Semibatch anionic ring-opening polymerization of octamethylcyclotetrasiloxane in emulsion

The semibatch anionic ring-opening polymerization of octamethylcyclotetrasiloxane in emulsion was studied under the condition of no seed particles used in polymerization system. Concentration of emulsifier was set above critical micelle concentration. Effect of monomer feed rate on the chemical kinetics, average particle size and distribution and on the polymer molar mass and distribution was investigated. During monomer addition, polymerization rate was constant and controlled by the monomer feed rate. According to the proposed mechanism for anionic polymerization in emulsion, it was assumed that also the number of active polymerization sites and monomer concentration at the particle surface, where propagation occurs, remain constant. A continuous increase of average particle size and absence of extensive condensation reactions at high conversion suggested that the freshly added monomer diffuses toward hydrophobic polymer particles, where it is consumed in propagation reaction and/or accumulated in the particle core.     

Radical ring-opening emulsion polymerization of vinylcyclopropanes

Radical emulsion polymerizations of vinylcyclopropanes, 1,1-bis(ethoxycarbonyl)-2-vinylcyclopropane (ECVCP) and 1,1-dichloro-2-vinylcyclopropane (CVCP) were examined. ECVCP underwent soap-free and soap-in emulsion polymerizations satisfactorily to afford the ring-opened polymer in good yields. Polymer emulsions were obtained in a spherical shape with single particle size distribution. Meanwhile, emulsion polymerization of CVCP proceeded in only a low conversion. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 497–501, 1998     

Anionic polymerization of octamethylcyclotetrasiloxane in aqueous emulsion I: Preliminary results and kinetic study

The synthesis of poly(dimethylsiloxane) (PDMS) by anionic polymerization of octamethylcyclotetrasiloxane (D₄) in aqueous emulsion using an emulsifying agent acting also as initiator (benzyldimethyldodecylammonium hydroxide) is described. Stable emulsions of α,ω-dihydroxy PDMS with an easily controlled molar mass (up to 15 000), a low polydispersity index and high yields were obtained. The amount of cyclics formed (essentially D₄ to D₇) is lower than that observed in bulk. Kinetics analysis and computerized simulations are in good agreement with a reaction scheme involving simultaneous polyaddition/polycondensation processes. At high monomer consumption, polycondensation predominates leading to a broadening of the molecular weight distribution (MWD). The apparent rate constants of initiation, propagation and condensation at various temperatures and the corresponding activation energies were determined.     

D4开环乳液聚合制备聚硅氧烷微乳液的研究

采用动态光散射法研究了八甲基环四硅氧烷(D4)阴离子开环乳液聚合，制得了稳定且接近于透明的聚二甲基硅氧烷阳离子型微乳液。研究发现，聚合过程体系中的粒子分别出现单峰、双峰和三峰分布；由于体系中乳化剂浓度远大于常规的乳液聚合，导致单体液滴消失时仍存在胶束，聚合过程中没有出现明显的恒速期。     

Anionic polymerization of 2-haloethyl methacrylates

The anionic polymerizations of 2-chloroethyl methacrylate (1), 2-bromoethyl methacrylate (2), and 2-iodoethyl methacrylate (3) were carried out in THF at −78 °C with 1,1-diphenyl-3-methylpentyllithium in the presence of LiCl. The polymerizations proceeded in a controlled manner to quantitatively afford polymers with predictable molecular weights and narrow molecular weight distributions. Under similar conditions, the anionic block copolymerizations by the sequential addition of methyl methacrylate (MMA) followed by 1, 2, and 3 generated the corresponding diblock copolymers with well-defined structures. On the other hand, in the block copolymerization by the reverse addition of monomer, a well-defined diblock copolymer, poly(1)-block-PMMA, could be synthesized only by the sequential addition of 1 followed by MMA, whereas the block copolymerizations using 2 and 3 were not successful because of instabilities of the propagating chain-end anions derived from 2 and 3. The side reactions which occurred during the polymerization were discussed.     

