Molecular weight development in emulsion copolymerization of n‐butyl acrylate and styrene

The seeded emulsion copolymerization of n‐butyl acrylate and styrene in a weight ratio of 50/50 was investigated. The effect of the type of process (batch vs. semicontinuous) and the amounts of initiator and emulsifier charged into the reactor on the time evolution of the fractional conversion, number of polymer particles, and weight‐average molecular weight (M_w) was analyzed. It was found that the M_w depends to a slight extent on the type of process and the emulsifier concentration and to a larger extent on the initiator concentration. The molecular weight distributions (MWDs) and the gel content of the final latexes were also analyzed. In the absence of chain transfer agents (CTAs), the fraction of gel was higher in the semicontinuous processes. It was also found that the gel content increased with increasing initiator concentration in the recipe. The addition of 1 wt % CTA avoided gel formation and led to an important reduction of the M_w. Nevertheless, the MWDs presented a shoulder or even a second peak at high molecular weights that was due to reactions of chain transfer to the polymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1918–1926, 2003     

溴化苯乙烯/苯乙烯/丙烯腈乳液聚合试验条件探索

以过硫酸钾为引发剂,十二烷基硫酸钠为乳化剂,叔十二烷基硫醇为链转移剂,通过乳液法对溴化苯乙烯、苯乙烯、丙烯腈进行共聚得到溴化苯乙烯-丙烯腈共聚物.考察了引发剂、乳化剂、链转移剂的添加量,反应温度,反应时间,水和单体比例等对聚合反应收率的影响.研究表明：较适宜的反应条件为反应温度80℃,反应时间6h,水与单体质量比4∶1,引发剂质量为单体总质量的0.4％,乳化剂质量为单体总质量的4％,叔十二烷基硫醇为单体总物质的量的2％;上述条件下的产物收率高,相对分子质量4万左右,热分解温度高于350℃.     

Ionomer synthesis by emulsion polymerization of styrene and sodium acrylate

The emulsion copolymerization of styrene and sodium acrylate is reported using either a water-soluble initiator (potassium persulfate, or KPS), or an oil-soluble one [2,2-azoisobutyronitrile (AIBN)]. Reaction rates are fast with both KPS and AIBN. With KPS, conversions >90% are achieved in 50 min, with AIBN, conversions reach 85% in 100 min. Particle size, measured by quasielectric light scattering (QLS), increases with conversion. Particle size in final latices is ∼ 70–80 nm. Copolymer formation is confirmed by infrared (IR) spectroscopy, plasma emission spectroscopy (PES), and scanning electron microscopy (SEM). IR and PES indicate that mainly sodium acrylate reacts at the beginning of the reaction and then styrene is incorporated in the copolymer backbone. The copolymer produced with KPS contains more sodium acrylate than the one made with AIBN. These differences can be explained in terms of the reactivities and partitioning (local concentrations) of the monomers and of the type of initiator used. Thermomechanical analysis (TMA) of the copolymers reveals two transitions: one at ∼ 100°C, which is due to the glass transition temperature (T_g) of polystyrene blocky segments in the copolymer, and another one at higher temperatures, which is associated to the T_g of segments composed of alternated sodium acrylate and styrene units. The higher-temperature transition shifts to lower values as the reaction proceeds because these segments become richer in styrene. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 879–889, 1997     

Emulsifier‐free emulsion copolymerization of styrene with quaternary ammonium cationic monomers

