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1.
The non-steady state theory for the kinetics of free radical polymerization taking no account of gel-effect is reviewed. Considering the facts that the monomer consumption in chain propagation is much higher than that in chain initiation and the rate constant of chain termination is much larger than that of chain propagation or transfer, a few very close approximations are introduced to solve the set of kinetical differential equations of free radical polymerization. The expressions for various molecular parameters, such as the molecular size function, the number- and weight-average degrees of polymerization and the dispersity, are derived. In accord with the non-steady state theory, the curves of free radical decay with reaction time or monomer conversion and the molecular parameters mentioned can be predicted from the reaction conditions. Several numerical examples are given. 相似文献
2.
M. Arvis I. Kralji † J. P. Girma ‡ J. L. Morgat ‡ 《Photochemistry and photobiology》1978,28(2):185-190
Abstract— The 3-tyrosinyl free radicals (3-Tyr) and iodine atom are formed by flash photolysis of 3-iodotyrosine (3-Tyr-I) in aqueous solutions at pH 5. The presence of iodine atoms in the medium is characterized by the absorption spectrum and the decay kinetics of I formed when KI is added to the system. In the absence of radical scavengers, the 3-Tyr adds to or reacts with the parent molecule to produce a transient species, probably a radical dimer, which has an absorption maximum at 405 nm. The decay of this transient follows second order kinetics whose rate constant increases with decreasing 3-iodotyrosine concentration. Measurements of the dependence of the transient yield on the concentration of added ethanol indicate that the 3-Tyr radical reacts with ethanol by hydrogen abstraction. The rate constants of reaction of the 3-Tyr radical with 3-iodotyrosine and ethanol are deduced from results. 相似文献
3.
环氧树脂/氨酯丙烯酸酯树脂互穿聚合物网络生成动力学研究 总被引:3,自引:0,他引:3
用FTIR跟踪研究了由不同分子量聚氧化丙烯(PPO)合成的氨酯丙烯酸酯树脂(UAR)/环氧树脂(epoxy)同步互穿网络(SIN)的生成动力学.结果表明,在聚合反应初期(转化率<04)环氧基和不饱和双键的转化率均和反应时间呈近似线性关系,聚合反应主要由单体的扩散控制;由不同分子量UAR合成的epoxy/UARSIN的生成动力学有较大差异,与SIN形成过程中的形态发展有关.通过不同用量的AIBN,可以调节UAR网络的形成速度,导致SIN中两个网络的生成顺序发生改变. 相似文献
4.
In this work the minimum reaction time was studied for a specific final monomer conversion and number-average chain length by adjusting the amount of initial initiator concentration in the presence of a fixed amount of chain transfer agent at the best isothermal temperature. A new method for the determination of the best initial initiator concentration ([I]0) and isothermal temperature (T) in the presence of chain transfer agent was developed by the application of a simple optimization algorithm, based on the Lagrangian multiplier, to the basic free radical kinetics. Numerical examples for the polymerization of styrene are presented. It is shown that in the presence of a fixed amount of chain transfer agent the best isothermal policy for minimum time would deviate from dead-end polymerization. As the concentration of chain transfer agent increases, a stronger deviation from dead-end polymerization is observed. It was found that for a given pair of desired conversion and number-average chain length the usage of a chain transfer agent would result in a longer reaction time. The results give insights into operation of batchwise bulk free radical polymerization for minimum reaction time under isothermal conditions. 相似文献
5.
Josephine L. Y. Kong Kenneth G. Spears Paul A. Loach 《Photochemistry and photobiology》1982,35(4):545-553
Abstract— The fluorescence properties of a covalently-linked porphyrin-quinone complex and its zinc derivative were studied in a variety of organic solvents. The kinetics of fluorescence decay for both the quinone and hydroquinone oxidation states were measured in acetonitrile, dichloromethane, dimethyl-formamide, and pentane. The fluorescence yield and kinetics of decay at room temperature were little affected in the porphyrin or zinc porphyrin complexes when the attached quinone was reduced. However, for these complexes the fluorescence yield and lifetimes were both substantially decreased in acetonitrile and dichloromethane when the quinone was in its oxidized state. These latter decay kinetics were not explainable by a process having a single exponential decay. On the other hand, little fluorescence quenching or lifetime shortening was observed in dimethylformamide or pentane, indicating unique solvent dependencies for the quenching process. Evidence was obtained for photoproduced charge separation from EPR measurements on the covalently-linked zinc porphyrin-quinone complex. The EPR data showed equivalent concentrations of a Zn porphyrin cation radical and a benzoquinone anion radical in acetonitrile or dichloromethane at both room temperature and 77 K. The charge separated state rapidly decayed at room temperature (in sub-millisecond times) but was quite stable at 77 K. It is concluded that light-induced charge separation in acetonitrile and dichloromethane at room temperature may occur from the excited singlet state with a high quantum efficiency. A photoproduced charge separated state also occurred when the covalently-linked complexes were incorporated into egg yolk phosphatidylcholine liposomes. The quantum yield for radical formation in this latter system was 0.1 and the lifetimes of the radical species formed were many minutes. 相似文献
6.
