Radiation-induced emulsion polymerization of vinyl acetate and styrene

Studies have been made of the γ-induced emulsion polymerization of styrene and comparisons made with chemically initiated emulsion polymerization. The polymerization proceeded smoothly to high conversions at 0 and 60°C, the reaction showing a high G (monomer) value. Complete conversions were obtained with total doses of less than 0.05 Mrad. In accordance with the behavior expected of systems having a constant rate of initiation, the molecular weight was found to decrease with decreasing temperature. The molecular weight and particle size distributions were narrower than those obtained in chemically initiated emulsion polymerizations at the same temperature. The radiation-induced emulsion polymerization of vinyl acetate proceeded smoothly at temperatures in the range 0–50°C to give polymers of much higher molecular weight than these obtained from chemically initiated polymerizations at the same temperature. Complete conversion was attained after a dose of 0.02 Mrad for latices approaching 50% solids. The elimination of ionic endgroups in the poly(vinyl acetate) radicals tends to drive the polymerization from the aqueous phase, resulting in faster rates and higher molecular weights than are obtained from chemically initiated systems. Rates of polymerization were found to be independent of temperature and the molecular weight of the polymer to be independent of dose rate. Latices of poly(vinyl acetate) of high solids content were evaluated for latex and film properties and found to have improvements over commercially available samples in both areas, especially in clarity of film and scrub resistance. A number of acrylate and maleate esters were copolymerized with vinyl acetate in a radiation-initiated emulsion system. High molecular weight copolymers were produced after low dose.     

On‐line monitoring of methyl methacrylate–vinyl acetate emulsion copolymerization

An adaptive calorimetric method, coupled with state estimators for emulsion copolymerization, is shown to provide accurate, on‐line information on the evolution of the composition and kinetics of an emulsion copolymerization. This method was evaluated for the emulsion copolymerization of methyl methacrylate–vinyl acetate (MMA–VAc) under nonisothermal conditions. In addition to providing on‐line estimates of the number of moles of each polymerizing species in the reactor, the state estimator provides a value for a lumped kinetic parameter proportional to the product of n N_p. This information can be combined with off‐line measurements to study the evolution of polymerization kinetics and to explain the trends observed for the molecular weight distribution and glass transition temperatures. Values of n were found to vary from 0.5 to 30 for the homopolymerization of MMA. However, the presence of VAc in the copolymerizing system drastically reduces n . This can lead to a dramatic increase in the average molecular weight of the copolymer since it alters the ratio of propagation to termination in the polymerizing particles. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1667–1683, 2000     

Kinetics of high conversion polymerization of vinyl acetate. Effects of mixing and reactor type on polymer properties

In the present article the kinetics of polymerization of vinyl acetate in suspension up to high conversion was studied. The molecular weight distribution and the side chain branching of polyvinyl acetate produced were examined with respect to micro and macro mixing as well as to reactor type. The following results were achieved: the time–activity curves of the polymerization can be described up to high conversions considering the exponential increase in viscosity of the polymerizing system and combining the viscosity with rate constants of the polymerization. The change of volume of the polymerizing system has no significant influence on kinetics. The narrowest molecular weight distribution of the poly(vinyl acetate) produced was achieved when polymerizing in the homogeneous continuous stirred tank reactor while the broadest molecular weight distribution was observed in the segregated continuous stirred tank reactor. The batch reactor and the flow tube reactor produce polymers with molecular weight distributions lying in between. Considering the side chain branching, another order was found. The batch reactor and the tube reactor show the lowest side chain branching, the homogeneous continuous stirred tank reactor shows a larger one and the segregated continuous stirred tank reactor shows the largest. Possible reasons for the different behavior of the different reactors are discussed. The degree of segregation was determined by experiments.     

高温溶液法制备SBR的结构和性能研究

以正丁基锂（n-BuLi）为引发剂、醚类化合物为调节剂、环己烷／正己烷为溶剂,采用阴离子高温聚合工艺合成了溶聚丁二烯／苯乙烯橡胶（SSBR）。通过GPC、NMR分别测试了SSBR的相对分子质量及其分布和微观结构;并对硫化胶性能和门尼粘度进行了测定。考察了调节剂、温度等因素对SSBR的相对分子质量及其分布、共聚物微观结构、序列分布以及动态力学性能和物理机械性能的影响。研究结果表明：所用调节剂是有效的SSBR高温聚合调节剂,可很好地调节SSBR中的乙烯基含量,获得微观结构适中的中高乙烯基丁苯共聚物;n（调节剂）／n（Li）对聚合速率及共聚物的1,2-结构含量有明显的影响,但对共聚物的相对分子质量分布无明显影响;温度对共聚物的转化率及微观结构均有一定的影响。     

Emulsion polymerization of vinyl acetate in a tubular loop reactor

A study was conducted on the emulsion polymerization of vinyl acetate using a loop reactor. Among the variables studied were the agitation, that is, the Reynold's number, and the effect of the presence of silver ions on the reaction rate. The molecular weight and molecular weight distribution of the polymer were determined as well as its particle size. The results are compared with earlier work done in a batch, a continuous tubular, and in a tubular loop reactor. © 1994 John Wiley & Sons, Inc.     