Emulsifier‐free emulsion binary copolymerizations of styrene with four types of quaternary ammonium cationic monomers, diallyldimethylammonium chloride (DADMAC), (3‐(methacryloylamino) propyl) trimethyl ammonium chloride (MAPTAC), (2‐methacryloyloxy) ethyl) trimethyl ammonium chloride (MATMAC), and vinylbenzyl trimethyl ammonium chloride (VBTMAC), were conducted at 70°C. 2, 2'‐azobis (2‐methylpropionamidine) dihydrochloride (V50) and potassium persulphate (KPS) were used as cationic and anionic initiator, respectively. Ternary copolymerizations were also carried out in the presence of acrylamide as a second comonomer. Monomer conversions were followed by ultraviolet spectroscopy and the polymer microparticles were characterized using photon correlation spectroscopy, electrophoresis, colloid titration, and scanning electron microscopy. The results indicated that VBTMAC and MATMAC were highly reactive in the copolymerization with styrene whereas the incorporation of DADMAC was slow. MAPTAC had an intermediate reactivity. Binary copolymerization with VBTMAC, MATMAC, and MAPTAC produced particles smaller in size, but higher in surface‐charge density, than styrene homopolymer particles. However, significant agglomerates were detected in the VBTMAC and MATMAC‐containing latexes. In contrast, DADMAC‐containing polymer particles were almost identical to styrene particles. Continuous nucleation took place in the binary copolymerizations with VBTMAC and with MATMAC when using V50 initiator. In the case of using KPS, VBTMAC‐containing particles grew continuously to a mean size much larger than the corresponding particles initiated by V50. The presence of acrylamide reduced DADMAC‐containing particle size and diminished the agglomeration in the VBTMAC‐ and MATMAC‐containing latexes. The results were interpreted via particle formation mechanism. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1129–1140, 2000     

Statistical experimental strategies approach to emulsion copolymerization of styrene and n-butyl acrylate

A batch emulsion copolymerization for the preparation of styrene-n-butylacrylate (St/BA) copolymer latexes is investigated. A series of n-butylacrylate-styrene copolymer latexes were obtained by emulsion copolymerization in the presence of K₂S₂O₈ (KPS) as initiator and with/without emulsifier (sodium lauryl sulfate). The effect of such preparation conditions as initiator concentration, the St/BA ratio, reaction temperature, agitation rate, and emulsifier concentration on the polymerization rate, particle size of copolymer latex, and molecular weight distribution of the resulting copolymer (∼ 80% conversion), respectively, is systematically studied using fractional factorial design methodology. Fractional factorial analysis indicates that the effects of the St/BA ratio, reaction temperature, emulsifier concentration, as well as the two-factor interaction of temperature and emulsifier concentration, are the key variables influencing the polymerization rate. At ∼ 80% monomer conversion, statistical analysis clearly isolates emulsifier concentration as the dominant factor affecting average particle size of copolymer latex; results also indicate that the effects of the St/BA ratio, reaction temperature, and emulsifier concentration are major effects influencing the polydispersity of polymer molecular-weight distribution. For 7.30 g KPS/100 g monomer and 500 rpm agitation rate, the conditions for minimizing molecular-weight distribution (∼ 80% conversion) occur for a reaction temperature, St/BA ratio, and surfactant concentration of 70°C, ∼ 3.59/1, and ∼ 2.08 g/100 g monomer, respectively, generating a minimum molecular-weight polydispersity of ∼ 3.0. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 551–563, 1998     

Ultrasonically initiated emulsion polymerization of n‐butyl acrylate

Ultrasonically initiated emulsion polymerization of n‐butyl acrylate (BA) without added initiator has been studied. The experimental results show that high conversion of BA can be reached in a short time by employing an ultrasonic irradiation technique with a high purge rate of N₂. The viscosity average molecular weight of poly(n‐butyl acrylate) (PBA) obtained reaches 5.24 × 10⁶ g mol^?1. The ultrasonically initiated emulsion polymerization is dynamic and complicated, with polymerization of monomer and degradation of polymer occurring simultaneously. An increase in ultrasound intensity leads to an increase in polymerization rate in the range of cavitation threshold and cavitation peak values. Lower monomer concentration favours enhancement of the polymerization rate. ¹H NMR, ¹³C NMR and FTIR spectroscopies reveal that there are some branches and slight crosslinking, and also carboxyl groups in PBA. Ultrasonically initiated emulsion polymerization offers a new route for the preparation of nanosized latex particles; the particle size of PBA prepared is around 50–200 nm as measured by transmission electron microscopy. © 2001 Society of Chemical Industry     

Ultrasonically initiated emulsifier-free emulsion copolymerization of n-butyl acrylate and acrylamide. Part I: Polymerization mechanism

The polymerization mechanism of ultrasonically initiated emulsifier-free emulsion copolymerization of n-butyl acrylate (BA) and acrylamide (AM) was investigated. A four-step polymerization mechanism of the ultrasonically initiated emulsifier-free emulsion was put forward based on the monomer conversion and the main reaction locus. Improving the power output would increase the monomer conversion and the rate of polymerization. However, when the reaction temperature was 30 °C and the concentration of Na₂SO₄ was 0.1%, the monomer conversion and the rate of polymerization achieved maximum. The FTIR spectra showed that the sample obtained by this way was the copolymer of BA and AM, but not the blend of poly(butyl acrylate) and polyacrylamide.     

