六甲氧基甲基三聚氰胺-多元醇-丙烯酸酯混杂聚合中酸的双重作用

六甲氧基甲基三聚氰胺 (HMMM) 多元醇 丙烯酸酯混合体系在较高温度下可同时进行缩聚和自由基聚合并表现出加速固化、热互补、原位形成高分子合金等协同效应 .通过凝胶化时间和聚合反应速度的研究 ,发现酸既是HMMM 多元醇缩聚反应的催化剂 ,也是促进过氧化氢物分解产生自由基引发丙烯酸酯自由基聚合的催化剂 .研究还发现 ,以潜酸催化剂作为酸的来源可以使体系达到室温稳定 ,高温快速固化的目的     

六甲氧基甲基三聚氰胺-多元醇-丙烯酸酯混杂聚合体系的研究

六甲氧基甲基三聚氰胺 (HMMM) 多元醇 丙烯酸酯 酸催化剂混杂聚合体系在高温下同时进行缩聚和自由基聚合并表现出协同效应 .体系中的活泼亚甲基在HMMM的催化下被空气氧化成过氧化氢物 ;过氧化氢物在酸催化下分解成自由基进而引发自由基聚合反应 .研究结果表明 ,体系中存在固化加速的协同效应 ;同时体系中还存在热互补效应 ,丙烯酸酯的自由基聚合反应放出的热可以传递给缩聚反应 ,满足缩聚反应吸热的要求 .混杂聚合得到的高分子合金膜具有优良的机械性能和耐溶剂性能 ,这是由于在混杂聚合过程中形成了互穿聚合物网络 (IPN)结构 .使用潜酸催化剂作为酸的来源 ,可以提高体系的储存稳定性 ;交联 引发剂的使用可以拓宽它的使用范围 ;对超枝化聚合物在混杂体系中的应用也进行了初步研究     

六甲氧基甲基三聚氰胺-多元醇-丙烯酸酯混杂聚合过程热互补效应的研究

六甲氧基甲基三聚氰胺（HMMM）－多元醇－丙烯酸酯－酸催化剂的混合体系在较高温度下同时进行缩聚和自由基聚合并表现出协同效应，DSC研究结果表明，丙烯酸酯在HMMM和酸的催化作用下可在较低温度下发生自由基聚合反应，并把反应释放出来的大量的热量有效地传递给缩聚发反应，满足缩聚反应吸热的要求，从而节省固化所需要的能量，为了提高储存稳定性。本文以潜酸催化剂作为酸的来源，对该混杂聚合体系进行了研究，仍有明显的热互补效应。     

聚2,2′-二氨基二缩三乙二醇苯酚醚的电化学合成及其电化学性质

用循环伏安法研究了2,2′-二氨基二缩三乙二醇苯酚醚(DATGPE)在ITO电极上的聚合,讨论了实验条件对聚合过程的影响,初步探讨了聚2,2′-二氨基二缩三乙二醇苯酚醚(PDATGPE)的电化学性质.结果表明,在乙腈/水溶液中,DATGPE与HCl的浓度比为1/3,电位扫描-0.2～1. 0 V时,能发生快速的电聚合反应.形成的导电膜具有良好的电化学稳定性,且对H+呈现很好的能斯特响应.     

有机过氧化氢物与芳叔胺体系引发甲基丙烯酸甲酯聚合的研究

以有机过氧化氢物叔丁基过氧化氢(TBH)或异丙苯过氧化氢(CHP)与芳叔胺N,N-二甲基苯胺(DMA)或其衍生物组成的体系引发甲基丙烯酸甲酯(MMA)聚合。研究有机过氧化氢物与芳叔胺结构对聚合的影响,测定了TBH-胺与CHP-胺体系引发MMA聚合的总活化能分别为50-57KJ/mol与39-62KJ/mol,并对CHP-DMT(N,N-二甲基对甲苯胺)引发MMA聚合动力学以及有关引发聚合机理进行了研究。     

双烯化合物为支化单体的原子转移自由基聚合研究

分别以双甲基丙烯酸二缩三乙二醇酯和二乙烯苯为支化单体合成支化聚苯乙烯.用GC、1 H-NMR和三检测体积排除色谱( TD-SEC)对聚合反应过程、支化发展和聚合物的支化结构进行了详细的分析表征.两个聚合反应体系内单体转化速率几乎一样,相同单体转化率下,初级链的分子量近似相等.但是由于双甲基丙烯酸二缩三乙二醇酯与苯乙烯单...     