ARGET ATRP法合成聚氯乙烯接枝丙烯酸丁酯共聚物

以不稳定氯含量高的聚氯乙烯（U-PVC）和氯乙烯-溴代异丁酸烯丙酯共聚物（PVC-co-ABrMP）为大分子引发剂,使用电子转移催化再生原子转移自由基聚合（ARGET ATRP）进行丙烯酸丁酯（BA）的溶液接枝共聚。在固定CuCl₂：三（2-吡啶甲基）胺：辛酸亚锡（摩尔比）时,当CuCl₂用量（相对于氯乙烯链节数）小于0.1%时,BA转化率随CuCl₂用量增加而明显增加;辛酸亚锡与CuCl₂摩尔比大于50时,辛酸亚锡用量对聚合速率的影响较小;相同催化体系用量下,采用PVC-co-ABrMP为引发剂,可获得更高的BA转化率。通过PVC-co-ABrMP酯基水解得到PBA支链,其分子量分布指数为1.29,符合“活性”自由基聚合的特征。接枝PBA对PVC有明显的内增塑效果,PBA摩尔分数为32.75%的PVC-g-BA的玻璃化温度为8.34℃。     

复合偶氮引发剂在醋酸乙烯酯乳液聚合中的应用研究

分别用过硫酸铵(APS)、水溶性的偶氮二异丙基咪唑啉盐酸盐(AIB I)和油溶性的偶氮二异丁腈(AIBN)以及两者组成的复合偶氮引发剂引发醋酸乙烯酯(VAc)、丙烯酸丁酯(BA)乳液聚合。对比研究了不同引发剂对VAc/BA共聚乳液转化率、残余单体含量、分子量及其分布、电荷稳定性和乳胶粒粒径分布及形貌的影响,并对其成核机理进行了分析。结果表明,采用水溶/油溶复合偶氮引发剂制得的PVAc共聚乳液聚合温度低(65℃),转化率高(99.13%),残余单体含量低(230.47×10-6),电荷稳定性好。     

Emulsion copolymerization of vinyl acetate and 2‐ethyl hexyl acrylate using nonionic emulsifiers in loop reactor

Batch emulsion copolymerization of vinyl acetate and 2‐ethyl hexyl acrylate (VAc/2EHA = 90 : 10) was initiated by the thermal initiators ammonium persulfate and potassium persulfate at 70°C in the presence of nonylphenol ethoxylates with varying chain lengths and poly(vinyl alcohol). VAc–2EHA copolymer latexes were synthesized as two different series in a loop reactor. The first series was initiated by ammonium persulfate, and the second series was initiated by potassium persulfate. The influence of the counterions or initiators and chain lengths of a nonionic emulsifier on the properties of VAc–2EHA copolymer latexes were determined by measuring the viscosities, weight‐average molecular weights, number‐average molecular weights, molecular weight distribution, and surface tension of latexes to air. The results for the copolymer latexes indicated that some of their physicochemical properties increased with increasing chain length of the nonionic emulsifier, but some of them followed a different trend for the two initiators. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1380–1384, 2005     

Synthesis of high-molecular weight poly(vinyl alcohol) by low-temperature emulsifier-free emulsion polymerization of vinyl acetate and saponification

High-molecular weight (HMW) poly(vinyl alcohol) (PVA) was prepared via an emulsifier-free emulsion polymerization of vinyl acetate (VAc) using a redox initiation system in low temperatures, and the subsequent saponification with potassium hydroxide in methanol. The effect of the polymerization conditions on the conversion, molecular weight, and branching degree was investigated. PVA with maximum viscosity-average degree of polymerization (DP) of 8270 could be prepared by saponification of poly(vinyl acetate) (PVAc), with DP of 10,660 obtained at temperature of 10°C, monomer concentration of 30%, potassium persulfate molar ratio to monomer of 1/2000, agitation speed of 160 rpm. The conversion was above 90%. From the emulsifier-free emulsion polymerization of VAc in low temperature, PVAc with HMW and high linearity was effectively prepared, which might be useful for the preparation of high-strength and high-modulus PVA fiber. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of pH Value on the aqueous precipitation copolymerization of acrylonitrile and vinyl acetate

