Morphology of latex particles formed by poly(methyl methacrylate)-seeded emulsion polymerization of styrene

Poly(methyl methacrylate)–polystyrene composite particle latexes were prepared by poly(methyl methacrylate)-seeded emulsion polymerization of styrene employing batch, swelling-batch, and semibatch methods. The changes in particle morphology taking place during the polymerization reaction were followed by electron microscopy. Anchoring effect exerted by ionic terminal groups introduced by ionic initiator was found to be the main factor in controlling the particle morphology. The polymer particles obtained by oil-soluble hydrophobic initiators such as azobisisobutyronitrile and 4,4′-azobis-(4-cyanovaleric acid) gave the inverted core-shell morphology. Water-soluble hydrophilic initiator, K₂S₂O₈, also gave the inverted core-shell morphology. However, in this case the occurrence of the halfmoonlike, the sandwichlike, and the core-shell morphologies were also observed depending upon the polymerization conditions. The distribution of terminal ? SO groups on the surface area of polystyrene particles could be controlled by initiator concentration and polymerization temperature. Viscosity of polymerization loci dictated the movement of polymer molecules, thus causing the unevenness of particle shape and phase separation at high viscosity state. Viscosity was controlled by the styrene/poly(methyl methacrylate) ratio, the addition of a chain transfer agent or a solvent which is common to polystyrene and poly(methyl methacrylate).     

氢化钠/三异丁基铝体系合成星形聚苯乙烯的研究

采用阻滞阴离子调控技术,通过"先核后臂"法以NaH/三异丁基铝(i-Bu3Al)与苯乙烯、二乙烯基苯(DVB)反应制备的多钠引发剂为核,乙苯为溶剂,合成了星形聚苯乙烯(PS)(cs-PS);通过"先臂后核"法,以NaH/i-Bu3Al直接引发苯乙烯聚合,DVB为偶联剂,也合成了星形聚苯乙烯(as-PS)。采用气相色谱测定了聚苯乙烯钠与DVB中四种组分在100℃下的聚合反应速率,并用凝胶渗透色谱分析测试了聚合物的分子参数及平均臂数。结果表明:聚苯乙烯钠与DVB中四种组分的聚合反应速率与单体浓度呈假一级动力学关系;随着n(DVB)/n(NaH)的增加,cs-PS和as-PS的相对分子质量均逐渐增加,相对分子量分布均变宽,平均臂数也随之增大。     

Mini-emulsion formation and polymerization of styrene

The morphology of an anionic emulsifier/long chain fatty alcohol complex and its change during the formation process were studied. The main factors affecting the morphology, such as various types of anionic emulsifiers and fatty alcohols, their molar ratios and the addition of styrene, were investigated. It was discovered that the rod-like particles of the complex had a length of 0.1 -0-2 μm and diameter of 0.01-0.02 μm. A model of a rod-like particle or molecular aggregate was proposed. Both water-soluble and oil-soluble initiators were used to study the kinetics of styrene mini-emulsion polymerization and polystyrene latex size characteristics.     

Effects of styrene oligomers and polymers on the suspension polymerization behavior and properties of expandable polystyrene

Styrene oligomers are formed by a free‐radical mechanism during the thermal polymerization of styrene in storage. The effects of these compounds on the preparation of expandable polystyrene (EPS) were investigated with respect to suspension polymerization behavior and the properties of the impregnated polystyrene beads produced. Styrene dimers and trimers up to concentrations of 0.2 wt % did not affect the stability of the suspension during the polymerization and impregnation stages. Besides differentiated effects on the particle size distributions of the polymers and on the polymerization rate, no chain‐transfer activity of the oligomers was observed, and this confirmed the assignment of chain transfer to the Diels–Alder dimer in the literature. The investigation of the foaming behavior of the pentane‐impregnated EPS beads indicated a significant reduction of the prefoaming density caused by styrene dimers and trimers. This behavior resulted from a decrease in the glass‐transition temperatures of these polymers. The effects of high‐molecular‐weight polystyrene, formed in addition to oligomers during storage by the thermal polymerization of styrene, on the polymerization behavior and polymer properties of EPS were also investigated. The results showed a significant impact on the suspension stability that was dependent on the concentration of the high‐molecular‐weight polystyrene. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

乳液法聚苯乙烯纳米微球的制备

采用十二烷基硫酸钠为乳化剂、过硫酸盐为引发剂、苯乙烯为单体,在低水油比的条件下,采用乳液聚合方法合成了聚苯乙烯纳米微球,探讨了乳化剂用量、乳化时间、反应温度、引发剂用量和反应时间对单体转化率及产物分子量的影响.结果表明:在低水油比条件下,反应参数对苯乙烯的转化率和聚苯乙烯的分子量具有一定的影响.在最优条件下苯乙烯的转化率达到98%、聚苯乙烯的分子量达到32万.激光粒度分布测试结果显示,所得产物为单分散纳米微球.     

