过氧化物复合引发剂分解动力学模型及应用

过氧化物分解动力学是控制自由基聚合反应的重要因素 .单一的过氧化物在某一温度下只有固定的分解速率常数 ,而聚合反应往往需要在较宽的温度范围调节聚合反应速度和聚合物质量 .单一引发剂无法满足要求 ,工业上常常使用多种 (高、中、低活性 )引发剂复合 [1,2 ] .过氧化物引发剂分解速率常数测定方法主要有碘量法 [3] 和示差扫描量热法 (DSC) [4 ] 两种 .单一引发剂分解动力学基本符合Arrhenius模型 ,有时也会出现诱导分解现象 [5] . VC悬浮聚合单一引发剂用量已有理论估算 [6] ,但多元复合引发剂用量未见研究 ,史悠彰 [7] 曾提出用“折…     

N-叔丁基-α-苯基硝酸酮调控氯乙烯悬浮聚合

以过氧化新癸酸α-异丙苯酯(Lup188)作为引发剂,聚乙烯醇(PVA)和羟丙基甲基纤维素(HPMC)作为复合分散剂,加入N-叔丁基-α-苯基硝酸酮(PBN)用氮氧自由基在40～70℃下调控氯乙烯(VC)悬浮聚合.PBN能有效控制聚氯乙烯链增长,聚合后期无自加速现象,体现出可控/"活性"自由基聚合的特点.用重量法测定转化率、GPC测定聚合物分子量与分布,研究了引发剂用量、PBN用量以及聚合温度对聚合动力学和聚合物分子量及分布的影响.得到该聚合体系下VC、Lup188、PBN的最佳摩尔配比为10000∶7∶1,最佳聚合温度为50℃,将转化率控制在50%以下时,能得到较窄分子量分布的聚氯乙烯产物.     

2,2′-二邻甲氧基苯基-4,4′,5,5′-四苯基-1,2′-二咪唑复合光引发体系的光聚合动力学研究

本文研究了对2,2′-二邻甲氧基苯基-4,4′,5,5′-四苯基-1,2′-二咪唑(BMOIM)复合光引发体系引发聚合动力学过程.采用紫外光谱仪对引发剂、供氢体、增感剂在紫外区的吸收谱图进行了表征.利用实时红外光谱仪对复合光引发体系引发聚合动力学过程进行实时监测,考察了不同光强、引发剂浓度以及不同官能度单体对反应速率及最终双键转化率的影响.结果表明,在引发剂浓度为0.6%(质量分数)时,20s内双键转换率达到96%,随着引发剂浓度的提高,聚合速率增大.聚合速率以及最终双键转化率随着光强增大而增大;双官能团单体的最终双键转化率比三官能团单体的最终双键转化率要高.     

甲基丙烯酸甲酯水溶性对其悬浮均聚动力学的影响

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     

超声辐照引发MMA微乳液聚合动力学研究

用自由基捕捉剂N,N-二苯基-2,4,6-三硝基苯肼基(DPPH)进行超声辐照引发甲基丙烯酸甲酯(MMA)微乳液聚合引发过程的动力学研究,结果表明,所得速率常数比超声辐照引发纯单体聚合的速率常数大一个数量级,说明超声辐照在微乳液聚合体系中的引发作用远远强于本体聚合;得到的表观活化能为正值,说明升温有利于超声辐照引发微乳液聚合.对聚合过程动力学的研究表明,引发剂用量决定聚合反应速率曲线恒速期的长短.     

一种可聚合光引发体系及其性能研究

合成了一种可聚合双分子光引发体系——甲基丙烯酸-4-二苯酮甲酯(BPMM)光引发剂和甲基丙烯酸-3,4-亚甲基二氧基苯甲酯(MDBMM)助引发剂.采用含有水平样品支架的实时红外光谱仪(RTIR)监测光聚合动力学,动态力学分析仪(DMA)研究固化膜的机械性能.结果表明,聚合体系的聚合速率(Rp)和最终双键转化率(Pf)随MDBMM浓度的增加而增加,但是,随BPMM的浓度变化出现一最佳值(0.8%);相同的聚合条件下,与传统引发体系相比,BPMM/MDBMM虽然引发活性较差,但是其固化膜的Pf和玻璃化转变温度以及在37℃左右的储能模量与传统引发体系相近,并且MDBMM作为天然可食用植物化学成分衍生物的特点使其有可能适宜于在生物相容性要求较高的领域中应用.     