Ultrasound‐assisted emulsion polymerization of methyl methacrylate and styrene

In this article, we report on the effect of using ultrasound during emulsion polymerization. This work differs somewhat from that previously reported in that ultrasound is used in conjunction with conventional initiators. The aim is to observe the changes in the nature of polymerization and the synthesized polymer. In this work, reaction conditions and compositions typical of conventional emulsion polymerization are used. Azo‐bisisobutyronitrile and potassium per sulfate are the initiators used. The initial indication is that the rate of polymerization and the final conversion are higher when ultrasound is introduced into the polymerization system. This effect is more pronounced at lower temperatures (50°C) and low initiator concentrations (0.01%). At higher temperatures (70°C) the polymerization rate is seemingly unaffected by the use of ultrasound. The final product in all the experiments is a latex. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 101–104, 2000     

A kinetic investigation of thermally initiated emulsion copolymerization of styrene and methylmethacrylate without conventional initiators

The thermally initiated emulsion copolymerization of styrene (ST) and methyl methacrylate (MMA) was carried out in the absence of conventional initiators. The hydroperoxide (HPO) concentration in the monomers, sodium dodecyl sulfate (SDS), deionized water, and the formulation of those for emulsion copolymerization were measured. The HPO concentration in ST and MMA increased with the storage time, and were considered to be the major sources of HPO. The thermal decomposition of hydroperoxide in monomers, the thermal initiation of ST by Mayo mechanism, and the complex formation between SDS and the monomers were proposed to be three main sources of the radical generation. It was confirmed that new polymer particles were generated throughout the polymerization process, and consequently resulted in a broader distribution of polymer particle size, compared with that for conventional emulsion polymerization. Approximately 80 wt % of monomer conversion was obtained in the presence of SDS at 373 K in 24 h. The initiation rate of the 30 wt % monomer charge was faster than those of 10 wt % and 20 wt % monomer charge. The latex instability at higher solid content was improved by adding electrolyte to promote the electrostatic repulsion force between the polymer particles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 455–467, 2002; DOI 10.1002/app.2343     

Kinetics of emulsion polymerization of styrene using the reactive surfactant HITENOL BC20

The effect of the reactive surfactant HITENOL BC20 (polyoxyethylene alkylphenyl ether ammonium sulfate; 20 U of ethylene oxide (EO)) on the emulsion polymerization of styrene was studied via reaction calorimetry (Mettler RC1; 70°C). For polymerizations carried out above the cmc of BC20, the reaction kinetics and evolution of the number of particles (N_p) resembled those reported using the conventional surfactant sodium lauryl sulfate, indicating that nucleation proceeded by a combination of micellar and homogenous nucleation (Interval I and Stage 2). The reaction rate (R_p) not only increased with increasing initiator (K₂S₂O₈) and surfactant concentrations, as expected, but the increase in rate in Stage 2 was dependent on the initiator concentration and independent of the surfactant concentration. This is consistent with the proposed nucleation mechanisms. The molecular weight increased with increasing surfactant concentration and decreasing initiator concentration as would also be expected for a conventional surfactant. The dependencies of R_p and N_p on the BC20 and initiator concentrations, however, were lower than the classical Smith‐Ewart values (R_p ∝ [E]^0.47–0.52; R_p ∝ [I]^0.21–0.25) although R_p was found to be directly proportional to N_p. Chain transfer to the reactive surfactant is considered a likely source of divergence. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Aspects of coagulation during emulsion polymerization of styrene and vinyl acetate

The influence of recipe and process conditions on the coagulation behavior of polystyrene (PS) and polyvinyl acetate (PVAc) latices has been studied. Seeded batch experiments reveal a significant influence of electrolyte concentration on the coagulation behavior of both PS and PVAc latices. Within the experimental error, no dependency of the coagulation behavior on process conditions, in terms of energy dissipation, reactor scale, impeller type, and impeller diameter, has been observed for the reactor scales investigated. These results indicate that intrinsic chemical influences such as electrolyte concentration dominate the coagulation behavior during emulsion polymerization and also in the absence of polymerization over the process conditions. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2409–2421, 1998     