The aqueous precipitation copolymerization of acrylonitrile (AN) and vinyl acetate (VAc) with NaClO₃/NaHSO₃ redox initiation system is carried out continuously in a 10L pilot‐plant reactor. The effects of pH value on ionization equilibrium of NaHSO₃, polymerization rate, particle morphology, particle size and its distribution, molecular weight and its distribution have been investigated. It has been found that effective concentration of reductant H₂SO₃ increases with the decrease in pH value. On the other hand, deceasing pH value intensifies the coalescence among particles and then reduces diffusion rate of monomer and radicals into particles. Experimental data shows that the increase of pH value results in higher conversion. It indicates that pH value's effect on particle stability prevails its influence on effective concentration of the reductant. This conclusion is verified by the molecular weight, particle size, and particle morphology. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polymerization of vinyl chloride at reduced monomer accessibility. IV. The effect of diffusion control on polymerization rate,molecular weight,and thermal stability

The effect of diffusion control on the polymerization of vinyl chloride has been studied by observing the rate as well as the molecular weight and the thermal stability of the polymer formed. The polymerizations were performed at 97% of saturation pressure in a water-suspended system at 55°C, using emulsion PVC latex as seed and a water-soluble initiator. The monomer was charged as vapor from a storage vessel kept at a lower temperature. Characterization included determination of molecular weight distribution by GPC and viscometry, and thermal dehydrochlorination. The gas–liquid contact was varied by changing the speed of agitation and the design of the stirrer. With a propeller the polymerization rate increased with the agitation up to ca. 1000 rpm, where after it became almost constant. Simultaneously, the molecular weight and the thermal stability increased. This indicates diffusion control, and thus decreased monomer concentration, at low agitation speeds, while the polymerization becomes reaction controlled at higher speeds. By a comparison with earlier data, obtained at different pressures and under reaction control, the actual monomer concentration could be calculated, which allowed an evaluation of the mass transfer constant. The possibilities to encounter problems with diffusion control in commercial polymerization of vinyl chloride is discussed. It is demonstrated that diffusion control is utilized in continuous polymerization of vinyl chloride, which explains the lower thermal stability of such materials.     

Improvement of film properties of vinyl acetate based emulsion polymers by using different types of maleic acid diesters

Two types of maleic acid diesters, dibutyl maleate (DBM) and dioctyl maleate (DOM) were used as comonomers in semicontinuous emulsion copolymerization of vinyl acetate (VAc) in order to improve the film properties of poly(vinyl acetate), PVAc emulsion polymer. The effects of the comonomer type and comonomer ratio on minimum film forming temperature (MFFT), glass transition temperature (T_g), polymer structure, molecular weights, water contact angle and water resistance of PVAc latex films were examined. It was found that MFFT and T_g of the PVAc emulsion polymer decreased by the presence of the maleic acid disters in copolymer composition. This decrease was more affected by the increasing content and alkyl chain length of the comonomers. The molecular weights of the emulsion polymers were also affected by the comonomers and their ratios. Moreover, hydrophobicity and water resistance of the PVAc latex films were increased by using DBM and DOM as comonomer.     

Emulsion copolymerization of vinyl esters in continuous reactors: Comparison between loop and continuous stirred tank reactors

The high solids emulsion copolymerization of vinyl acetate and veova 10 was studied in a continuous loop reactor and in a continuous stirred tank reactor (CSTR) in an attempt to elucidate the similarities and differences between these reactors. Reactions were carried out under comparable conditions, namely, similar macromixing and the same feed composition and space time. The behavior of both reactors was almost the same when the heat generation rate was low; otherwise, thermal runaway occurred in the CSTR whereas the loop reactor temperature was easily controlled. © 1995 John Wiley & Sons, Inc.     

Kinetics of vinyl chloride and vinyl acetate emulsion polymerization

The kinetics of vinyl chloride and vinyl acetate emulsion polymerization are reexamined. The validity of Ugelstad's model for systems with high desorption rate is confirmed by simulating conversion histories for both systems at different initiator concentrations and particle numbers. On the basis of the model, it is shown that at ordinary initiation rates, termination reactions are unimportant with respect to molecular weight development in both systems, and as a consequence, molecular weight development is independent of number and size distribution of polymer particles and of initiator and emulsifier level. Based on this conclusion, it is shown that in accordance with experimental facts, the molecular weight distribution obtained in vinyl chloride emulsion polymerization is the most probable distribution, and it is concluded that the number of long-chain branch points per repetition unit is less than 2 × 10^?4 at high conversions. In vinyl acetate emulsion polymerization, an almost logarithmic normal distribution is obtained. The distribution is strongly broadened by branching reactions with the number of long-chain branch points increasing rapidly with monomer conversion. The increase of M_n with increasing conversion is due to terminal double-bond polymerization, while the increase in M_w is due mainly to transfer to polymer.     

