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Latex

In the authors' previous work (J.Colloid Interface Sci., 2006, 302, 187), a generalised stability model was proposed, which accounted simultaneously for the interrelationships among three important physicochemical processes, i.e. colloidal interactions, surfactant adsorption equilibrium, and association equilibria of surface charge groups with counterions at the particle-liquid interface. To further validate the model's reliability, in the present work the model was applied to describe the stability of two polymer colloids (styrene-acrylate copolymers) that were stabilised not only by mobile ionic surfactants but also by fixed charges originating from polymer chain end groups. Furthermore, two different surfactants, a carboxylate and a sulphonate, were considered in order to investigate the effect of largely different protonation efficiencies. It was found that the generalised stability model could well describe the stability behaviour of the two polymer colloids. It was found from the model predictions that the trends of surface charge variations with ionic strength, counterion type, and pH, and their effects on surfactant partitioning between the particle surface and liquid phase, could be substantially different, depending on the protonation efficiency of charge groups and the presence of fixed charges. 30 refs.

Using principles and specifics of formulation, compounding and testing from part I (Paint and Coatings Industry, Feb.2006, Rapra Accession number 959558), studies were conducted of interior latex paint properties provided by four structured pigments that are produced and used in the Southeastern United States. These pigments were conventional calcined clay, premium (fine particle size) calcined clay, flash refined clay and synthetic structured silicate pigments. Approaches were used which kept certain calculated parameters and certain paint properties constant while studying the effects of structured pigment substitution on opacity and film integrity. The benefits of using volume relationships and pigment volume concentration(PVC)/critical PVC calculations in formula design were demonstrated. In addition, information was obtained on properties contributed by the various structured pigments and an attempt was made to rate the relative values of these contributions.

The preparation of a novel photonic crystal assembled from poly(styrene/alpha-tert-butoxy-omega-vinylbenzyl-polyglycidol) microspheres was studied. The latex particles were fully characterised in terms of size, electrophoretic mobility and surface chemical composition (evidence for a polyglycidol-rich particle surface). They were then assembled into three-dimensional colloidal crystals showing an optical stop band in the visible region. The maximum wavelength for the Bragg diffraction peak was 570 nm. As the particles under study are highly hydrophilic and biocompatible, this work opens up new opportunities for the design of photonic crystal-based biosensing devices. 19 refs.

A vinyl triisopropoxide silane-co-methyl methacrylate-co-n-butyl acrylate-co-styrene latex was prepared by emulsion polymerisation using a redox system. The latices obtained had good reaction and storage stabilities when conditions such as temperature, pH value and vinyl triisopropoxide silane content were suitably controlled during the polymerisation process. The crosslinked structure was formed in the copolymer latex film and the degree of crosslinking of the copolymer latex film increased with the increasing vinyl triisopropoxide silane content. The tensile stress and water repellent properties were also strengthened when the vinyl triisopropoxide silane was introduced into the copolymer latex film. The latices should have potential applications in coatings requiring good water resistance. 38 refs.

Novel waterborne systems from Arkema (KYNAR Aquatec) based on PVDF polymers and copolymers, with durability and performance comparable with those of the solvent-borne analogues, are described. The morphology of the systems is examined and justification provided for the chosen structure. Data from South Florida-exposed test panels are presented, which demonstrate that the influence of latex particle morphology on durability is the same for both accelerated test cabinet and outdoor exposures. The formulation of the product for after-market roof coatings is discussed and coatings for EPDM membranes are examined. The performance edge of the fluoropolymer system over conventional binder systems is considered, together with some challenges for future developments. 11 refs. (The Waterborne Symposium, Advances in Intelligent Coatings Design, New Orleans, Feb.2007)

A versatile non-aqueous emulsion polyaddition process for the one-step fabrication of spherical PU nanoparticles is presented. Three different emulsion systems were used consisting of DMF dispersed in n-hexane, acetonitrile dispersed in cyclohexane, and acetonitrile dispersed in tetradecane. After successful stabilisation of the emulsion systems by using an isoprene-methyl methacrylate block copolymer, the fabrication of the PUs was carried out within the dispersed polar phase. The PU particles showed average diameters as small as 35 nm. In addition, IR characterisation revealed that the formation of any urea, which decreased the mechanical properties of the PUs, was prevented during the polyaddition. This was attributed to the anhydrous reaction conditions. GPC analysis demonstrated the average molec.wts. of the PUs to be as high as 16,500 g/mol, corresponding to conversions of 0.98. Comparable molec.wts. and conversions had not previously been achieved without the formation of urea. Preliminary experiments revealed that these PU nanoparticles could be used for the fabrication of thin coatings for metallic surfaces, suitable for prevention of corrosion using only 25% of the material traditionally used for this application. 19 refs.