Studies on heterogeneous polymeric systems. I. Influence of morphology on mechanical properties

Polybutadiene rubbers of well-defined and varying molecular weight were prepared by anionic polymerization and used in the preparation of mass-polymerized polystyrene blends. The particle size of the dispersed rubber phase was varied by (1) controlling the relative viscosity, at phase inversion, of the two liquid phases composed of polystyrene and polybutadiene in styrene monomer; (2) by varying the intensity of mixing, and (3) by adding preformed polystyrene to the prepolymer, prior to phase inversion. The mechanical and dynamic properties of the resulting blends are found to be determined mainly by the particle size of the dispersed rubber phase, independently from the method used to obtain such size. The weight fraction of rubber phase, rather than the weight fraction of rubber charged, is found to correlate with the blend modulus and may also affect its level of toughness. Low molecular weight rubbers are found capable of efficient blend reinforcement, if the excessively small rubber particle size obtained by conventional processes is enlarged by incorporation of preformed polystyrene prior to phase inversion.     

Solvent effect on TEMPO-mediated living free radical dispersion polymerization of styrene

Living free radical dispersion polymerization of styrene in the presence of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) and 2,2-azobisisobutyronitrile (AIBN) was conducted in various glycol media having different solubility parameters. Genuine heterogeneous polymerization nature was observed from the initial stage of the reaction. The solubility parameter of the media was found to significantly influence the living characteristics of the polymerization including the polymerization kinetics and the molecular weight evolution at a fixed concentration of TEMPO. A grafting of stabilizer molecules onto monomer and a possible partitioning of TEMPO between the continuous medium and particle phase were postulated for the deviation of the experimentally obtained molecular weight from the calculated value. For a poor medium for styrene, such as diethylene glycol, the living nature was achieved by increasing the amount of TEMPO. The polystyrene (PS) microsphere was well obtained in all tested glycol media and the average size was increased with enhanced affinity of the media to styrene and with decreasing concentration of TEMPO.     

Synthesis of a perfluorinated azo initiator

Summary A method to determine the recombination/disproportionation rate during the polymerization of styrene is described. In this method, a perfluorinated azo initiator used to prepare a perfluorinated polystyrene was first synthesized. Then, the recombination/disproportionation rate was calculated by comparing the number-average molecular weight and the fluorine content in weight of this resulting polystyrene.     

Anionic polymerization of styrene: The search for an industrial process

Anionic polymerizations were carried out in the laboratory using a CSTR reactor design and conditions typical of current commercial mass polystyrene plants. Polystyrene having excellent color and polydispersity was produced. Polymer quality, styrene conversion, and molecular weight control were all linked to use of polymerization feed of consistently high purity and polymerization in the 90–110°C temperature range. The results of this study clearly show that high quality polystyrene can be made utilizing anionic polymerization chemistry in existing well mixed mass polystyrene reactors of the CSTR design. The key to the successful practice of this technology is the ability to produce consistently high purity polymerization feed.     

Anionic polymerization of styrene: Integration with styrene monomer production

Anionic polymerization and ethylbenzene dehydrogenation were carried out in the laboratory using continuous reactor designs and conditions typical of current commerical processes. The dehydrogenator was operated at 43–55% conversion with continuous distillation of the ethylbenzene/styrene mixture to remove byproducts that would interfere with the subsequent anionic polymerization. The anionic polymerization was carried out using a reactor of the CSTR type which operated at > 99% conversion of styrene. The volatiles were recovered from the polymer syrup and recycled back to the dehydrogenator. During 4 months of continuous operation the integrated process showed no detrimental buildup of impurities which affected the anionic polymerization or dehydrogenation. The polystyrene produced had excellent color, clarity, thermal stability, and polydispersity (M_w/M_n = 2.1–2.4). The ability to control weight average molecular weight was within a range of 20,000 using an on-line GPC in concert with a colorimeter.     