以十二烷基苯磺酸钠(SDBS)为乳化剂,硫酸或盐酸为催化剂,八甲基环四硅氧烷(D4)为单体,十六烷为共稳定剂,超声预乳化,制备了聚硅氧烷细乳液,研究了超声时间、催化剂用量、乳化剂用量和温度对聚合动力学的影响.结果表明,在一定酸度范围内,聚合速度与硫酸浓度0.81次方、与盐酸浓度1.02次方、与乳化剂浓度-0.66次方成正比,反应的表观活化能为40.56kJ/mol. 相似文献
7.
Vladislav Jašo Radmila Radičević Dragoslav Stoiljković 《Journal of Thermal Analysis and Calorimetry》2010,101(3):1059-1063
Free radical polymerization of n-dodecyl methacrylate (DDMA) in bulk has been investigated by differential scanning calorimetry (DSC). Autoacceleration of
reaction was observed at the temperatures 70, 80, and 90 °C, with 0.25, 0.5, and 1 wt% of initiator, and was absent at 100 °C.
DSC curves obtained at the temperatures below 100 °C were characterized by two maxima. Two-peak deconvolution was used to
separate DSC curve into two constitutive unimodal curves, i.e., to calculate the contribution of polydodecyl methacrylate
formed before (first maximum) and after (second maximum) the onset of autoacceleration. The share of second maximum decreases
as the polymerization temperature and initiator concentration are increased. As the organization of monomer is known to decrease
with increasing temperature, it can be expected that the fraction of polymerized disordered phase of monomer (first maximum
in DSC curve) is the highest at 90 °C. Our results confirm this prediction and are in good agreement with those observed from
conversion versus time curves of DDMA polymerization. 相似文献
8.
9.
采用称量法和GPC,研究了以二甲基乙酰胺为溶剂,偶氮二异丁腈为引发剂,自由基溶液聚合制备含芳酰胺结构的新型甲壳型液晶高分子聚[乙烯基对苯二甲酸二(4-甲氧基苯胺)](PMPACS)的聚合反应动力学.研究发现,(1)MPACS的聚合反应在60℃时主要为双基偶合终止,所以反应后期聚合物分子量明显增大,分子量分布变窄;(2)该反应的聚合反应速率方程为Rp=kp[M][I]1/2,表观活化能Eα=44 kJ/mol,在60℃时的聚合反应常数kp=1.04 L·mol-1·h-1;(3)相同聚合条件下,单体的转化率和数均分子量随单体初始浓度[M]0的增加而增大,当引发剂浓度[I]0增加时,聚合物的分子量随之降低,分子量分布增大;(4)该研究虽采用普通自由基聚合,所得聚合物的分子量分布却较窄,仅为1.1~1.4. 相似文献
10.
Bayrakçeken F Aktaş S Toptan M Unlügedik A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(1):135-138
High resolution absorption spectra of anisole and phenoxyl radical has been recorded in the vapor phase at room temperature by flash photolysis technique, and subsequent reactions have been investigated by kinetic spectroscopy. It was possible to follow the kinetics of the radical's decay which occurred predominantly by bimolecular recombination. The concentration of the phenoxyl radical calculated from the concentration of diphenoxyl molecules formed in the reaction cell during the optical pumping. The absolute extinction coefficient of this radical was measured from the absorption band at 291 nm, and found to be 0.95 x 10(+4) mol(-1) 1 cm(-1). 相似文献
11.
