Adsorption of amphiphilic polysaccharides onto polystyrene latex particles

Adsorption properties of hydrophobically modified carboxymethylpullulans (HMCMP) with different degree of modification of alkyl chains (C8) onto polystyrene latex particles have been investigated. Hydrophobic interactions between the grafted alkyl chains and the surface are responsible for the adsorption of these polymers. Their adsorption isotherms are Langmuir type, therefore, there is only a monolayer of adsorbed polymer chains. Variations of plateau adsorbed amounts and adsorbed layer thicknesses show a competition between the number of anchors (alkyl chains) and size of loops. Desorption of adsorbed polymer chains has been tested in three different media (0.1 M NaCl, pure water and 0.01 M NaOH). The greater desorbed amount has been obtained in 0.01 M NaOH (hydrolysis of ester bonds).     

An experimental appraisal of the Cox-Merz rule and Laun's rule based on bidisperse entangled polystyrene solutions

The empirical relationship provided by the Cox-Merz rule or Laun's rule has frequently been employed for linking rheological data collected in steady-state shear experiment to those in dynamic oscillatory experiment for entangled polymer liquids. Good applicability of these empirical rules has generally been found, especially for nearly monodipserse systems; for polydisperse systems, however, discrepancies have occasionally been reported without explanations. To throw some light on the impact of blending on the applicability of these empirical rules for entangled polymer liquids, we scrutinize simultaneously the steady state and dynamic oscillatory data on a series of bidisperse entangled polystyrene solutions. The primary finding is that deviations from the predictions of these empirical rules are generally observable as the long chain becomes markedly dilute, especially for the case of Laun's rule. The phenomenological effects of blending are tentatively interpreted in view of the contribution of chain stretching.     

Structured latex particles with improved mechanical properties

Structured polymer latex particles are prepared by a swelling emulsion polymerization process, in which the initial particles are first swollen by ethylenically unsaturated monomers and the polymerization of the latter is then carried out. This special polymerization process leads to multi-phase particle morphology. Instead of a thermodynamically more favorable large-scale phase-separation, we obtain multiple, near-spherical domains dispersed within the particles. TEM analysis after selective staining reveals the size and distribution of the microdomains. Dynamic mechanical analysis of the polymer films confirms the absence of a distinct, large second phase and indicates that such microdomains interfere at the molecular level with the segmental mobility of the dispersing phase. We present examples of soft polymers as the continuous phase and hard polymers as the dispersed phase. The inclusion of hard microdomains into soft continuous phase increases dramatically both the films tensile strength and elongation, which means improved cohesive strength of the polymer material. The increase in tensile strength of the polymer film correlates directly with the hardness of the dispersed phase. Improvement in tensile strength and elongation is important in a number of industrial applications of polymers, such as flexible coatings, coalescent-free paints and pressure sensitive adhesives (PSAs). Examples are presented which demonstrate the potential applications of the swelling emulsion polymerization process.     

Characterization of electrosterically stabilized polystyrene latex; implications for radical entry kinetics

Electrosterically stabilized polystyrene latexes with a poly(acrylic acid) hydrophilic layer with either perdeuterated core or perdeuterated hydrophilic layer were prepared in situ in a styrene/acrylic acid copolymerization, in a manner similar to that commonly employed industrially. Small angle neutron scattering (SANS) measurements were made over a range of contrasts for three latexes at high and low pH. Parameters obtained by fitting to standard core/shell models were consistent with the shell being highly hydrated (about 89% at low pH and about 94% at high pH). The core was found to contain about 3% acrylic acid. Doubling the proportion of acrylic acid in the recipe increased shell thickness by about 20%, slightly reduced particle size and slightly increased the proportion of acrylic acid incorporated into the core. The maximum degree of polymerization (DOP) of the entering (and therefore grafted) species was estimated from the shell thickness to be about 44 monomer units for 0.02 M acrylic acid and 66 for 0.04 M. The observed dependence of hairy layer (shell) thickness on the initial amount of acrylic acid suggests that the critical DOP for entry (and therefore true grafting) of the electrosteric stabilizer is thermodynamically (not kinetically) controlled.     

Modelling the zero shear viscosity of bimodal high solid content latex: Calculation of the maximum packing fraction

Different rheological tests were performed on monodisperse polystyrene latices and mixtures of two different latices with different particle sizes. A critical volume fraction φ_c was defined for each of the latices. Subsequently, a method based on the estimation of the porosity of a bed of randomly placed spherical particles was adapted to allow us to define the maximum packing fraction for any bimodal system. This method can be used for any ratio of particle diameter and volume fraction for the two populations provided one has knowledge of the critical volume fractions of related monodisperse latices (see Pishvaei et al., 2005. Polymer 46, 1235-1244). The model was tested experimentally, and rheological tests allowed us to validate the values of the critical volume fraction (φ_c) of different bimodal latices. A master curve of viscosity vs. polymer concentration was obtained using the concept of reduced volume fraction. The results prove that we can predict the viscosity of multimodal systems from the knowledge of monomodal packing fraction.     

