈ的后处理，热变形温度达到３００℃。     

Graft copolymerization of styrene onto casein initiated by potassium diperiodatonickelate (IV) in alkaline medium

A novel redox system, potassium diperiodatonickelate (Ni(IV))‐casein is used to initiate graft copolymerization of Styrene onto casein under different conditions in aqueous alkaline solution. Graft copolymers with both high grafting efficiency (>98%) and percentage of grafting(>300%) are obtained, which indicated that (Ni(IV))‐casein redox pair is an efficient initiator for this grafting. The effects of reaction parameters, such as monomer‐to‐casein weight ratio, initiator concentration, pH, time, and temperature, are investigated. A tentative initiation mechanism is proposed. The structures and properties of the graft copolymer are characterized by Fourier transform infrared Spectroscopy, X‐ray diffraction diagrams, and Scanning Electron Microscope. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4247–4251, 2006     

Preparation of iodine containing quaternary amine methacrylate copolymers and their contact killing antimicrobial properties

A novel quaternary amine methacrylate monomer (QAMA) was synthesized by amination of dimethacrylate with piperazine followed by its quaternization using an alkyl iodide. Copolymerization of QAMA with 2‐hydroxyethyl methacrylate was carried out by free radical bulk polymerization technique at room temperature using ammonium persulfate and N,N,N′,N′‐tetramethyl ethylenediamine as a redox initiator. The monomer as well as copolymers was characterized by FTIR and ¹H NMR spectral studies. Thermal and physical characteristics of copolymers of varying compositions of QAMA were evaluated by thermogravimetric analysis, differential calorimetry, contact angle and scanning electron microscopy. The antibacterial activity of the synthesized quaternary amine dimethacrylate copolymers against Escherichia coli and Staphylococcus aureus was studied by zone of inhibition and colony count method. QAMA copolymers showed broad‐spectrum contact killing antibacterial properties without releasing any active agent as checked by iodide‐selective ion meter. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1038–1044, 2006     

Copolymeric photoinitiators containing in‐chain thioxanthone and coinitiator amine for photopolymerization

Two kinds of copolymeric macromolecular photoinitiator, PTXPM and PTXPC, were prepared by introducing methylacryloyl or cinnamoyl groups to the side chain of PTXP. The photopolymerizations of poly(propylene glycol)diacrylate (PPGDA) and trimethylolpropane triacrylate (TMPTA), using PTXPM and PTXPC as photoinitiators, were studied by photo‐DSC. PTXPM and PTXPC have UV–vis spectra similar to that of PTXP with blue‐shift absorption maxima. The photopolymerization behavior of TMPTA, initiated by three photoinitiators, appears similar to that of PPGDA. Compared with PTXP and PTXPC, PTXPM gives higher polymerization rate and final conversion, in photopolymerization of PPGDA and TMPTA, which shows that the introduction of methyl acrylate to the PTXP chain has a greater effect on photopolymerization of PPGDA and TMPTA than that of cinnamoyl acrylate. The polymerization rate and final conversion, for photopolymerization of PPDGA initiated by PTXP, can be more effectively increased by the introduction of methyl acrylate group to the PTXP chain, than are those for TMPTA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2395–2400, 2004     

The 31 Helix-Coil Transition for Polypeptides.: Circular Dichroism Studies

Abstract

Circular dichroism has become a popular method for following conformational transitions induced in optically active polymers. Recent refinement of experimental spectra obtained from model polypeptides by computer fitting to spectra obtained from solutions of proteins of known conformation has verified the applicability of the models chosen for the α helical and β conformations. However, the spectrum required for disordered regions was in conflict with much of the literature and agrees with our assignment based on studies of collagen and collagen models at elevated temperature. This spectrum consists of two troughs, one at ~225 nm and the other at ~200 nm. The latter had previously been associated with random polypeptides and we have shown the former to be sensitive to disorder in polymers approaching the 3₁ helical conformation. This paper presents the results from a study of three polypeptides which undergo a 3₁ helix → disorder transition.     

