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.     

激光光散射法研究紫外光引发聚合

采用激光光散射法跟踪,发现紫外光引发聚合体系中有关助剂及紫外光强度对体系的光固化的诱导期和聚合反应速度具有明显的影响,而过程中使用硫醇类光固化促进剂具有最佳效果.同时发现,体系中表观聚合速度与紫外光强的1.2次方成正比.     

Determination of molecular weight and size distribution and branching characteristics of PVAc by means of size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS)

SEC/MALLS has been applied for the determination of molecular weight and size distributions and to quantify branching in polyvinyl acetate (PVAc). Linear and branched samples obtained by solution and bulk polymerization were analyzed. The molecular weight distribution of the branched polymer was broader and the mean square radius was found to be smaller, 38.8 nm (with molecular weight of 770?000), than for the linear polymer, 42.3 nm (with molecular weight of 740?000). Branching characteristics could be determined by using Zimm and Stockmayer equations. It has been found that the number of branches for the branched sample increases from about 1 to 9, per molecule, with increasing molecular weight.     

Phase behavior study of PEB/PES blend by time resolved laser light scattering

The phase behavior of PEB/PES (poly(ethylene-co-styrene)/poly(ethylene-co-butene)) blend system was studied by time resolved laser light scattering with both wide angle and small angle laser light scattering. The phase separation kinetics show that the phase diagram of this system is a closed loop with both lower critical solution transition (LCST) and upper critical solution transition (UCST), which is inconsistent with the results obtained by optical microscope we reported before. All of the phase separation processes including early, middle and late stages have been studied. The coarsening behavior of the blend was characterized in terms of the time change of the maximum intensity I_m, and the magnitude of the scattering vector q_m, at which the intensity becomes maximum. The theory to interpret the phenomena has been studied by many researchers, and it is waiting for further theoretical systematic research.     

Behavior of free radical transfer between aqueous phase and latex particles in emulsion polymerization

The free radical transfer between aqueous phase and latex particles was investigated in the seeded emulsion polymerization using potassium persulfate (KPS) as an initiator. The effects of seed particle size, initiator concentration and polymerization temperature on the radical entry into and/or exit from the particles were emphatically examined. The results suggest that the aqueous-phase radical entry into the particles should be a competitive process, i.e. the competition between radical diffusion from the bulk aqueous phase to the interface of particles and its reactions in the aqueous phase determines whether it may be adsorbed into the particles or not. This implies that the reactions and properties of radicals in the aqueous phase play an essential role in particle nucleation in the emulsion polymerization.     

Kinetic study on free radical polymerization of alkyl acylamidoacrylates by pulsed laser polymerization using nitrogen laser

Radical polymerization of captodatively substituted alkyl acylamidoacrylates was studied by pulsed laser polymerization using a N₂ laser. Propagation rate coefficient of the acrylates was varied with solvents used in spite of a radical mechanism, but little varied with methyl, n-propyl, and isopropyl substituents on the acrylates. Arrhenius parameters for the propagation indicated that a solvent affected mostly on a frequency factor rather than a activation energy. In addition, it was suggested that these captodatively substituted propagating radicals were thermodynamically persistent but kinetically active in propagation, which resulted in rather smooth propagation in spite of bulky 1,1-disubstituted olefins. The mechanism of the polymerizations was discussed in detail on the basis of the kinetic studies and ESR spectroscopy.     

Comparison of the gelation dynamics for polystyrenes prepared by conventional and living radical polymerizations: a time-resolved dynamic light scattering study

The structure and dynamics for the two types of polystyrene gels prepared by conventional and living radical polymerizations have been investigated by time-resolved dynamic light scattering (TRDLS). The reaction was initiated with the monomer solutions with and without a reversible addition-fragmentation chain transfer (RAFT) agent and was monitored through the gelation process. In the absence of a cross-linker, the reaction process was characterized by the appearance of a maximum when the excess scattering intensity divided by concentration was plotted as a function of reaction time. The intensity maximum was ascribed to an increase in the molecular weight and subsequent suppression of the concentration fluctuations, which was qualitatively reproduced by the Flory-Huggins free energy formula. As the concentration became higher, the time-intensity correlation functions (ICFs) exhibited two modes, suggesting the formation of larger aggregates in addition to the cooperative mode. The intensities were successfully decomposed into the two components by taking account of the relative amplitude of the fast and slow modes. The difference of the time-course between the two types of polymerizations was clearly detected by combining TRDLS and gel permeation chromatography, GPC, data. For the cross-linking system, the kinetics was characterized by the universal gelation mechanism, namely: (1) divergence of the slow mode and (2) appearance of the power law in ICF around the gelation threshold regardless of the polymerization method. On the other hand, the real time intensity decomposition analysis revealed striking differences in the gelation mechanism between the two types of polymerization. For example, the slow mode appeared at an early stage of reaction for the conventional system and sustained its amplitude through the gelation process. For the living (RAFT) system, the appearance of the slow mode was limited in a narrower range of the reaction time with a much smaller amplitude.     