通过比较在大水油比下的甲基丙烯酸甲酯 (MMA)悬浮均聚的实验数据以及本体聚合实验结果 ,发现单体的水溶性对其聚合动力学有影响 ,不能用本体聚合动力学代替其悬浮聚合动力学 .为了能更好了解单体的水溶性对其悬浮聚合动力学的影响以及影响动力学的原因 ,在MMA本体聚合动力学模型基础上 ,进一步提出 3个假设 :扣除溶于水相部分的单体量、增长和终止速率参数降低、少部分的油溶性引发剂被带到水相中 ,得到改进的悬浮聚合动力学模型 .运用该模型能很好预测水油比、聚合温度、引发剂浓度等对MMA悬浮聚合动力学的影响 ,且与实验数据能较好吻合 相似文献
12.
R. Ž. Radičević D. M. Stoiljković J. K. Budinski-Simendić 《Journal of Thermal Analysis and Calorimetry》2007,90(1):243-247
The free radical polymerizations of higher n-alkyl methacrylates were not investigated in detail until now. In this work, the courses of the isothermal free radical bulk
polymerization of dodecyl, quatrodecyl and hexadecyl methacrylates were investigated by differential scanning calorimetry.
The effects of the polymerization temperature and the alkyl group length in the esters on the monomer conversions during polymerization
were studied. It was found that the polymerization rate vs. time curves have two maxima. The free radical polymerizations of above-mentioned monomers proceed with slightly expressed
gel effect at the temperatures below 90°C, at initiator concentration 1 mass% in monomer. 相似文献
13.
Timo Rager 《Helvetica chimica acta》2004,87(2):400-407
Pre‐irradiation grafting of styrene/divinylbenzene (DVB) onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) films from isopropanol (iPrOH) solution was investigated with respect to the effect of irradiation dose, film thickness, cross‐linker concentration, and reaction temperature. A mathematical model was applied to the kinetic curves to extract information on the polymerization rate, the radical‐recombination rate, and the grafting through time. It turned out that the two closely correlated reaction rates for polymerization and radical recombination can be varied over a wide range by changing the irradiation dose, the cross‐linker concentration, and the reaction temperature. On the other hand, the time until the grafting front has progressed to the center of the film is mainly affected by the film thickness and the reaction temperature. The formation of homopolymer in the grafting solution increases steeply with temperature and cross‐linker concentration. 相似文献
14.
The kinetics of atom transfer radical polymerization (ATRP) of styrene using bis(1,10‐phenanthroline)copper bromide was investigated. The concentration of the copper catalyst does not affect the propagation rate but does affect the termination process of polymerization appreciably. With increasing reaction temperature the molecular weight distribution of the produced PS becomes more narrow. The apparent activation energy was found to be 75 kJ/mol. 相似文献
15.
Abstract— Wool fibres were exposed to visible light in the blue range. The free radicals created by the illumination were studied using electron paramagnetic resonance. It is shown that by control of the light intensity and frequency it is possible to get considerable insight into the mechanism of the creation and the decay of the free radicals. The radical population under the above conditions appears to consist of an initial stable radical insensitive to radiation, and three other radicals, two of which follow decay kinetics considerably different from that of the remaining free radical. All the latter three radicals are probably caused by N–H or C–H bond scission.
The kinetics of radicals in irradiated proteins is discussed. It is shown that the mechanisms previously suggested in the literature are inadequate to account for the form of the experimental curve describing the number of radicals vs. time in irradiated protein. A new mechanism is suggested in which the decayed radicals form sites immune to further irradiation. Such a mechanism is shown to be consistent with the experimental curves. The kinetics of the decay of radicals after the cessation of illumination is examined in detail. It is found that in the case of irradiated keratin the mechanisms assuming first order decay are inconsistent with the experimental results, while the assumption of second order decay for two different species of radicals yields results consistent with the experimental evidence. 相似文献
The kinetics of radicals in irradiated proteins is discussed. It is shown that the mechanisms previously suggested in the literature are inadequate to account for the form of the experimental curve describing the number of radicals vs. time in irradiated protein. A new mechanism is suggested in which the decayed radicals form sites immune to further irradiation. Such a mechanism is shown to be consistent with the experimental curves. The kinetics of the decay of radicals after the cessation of illumination is examined in detail. It is found that in the case of irradiated keratin the mechanisms assuming first order decay are inconsistent with the experimental results, while the assumption of second order decay for two different species of radicals yields results consistent with the experimental evidence. 相似文献
16.