Polymerization of epoxy resins initiated by metal complexes

BACKGROUND: Processing parameters and material properties of epoxy resins can be vastly influenced by choice of curing agent. In this work, metal complexes were investigated as initiators for anionic and cationic epoxide polymerization. Systems for thermally induced and electron beam‐induced curing are described. RESULTS: Zinc or cobalt imidazole complexes of the type [M(imidazole)₂(anion)₂] are efficient initiators for anionic polymerization of glycidyl‐based epoxy resins. The complexes can be employed to prepare tailored resin systems ranging from fast curing systems at slightly elevated temperatures to systems with very high thermal latencies curable at temperatures far above 150 °C. Silver complexes [Ag(L)_n]SbF₆ (L = crown ether or alkene) are highly efficient initiators for cationic curing and low initiator contents of around 1% are sufficient to reach high degrees of crosslinking. The complexes are excellent initiators for both thermally induced and electron beam‐induced polymerizations. CONCLUSION: Metal complexes are powerful initiators for the homopolymerization of epoxy resins and can be designed not only for anionic and cationic polymerization but also for thermal and radiation curing. Based on this study and additional work, a library can be compiled which allows retrieval of optimized metal–ligand–anion combinations and adjustment of the initiators to the respective processing and material demands. Copyright © 2009 Society of Chemical Industry     

Homo‐oligomerization of maleic anhydride in nonpolar solvents: A kinetic study of deviations from nonlinear behavior

Deviation from nonlinear first order polymerization kinetic models is usually observed for cases where steric effects are dominant. A kinetic model was developed for the homo‐oligomerization of bulky maleic anhydride units. Factors affecting the kinetics of homo‐oligomerization of maleic anhydride have also been studied using two different initiators, azoisobutyronitrile (AIBN) and benzoyl peroxide, at 10 mol % concentrations in two different solvents o‐xylene and toluene. Maleic anhydride polymers having a number average molecular weight by SEC, between 300 and 900, and a polydispersity of between 1.0 and 2.0 were observed, and data were justified by the model. The molecular weight of the polymers increased with the conversion, and steric effects dominated at higher molecular weight as observed from the decrease in magnitude in the corresponding termination rate constants. The model values of conversion were compared with experimental data and cross verification of the model was done using molecular weight calculations. The present model represents the data with an average error of less than 5% over the entire experimental range. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3404–3412, 2006     

Direct synthesis of highly reactive polyisobutylenes via cationic polymerization of isobutylene co‐initiated with TiCl4 in nonpolar hydrocarbon media

Living cationic polymerization of isobutylene (IB) with 1‐chlorine‐2,4,4‐trimethyl pentane (TMPCl)/TiCl₄/isopropanol (iPrOH) or isoamylol (iAmOH) has been achieved in the presence of 2,6‐di‐tert‐butylpyridine (DtBP) at ?80°C. Polyisobutylenes with nearly theoretical M_n based on TMPCl molecules and more than 90% of tert‐chlorine‐end groups could be obtained at high [TMPCl]. The β‐proton elimination from ? CH₃ in growing chain ends increased with increasing polymerization temperature and decreasing solvent polarity. A chain‐transfer‐dominated cationic polymerization process with H₂O/TiCl₄/iAmOH could be achieved in n‐hexane at ?30°C. The monomer conversion and content of exo‐olefin end groups increased while molecular weight decreased with increasing [iAmOH]. To the best of our knowledge, this is the first example to achieve the direct synthesis of highly reactive polyisobutylene with low M_n of 1200～1600, carrying more than 80% of exo‐olefin terminals by a single‐step process via cationic polymerization co‐initiated by TiCl₄ in nonpolar hydrocarbon. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42232.     

Novel N‐ethyl‐2‐styrylquinolinium iodides as sensitizers in the photoinitiated free‐radical polymerization of trimethylolopropane triacrylate. II

Results of kinetic studies of two‐component photoinitiator systems used in the visible‐light photoinduced polymerization of 2‐ethyl‐2‐(hydroxymethyl)‐1,3‐propanediol triacrylate are presented. Nine different styrylquinolinum dyes coupled with n‐butyltriphenylborate as a coinitiator have been used as photoinitiating systems. Reactive radicals that initiate the polymerization are formed by the well‐known mechanism of photoinduced electron transfer between dye cations acting as electron acceptors and borate anions acting as electron donors. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010