β-二酮-茂基二氯化钛/MAO催化体系用于苯乙烯间规聚合

制备了 β 二酮类配体 [O ,O]的茂基二氯化钛配合物CpTi(dbm)Cl2 .实验证明 ,这类配合物在助催化剂甲基铝氧烷MAO作用下 ,可催化苯乙烯间规聚合 .显示较高的活性 (10 7× 10 5gPS molTi·h) .所得聚合物具有较高的间规度 .CpTi(dbm)Cl2 MAO体系催化活性随铝 钛比的增加呈上升而后衰减 ,当铝 钛比为 5 0 0左右时活性最高 ;聚合温度较高时会导致催化活性下降 .对聚合物进行了1 3C NMR表征     

脲甲醛缩聚物制备电子墨水微胶囊研究

在原位聚合法制备脲甲醛树脂微胶囊的过程中 ,使用水溶性低分子量脲甲醛缩聚物代替传统的脲甲醛预聚体 (一羟甲基脲、二羟甲基脲 )作为反应单体 ,由于脲甲醛缩聚物比后者更容易吸附在分散相液滴表面 ,解决了用原位聚合法制备脲甲醛微胶囊所常有的结块、粘连、表面粗糙、产率低的问题 .研究了低分子量脲甲醛缩聚物水溶液的粘度特征和表面活性及其与胶囊包封率的关系 .使用这种方法制备出了电子墨水微胶囊     

聚离子液体催化碳酸乙烯酯与甲醇的酯交换反应

通过N-乙烯基咪唑鎓离子液体、 丙烯酸钠(NaAA)和交联剂二乙烯基苯(DVB)或1-乙烯基-3-三乙二醇基咪唑溴盐{[(EG)₃-DVIm]Br₂)}自由基聚合合成了一系列含羧酸根的聚离子液体. 将所合成的聚离子液体用于催化甲醇与碳酸乙烯酯(EC)酯交换反应制备碳酸二甲酯(DMC). 研究结果表明, 在甲醇和EC混合溶剂中具有最大溶胀度的聚离子液体催化剂poly[VOIm-AA-DVIm]活性最高. 在优化反应条件[120 ℃, 6 h, 1.0%(摩尔分数)催化剂用量, n(甲醇)/n(EC)=10∶1]下, DMC收率为76.6%, 选择性为90.1%, 达到了与均相催化剂1-丁基-3-甲基咪唑醋酸盐([BMIm]OAc)相当的活性.     

甲基咪唑乙酸盐介质中CuBr催化的MMA活性聚合

以甲基咪唑乙酸盐为聚合介质、α-溴代异丁酸乙酯/溴化亚铜为引发体系,研究了甲基丙烯酸甲酯(MMA)的原子转移自由基聚合(ATRP).结果表明:MMA的聚合具有活性自由基聚合的特征.聚合体系中的引发剂和催化剂CuBr比例分别为0.33:1、1:1和1:3时,聚合体系具有活性可控的特征,所得的PMMA分子量分布较窄Mw/Mn＜1.26,体系的引发效率随着引发剂浓度的增加而降低.     

Spectroscopic characterization of a molecule with a weak bond: the BrOO radical

Pure rotational spectra of the BrOO radical for the 79Br and 81Br isotopomers have been observed using a Fourier transform microwave spectrometer. The radical was produced in a supersonic jet by discharging a mixture gas containing bromine and oxygen diluted in argon. A-type rotational transitions are observed for N" = 1-5, K(a) = 0 with spin doublings and hyperfine splittings due to the nuclear spin of the bromine atom. High-level ab initio calculations by RCCSD(T) and MRCI have also been performed, and results are compared with the experimental data. Molecular structure of BrOO has been discussed based on the present experimental data, supplemented by the tendency among the halogen peroxide series and the results of the ab initio calculations; the Br-O bond is found to be anomalously long and weak. Systematic comparisons with other halogen peroxides have revealed anomalous nature of the X-O (X = halogen atom) bonds for this series of radicals.     