甲基丙烯酸甲酯本体自由基聚合的引发效率f

基于ESR技术测定的自由基浓度和终止速率常数,用严格的非稳态动力学公式第一次获得了AIBME引发MMA本体聚合体系各个转化率下的引发效率f数据,提出了扩散控制引发反应模型。在反应全程中理论结果与实验结果相符。     

新型引发剂引发苯乙烯聚合的动力学

采用过氧化2-乙基己基碳酸叔丁酯为引发剂,研究了苯乙烯自由基本体聚合的动力学过程,考察了引发剂浓度、温度、乙苯质量分数对聚合反应速率和聚苯乙烯分子量的影响.结果表明:在117℃下,聚合速率(Rp)对引发剂浓度的反应级数为0.42,对苯乙烯浓度的反应级数为1,聚合反应的表观活化能为54.8 kJ/mol.引发剂浓度、温度、乙苯质量分数的提高导致聚苯乙烯数均分子量分别下降了约30％、20％和15％,其中引发剂浓度的影响最为显著.     

二苯酮-可聚合胺引发1,6-己二醇二丙烯酸酯的光聚合研究

以UV-Vis分光光度计法和Photo-DSC法分别研究了合成的3种可聚合胺类助引发剂DMPDA、EGDPM、EGMPM与二苯甲酮(BP)组成的引发体系的光化学初级过程及引发1,6-己二醇二丙烯酸酯(HDDA)的紫外光聚合动力学.考察了助引发剂胺的含量对BP的光化学初级过程和对引发HDDA光聚合动力学的影响,以及光强和温度对聚合动力学的影响.结果表明,随着胺含量的增加,BP的光化学初级反应速率增加,从而使体系的聚合反应速率增加.随着温度和光强的增加,单体最终转化率、最大反应速率增大,达到最大反应速率所需的时间减小.     

光聚合制备PVC大分子引发剂及两亲接枝共聚物

利用UV光照自引发、双异丙基硫杂蒽酮(BIITX)和异丙基硫杂蒽酮(ITX)引发氯乙烯(VC)聚合得到含缺陷结构或/和ITX残基的PVC.考察了不同引发方式时单体浓度、光强、反应时间和温度对单体转化率、产物分子量及其分布的影响,UV-Vis、1H-NMR和FTIR分析表明所得PVC含缺陷氯或/和ITX残基.以此PVC为大分子引发剂(缺陷结构和ITX残基为引发点),50℃下有效引发了甲基丙烯酸二甲氨基乙酯(DMAEMA)聚合,获得了PVC-g-PDMAEMA共聚物.相比起始PVC,接枝共聚物分子量稍有提高,PDI下降.1H-NMR和FTIR分析证实了接枝共聚物的形成,接枝共聚物在水(pH=3)中组装形成了稳定核-壳结构胶束,显示其具有两亲性.     

Suspension polymerization of vinyl chloride initiated by in situ generated diisobutyryl peroxide

It was found that diacyl peroxides can be formed in situ in a polymerization medium by the reaction of an acid anhydride with hydrogen peroxide. For the specific application to aqueous vinyl chloride polymerization, an initiator system based on the base-catalyzed reaction of isobutyric anhydride with hydrogen peroxide to produce diisobutyryl peroxide gave very good results. In contrast, the acid chloride was completely ineffective as a peroxide precursor in this reaction. Studies pointing to diisobutyryl peroxide as the initiating species; investigations of reactant stoichiometry; and comparison of the in situ system with preformed diisobutyryl peroxide were conducted. It was shown that this system makes possible the polymerization of vinyl chloride at 30°C at rates comparable to those obtained with dialkyl peroxydicarbonates at 50°C, thus demonstrating the ability of this system to initiate vinyl chloride polymerization at low temperature. The rates of vinyl chloride polymerization with the use of different concentrations of in situ diisobutyryl peroxide at 30, 40, and 50°C were determined. Similarly, polymerization rates with the use of combinations of in situ diisobutyryl peroxide and n-propyl peroxydicarbonate were determined. The data obtained demonstrate rapid initiation of the polymerization reaction and a reduction in polymerization time made possible by this dual initiator system. These results were verified in pilot-plant and commercial-scale PVC polymerizations.     

Primary Radical Termination in Vinyl Chloride Polymerization

The rate of vinyl chloride polymerization initiated by doubly labeled benzoyl peroxide ('H in the phenyl ring and ¹⁴C in the carboxyl group) in dichloroethane solution was measured by a dilatometric method. The relative significance of primary radical termination in polymerization is examined by kinetic analysis of the polymerization rate data and analysis of the polymer samples recovered at 10% conversion for combined initiator fragments.     

Non-ideal kinetics in vinyl polymerization: Note on primary radical termination in benzoyl peroxide initiated polymerization of vinyl chloride in dichloroethane

The kinetics of vinyl chloride polymerization initiated by benzoyl peroxide doubly labelled with ¹⁴C and 'H were studied in 1,2-dichloroethane solution at 60°. The importance of primary radical termination in the polymerization is examined by kinetic analysis and by analysis of polymers for combined initiator fragments.     