The preparation of small polystyrene latex particles

The effects of several variables in the preparation of small-sized polystyrene latex particles are described. A semicontinuous preparation using microlatexes obtained by microemulsion polymerization as a seed is compared with a batchwise preparation employing the same ingredients. The particles in the batch products prove to be slightly larger in size but are more narrowly distributed. Furthermore, the effects of both the surfactant type and the ionic strength on the particle size in the batchwise emulision polymerization of styrene are reported. The systems do not obey the linear Smith–Ewart relationship with respect to the micellar surfactant concentration, although in the microemulsion polymerization of styrene the Smith–Ewart relationship is found to be valid with respect to the initiator concentration. Surfactants with a low critical micelle concentration increasingly promote the formation of smaller particle sizes. Salt is found to decrease the particle size when using a strong adsorbing surfactant. However, in the case of a weak adsorbing surfactant, an increase in particle size has been observed above a certain salt concentration.     

The dynamics of morphology development in multiphase latex particles

The use of multistage emulsion polymerization to produce particles containing multiple polymer phases is widespread throughout the coatings, impact plastics and adhesives industries. Such composite particles often improve various application properties compared to related single-phase latices or latex blends. The properties obtained depend in large part on the morphology of the multiphase particles, creating an incentive to understand the underlying mechanisms that drive morphology development in these particles as they are formed in the polymerization reactor. Much attention has been devoted to understanding the thermodynamic factors that influence morphology control, but in fact the majority of systems are produced under kinetic control, resulting in non-equilibrium structures. There are three main kinetic factors involved as the morphology develops during the second stage polymerization. These are (1) penetration of polymer radical chains into the particle interior after entry from the water phase, (2) phase separation of immiscible polymer chains produced in the different polymerization stages and (3) spatial rearrangement of phase separated domains. We have summarized our knowledge and understanding of morphology development in a concise decision tree flow chart which can be used for morphology prediction. The validity and use of this decision tree is illustrated through a series of experimental examples.     

Monodisperse ellipsoidal polystyrene latex particles: Preparation and characterisation

An improved version of a novel method first employed by Nagy & Keller for the preparation of monodisperse ellipsoidal polystyrene latex particles is described. The method involves embedding monodisperse spherical polystyrene latex particles as starting material in a deformable polymer matrix such as poly(vinyl alcohol) and deforming these mechanically to various predetermined macroscopic draw ratios to give ellipsoids of various axial ratios. Ellipsoids with lengths ranging from about 350 to 12250nm were prepared. Stable aqueous dispersions of these were recovered and characterised with respect to particle size and axial ratio distributions and surface morphology using electron microscopy. Axial ratios ranging from 2.0 to 5.65 were obtained for the resulting ellipsoids. Various factors influencing the monodispersity of the resulting ellipsoids in the preparation method are discussed.     

Phase distribution and separation in poly(2-acetoxyethyl methacrylate)/polystyrene latex interpenetrating polymer networks

A series of latex interpenetrating polymer networks (LIPNs) were prepared via two-stage soap-free emulsion polymerization of styrene on cross-linked poly(2-acetoxyethyl methacrylate) (PAEMA) seed latexes, using potassium persulfate as initiator. It was found that a compositional gradient was present when PAEMA seeds cross-linked either lightly or highly were used. The polystyrene (PS) phase is localized near the particle center in the former case, while it is segregated near the surface in the latter case. A uniform distribution of PS phase in LIPN was formed, if moderately cross-linked PAEMA seed was used. All the LIPNs appeared to be microphase-separated, and increase of cross-linking degree in seed latexes decreased the PS-rich domain size. The results were explained by the particle growth mechanism that involved the formation of surface-active oligomeric radicals in water phase, adsorption of the radicals onto monomer-swollen particle/water interface, and chain propagation in the interface with subsequent phase migration dominated by the competitive effects of thermodynamics and kinetics.     