Jean Pierre Quaegebeur Tadao Seguchi Henri Le Bail Claude Chachaty 《Journal of polymer science. Part A, Polymer chemistry》1976,14(11):2703-2724
The γ-ray-induced postpolymerization of acrylonitrile and methyl methacrylate adsorbed on Linde zeolite 13X irradiated at 77°K has been studied between 303 and 343°K as a function of the amount of adsorbed monomer and of the irradiation dose. The change in the nature and the concentration of free radical with temperature and duration of the postpolymerization was followed by the ESR method, whereas the formation of polymer was monitored continuously by the decay of the 1H-NMR absorption line of the monomer under high-resolution conditions. It was found that the overall postpolymerization kinetics may be accounted for by assuming an exponential decay of radical propagation and recombination reactions with chain length. The tacticity of the polymer recovered by destroying the matrix in hydrofluoric acid was determined by 13C-NMR. The probability of isotactic addition of AN and MMA is larger than in the radical polymerization in solution owing likely to the association of adsorbed monomer molecules in pairs preforming an isotactic diad. 相似文献
17.
系统研究了近临界水中聚丙烯腈无催化水解反应动力学.在实验数据重现性和物料配比对PAN水解反应影响的考察基础上,系统测定了210~250℃下聚丙烯腈的水解反应动力学数据,采用元素分析仪、傅立叶变换红外光谱仪、热分析仪、凝胶色谱仪对水解产物进行了表征.结果表明,近临界水中聚丙烯腈无催化水解是可行的,其中温度与物料配比是影响水解速率的主要因素;通过控制不同水解条件,可得到不同含量的腈基(—CN)、酰胺基(—CONH2)和羧基(—COOH)二元或三元共聚物,产物侧基含量的不同有可能在不同的领域得到应用;以一级连串反应动力学模型对实验数据进行了拟合,得到了聚丙烯腈和聚丙烯酰胺水解反应活化能分别为53.37 kJ.mol-1和120.55 kJ.mol-1. 相似文献
18.
双官能度引发剂引发苯乙烯聚合微观动力学 总被引:1,自引:0,他引:1
采用 2 ,5 二甲基 2 ,5 二己酰基过氧化己烷 (DMDEHPH)为引发剂 ,在 5 5~ 80℃下引发苯乙烯聚合 .通过研究影响聚合速率的各种因素 ,得出了聚合速率对单体浓度和引发剂浓度的级数分别为 1 0和 0 5次、聚合活化能为 92 0kJ mol、引发效率为 0 5 5± 0 0 3.温度一定 ,引发效率随引发剂浓度的增加而减小 .求得 6 0和70℃下DMDEHPH向引发剂的链转移常数分别为 0 0 37和 0 0 4 8、向单体的链转移常数分别为 0 5 9× 10 - 4和0 75× 10 - 4. 相似文献
19.
Lian-yingLiu Zhi-xingZhang Wan-taiYang 《高分子科学》2005,(2):219-225
Photoinitiated inverse emulsion polymerization of sodium acrylate (AANa) in kerosene was carded out at room or lower temperature, using 2,2-dimethoxy-2-phenylacetophenone (DMPA) as the initiator. Kinetic investigations indicated that the polymerization could be completed in about 30 min and produce polymer with high molecular weight (10^6-10^7). It was found that monomer droplets are the main sites for the polymerization (nucleation). With the increase of DMPA concentration, polymerization rate (Rp) reaches a maximum value while molecular weight of the produced polymer has an adverse result, but the dependence of Rp on incident light intensity is similar. Influences of other parameters such as monomer concentration, emulsifier content and reaction temperature, etc. were also studied. At lower pH values of water phase, Rp depends strongly on the pH due to the electrostatic interaction between the ionized radicals and the monomer. At higher pH, Rp shows a slight dependence on pH. 相似文献
20.
ZILI xu 《Journal of Dispersion Science and Technology》2013,34(7):869-882
The kinetics of dispersion polymerization of styrene in alcohol/methyl or butyl cellosolve was investigated with dried-weigh methods. The reaction parameters, such as concentration of initiator, polymerization temperature, and solvent, play an important role in determine polymerization rate. It was found that polymerization rate increases with the reaction temperature. The apparent activation energy is of 42.2kJ/mole and 52.6kJ/mole for the initial polymerization stage and the stationary polymerization interval. The polymerization rate increases with the concentration of the initiator with approximately 0.67 order dependence at conversion about 5%. It was described that the relation of conversion with the Hansen Parameters of media in detail by analysis of solvent dispersion, polarity and hydrogen bonding contributions. More significant was the result that polymerization rate versus conversion curve consisted of 3 intervals (2 non-stationary and 1 stationary one). The plateau of polymerization rate was observed in the curve of polymerization rate vs. monomer conversion. 相似文献