A critical evaluation of reaction calorimetry for the study of emulsion polymerization systems: thermodynamic and kinetic aspects

Protocols were examined for the measurement of rates and enthalpies of polymerization (ΔH_p) using reaction calorimetry. ΔH_p was determined to be 70.2 kJ mol⁻¹ for a series of seeded styrene emulsion polymerizations under typical emulsion conditions, in good agreement with literature values. However, there was a significant deviation from this value for small-particle systems, which is ascribed to surface effects, i.e. environmental effects on ΔH_p. Careful comparison between rate data obtained by calorimetry and by dilatometry leads to recommended procedures for obtaining reliable and accurate rate data using the former technique.     

有机硅改性丙烯酸酯乳液的研究

通过乳液聚合聚制备有机硅改性丙烯酸酯乳液。乳液中的有机硅分子在催化剂的作用下与基材表面的羟基脱水交联,使粘接力大大提高。研究了有机硅功能单体用量以及丙烯酸交联单体对乳液性能的影响。ＦＴＩＲ分析表明有机硅烷与他共聚单体完全共聚 。     

Anionic polymerization of 2-(N-carbazolyl)ethyl methacrylate

The homopolymer, poly(CzMA), with controlled molecular weight (MW) and narrow molecular weight distributions (MWD) was successfully synthesized by using (1,1,4,4-tetraphenylbutanediyl)dipotassium and diethylzinc (Et₂Zn) in THF at various temperatures, 25, −45, and −78 °C, under high vacuum conditions. The Et₂Zn acted both as a protective group through the formation of coordination with ester enolate anion and as a scavenger to remove impurities. Block copolymers, poly(CzMA-b-styrene-b-CzMA) and poly(MMA-b-CzMA-b-MMA), with narrow MWD were also successfully synthesized by sequential anionic living polymerization.     

The dissociation rate coefficient of persulfate in emulsion polymerization systems

The effects of various components in an emulsion polymerization system on the dissociation rate coefficient of persulfate at 50 °C are examined using iodometry. Styrene monomer is found to enhance greatly the dissociation, while there is either no effect or possibly a slightly reduced rate of dissociation with methyl methacrylate monomer. The saturated analogues of these monomers (ethylbenzene and methyl isobutyrate) also enhance the dissociation, although not as much as styrene. Thus, such analogues should not be used as model compounds for determining the effect of a monomer on decomposition rate. The presence of metal parts in the reactor (e.g. as part of the agitation system) also could enhance the dissociation. The accelerations are consistent with literature mechanisms involving transfer reactions of aqueous-phase species. These results have significant implication for the interpretation and prediction of entry efficiencies and particle formation rates in emulsion polymerization systems.     

New green surfactants for emulsion polymerization

Nonylphenol ethoxylates (NPEOs) are widely used as surfactants for emulsion polymerization and for post adding stabilization for latex applications in formulations with high filler content. However, the current exposure situation of NPEOs in Europe gives rise to environmental concern, despite of the fact that some industry associations have already pro-actively taken measures to phase out these chemistry of their products, e.g. the European detergent industry (AISE) by a voluntary commitment. As a consequence, the EU Commission has recommended to implement a risk reduction strategy, which foresees the ban of all applications leading to direct emissions to waste water and strict emission controls for all other technical processes using NPEOs as surfactant. The effectiveness of the risk reduction measures will be monitored by the authorities. In case that the environmental concentrations of NPEOs and their metabolites do not decrease by at least 70 percent, additional risk reduction measures for technical applications are planned. In one of the major fields of application, alkyl phenol-free emulsifiers with a more favorable ecological profile are becoming key ingredients for eco-friendly emulsion polymers and polymer dispersions: the Disponil^® AFX-Series (Cognis) is a NPEO-free surfactant system for emulsion polymerization and polymer dispersant also as a supposition for getting the European eco-label for indoor paints and varnishes.

These new non-ionic surfactant system exhibits an effective performance during polymerization and as post reaction stabilizers. These products are environmentally compatible, mostly derived from natural renewable resources and readily biodegradable. The underlying chemistry is in compliance with relevant indirect food contact applications [BfR recommendations, respectively, FDA CFR 21 (federal drug administration)], and a dossier to register the surfactants in the positive list of the EU Directive 2002/72/EC for application in plastic has recently been submitted.

Clear, high solid liquids at room temperature, these surfactants are easy to handle and very effective with regard to controlling particle size, film properties and overall latex stability. This paper summarizes their chemical and surface properties, as well as their performance in model emulsion polymerization formulations for architectural coatings.     