共振光散射法测定水中痕量总锰

建立一种环境水样中总锰的共振光散射分析新方法。在pH=6.0的Tris-HC l缓冲溶液中,锰(Ⅶ)氧化二甲基亚砜(DMSO)成为二甲基砜(DMSO2),生成的Mn2+与DMSO2结合形成离子缔合物,使体系的共振光散射急聚增强。在优化的实验条件下,在6.3×10-9~7.5×10-5mol/L浓度范围内,体系的△I值与锰(Ⅶ)浓度之间具有良好的线性关系,线性回归方程为△IRLS=-217.3+114.7 c(r=0.999 1);检出限为1.9×10-9mol/L;样品加标回收率为102.3%~106.5%。该法简便,特异,灵敏度高。用于环境水样中总锰的测定,结果满意。     

Simultaneous multiple sample light scattering for analysis of polymer solutions

An instrument for performing Simultaneous Multiple Sample Light Scattering (SMSLS) is introduced, which allows multiple, independent polymer samples to be analyzed simultaneously. Three demonstrations of SMSLS capabilities are made; proof of the SMSLS ability to make absolute Rayleigh scattering ratio measurements on well‐defined standards, the monitoring of a biopolymeric degradation process (hyaluronate degradation using hyaluronidase), with subsequent determination of the Michaelis‐Menten constant, and an aggregation process (low concentration gelatin solutions). It is hoped that SMSLS will become a valuable tool for rapid screening and characterization of both equilibrium properties and nonequilibrium processes in polymer solutions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2724–2732, 2004     

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.     

Determination of mutual solubilities in aniline + n -hexane and furfural + cyclohexane systems by a laser light scattering technique

A newly developed laser light scattering technique was used for the determination of mutual solubilities in two liquid systems at moderate pressures. The solubility data and the upper critical solution temperatures are reported for the aniline + n-hexane and furfural + cyclohexane systems. The experimentally determined cloud points were satisfactorily correlated by the NRTL equation.     

共振光散射法测定甲哌鎓水剂中的氯含量

研究了氯化银胶体的共振光散射光谱特征,讨论了硝酸银用量、乙二醇用量、硝酸用量、时间及加入顺序对共振光散射强度的影响。建立了用共振光散射技术测定甲哌鎓水剂中总氯含量的新方法。在试验确定的优化条件下,方法的线性范围为1.0￣10mg/ml,线性回归方程为ΔIRLS=38.525c(Cl-,mg/ml) 48.322,R=0.9971,检出限为16ng/ml(3s/K)。该方法灵敏度、精密度高,操作简单,样品需要量小,能满足检测要求。     

Molar mass distribution by size exclusion chromatography: Comparison of multi-angle light scattering and universal calibration

Series of polymers of various molar mass, chemical composition, and molecular architecture was analyzed by size exclusion chromatography (SEC) coupled with a multi-angle light scattering (MALS) photometer and an online viscometer. The molar mass averages were determined from the signal of MALS or calculated from the intrinsic viscosity and universal calibration. The comparison of the obtained results showed significant differences between the two methods. The MALS detection was shown to be more accurate for the determination of the weight-average molar mass and less vulnerable to the spreading of polymer peak by band broadening. The universal calibration can yield more accurate estimation of the number-average molar mass of branched polymers. It is also significantly more accurate for the characterization of fluorescent polymers than MALS with a regular laser of 660 nm. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47561.     

激光衍射光散射法在聚氯乙烯树脂粒度分析中的应用

主要介绍激光衍射光散射法在聚氯乙烯树脂粒度分析中的应用。并与筛分法对照,比较了两种方法测得样品的平均粒径,分布宽度,三目集中率,同时论述了颗粒形态与加工性能之间的关系。     

Determination of molecular weight and molecular sizes of polymers by high temperature gel permeation chromatography with a static and dynamic laser light scattering detector

Flow-mode static and dynamic laser light scattering (SLS/DLS) studies of polymers, including polystyrene, polyethylene, polypropylene and poly(dimethylsiloxane) (PDMS), in 1,2,4-trichlorobenzene (TCB) at 150 °C were performed on a high temperature gel permeation chromatography (GPC) coupled with a SLS/DLS detector. Both absolute molecular weight (M) and molecular sizes (radius of gyration, R_g and hydrodynamic radius, R_h) of polymers eluting from the GPC columns were obtained simultaneously. The conformation of different polymers in TCB at 150 °C were discussed according to the scaling relationships between R_g, R_h and M and the ρ-ratio (ρ=R_g/R_h). Flow-mode DLS results of PDMS were verified by batch-mode DLS study of the same sample. The presented technique was proved to be a convenient and quick method to study the shape and conformation of polymers in solution at high temperature. However, the flow-mode DLS was only applicable for high molecular weight polymers with a higher refractive index increment such as PDMS.     