高分子表面活性剂存在下超声辐照引发苯乙烯乳液聚合的研究

采用高分子表面活性剂(CMC-A9)和十二烷基硫酸钠(SDS)做乳化剂,用超声辐照乳液聚合方法制备了相对分子质量高(>106)的寡链聚苯乙烯纳米粒子。研究结果表明,在适当的反应条件下,CMC-A9的加入使反应速率大大提高,反应60min单体转化率能达到85%,制得直径30～60nm的聚苯乙烯胶乳粒子,乳胶粒子中含平均分子链数为3～20。CMC-A9或SDS质量浓度提高,能降低乳胶粒径和乳胶中所含的平均分子链数,增加聚合物相对分子质量。超声波输出功率对乳胶粒径影响不大。     

Free‐radical bulk polymerization of styrene with a new trifunctional cyclic peroxide initiator

The bulk free‐radical polymerization of styrene in the presence of a new cyclic trifunctional initiator, 3,6,9‐triethyl‐3,6,9‐trimethyl‐1,4,7‐triperoxonane, was studied. Full‐conversion‐range experiments were carried out to assess the effects of the temperature and initiator concentration on the polymerization kinetics, molecular weight, and polydispersity. Gel permeation chromatography was used to measure the molecular weight and the molecular weight distribution of polystyrene. When this multifunctional initiator was used for styrene polymerization at higher temperatures, it was possible to produce polymers with higher molecular weights and narrower molecular weight polydispersity at a higher rate. This showed that the molecular weight and polydispersity were influenced by the initiator concentration and the polymerization temperature in an unusual manner. Moreover, polystyrene, obtained with trifunctional peroxide, had O? O bonds in the molecular chains and was investigated with differential scanning calorimetry and gel permeation chromatography. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1035–1042, 2004     

Effect of the molecular architecture of graft copolymers on the phase morphology and tensile properties of PS/EVA blends

Graft copolymers of poly(ethylene‐co‐vinyl acetate) (EVA) grafted with polystyrene (PS) with different molecular weight and different EVA/PS ratio were prepared by coupling reaction between acyl chloride functionalized PS (PS‐COCl) and hydrolyzed EVA. PS‐COCl with controlled molecular weight was prepared by anionic polymerization of styrene, followed by end capping with phosgene. The effect of the molecular architecture of the graft copolymer on the compatibilization of PS/EVA blends was investigated. Substantial improvement in the elongation at break and ductility was observed using the graft copolymer with PS segments with molecular weight as high as 66,000 g/mol and with a PS proportion equal or higher than EVA. The effect of the compatibilization on the morphology was also investigated by scanning electron microscopy and atomic force microscopy. The blend that presented the highest value of elongation at break also displayed dispersed phase constituted by inclusions of the PS phase inside the EVA particle forming a cocontinuous structure, as observed by AFM. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Kinetics of Miniemulsion Polymerization of Styrene in the Presence of Organoclays

The impacts of nanoclays on the miniemulsion polymerization kinetics of styrene were studied. It was found that both R_P and the fractional conversion decreased upon increasing the organoclay content in the miniemulsion system. In the presence of nanoclay the molecular weight of polystyrene nanoclay composite is lower and the particle size polydispersity of the final composite latex is greater than that of pure styrene miniemulsion polymerization. The effect of the nanoclays is mainly caused by the destabilization of the miniemulsion by the organoclay particles. The increase in the monomer viscosity and the decrease in the diffusion rate of the monomer and the living polymer inside the monomer droplet also accounts for the reduction in the polymerization rate.

     

Preparation of a water soluble polyester surfactant and its use in the emulsion polymerization of styrene

Summary The synthesis procedure of Chen and Liu (1) was used to prepare a polyester surfactant from dimethyl 5-sulfoisophthalate, sodium salt, polyoxyethylene (MW 200) and phthalic anhydride by a two step esterification process. The surfactant has the unique structural features of multiple ionic groups and polyoxyethylene chains for hydrophilicity and aromatic ester linkages for hydrophobicity. The polyester surfactant exhibited a CMC of 0.25% (w/v) and a surface tension lowering of 23 dynes/cm. The use of the surfactant as stabilizer for the emulsion polymerization of styrene produced some unusual results. While the rate of polymerization was independent of surfactant concentration, the number of particles increased as N [S]^0.91. The molecular weight of polystyrene produced was low and found not to be a function of surfactant concentration. The structural features of the surfactant suggest that a depletion stabilization mechanism might be operative in this system.     