乳液聚合中乳化剂对聚合物乳液稳定性的影响

简要叙述了聚合物乳液稳定性的测定方法，详细地讨论了乳化剂的类型、用量及加入方式等对丙烯酸酯类聚合物乳液的化学稳定性、机械稳定性及贮存稳定性的影响。     

超声波对乳液聚合丁腈胶的影响研究

研究了超声波作用时间对乳液聚合丁腈胶固含量、转化率的影响,对丁腈胶的微观结构进行了红外测试分析。结果表明,随着超声波作用时间的延长,聚合物的固含量和转化率增加,超声波作用的反应体系所得聚合物的微观结构与传统乳液聚合所得聚合物的微观结构一致。     

Emulsifier-free, organotellurium-mediated living radical emulsion polymerization of Styrene: Initial stage of polymerization

Behavior of the particle formation based on self-assembling in emulsifier-free, organotellurium-mediated living radical emulsion polymerization (emulsion TERP) of styrene was studied from the molecular weight distributions (MWDs) of polystyrene (PS) formed in an initial stage of the polymerization at different temperatures from 50 °C to 70 °C. As the polymerization temperature was decreased, the larger number of poly(methacrylic acid) (PMAA; degree of polymerization, 30)-methyltellanyl (TeMe) (PMAA₃₀-TeMe) participated in the polymerization, resulting in amphiphilic PMAA₃₀-b-PS-TeMe oligomers. Almost all control agents were consumed and a self-assembly nucleation occurred in the initial stage of the polymerization at 50 °C, which lead to depress of particle formation of a homogeneous nucleation. The consumption rate of PMAA₃₀-TeMe affected directly the particle formation. From these results, it is concluded that it is important for the emulsion TERP of styrene with excellent control/livingness that the self-assembly nucleation proceeds without the homogeneous nucleation in the initial stage of the polymerization.     

Surfactant-enhanced free radical polymerization of styrene in emulsion gels

The presence of a surfactant (such as hexadecyltrimethylammonium bromide, CTAB) enhanced the rate of polymerization of styrene in emulsion gels with and without silica. The emulsion gels consisted of styrene, azobisisobutyronitrile (AIBN), surfactant, water, and, in some cases, fumed silica. Polymerization of the emulsions was carried out at room temperature in one or several days depending on the composition of the emulsion. The conversion of monomer to polymer could exceed 90% in a couple of days. In contrast, very little polymerization occurred in the absence of surfactant. A simple model, incorporating a surfactant-initiator complex and standard free radical polymerization, successfully fits the experimental kinetics data. This analysis suggests that the initiator is complexed with approximately three surfactant molecules.     

Comparison of RAFT polymerization of methyl methacrylate in conventional emulsion and miniemulsion systems

In this study, we have conducted the reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) in two heterogeneous systems, i.e. conventional emulsion and miniemulsion, with identical reaction conditions. The main objective is to compare the living character in both systems according to the nucleation mechanism, the latex stability, the particle sizes and particle size distributions of latexes, the molecular weights and molecular weight distributions (or polydispersity index, PDI) of PMMA, and the kinetics of the RAFT polymerization. The RAFT agent used in both systems was 2-cyanoprop-2-yl dithiobenzoate (CPDB). The effects of an oil-soluble initiator 2,2′-azobisisobutyronitrile (AIBN) and a water-soluble initiator kalium persulfate (KPS) on the RAFT/emulsion and RAFT/miniemulsion polymerizations were investigated. Methyl-β-cyclodextrin (Me-β-CD) was used as a solubilizer. The average molecular weights and molecular weight distributions (PDIs) of dried PMMA samples were characterized by gel permeation chromatography (GPC). The experimental results showed that the RAFT/miniemulsion polymerization of MMA exhibited better living character than that of RAFT/emulsion polymerization under the conditions of our experiment. The PDI of PMMA in RAFT/miniemulsion polymerization was decreased with the addition of Me-β-CD. However, Me-β-CD did not have influence on the PDI of PMMA prepared in RAFT/emulsion polymerization.     