Agitation effects in the semicontinuous emulsion polymerization of styrene and butyl acrylate

The effect of agitation on the semicontinuous emulsion copolymerization of styrene and butyl acrylate was investigated. Both neat monomer addition and preemulsified feed were used. Experiments with and without a chain‐transfer agent were carried out. For neat monomer addition, a mild degree of agitation (≥ 0.1 kW/m³) was required to avoid monomer mass‐transfer limitations, but even a moderate degree of agitation (0.3 kW/m³) was not enough to overcome the CTA mass‐transfer limitations. Agitation was much less critical when preemulsified feeds were used. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 841–851, 2001     

Preparation of monodispersed core-shell microspheres with surface antibacterial property employing N-(4-vinylbenzyl)-N,N-diethylamine hydrochloride as surfmer

One-stage synthesis of monodispersed core-shell microspheres by exploratorily introducing a quaternary ammonium cationic surfmer of N-(4-vinylbenzyl)-N,N-diethylamine hydrochloride (VEAH) to emulsion polymerization of styrene (St) is reported. Due to the surface quaternary ammonium moieties and core-shell structure, the resultant PS-co-PVEAH core-shell microspheres have shown antimicrobial activity against Gram-negative bacteria E. coli and Gram-positive bacteria S. aureus. It is found that the quaternary ammonium group of VEAH moieties was the key factor that presented biocidal activity and the antimicrobial activity of the core-shell microspheres shows size dependence and core-shell microspheres with smaller particle size display higher antimicrobial activity.     

Seeded emulsion polymerization of styrene: influence of acrylic acid on the particle growth process

The seeded batch emulsion copolymerization of styrene and acrylic acid was studied. The polymerization rate was investigated with pH as the main parameter. Some attempts were made to evaluate the average number of growing chains per particle during Stage II of the emulsion polymerization process. The final latex products were characterized by means of conductometric aqueous titration and potentiometric titration in an organic solvent mixture. The distribution of the acid groups over the aqueous phase, the particle surface, and the interior of the particles together with the kinetic results provided insight into important features governing the incorporation of acrylic acid. The results indicate that pH is the dominating parameter for the incorporation process. An optimal incorporation on the surface of the particles is observed for a low value of pH. In that case, all the acid groups are protonated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1186–1196, 2000     

The first study of the effect of surfmer backbone structure on the stability and the course of emulsion polymerization of methyl methacrylate and butyl acrylate monomers

This is the first study of the effect of structure of the surfmer on the stability, morphology, and kinetics of the emulsion polymerization of butyl acrylate (BuA) and methyl methacrylate (MMA). Poly(ethylene glycol) behenyl ether methacrylate (PEGBEMA) was used as surfmer in the emulsion polymerization of BuA and MMA and compared with the same type surfmer with different backbone structure (with four bulky phenyl groups in the backbone of the surfmer) poly(ethylene glycol) 2,4,6‐tris (1‐phenylethyl) phenyl ether methacrylate. It was found that the straight chain surfmer produces less stability, lower order reaction less particles size (D_max) greater number of polymer particles N_t, worse morphology D_w/D_n, than the bulky surfmer. The order of polymerization reaction of BuA with respect to PEGBEMA was 0.8 compared with 2.6 in case of using PEGTPMA. The surface charge density was dramatically changed when using PEGBEMA from 39.8 to 204 μC in case of PEGTPMA at the same conditions of surfmer concentration, temperature, and other parameters. The D_v was found to be 897 nm for particles prepared in the presence of PEGTPMA surfmer while it was 159 nm for particles prepared in the presence of PEGBEMA at the same surfmer concentrations and other experimental conditions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Continuous emulsion polymerization of styrene in a single Couette–Taylor vortex flow reactor

