Kinetics of diffusion-free radiation graft polymerization of styrene onto polyethylene

The diffusion-free radiation graft polymerization of styrene onto polyethylene has been studied. The grafting rate shows a dependence on monomer which is far different than what has been assumed. Further, the dependence on monomer changes with increasing dose rate as does the dependence of grafting rate on radiation dose rate. Three different regions of behavior are defined: (1) a region of low dose rate where the grafting rate is 1/2-order in dose rate and 3/2-order in monomer; (2) a region of intermediate dose rate where the grafting rate is intermediate between 1/2-and zero-order in dose rate and 5/2-order in monomer; and (3) a region of high dose rate, where the grafting rate is independent of dose rate and at least 5/2-order in monomer. Various possible mechanisms responsible for these effects are discussed, including the effects of viscosity on the initiation and termination reactions, the possibility of ionic graft polymerization, and energy transfer.     

应变速率和电位对应力腐蚀裂纹扩展的影响

以滑移-溶解-再钝化模型为基础,推导出应力腐蚀裂纹扩展速率与裂尖应变速率和电位之间的理论公式.计算表明,在裂纹扩展速率与裂尖应变速率的关系曲线中有两个特征区域.裂纹扩展速率在区域I随裂尖应变速率增加而增大,而在区域II不随裂尖应变速率的改变而变化.用慢应变速率拉伸技术（SSRT）测量了304L不锈钢的裂纹增长速率.当电位控制在区域II的阳极区时,理论计算的裂纹扩展速率与实验得到的结果比较吻合.     

试液进样量对ICP光源中稀土元素谱线的影响

研究了ICP光源中试液进样量对稀土元素谱线强度、背景强度、谱线强度测量的相对标准偏差,元素检出限,发光效率及试样相对利用率的影响。结果表明,降低试液进样量对稀土元素谱线强度有轻度影响,并 不影响测量的相对标准偏差和元素的检出发。降低试液进行量将提高发光效率及试样利用率,节省稀有和贵重样品用样量。     

浅析广州市花都区预防梅毒母婴传播的实施成效

目的了解花都区开展预防梅毒母婴传播阻断项目的实施成效,降低梅毒母婴传播率。方法对首次就诊的孕产妇进行梅毒筛查,对检出的梅毒阳性孕产妇进行规范治疗,并对其所生婴儿进行随访管理。结果 2012—2016年感染产妇孕期确诊率达71.18%,接受规范治疗率达53.02%,新生儿预防性治疗率75.8%,儿童3月龄梅毒检测率为50.86%,6月龄检测率42.55%。结论实施预防梅毒母婴传播项目,可以有效地阻断梅毒的母婴传播,降低梅毒母婴传播率,提高妇女儿童的健康水平。     

剪切均匀性对流动诱导等规聚丙烯结晶的影响

固定应变和最终应变速率,采用瞬时和缓慢2种电机加速方式对样品施加剪切,研究了流场加载模式对样品流变和结晶行为的影响.实验结果显示缓慢加速能够消除剪切过程中流场的非均匀性,使样品取向度增加,提高流场对聚合物熔体的作用效果.同时,流动诱导结晶对于加速时间有依赖性.对于速率为17.7 s-1的剪切,加速时间为1 s时,熔体流动均匀且流动诱导的晶体取向最强,短加速时间(0.5 s)和长加速时间(1.5 s)样品的流动诱导结晶效果都弱于加速时间为1 s的样品.但是,对于不同剪切速率,其对应的最优加速时间不同.对于流动诱导结晶来说,加速时间应当作为一个重要参数来考虑,其背后的真实物理含义还需要进一步研究来说明.     

Kinetics of copolymerization—II. Kinetic investigation of the polymerization of methyl acrylate in solution

The kinetics of methyl acrylate polymerization initiated by azobisisobutyronitrile were investigated in dimethylformamide at 40–60. The polymerization was 1/2 order with respect to initiator; the rate of initiation was independent of the initial concentration of monomer. The rate and the overall rate constant of polymerization strongly depend on the medium: the overall rate constant decreases with increase of solvent concentration. The solvent dependence of overall rate constant can adequately be described by the hot radical theory.     

Molecular weight distribution in thermal polymerization of styrene

The molecular weight distribution in thermal polymerization, for which the termination rate is comparable with the transfer rate, is analyzed by assuming that (1) the termination rate is independent of chain length; (2) the rate is translational diffusion-controlled; and (3) the rate is influenced by the excluded volume. The theoretical distribution, based on the assumption that the rate is translational diffusion-controlled, is the best fit to the experimental data at high temperature. The dependence of the rate on chain length is stronger at higher temperature (>80°C). The ratio of the termination rate to the transfer rate increases with increasing temperature.     