激光光散射法测定混凝絮体形成时间的初步研究

运用激光光散射法对低浊度水样中三氯化铁、聚合氯化铝、硫酸铝絮体形成时间进行测定。研究表明混凝过程中絮体形成时间与混凝剂的种类有关,并且絮体形成时间受混凝剂的投加方式和水样pH值条件影响。在18℃,pH值为7.2的常规高岭土模拟水样中,在一次性加入最佳投加量的情况下,3种絮体的初始出现时间分别是:三氯化铁为25s;聚合氯化铝为15s;硫酸铝为50.4s。     

Investigation of the self‐association behavior of a thermosensitive copolymer with lower critical solubility temperature near human heat by dynamic laser light scattering

The special thermosensitive copolymer with lower critical solubility temperature near human heat of 37°C in aqueous solution has been prepared successfully by copolymerizing N‐isopropylacrylamide (NIPAM) and N‐isopropylmethacrylamide (NIPMAM) randomly at an appropriate monomer ratio. The self‐association behavior of the poly[NIPAM‐ran‐NIPMAM] copolymer has been studied by dynamic laser light scattering (DLLS) at a concentration higher than the critical concentration of the self‐association calculated from viscosity data according to cluster theory. The effect of the concentration and temperature on the self‐association behavior in water has been discussed respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 583–588, 2005     

Dynamic light scattering of dilute PVA-borax aqueous solutions

Poly(vinyl alcohol)-borate (PVA-borate) complexes in dilute aqueous solutions were investigated by dynamic light scattering (DLS). Two relaxation modes obtained, were scattering vector-q² dependent and diffusive. The amplitude of slow mode was independent of borax concentration. In the very dilute PVA concentration regime ( [PVA] < 5 g/L), the PVA di-diol-borate complexation was dominated by intra-molecular reaction, and the fast mode correlation length ς_f which corresponds to the polymer chain dimension increased rapidly with borax concentrations lower than 0.06 M, and reached an asymptote in the higher borax concentration regime. However, for a dilute PVA aqueous solution with higher PVA content (i.e., [PVA] = 9 g/L), both intra-and inter-molecular PVA di-diol-borate complexations might happen. The chain expansion and shrinkage of PVA-borate complex with increasing borax concentration was observed due to the balance between the electrostatic repulsion of the charged diol-borate complexes and the intra-molecular crosslink induced by the intra-molecular di-diol-borate complexation.     

Insight into dynamics of polyelectrolyte chains in salt-free solutions by laser light scattering and analytical ultracentrifugation

We have investigated the dynamics of xanthan aqueous solutions with and without added salt (NaCl) by using laser light scattering (LLS) and analytical ultracentrifugation (AUC) via sedimentation velocity (SV). The fast and slow modes are observed in salt-free and low-salt xanthan solutions by dynamic light scattering (DLS). The scattering ratio (KC/R_s(q)) and apparent diffusion coefficient (D_s,app(q)) of the slow mode is linearly related to scattering vector (q²), indicating that it is related to the diffusion of scattering objects. The intensity contribution (α_s) of the slow mode is independent of scattering angles, indicating that the slow mode is not related to some scattering objects larger than the LLS observation length. However, the slow mode disappears in SV experiments, indicating that it arises from the temporal aggregates due to long range electrostatic interactions between chains, which can be destroyed in centrifugal field. The diffusion coefficient measured by SV is close to that of the fast mode in DLS measurements, indicating that it is the coupling diffusion of macroions and counterions. The present studies also demonstrate that the chain stiffness does not change the characteristics of the dynamics of polyelectrolyte in solutions.     

Emulsion atom transfer radical polymerization of 2-ethylhexyl methacrylate

The emulsion atom transfer radical polymerization (ATRP) of 2-ethylhexyl methacrylate (EHMA) was carried out with ethyl 2-bromoisobutyrate (EBiB) as an initiator and copper bromide (CuBr)/4,4′-dinonyl-2,2′-bipyridyl (dNbpy) as a catalyst system. The effects of surfactant type and concentration, temperature, monomer/initiator ratio, and CuBr₂ addition on the system livingness, polymer molecular weight control, and latex stability were examined in detail. It was found that the polymerization systems with Tween 80 and Brij 98 as surfactants at 30 °C gave the best latex stability. The polymer samples prepared under these conditions had narrow molecular weight distributions (M_w/M_n=1.1-1.2) and linear relationships of number-average molecular weight versus monomer conversion.