Kinetic study on the ring-opening polymerization of octamethylcyclotetrasiloxane (D4) in miniemulsion

A kinetic study on the ring-opening polymerization (ROP) of octamethylcyclotetrasiloxane (D4) in miniemulsion is presented in this work. The polymerization is initiated by dodecylbenzenesulfonic acid (DBSA) which also serves as the surfactant (inisurf). The influence of the size of monomer droplet and the concentration of DBSA on the polymerization rate were studied. Since the main place for the ROP of D4 was confirmed to be at the oil/water interface, a three-layer interface model was proposed to analyze the distribution of molecules at the interface and the effects of DBSA. A kinetic equation is then developed based on this model. In the equation, the polymerization rate (R_p) is related to the initial monomer concentration ([D4]₀), the droplet radius (r), the coverage of DBSA on monomer droplets surface (x). The polymerization rate can be predicted from the kinetic equation feeding all parameters with their experimental values. Finally, the equation gave a good accordance between the predicted polymerization rate data and the experimental results under different polymerization conditions.     

A physical insight into sonochemical emulsion polymerization with cavitation bubble dynamics

This paper tries to explain the physical features of the sonochemical emulsion polymerization process by coupling experiments with different conditions (such as monomer type, saturation level of the medium and the type of bubbling gas) with a mathematical model for the radial motion of cavitation bubble. Experiments have been performed without any added chemical initiator or surfactant. Time variation of the mean size and size distribution of polymer particles in the emulsion have been used as a measure for the analysis. This measure is found to be governed by various parameters such as rate of radical production from the cavitation bubbles, magnitude of the microturbulence and shock waves produced by the cavitation bubbles, glass transition temperature of polymer and the population density of polymer particles. The relative magnitudes of these parameters vary significantly with the experimental conditions. This variation has been explained on the basis of results of simulation of radial motion of cavitation bubble. It is revealed that the mean particle size and size distribution of particles are manifestation of simultaneous and resultant influence of these parameters.     

甲基丙烯酸甲酯与丙烯酸正丁酯乳液聚合的研究

以甲基丙烯酸甲酯与丙烯酸正丁酯为主要原料,过硫酸铵为引发剂,OP-10、十二烷基硫酸钠(K12)为乳化剂,用乳液聚合法合成了聚丙烯酸酯类共聚乳液,考察了聚合条件对乳液聚合的影响。实验结果表明,在单体、引发剂、水用量一定时,合适的反应条件为乳化剂(OP-10∶K12=1∶1)2%,单体滴加时间以60~90min,80℃反应2h左右。     

Preparation of transparent polystyrene nano-latexes by an UV-induced routine emulsion polymerization

Transparent polystyrene (PS) latexes were prepared by photo-polymerization of a routine styrene (St) emulsion with a surfactant concentration of 0.4 wt% and a monomer concentration of 10 wt%, by using UV light as well as a hydrophilic photo-initiator. The entire polymerization could be performed within 1-2 h and display a conversion higher than 90%. The particle sizes could be tuned in the range of 20-40 nm. The formation mechanism for these of nano-sized latex particles was attributed to an in situ formation of PS chains with terminal hydroxyl groups. The presence of the hydroxyl-functionalized polymer chains seemed to promote a colloidal stability of the small latex particles and prevent coagulation even at low surfactant concentrations.     

Polyether based side-chain liquid crystalline polymers: Anionic polymerization and phase structures

Side-chain liquid crystalline (SCLC) polyethers with different spacers are successfully synthesized via anionic polymerization for the first time. The molecular weights of the polymers can range up to ∼53 kg/mol with M_w/M_n <1.1. The precise chemical structures including end groups have been characterized by employing Matrix-Assisted Laser Desorption/Ionization-Time of Flight (MALDI-TOF) and the polymerization condition free of side reactions is further discussed. The phase behavior and structures of the polyethers have been investigated by combining various techniques including differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS) and polarized light microscopy (PLM). Two phase transformations are generally observed for each type of SCLC polyethers. Based on 2-dimensional (2D) X-ray patterns of oriented fiber and mechanically sheared samples, the low ordered liquid crystalline phase at high temperature is identified as a SmA phase for both SCLC polyethers. It is found that the polyether with a longer spacer exhibits a complex phase which is a mixture of a HexB phase and a frustrated HexB phase in analogy to smectic antiphase, whereas no such effect occurs for the polymer with a shorter spacer. Only HexB phase is observed for the low temperature phase of this polymer. The difference in phase structures is also revealed in the texture changes of PLM.