PHOTOSENSITIZATION BY ANTICANCER AGENTS—10. ortho-SEMIQUINONE AND SUPEROXIDE RADICALS PRODUCED DURING ANTHRAPYRAZOLE-SENSITIZED OXIDATION OF CATECHOLS

Photosensitized oxidation of catechol, 3,4-dihydroxybenzoic acid (DHBA), 3,4-dihydroxy-dihydrocinnamic acid (DHCA), and 3,4-dihydroxy-phenylalanine (DOPA) by novel anticancer agents, anthrapyrazoles (AP), has been studied employing EPR and the spin trapping technique. The formation of o-semiquinone radicals, the one-electron oxidation products of the catechols, stabilized in the form of zinc ion complexes, has been demonstrated. Rate constants for the disproportionation of the semiquinone radical/Zn2+ complexes in (DMSO)/acetate buffer (pH 4.5, 1:1 vol/vol; 100 mM Zn2+) mixture have been determined to be 0.35 x 10(4), 14 x 10(4), 8.8 x 10(4) and 3 x 10(4) M-1 s-1 for catechol, DHBA, DHCA and DOPA respectively. The presence of oxygen enhanced rather than inhibited the photogeneration of the o-semiquinone radicals and facilitated their EPR detection. The EPR spectrum of the superoxide radical adduct with the spin trap 5,5-dimethyl-1-pyrroline-N-oxide was observed for the first time during photosensitized oxidation of the catechols in acidic aqueous solutions and in DMSO/acetate buffer mixture.     

The effect of 4-vinylcyclohexene on the degradation of polystyrene and on the polymerisation of styrene

It has previously been postulated that the inhibition of polystyrene degradation observed in the initial stages of the isothermal degradation of polystyrene-polybutadiene blends is partly due to reaction of polystyryl radicals with 4-vinylcyclohexene (4VCH) evolved from the polybutadiene. This hypothesis has been tested by examining the effect of small amounts of 4VCH on polystyrene degradation and on the free radical polymerisation of styrene. The results provide support for the hypothesis: there is an induction period in the degradation and the polymerisation is retarded. From molecular weight measurements on polymers made in the presence of various amounts of 4VCH, a chain transfer constant in styrene polymerisation at 60°C of 117 × 10^?5 has been calculated.     

The role of hydroperoxides in photo-oxidative degradation of cis-1,4-polybutadiene

Hydroperoxides undergo various types of homolytic reactions on exposure to u.v. radiation. Free radicals formed from the photodecomposition of the hydroperoxide group (OOH) are oxy (HO.) and peroxy (HOO.) radicals which participate in further reactions. In cis-1,4-polybutadiene, they may initiate free radical oxidations. Cleavage of alkoxy (RO.) radicals and crosslinking of polymer radicals through polymer peroxides in the presence of air in solid film nearly balance. Most polymer radicals produced in the absence of oxygen undergo cross-linking but form peroxy radicals (POO.) in its presence. This paper presents results on the photodecomposition of tert-butyl hydroperoxide, cumyl hydroperoxide and 2,5-dimethyl-2,5-dihydroperoxyhexane in cis-1,4-polybutadiene in film and in solution.     

Photophysical and photochemical studies of 2-phenylbenzimidazole and UVB sunscreen 2-phenylbenzimidazole-5-sulfonic acid

The sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid (PBSA) and its parent 2-phenylbenzimidazole (PBI) cause DNA photodamage via both Type-I and Type-II mechanisms when UVB irradiated. We have studied the photophysical and photochemical properties of these compounds and their ability to photogenerate reactive oxygen species including free radicals. PBI and PBSA exhibit both oxidizing and reducing properties in their excited state. The absorption and fluorescence properties of PBSA depend strongly upon pH, and hence the photochemistry of PBSA was studied in both neutral and alkaline solutions. PBSA showed strong oxidizing properties when UV irradiated in neutral aqueous solution (pH 7.4) in the presence of cysteine, glutathione and azide, as evidenced by the detection of the corresponding S-cysteinyl, glutathiyl and azidyl radicals with the aid of the spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO). However, when an aqueous anaerobic solution (pH 10) of PBSA and either nitromethane (NM) or 4-nitrobenzoic acid (4-NBA) were irradiated, the corresponding nitro anion radicals were observed. This finding suggests that both NM and 4-NBA are reduced by direct electron transfer from the excited state PBSA. During UV irradiation of an aerobic solution of PBSA, O2*- and *OH radical were generated and trapped by DMPO. Further, PBI (in ethanol) and PBSA (in ethylene glycol : water 2: 1 mixture) showed low temperature (77 K) phosphorescence (lambdamax = 443, 476 and 509 nm) and also an electron paramagnetic resonance half-field transition (deltaMs = +/-2), which is evidence for a triplet state. This triplet produced singlet oxygen (1O2) with quantum yields 0.07 and 0.04 in MeCN for PBI and PBSA, respectively. These studies demonstrate that UV irradiation of PBSA and PBI generates a variety of free radicals and active oxygen species that may be involved in the photodamage of DNA.     