The effect of the geometrical and operational parameters on the mixing characteristics of a Couette–Taylor vortex flow reactor (CTVFR) were investigated and were correlated with the same parameters by using the tank‐in‐series model. Continuous emulsion polymerization of styrene was conducted at 50°C in a CTVFR to clarify the effects on kinetic behavior and reactor performance of operational parameters such as rotational speed of inner cylinder (Taylor number), reactor mean residence time, and emulsifier and initiator concentrations in the feed streams. It was found that steady‐state monomer conversion and particle number could be freely varied only by varying the Taylor number. In order to explain the observed kinetic behavior of this polymerization system, a mathematical model was developed by combining the empirical correlation of the mixing characteristics of a CTVFR and a previously proposed kinetic model for the continuous emulsion polymerization of styrene in continuous stirred tank reactors connected in series (CSTRs). On the basis of these experimental results, it was concluded that a CTVFR is suitable for the first reactor (prereactor) of a continuous emulsion polymerization reactor system. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1931–1942, 2001     

Monte Carlo模拟在丁二烯/苯乙烯乳液聚合中的应用研究

以概率论中的大数法则和中心极限定理为基础,通过对成核阶段条件的简化,建立了丁二烯/苯乙烯乳液聚合成核阶段的Monte Carlo模型,模拟考察了乳化剂、引发剂浓度对丁苯乳液聚合反应速率的影响,对丁苯乳聚成核阶段模拟结果进行回归表明,乳胶粒数目N p与乳化剂浓度[S]和引发剂浓度[I]的关系为：N p=k[S]0.606 2[I]0.405 5,与Smith-Ewart经典理论相吻合。改善乳液聚合生成的乳胶粒径分布以及乳胶粒数目是提高乳液聚合中单体转化率最为有效的方法。模拟计算结果表明,将单体转化率从62%提高到70%,引发剂浓度的增加量应在12.90%~34.89%（摩尔分数）之间,乳化剂浓度的增加量应在12.6%~22.16%（摩尔分数）之间。与实验结果进行对比,数据吻合,验证了模拟计算的可靠性和有效性。     

提高转化率对乳聚丁苯橡胶性能的影响

以吉林石化公司有机合成厂的乳聚丁苯橡胶(SBR)生产配方为标准配方,研究了聚合反应时间对转化率的影响,分析了提高转化率对SBR的生胶门尼黏度、结合苯乙烯含量、凝胶含量、相对分子质量及其分布、胶乳黏度等基本性能的影响。结果表明,在标准配方条件下,延长聚合反应时间,转化率可以达到70%。转化率为70%时所得SBR与转化率为62%时所得SBR相比,前者的生胶凝胶含量和胶乳黏度均增大了1倍,数均相对分子质量、重均相对分子质量和Z均相对分子质量均高于后者,相对分子质量分布变宽,且前者的生胶结合苯乙烯含量能够达到产品标准,而生胶门尼黏度和在50 m in时的300%定伸应力偏高于产品优级品要求。     

提高乳聚丁苯橡胶转化率的影响因素

以吉林石化公司生产的丁苯橡胶(1500)为研究对象,以12 h内聚合转化率达到(70±2)%、产品性能与转化率为(62±2)%者相当为目标,研究了引发剂、相对分子质量调节剂、电解质、单体配比与纯度及乳化剂等对丁苯橡胶聚合的影响,测定了不同转化率丁苯橡胶胶乳的机械稳定性及丁苯橡胶生胶和硫化胶的性能。结果表明,在不改变原材料品种和规格的前提下,于氧化剂用量110%(以标准配方所用质量为100%计,下同)、还原剂用量100%和助还原剂用量110%,硫醇初始量与补加量的质量比为100/20、补加时机在反应开始后2 h,电解质用量为110%~115%、初始时一次加入,丁二烯与苯乙烯的质量比为(72.0/28.0)~(72.5/27.5),乳化剂初始量与补加量的质量比为100/10、补加时机在反应开始后2 h的条件下,在12 h内可以使丁苯橡胶1500的聚合转化率提高到(70±2)%,并确保其产品性能全部达到国标优级品标准。     

苯丙乳液的性能研究

以苯乙烯、丙烯酸丁酯、甲基丙烯酸甲酯、丙烯酸为反应单体,过硫酸铵为引发剂,聚乙二醇辛基苯基醚和十二烷基磺酸钠为复合乳化剂,通过连续滴加的乳液聚合工艺制备苯丙乳液。结果表明,当软硬单体配比为1∶1(质量比),SDS∶OP-10=1∶1(质量比),引发剂含量为单体总量的0.3%,可制得较好的乳液。