Dynamic modelling of the continuous emulsion polymerization of vinyl chloride

A dynamic model for the continuous emulsion polymerization of vinyl chloride (VCM) in a train of stirred tank reactors has been developed. This model can predict monomer conversion, polymer particle size distribution (PSD), molecular weight distribution and long and short chain branching frequencies under non-steady reactor operation during startup, reactor switching and during unstable operation when conversion and polymer and polymer particle properties oscillate with time. The model has been used to design a flexible reactor train configuration which operates in a stable mode and can produce latexes with a wide range of properties including a bimodal polymer particle size distribution.     

Preparation and characterization of P(St‐co‐4VP) particles produced by using emulsifier‐free emulsion polymerization

Emulsifier‐free emulsion polymerization of styrene (St) and copolymerization of St and 4‐vinyl pyridine (4VP) in the presence of ammonium persulfate were studied. A comparison between the two polymerization systems was made. It was found that there were big differences comparing polymerization rate, the number and size of the particles and distribution, and molecular weight. For the St–4VP system, it was found that the additional amount of 4VP influenced the copolymerization of St and 4VP, molecular weight, and particle size. The formation mechanism of the particles was discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1502–1507, 1999     

反应性乳化剂参与的醋丙多元共聚及其压敏胶性能研究

采用种子半连续乳液聚合法,将反应性乳化剂α-烯丙基烷基酚聚氧乙烯醚硫酸铵(HS-10)引入醋丙乳液聚合体系,制备了稳定的醋丙压敏胶乳液。红外光谱实验结果表明,HS-10参与了醋丙体系共聚合反应。所得乳液的表面张力、粒径及分布、粘度及180°剥离强度都随HS-10用量增加而减小。耐水性性能实验表明采用HS-10的醋丙压敏胶体系,吸水率仅为传统型的35．9％,较好地改善了聚合物耐水性能。     

丙烯酸(酯)改性聚醋酸乙烯酯乳液的研制

采用半连续种子乳液聚合法,使用丙烯酸(AA)功能性单体和丙烯酸丁酯(BA)软单体对醋酸乙烯酯(VAc)进行了共聚改性,制备出高固含量(50.2%)的聚醋酸乙烯酯(PVAc)改性乳液。该乳液适合用于喷雾干燥法制备可再分散聚合物粉末,并且其耐水性和耐碱性等都得到了明显地改善。对影响共聚物的诸多因素进行了较为全面地考察,得出最佳的工艺条件为:AA用量为主单体质量的3%～4%,BA用量为主单体质量的5%～10%,保护胶体用量为混合单体质量的7.5%～15%,引发剂用量为混合单体质量的0.4%～0.5%,阴/非离子型复合乳化剂的质量比为1∶2～1∶3、用量为混合单体质量的2%～3%,分散剂、消泡剂和酸碱缓冲剂等助剂均为适量,加料时间为3～4h,反应温度为70～75℃。     

The Synthesis of Chitin-g-Poly(vinyl acetate) Copolymers with a Redox Initiator

Vinyl acetate monomer was graft polymerized onto chitin with a redox initiator, cerium ammonium nitrate. Both the graft copolymerization and emulsion polymerization of pure poly(vinyl acetate) (PVAc) were observed during the reaction and a stable dispersion solution was obtained after the reaction. After the PVAc homopolymer was removed by acetone extraction, the grafting efficiency and grafting percentage were calculated from the weight balance. Transmission and scanning electronic microscope were used to observe the morphologies of the reaction product. Experimental results indicated that at initial stage of reaction, graft copolymerization, which occurred on the surface of chitin particles, dominated over the emulsion polymerization. After that, the rate of emulsion polymerization increased greatly and became dominant. The existence of chitin not only provided the stability of the emulsion particles, but also increased the polymerization rate. Structures of copolymers were evidenced with the techniques of Fourier transform infrared and differential scanning calorimeter.     

Effect of emulsion polymerization conditions of vinyl acetate on the viscosity fluctuation and gelation behavior of aqueous poly(vinyl alcohol) solution

Poly(vinyl alcohol) (PVA) was prepared by emulsion polymerization of vinyl acetate (VAc) at 40, 50, and 60°C. PVAs of various molecular parameters were dissolved in water at concentrations of 3, 5, and 7% (g/dL) and aged at 30 and 60°C. The effects of the molecular weight and polymerization temperature on the viscosity fluctuation and gelation behavior of aqueous PVA solutions were investigated. Viscosity was increased with increasing molecular weight when other parameters were held the same. PVA of superior molecular regularity due to the lower polymerization temperature of VAc had higher relative viscosity. Viscosity and its fluctuation of PVAs with aging time varied with the polymerization temperature of the precursors, concentration of the aqueous solutions, and aging time. For PVA with a number‐average degree of polymerization of 2800 prepared from poly(vinyl acetate) polymerized at 40°C, a sharp increase in viscosity was observed after 500 min of aging at a concentration of 7%. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1897–1902, 2001