Aging and degradation of polyolefins. I. Peroxide-initiated oxidations of atactic polypropylene

Efficiencies of polymer radical production by thermal decomposition of di-tert-butylperoxy oxalate (DBPO) have been measured in bulk atactic polypropylene (PP) at 25–55°C; they range from 1 to 26%, depending on [DBPO], temperature, and presence of oxygen. Most of the polymer radicals thus produced disproportionate in the absence of oxygen but form peroxy radicals in its presence. Most of the pairs of peroxy radicals interact by a first-order reaction in the polymer cage. The fraction that escapes gives hydroperoxide in a reaction that is half order in rate of initiation. In interactions of polymer peroxy radicals, in or out of the cage, about one-third give dialkyl peroxides and immediate chain termination, two-thirds give alkoxy radicals. About one-third of the later cleave at 45°C; the rest abstract hydrogen to give hydroxy groups and new polymer and polymer peroxy radicals. The primary peroxy radicals from cleavage account for the rest of the chain termination. Cleavage of alkoxy radicals and crosslinking of PP through dialkyl peroxides nearly compensate. Up to 70% of the oxygen absorbed has been found in hydroperoxides. The formation of these can be completely inhibited, but cage reactions are unaffected by inhibitors. Concentrations of free polymer peroxy radicals have been measured by electron spin resonance and found to be very high, about 10^?3M at 58–63°C. Comparison with results on 2,4-dimethylpentane indicate that rate constants for both chain propagation and termination in the polymer are much smaller than those for the model hydrocarbon but that the ratio, k_p/(2k_t)^½, is about the same.     

Singlet oxygen-mediated protein oxidation: evidence for the formation of reactive side chain peroxides on tyrosine residues

Singlet oxygen (1O2) is generated by a number of enzymes as well as by UV or visible light in the presence of a sensitizer and has been proposed as a damaging agent in a number of pathologies including cataract, sunburn, and skin cancers. Proteins, and Cys, Met, Trp, Tyr and His side chains in particular, are major targets for 1O2 as a result of their abundance and high rate constants for reaction. In this study it is shown that long-lived peroxides are formed on free Tyr, Tyr residues in peptides and proteins, and model compounds on exposure to 1O2 generated by both photochemical and chemical methods. The yield of these species is significantly enhanced in D2O and decreased by azide. Nuclear magnetic resonance and mass spectroscopic analysis of reaction mixtures, or materials separated by high-performance liquid chromatography, are consistent with the initial formation of an (undetected) endoperoxide that undergoes rapid ring-opening to give a hydroperoxide situated at the C1 ring-position (i.e. para to the phenolic group). In the presence of a free alpha-amino group (e.g. with free Tyr), rapid ring-closure occurs to give an indolic hydroperoxide that decays into the corresponding alcohol, 3a-hydroxy-6-oxo-2,3,3a,6,7,7a-hexahydro-1H-indole-2-carboxylic acid. Hydroperoxides that lack a free alpha-amino group (e.g. those formed on 3-(4-hydroxyphenyl)propionic acid, N-Ac-Tyr and Tyr-containing peptides) are longer-lived, with half-lives of hours to days. These species undergo slow decay at low temperatures to give the corresponding alcohol. Their rate of decay is enhanced at 37 degrees C, or on exposure to UV light or metal ions, and gives rise to reactive radicals, via cleavage of the peroxide bond. These radicals have been characterized by electron paramagnetic resonance spin trapping. These studies demonstrate that long-lived Tyr-derived peroxides are formed on proteins exposed to 1O2 and that these may promote damage to other targets via further radical generation.     

含氧光敏引发体系的研究——II.BP/TEA/O_2引发体系中氧的加速作用

研究了二苯酮(BP)/三乙胺(TEA)/氧体系引发MMA聚合反应中氧的加速作用。体系中保持比较大的TEA/O_2浓度比值,是实现氧加速作用的必要条件。实验结果得出:系统中氧通过光氧化生成过氧化物的速度Vo_2=K[BP][TEA]~(0.8)。由于过氧化物的光敏分解,使初级自由基得到增殖。从测定的K_p/K_t~(1/2)值,说明存在初级自由基的终止作用。测定了光氧化动力学方程的数据并讨论了机理。