Effect of dose rate on emulsion and microemulsion polymerization of styrene

Emulsion and microemulsion polymerization of styrene were initiated with a gamma ray to study the effect of dose rate on polymerization. In both systems, there is an apparent plateau of polymerization rate in the curve of reaction rate vs. conversion. It was shown that emulsion polymerization conformed to the Smith–Ewart theory very well. Changing the dose rate in interval 2 had no great influence on polymerization rate, but it changed the average lifetime of radicals in polymer particles and affected the molecular weight of polymer produced. For microemulsion polymerization it was assumed that in the plateau it is the number of growing polymer particles being kept constant, not the number of polymer particles. When the dose rate was changed while the polymerization came into the constant period, the polymerization rate and the molecular weight of the polymer varied with the dose rate. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 257–262, 1998     

The effect of carbon dioxide on xylose fermentation byPichia stipitis

Carbon dioxide was found to reduce the xylose fermentation rate of two different strains ofPichia stipitis (CBS 5773 and CBS 5776) significantly in anaerobic batch fermentations. The maximum specific fermentation rate in a carbon dioxide atmosphere was about 45% lower than the fermentation rate in nitrogen atmosphere. Further-more, the fermentation rate was found to be correlated to the growth rate. It is probable that the carbon dioxide influences the fermentation rate partly through decreasing the growth rate. It was also found that the fermentation rate of CBS 5773 was higher than for CBS 5776 and that the specific fermentation rate was lower at a higher cell density.     

Determining Role of the Chain Mechanism in the Temperature Dependence of the Gas-Phase Rate of Combustion Reactions

It is shown that the strong dependence of the rate of gas-phase combustion reactions on temperature is determined by the high values of the reaction rate constants of free atoms and radicals. It is established that with a branched chain mechanism, a special role in the reaction rate temperature dependence is played by positive feedback between the concentrations of active intermediate species and the rate of their change. The role of the chemical mechanism in the temperature dependence of the process rate with and without inhibitors is considered.     

Kinetics of Radical Polymerization. XXIX. Kinetics of Initiation in the Polymerization of Ethyl Acrylate

The rate of initiation has been investigated in the free-radical polymerization of ethyl acrylate at 50°C in two solvents, benzene and dimethylformamide. The rate constant of initiation and the rate constant of the decomposition of AIBN was determined by the inhibition method and nitrogen volumetry, respectively. The rate constant of initiation was found to be constant over the whole range of monomer concentration in benzene solutions, but it proved to depend on the concentration of monomer in dimethylformamide solutions. The latter dependence is not linear. It was pointed out that the change in the rate constant of initiation is due to the solvent effect on the rate constant of decomposition of AIBN, because the factor of radical efficiency is practically constant over the whole range of monomer concentration. The observed relationship between the rate constant of initiation and the molar fraction of monomer was interpreted on the basis of the selective solvation of initiator molecules.     

Radiation-induced emulsion polymerization of ethylene. I. Effect of reaction conditions on the polymerization

The effect of reaction conditions on the rate of radiation-induced emulsion polymerization of ethylene was studied by use of a 500-ml autoclave. Among various kinds of emulsifiers, a series of potassium salts of fatty acids gave high rates of the polymerization. The polymerization was inhibited by the presence of oxygen, but the rate of polymerization followed by the induction period was not influenced by the initial presence of oxygen. Stirring rate and the monomer: water ratio did not affect the rate of polymerization. The rate of polymerization was maximum at about 80°C, and number-average molecular weight was influenced by the temperature in a similar manner as the rate of polymerization. This suggests that the change of mobility of propagating radical in the polymer particle changes the rate of termination reaction. The rate of polymerization was proportional to the 1.7 power of the reaction pressure.     

Radiation-induced emulsion polymerization of ethylene. IV. Effect of pressure,temperature, and additives on rate in connection with number of polymer particles

The effects of pressure, temperature, and additives on the rate of radiation-induced emulsion polymerization of ethylene with FC-143 as emulsifier were studied kinetically. The rate of polymerization was proportional to the 2.5 power of ethylene fugacity, and the apparent rate constant (rate of polymerization/2.5 power of ethylene fugacity) was constant below 78°C. Above this temperature, the rate constant decreased with an apparent activation energy of ?8.2 kcal/mole. These facts can be interpreted in connection with the polymer structure and the change of rate of escape of radicals from the polymer structure and the change of rate of escape of radicals from the polymer particle into the aqueous phase. The rate of polymerization decreased on addition of a series of n-aliphatic alcohols due to the chain-transfer reaction and consequent escape of radicals to the aqueous phase. On the other hand, the addition of tert-butyl alcohol increased the rate of polymerization, probably because of its effect in increasing swelling of the polymer particles. Addition of electrolytes increased the rate of polymeriaztion as a result of the increase of the number of polymer particles.     

