复合引发剂体系引发下氯乙烯悬浮聚合动力学模型及应用

在建立复合引发剂分解动力学模型的基础上,推导了复合引发剂体系引发下的氯乙烯(VC)悬浮聚合动力学模型.用模型预测不同温度、引发剂复合体系引发的氯乙烯聚合动力学与实验数据能较好地吻合.其中TxEHP,Tx99,Tx23和Tx36在51和57℃下的引发效率由单一引发剂引发的VC动力学数据计算     

悬浮PVC颗粒形成机理探讨

本文提出了悬浮PVC颗粒形成的新理论:借助于搅拌作用,液态氯乙烯以～0.7μm的微滴分散在水中,聚合反应在这些微滴里进行。当聚合转化率达到～25%时,这些微滴凝聚成～130μm的颗粒。该理论被大量实验事实和文献资料数据充分证实,逻辑推理也得到令人满意的结果。     

偏氯乙烯-丙烯腈悬浮共聚物的组成研究

研究了偏氯乙烯 丙烯腈 (VDC AN)悬浮共聚体系中AN的水溶性对单体相组成和树脂组成的影响 .结果表明 :由于AN部分地溶于水 ,使有机相AN的含量降低 ,导致共聚树脂的组成明显地不同于本体聚合模型的计算预测值 .为了准确地计算预测VDC AN共聚树脂的组成 ,本文假设溶于水的AN向有机相迁移的速度比聚合反应速度快得多 ,AN在两相的溶解分配近似为平衡态 .计算中先用描述AN在VDC/水系统中溶解分配的Marker式校正有机相AN的含量 ,然后根据校正后的AN含量用Mayo Lewis式计算预测VDC AN悬浮共聚物的组成 ,计算中有关的竞聚率值取自于文献中本体聚合的值 .计算结果与实验值一致     

甲基丙烯酸甲酯的原子转移自由基悬浮聚合

以 1 苯基氯乙烷为引发剂 ,氯化亚铜为催化剂 ,2 ,2 联吡啶为配体 ,外加搅拌 ,氮气保护下进行了甲基丙烯酸甲酯 (MMA)在 80℃下的原子转移悬浮聚合 .结果表明 ,聚合反应符合对单体浓度为一级的动力学关系 .经计算聚合体系的增长自由基浓度为 5 .74× 10 - 8mol L .聚合物分子量随转化率呈线性增加 ,分子量分布较窄 ,Mw Mn 在 1.37～ 1.40之间 .还以AIBN为引发剂 ,在三氯化铁和三苯基膦存在下进行了MMA的反向原子转移本体和悬浮聚合研究 .结果证明本体聚合具有好的可控特征 ,分子量随转化率呈线性增长 ,分子量分布指数在 1.2 7～ 1.31之间 .聚合反应速率较快 ,聚合体系中的增长自由基浓度较高 ,为 1.6 4× 10 - 7mol L .而在此催化体系下的悬浮聚合则完全失去了活性特征     

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     

铁-芳烃络合物引发氧化环己烯阳离子光聚合反应动力学研究

以环戊二烯异丙苯铁六氟磷酸盐为引发剂,用示差扫描量热法研究了氧化环己烯(CHO)阳离子聚合反应动力学.实验结果表明,温度对CHO聚合反应影响很大.CHO在一系列温度下等温聚合时,放热量和转化率均在40℃左右最高,而聚合反应速率则随着温度的升高而降低.CHO聚合反应属一级反应,活化能为-9.87kJ/mol,并对聚合反应历程进行了理论推导,其结果与实验结果相符合.     

甲基丙烯酸甲酯高转化聚合模拟动力学研究

<正> 聚合体系在高转化阶段,其动力学用常规方法难以解决,为了在实际生产中控制聚合反应,人们对聚合体系的高转化动力学进行了研究,但与实验相比都存在较大的偏。本文则用模拟函数方法,重新处理了这一问题,并根据实验散点图,拟合本实验条件下甲基丙烯酸甲酯本体聚合高转化阶段的动力学模型比前人更能精确地反映了实验事实,并且计算简便直观,无需其它动力学参数,从而为生产的自动控制提供了理论依据。 实验     

红外光谱法研究苯乙烯原子转移自由基聚合反应动力学

利用红外光谱法测定反应转化率研究原子转移自由基聚合反应动力学。在环己酮溶液中,以卤代烃为引发剂,过渡金属卤化物与配位剂２,２‘－联吡啶为催化体系,进行了苯乙烯聚合。分别就反应温度,反应物浓度和引发体系对苯乙烯聚合速率的影响进行了动力学测定,证实了原子转移自由基聚合具有活性聚合的特征,同时计算并讨论了苯乙烯原子转移自由基聚合反应的动力学数据。     

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.     

氯乙烯交联共聚凝胶点前的分子量模型与仿真

从氯乙烯(VC)两相聚合的特点出发,根据拟动力学常数法和分子量分布矩理论,建立了VC-微量二烯类单体悬浮交联共聚凝胶点前的分子量模型,并根据模型,对平均聚合度变化作了计算机仿真。     

Effects of acrylonitrile water solubility on limiting conversion and copolymer composition in suspension polymerization

The effects of acrylonitrile (AN) water solubility on the limiting conversion and copolymer composition of the AN and AN/vinylidene chloride (VDC) suspension polymerization were investigated. It was found that AN dissolved in aqueous phase does not transfer back to oil phase in AN suspension homopolymerization but partially does in AN/VDC suspension copolymerization, and thus the limiting conversion is lowered and decreases with water/oil ratio increasing in both AN and AN/VDC suspension polymerization. For the continuous transport of AN in aqueous phase to oil phase during suspension polymerization, the composition distribution of AN/VDC copolymer prepared by suspension polymerization is narrower than that by bulk polymerization. The calculated composition of AN/VDC suspension copolymer with considering AN water solubility is consistent with the experimental data.     