Mechanism of vinyl chloride polymerization

An overall mechanistic scheme for the suspension polymerization of vinyl chloride is presented. The process can be resolved into five discrete stages, each of which presents a unique environment for the interaction of the systems parameters. It is shown that the surface area of the polymer formed during the reaction is not a major factor in autoacceleration and that the increase of kinetic chain length with conversion is due to a radical dilution effect. The latter is a direct result of the difference in rates between polymerization and radical formation, the former being greater. The increase of the initial polymerization rate and the reduction of autoacceleration brought about by chain transfer agents can be explained by the lower diffusion rate and greater bulkiness of the chain transfer agent radical relative to that of the monomer radical. The chaintransfer agent CBr₄ is preferentially absorbed by PVC from solution in vinyl chloride. With lauryl peroxide as initiator it is shown that the “hot spot” is the result of a build-up of initiator in the monomer caused by its exclusion from the polymer phase. Vinyl chloride was found to dissolve 0.03% PVC at ambient temperature and to have no effect on the decomposition rate of lauryl peroxide.     

Front velocity dependence on vinyl ether and initiator concentration in radical-induced cationic frontal polymerization of epoxies

Formulations containing vinyl ethers and epoxy were successfully polymerized through a radical-induced cationic frontal polymerization mechanism, using an iodonium salt superacid generator with a peroxide thermal radical initiator and fumed silica as a filler. It was found that an increase of vinyl ether content resulted in higher front velocities for divinyl ethers in formulations with trimethylolpropane triglycidyl ether. However, increased hydroxymonovinyl ether either decreased the front velocity or suppressed frontal polymerization. The kinetic effects of the superacid generator and thermal radical initiator with varying vinyl ether content were also studied. It was observed that increasing concentrations of initiators increased the front velocity, with the system exhibiting higher sensitivity to the superacid generator concentration.     

Studies in vinyl chloride polymerization. Determination of primary radical termination by initiator fragment method

The rate of vinyl chloride polymerization initiated by doubly labelled benzoyl peroxide in dichloroethane at 60° was measured dilatometrically. The extent of primary radical termination, evaluated from the assay of the polymer samples recovered at 10% conversion, is compared with values deduced from analysis of the kinetic data.     

Block copolymerization with trapped radicals

Acrylonitrile–styrene, vinyl chloride–styrene and vinyl chloride–methyl methacrylate block copolymers were obtained by employing trapped radicals in polyacrylonitrile or poly(vinyl chloride) formed in a heterogeneous system by tri-n-butylboron in air as initiator. The trapped polymer radicals were activated on addition of dimethylformamide as solvent. Confirmation of block copolymers was carried out with solvent extractions, elementary analysis, and turbidimetry. In block copolymerization, the polyacrylonitrile trapped radical was more active than the poly(vinyl chloride) radical. Results of kinetic studies were used to consider the mechanism of polymerization.     

Characteristics and applicational properties of peroxide suspensions

Peroxide suspensions are liquid initiators for the manufacture of PVC with the following characteristics: low viscosity (50–500 mPa.s), good pumpability, small average particle size (5–20 μm), good dissolution rate in vinyl chloride and complete safety. Possible applicational advantages are: marginally faster polymerization, higher porosity and lower fish-eye level of PVC. A review is given of possible causes of fish-eyes. One of the causes is an inhomogeneous distribution of initiator over vinyl chloride droplets. An explanation of the low fish-eye level realized with peroxide suspensions, is that (because of good dispersability in water and a small average particle size) a homogeneous distribution of the peroxide over vinyl chloride droplets is obtained in an early stage of the process.     

Effect of oxygen on the polymerization of vinyl chloride. I. Kinetic features

The effect of oxygen on the liquid-phase polymerization of vinyl chloride at 55°C in the presence of an added initiator, bis(4-tert-butylcyclohexyl) peroxydicarbonate (Perkadox 16), has been studied by the technique of tumbled dilatometry. With this method, at constant initiator concentration, the induction period showed a half-order dependence on the initial oxygen concentration. At a constant initial oxygen concentration, the induction period varied inversely as the square root of the initiator concentration. Under the experimental conditions empolyed, the polyperoxy radicals with chloroalkyl (～CH₂?HCl) endgroups were not wholly scavenged by molecular oxygen but could undergo various decomposition reactions. The degree of conversion of the initial oxygen to peroxidic compounds did not exceed 30% by weight and was dependent on the shape of the reaction vessel empolyed. The existence of other oxidation products has been demonstrated. At 55°C, the average velocity constant for decomposition of the peroxide products from vinyl chloride, measured in dichloromethane solution, was found to be 8 × 10^?5 sec^?1. A kinetic scheme involving a predominant cross-termination reaction is proposed to explain the experimental results.