Kinetics of radical polymerization. XXX. Polymerization of styrene in solution

A study was made on the AIBN-initiated polymerization of styrene in benzene and dimethyl formamide at 50°C. The overall rate and the rate of initiation of the polymerization were determined and the number-average and weight-average molecular weights of the polymers formed were measured. The decrease in the rate and degree of polymerization with the decrease in styrene concentration was caused by the corresponding decreases in the rate constants of chain propagation and initiation steps. In the systems studied no chain transfer process occurred with an experimentally measurable rate.     

三维结构和氧化度对C6位氧化再生纤维素止血材料性能影响

C6位氧化再生纤维素作为可吸收止血材料,其止血性能受材料理化性质的影响。通过比较氧化再生纤维素的吸水率、凝胶化速率、溶解速率、降解速率、抗老化性能和止血效果,研究三维结构和氧化度对氧化再生纤维素性能影响。结果发现,氧化度增高,氧化再生纤维素吸水率增强,凝胶化速率加快,溶解速率和降解速率变快,抗老化性能变差,产品有效期变短。纤丝松散网状多孔结构比纱布致密结构更有利于提高吸水率,加快凝胶化速率和溶解速率;同时降低氧化剂用量,提高抗老化性能。同一氧化度条件下,纤丝止血速率优于纱布,止血效果更好。     

Temperature dependence of rate constants of thermal activated processes and vibrational relaxation in starvation kinetics

The purpose of this paper is to study the conditions under which the rate constant exhibits the Arrhenius type of temperature dependence and the damping effect on the rate constant. According to the starvation kinetics, the rate of reaction is determined by the rate of energy flow in the high temperature range. We shall show that the rate of energy flow (vibrational relaxation) reaches a finite limit in the high temperature condition.     

Different influences of nucleating agents on crystallization behavior of polyethylene and polypropylene

The crystallization behavior of polyethylene (PE) and polypropylene (PP), including the neat ones and the ones nucleated with the same nucleating agent (NA), was studied by DSC. It was found that the nucleating agent decelerated the PE nonisothermal crystallization process. NA did enhance the nucleating rates for both PE and PP, but the linear growth rate dominated the volumetric growth rate for PE, and the volumetric growth rate dominated the overall crystallization rate. That is why PE nucleated with NA had a slower overall crystallization rate than the neat one.     

冠醚配合物的研究 XI: 若干苯并-18-冠-6甲基衍生物液膜传输碱金属离子

本文研究了2,3-苯并-11-甲基-18-冠-6,2,3-苯并-8,15-二甲基-18-冠-6和2,3-苯并-8, 11, 15-三甲基-18-冠-6的氯仿液膜对Na^+, K^+, Rb^+的传输速率。结果指出,传输速率随膜相冠醚浓度增是加而增加, 两者成线性关系; 当冠醚的醚环上甲基数增加则传输速率减小; 对同一冠醚, 不同金属离子的传输速率与相应配合物稳定常数的大小顺序有一致关系; 冠醚传输金属离子时, 阴离子一起迁移, 阴离子水合能力越强则传输能力越小; 传输速率与搅拌速度成线性关系。     

Effect of dose rate on radiation-induced polymerization of styrene adsorbed on silica gel

The effect of dose rate on the rate of polymerization and molecular weight distribution of radiation-induced polymerization of styrene adsorbed on silica gel was studied in a wide dose rate range of 4.4 × 10⁴ to 3 × 10⁸ rad/hr by γ rays of ⁶⁰Co and electron beams with a Cockcroft-Walton-type accelerator. Dose rate dependence on the initial rate of polymerization was about 1 below 3 × 10⁷ rad/hr, and it decreased gradually at high dose rates. Throughout the dose rate range, graft polymerizations and homopolymerizations by cationic and radical mechanisms proceeded simultaneously. Dose rate dependence of the cationic polymerization was 1 below 3 × 10⁷ rad/hr, while dose rate dependence of the radical polymerization was 0.65 below 3 × 10⁷ rad/hr. At high dose rates, molecular weight and fraction of graft polymer decreased, and fraction of cationic polymerization increased. A very high-molecular-weight graft polymer was formed above 4.4 × 10⁵ rad/hr at the initial stage of the polymerization. The dose rate dependence of this polymerization was larger than 1 and decreased with increase in dose rate. The polymerization seems to be related to an excitation of monomer or growing chain.     

Study of Kinetics of Dispersion Polymerization of Styrene in Organic Media

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.