Grafting of Vinyudene Chloride. Model Studies with Poly(Vinyl Alcohol) as Substrate

The modification of coatings resins by graft polymerization of vinylidene chloride should produce a coatings binder with improved barrier properties. For superior color stability, vinylidene chloride must be copolymer-ized with other monomers such as alkyl acrylates and methacrylates. Ceric ion initiation was used to graft vinylidene chloride free-radically onto a model alcohol-containing polymer, polyvinyl alcohol. The effects of various reaction parameters on vinylidene chloride grafting were studied. Graft copolymers were characterized using selective solvent extraction, FTIR, SEM, XES, DSC, and x-ray diffraction.     

Carbonization of polytetrafluoroethylene surface by UV-induced grafting of vinylidene chloride

A method has been developed for modifying the surface layer of polytetrafluoroethylene by incorporation of poly(vinylidene chloride) via UV radiation-initiated graft polymerization of vinylidene chloride from the vapor phase using a PRK-4 mercury lamp. By the subsequent treatment of the composition with aqueous ammonia, dehydrochlorination (carbonization) of the grafted poly(vinylidene chloride) has been performed. The kinetics of UV grafting and the distribution of the carbonized phase in the polytetrafluoroethylene matrix have been studied. A material with the carbonized surface layer of a 10—30 μm thickness and a contact angle of about 57° remaining stable over time has been obtained.     

Kinetics of heterogeneous free-radical polymerization of vinylidene chloride

Poly(vinylidene chloride) precipitates as a crystalline phase during the polymerization reaction. Under the conditions studied, this phase is made up of complex particles with a lamellar substructure. The detailed morphology is very sensitive to reaction medium. The morphology developed by particles formed during polymerization of vinylidene chloride in dioxane suggests a mechanism of polymerization followed by crystallization. The morphology observed in mass polymerization suggests that both processes occurs simultaneously. Kinetic data, however, suggest a solid-phase reaction mechanism for both cases. The results are analyzed by comparison with a model that takes into account the solid-phase morphology. The theoretical analysis is consistent with experimental results if it is assumed that polymerization occurs on the edges of the lamellar crystals.     

Thermal decomposition of poly(vinylidene chloride) prepared in presence of oxygen

The thermal decomposition of poly(vinylidene chloride) was studied for samples prepared in the presence of oxygen. The products from both mass and aqueous suspension polymerizations show two modes of thermal decomposition. A rapid initial mode varies in rate and extent with the amount of oxygen present. A slower mode is unaffected by oxygen and in similar in rate to the polymer made in the absence of oxygen. The chief volatile products are phosgene and formaldehyde for the rapid decomposition and hydrogen chloride for the slow decomposition. The rapid decomposition is interpreted to be an unzipping reaction of a vinylidene chloride–oxygen alternating copolymer initiated by homolysis of a peroxide bond. The absence of significant amounts of hydrogen chloride during this stage of decomposition shows that none of the free radicals generated are capable of initiating a chain reaction that would unzip hydrogen chloride from the poly(vinylidene chloride) backbone. The presence of oxygen during the aqueous suspension polymerization correlates with the generation of hydrochloric acid in the aqueous phase. By analogy with the high temperature decomposition, the hydrochloric acid is believed to result primarily from the hydrolysis of phosgene produced by partial decomposition of the polyperoxide. Initiation of the decomposition is believed due to a reaction of the chain propagating radical.     

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…     

A Study of Emulsion Polymerization Kinetics by the Method of Continuous Monomer Addition

The differences in the kinetics of emulsion polymerization between nonswelling and swellable latex particles were explored in an attempt to define the locus of polymerization. The systems studied included vinylidene chloride, which forms a nonswelling particle, and mixtures of vinylidene chloride and butyl acrylate, which copolymerize to form a swellable particle. The basic experiment involved growing a seed latex by adding monomer at a constant rate. At low feed rates the rate of polymerization R_p was controlled by the rate of monomer addition R_a. The data fit the equation R_p?KR_a where the proportionality constant had an average value of 0.91. K was not dependent on monomer composition and appears to be a constant characteristic of the monomer addition process. In the range where this relationship holds, the reaction runs starved, i.e., monomer is consumed almost as fast as it enters the reactor. At higher rates of addition the reaction floods and excess monomer in the form of droplets can be detected. In this condition the rate starts out at a lower value but increases with conversion.' R_p is not controlled by R_a but does depend on monomer composition. No major differences were found between the behavior of swelling and nonswelling systems. Neither followed che kinetics expected if the Smith-Ewart theory were applicable. The results argue strongly that polymerization takes place at the particle-water interface or in a surface layer on the polymer particle.     

KINETICS OF VINYL CHLORIDE (CO) POLYMERIZATION AT HIGH CONVERSION

This paper provides a summarized review on the kinetics of vinyl chloride homopolymerization inthe absence and presence of chain transfer agents, of VC/DAP(diallyl phthalate) copolymerization with chainextension and/or slightly crosslinking functions, and of vinylidene chloride/VC random copolymerization.Models of rate, degree of polymerization or molecular weight, copolymer composition, gel fraction andcrosslinking density were proposed and interpreted mechanistically.