Synthesis of polyacrylonitrile/polystyrene latex particles that contain platinum

Studies on the incorporation of highly dispersed platinum (Pt) nanoparticles into proton‐exchange membrane fuel cells (PEMFC) as a possible catalyst have gained tremendous attention in the past decade. The major obstacle to fully commercialize PEMFCs is the high cost of Pt as the catalyst. In this study, the incorporation of highly dispersed platinum molecules into poly(acrylonitrile) (PAN) or polystyrene (PS)/PAN latex particles was carried out to form a possible a catalyst precursor for fuel‐cell applications. Pt‐containing PAN/PS particles were prepared using miniemulsion polymerization. Both transmission electron microscopy (TEM) and induction coupled plasma (ICP) measurements indicated that Pt salt was encapsulated into PAN/PS copolymer latex particles. In addition, the encapsulation percentages of Pt salt are all above 90% for different PAN/PS ratios. Additional experiments have been carried out to convert these Pt molecules into nanoparticles and will be elaborated upon subsequent studies. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41933     

The effect of the polymerization route on the amount of interphase in structured latex particles and their corresponding films

Three series of hard/soft styrene-acrylic latex based systems with equivalent compositions were prepared either by blending of homopolymer latexes or by preparing structured latex particles having core shell (CS) or inverted core shell (ICS) morphologies. Transmission electron microscopy (TEM) was used to investigate the particle morphologies, which were correlated to the calculated fractional radical penetration for the propagating species during the reactions. The thermo-mechanical properties as well as the morphology of the resulting latex films were analyzed by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and TEM. The viscoelastic properties of the interphase between the first and second-stage polymers formed in the structured hard/soft latex films, as well as its qualitative amount and also the film morphologies were found to depend on the interplay between thermodynamic and kinetic parameters during the synthesis of the samples.     

胶乳型织物粘合剂的研究

本文对胶乳型织物粘合剂的硫化体系、防老化体系、增粘体系、稳定体系等分别进行了探讨,研究了胶乳型织物粘合剂的最佳配方,阐述了胶乳型织物粘合剂的性能、应用及其制备工艺。     

A relationship between maximum packing of particles and particle size

Experimental data indicate that the volume fraction of particles in a packed bed (i.e. maximum packing) depends on particle size. One explanation for this is based on the idea that particle adhesion is the primary factor. In this paper, however, it is shown that entrainment and immobilization of liquid by the particles can also account for the facts.     

The effect of clay particles on film formation from polystyrene latex

Film formation from surfactant‐free polystyrene (PS) latex was performed in the presence of 5% Na‐montmorillonite (NaMMT). The composite films were prepared from pyrene (P)‐labeled PS particles at room temperature and annealed at elevated temperatures above the glass‐transition (T_g) temperature of polystyrene. Scattered light (I_s) and fluorescence intensity (I_P) from P were measured after each annealing step to monitor the stages of composite film formation. Minimum film formation temperature, T₀, and healing temperatures, T_h, were determined. Void closure and interdiffusion stages were modeled and related activation energies were measured. From these results, it was found that the presence of NaMMT in the PS latex film only affects the minimum film formation, but does not affect the void closure and backbone motion activities. POLYM. COMPOS., 27:299–308, 2006. © 2006 Society of Plastics Engineers     

Polystyrene/melamine-formaldehyde hollow microsphere composite by self-assembling of latex particles at emulsion droplet interface

Submicron scale particle aggregates with defined shape were prepared by self-assembling of sulphonated polystyrene latex particles at the interface of emulsion droplets. Several parameters were considered during the preparation, including the sulphonation time of the polystyrene latex particles, the composition of the oil phase, and the zeta potential of the sulphonated latex particle. To further improve the mechanical stability of the particle aggregates, a hard composite layer was formed by addition of melamine-formaldehyde (MF) prepolymer into the emulsion. The prepolymer was crosslinked onto the particles surface of sulphonated PS particle aggregates. The crosslinking reaction was catalysed by the acidity of sulfogroup. After evaporating off solvent, PS/MF hollow microsphere composites were obtained as mechanically stable dry material. The hollow microsphere composite was characterized by TGA, FTIR, optical microscopy, scanning and transmission electron microscopy.     

Core-shell and other multiphase latex particles—confirming their morphologies and relating those to synthesis variables

Composite latex particles made from sequential processing steps may have a wide range of morphologies. The particular structure achieved is the result of a number of complex interactions between the chemical and physical aspects of the emulsion polymerization process. The intention is often to produce a core-shell particle structure, but in reality this is often a nontrivial task. In addition, it is challenging to develop confident conclusions about the detailed morphology of such particles, even when the two-component polymers are well phase-separated. This paper reports on an inter-laboratory study of acrylic-styrene copolymer latices in which the two-component polymers were not well phase-separated—a common result when attempting to make core-shell latex particles. Six different organizations each performed a number of analytical measurements to characterize two different latex systems. Their collective results were presented at a workshop in which the group strived to reach consensus on the detailed structures of the particles. Their conclusions were that multiple, complementary analytical results are required to reach a sound decision. While electron microscope results were always judged to be necessary, considered by themselves, it is often found that one can be led to false conclusions, especially for systems that are not well phase-separated. Given the results of this study it is clearly inappropriate to assume that the polymer formed in the second stage of a semibatch latex polymerization process forms a shell, giving rise to a core-shell morphology. Presented at 2007 FutureCoat! conference, sponsored by Federation of Societies for Coatings Technology, October 3–5, 2007, in Toronto, Ont., Canada.     