Preparation of polyamide 6/polystyrene quasi‐nanoblends by diffusion and subsequent polymerization of styrene in water‐sorbed polyamide 6 pellets

Polyamide 6 (PA6)/polystyrene (PS) blends with an average particle size of 103 nm were prepared by diffusion and subsequent polymerization of styrene in water‐sorbed PA6 pellets. The pretreatment of PA6 pellets in hot water is prerequisite for successful styrene diffusion. The diffusion process involves replacement of free water in the pellets by styrene, and should be carried out in neat styrene medium to provide concentration gradient between inside and outside of the pellets. The polymerization step was carried out in water medium with benzoic peroxide as the initiator. The diametrical distribution of PS in the blend pellets was investigated by Micro‐FTIR, and molecular weight of PS was measured by GPC. DSC measurements showed that the diffusion and polymerization of styrene occur in the amorphous regions of PA6 where the pre‐sorbed water locates. PA6/PS quasi‐nanoblends reported in this work cannot be obtained by conventional methods. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44554.     

几种不可逆加成-断裂型链转移剂在苯乙烯乳液聚合中的研究

研究了基于不可逆加成-断裂链转移机理的3种分子质量调节剂对苯乙烯乳液聚合的影响.主要考察了3种链转移剂对乳液聚合速率、乳胶粒子大小以及聚苯乙烯数均相对分子质量的影响.链转移剂的内在动力学、扩散和自由基解吸附行为决定了其分子质量调节效率、对聚合速率的影响程度和乳胶粒子大小.链转移常数高的α-苯磺酰甲基丙烯酸乙酯使苯乙烯乳液聚合速率下降明显,乳胶粒子粒径分布较宽,且聚合后期不能有效调节聚苯乙烯分子质量 ;而链转移常数相对较小的2,3-二氯丙烯对聚合速率和乳胶粒子粒径的影响轻微,并能全程控制聚苯乙烯分子质量 ;分子质量较大的正十二烷基-2-苯基烯丙基硫则因在乳液体系中的扩散较慢,难以调节聚苯乙烯的分子质量.     

烷基多苷微乳液中苯乙烯聚合的研究

在烷基多苷（APG）／苯乙烯／水三元体系O／W微乳液中,选用水溶性K2S2O8作为引发剂,制得小粒径（35．4nm）、单分散（P=0．180〈0．2）聚苯乙烯颗粒。研究了苯乙烯、过硫酸钾、烷基多苷以及NaCl质量浓度对产物粒径和多分散度的影响。结果表明：聚苯乙烯随苯乙烯的增加颗粒粒径变大（43．8nm）;随过硫酸钾的增加颗粒粒径变大（37．9nm）,多分散度变小（P=0．153）;随烷基多苷的增加颗粒粒径变小（33．4nm）,而多分散度变大（P=0．195）;随NaCl的增加颗粒粒径变大（45．6nm）。微乳结构的转变点对产物有重要的影响。     

Synthesis and characterization of polystyrene latex with an amphoteric emulsifier

An emulsion polymerization of styrene in the presence of an amphoteric emulsifier of amino-acid type, N-lauroyl-N,N-dimethyllysine (DMLL), has been studied at pH 7.0. The polymerization rate increased exponentially with the concentration of DMLL. The concentration of latex particles was proportional to the DMLL concentration to the 0.6 power. The latex particle size decreased with increasing concentration of DMLL. The molecular weight of polystyrene latexes increased with an increase in DMLL concentration. Furthermore, the zeta potentials of latex particles were significantly dependent on the pH, and showed the existence of an isoelectric point at about pH 4.0.     

The preparation of uniform polystyrene latices by true emulsion polymerization

Conventional emulsion polymerization of styrene produces some polydispersion in particle sizes in the latex. By carrying out a one-stage polymerization of finely emulsified monomer droplets of styrene formed in a mixture of methanol and water, it is possible to prepare stable latices of polystyrene in which the particles are perfectly uniform in size. The polymer has a relatively low molecular weight, but it is more stable to fragmentation by surfactant solutions than polystyrene prepared by conventional emulsion polymerization, the molecular weight of which is greater. The surface charge density of the particles is higher than that of particles produced by emulsion polymerization, and this probably accounts for the stability of the dispersion during polymerization and of the latex.