The effects of latex coalescence and interfacial crosslinking on the mechanical properties of latex films

The effects of latex coalescence and interfacial crosslinking on the mechanical properties of latex films were extensively investigated by means of several series of model latexes with varying backbone polymer crosslinking density and interfacial crosslinking functional groups. It was found that the tensile strength of crosslinked model latex films increased with increasing gel content (i.e. crosslinking density) of latex backbone polymers up to about 75% and then decreased with further increase in gel, while their elongation at break steadily decreased with increasing gel content. These findings showed that latex particle coalescence was retarded above a gel content of about 75% so that the limited coalescence of latex particles containing gel contents higher than 75% prevented the tensile strength of crosslinked latex films from increasing by further crosslinking the latex backbone polymers. This was contrary to the theory of rubber elasticity that the tensile strength increases with increasing molecular weight and crosslinking density. This limitation was found to be overcome by the interfacial crosslinking among latex particles during film formation and curing. This paper will discuss the effects of both latex backbone polymer and interfacial crosslinking on latex film properties. It will also discuss the development of self-curable latex blends and structured latexes containing co-reactive groups: oxazoline and carboxylic groups.     

Adhesion of latex films; influence of surfactants

The aim of the work presented in this article was to investigate the role of surfactants on adhesion properties of latex films. Several polymer/surfactant/support systems were used. Polymers were poly(2-ethyl hexyl methacrylate) or a methyl methacrylate/ethyl acrylate copolymer partially grafted onto a hydrophilic polyester. Surfactants were sodium dodecyl sulfate (SDS), hexadecyl pyridinium chloride (HPCI), or ethoxylated nonyl phenol containing 10 or 30 segments of ethylene oxide (NP10 or NP30). Supports were glass plates or poly(ethylene terephthalate) films. Adhesion was measured by a peel test at 180°. Loci of failure were determined by multitechnique analysis of the surfaces revealed after peeling. At medium and high peel rates, the peel energy versus surfactant concentration curves show either a maximum or a minimum, depending on the surfactant. When the peel rate is decreased, these maxima and minima flatten out and, at zero peel rate (extrapolated values), the peel energy becomes independent of the surfactant concentration. Surfaces analyses revealed that the surfactant is always present at the locus of failure. Rupture takes place in a thick (above 10 nm) (SDS), in a thin (a few nanometers) (NP30), or at the top of a surfactant layer (HPCI). The locus of failure is independent of the peel rate and of the surfactant concentration. The conclusion is that the surfactant strongly influences adhesion properties of latex films but several points remain unexplained.     

聚苯乙烯-聚甲基丙烯酸甲酯核-壳粒子的制备

由种子乳液聚合法制备了聚苯乙烯-聚甲基丙烯酸甲酯核-壳粒子。以过硫酸钾(KPS)为引发剂,辛基酚聚氧乙烯醚(OP-10)为乳化剂,合成了聚苯乙烯(PS)种子核;连续滴加甲基丙烯酸甲酯(MMA),在核表面富集MMA,制备了粒径范围在0.16~0.67μm的核-壳粒子;当单体苯乙烯与甲基丙烯酸甲酯(St/MMA)的比为30∶70(质量比)时,所得粒径在0.18μm,粒径分布为0.012。差示扫描量热(DSC)研究显示,复合粒子的玻璃化转变温度(Tg)为97.2℃,峰形单一,表现出良好的热性能。     

Investigation of deformation mechanisms during latex film formation by combination of unilateral NMR and near infrared measurements

Unilateral solid state NMR and near infrared measurements are combined to study latex film formation at different temperatures and humidities in order to cover a broad parameter-space of film formation conditions. From analysis of nuclear magnetic resonance (NMR) data the time evolution of water and polymer fraction at different (vertical) positions in the film were estimated. The mean water fraction was determined simultaneously by near infrared (NIR) reflection measurements. From the time-evolution of the water distribution within the film and the total water content, it was possible to differentiate between the different deformation mechanisms (e.g. capillary deformation, receding water front mechanism or skin formation). The experimental findings are compared to theoretical predictions by Routh and Russel [Langmuir 15 (1999) 7762–7773]. Although most of the predicted regimes could be identified, the experimental estimated transitions between different regimes deviate significantly from the theoretical boundaries. The complex rheological behaviour of polymers has been identified to be the main reason for these deviations.