PU was synthesised and used as costabiliser in the miniemulsion polymerisation of styrene initiated by 6 0Co gamma-ray radiation at room temperature. Only 2 wt% PU based on the monomer was enough to prepare a stable miniemulsion with a shelf life of more than 12 months. Preservation of original particle size and distribution throughout the polymerisation observed from dynamic light scattering measurements indicated the predominance of monomer droplet nucleation. Kinetic analysis showed that there was no constant rate stage, which also suggested a droplet nucleation mechanism. PS nanoparticles with relatively small diameters (40-70 nm) and narrow size distribution could be easily prepared. The effects of surfactant, costabiliser, and absorbed dose rate on the miniemulsion polymerisation are discussed. 31 refs.

The mechanism of adhesion of aramid fibre/coating interfaces was investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. a new combined carbon was observed on the surface of the aramid fibre upon treatment with blocked isocyanate and resorcinol-formaldehyde latex. The binding energy of the other combined carbon shifted to a higher value, nitrogen content increased and aramid fibre surface activity improved. 9 refs.

An alkaline-activated kaolinite/NR composite was prepared by coprecipitation of NR latex with modified kaolinite and the physical properties and structure of the composite investigated. Composites containing 40 phr of kaolinite possessed enhanced physical properties. Kaolinite was uniformly dispersed in the rubber and a transition layer was formed between the kaolinite and rubber matrix. 3 refs.

Transparent films were prepared by drying a suspension of latex particles prepared by emulsion polymerisation of styrene and butyl acrylate in the presence of Laponite clay particles intercalated with cationic initiator molecules. The morphology of the nanocomposite particles was investigated by cryo-TEM and cry-electron tomography and the thermal and mechanical properties of the composites determined by DSC, TGA and tensile testing. The nanocomposites possessed a unique network morphology characterised by a honeycomb distribution of Laponite platelets, an abnormal necking behaviour at low strain and a high elongation at break. 31 refs.

The dispersion polymerisation of n-butyl acrylate was carried out in a mixture of ethanol and water in the presence of hydrophilic poly(N-acryloylmorpholine) prepared by reversible addition-fragmentation chain transfer polymerisation to give hairy poly(n-butyl acrylate) latex particles. The poly(N-acryloylmorpholine) hairy layer was characterised by TEM and NMR spectroscopy. Pre-functionalisation of the poly(N-acryloylmorpholine) chains on the alpha-end by a carbohydrate derivative was also carried out to provide saccharidic surface-functionalised poly(n-butyl acrylate) particles. 15 refs.

Styrene and methyl methacrylate were graft polymerised onto deproteinised NR latex via emulsion polymerisation using ammonium peroxy disulphate as polymerisation initiator. The degree of grafting and copolymer composition were studied by NMR spectroscopy and a mechanism of seeded polymerisation, resulting in a graft copolymer of styrene and methyl methacrylate on NR, proposed. The composition of styrene and methyl methacrylate in the graft copolymer was calculated and found to be 12.78 and 11.28 wt.%, respectively. The higher amount of styrene in the graft copolymer was attributed to the higher reactivity ratio of styrene and instability of the NR backbone. 17 refs.

The preparation of hybrid nanoparticles composed of a PS/acetoacetoxyethyl methacrylate core and a titanium dioxide shell and the morphology of the nanoparticles, as determined by scanning electron microscopy, are reported. The presence of beta-diketone groups on the surface of the core particles is shown to invoke interaction between the Ti precursor and surface of the core and result in precipitation of the nanoparticles on the template. 17 refs.

Transparent coatings releasing an antifouling agent was used to reduce the marine fouling of optical lenses. A variety of water-borne coatings based on methyl methacrylate-butyl acrylate copolymers were synthesised using a two-stage miniemulsion process. A release rate of SeaNine 211 was studied for polymers of different Tg. 27 refs.

The fabrication of homogeneous nanocomposite films of polystyrene (PS) and single-walled carbon nanotubes (SWNTs) by directly mixing aqueous suspensions of exfoliated SWNTs and PS latex particles, followed by freeze-drying and compression moulding, is described. The nanocomposites were characterised by SEM, electrical conductivity and modulated temperature DSC, and the effects of low molecular weight PS in the system on nanocomposite properties are discussed in terms of improved wetting of the filler surface by the matrix polymer. 36 refs.

A novel method for the formation of nanometre-scale polymer structures via template assisted admicellar polymerisation is described. The method uses the interstitial sites of a two-dimensional self-assembled crystal of latex spheres. There is a significant separation distance between the template and the polymer. The size and shape of the nanostructures formed is dependent on the size of the spheres utilised and the polymerisation conditions. 10 refs.

Latexes based on acrylic acid, acrylamide, ethyl methacrylate, and ethyl acrylate were synthesised via emulsion polymerisation with different monomer compositions. The resultant latices were thickened with different molar ratios of NaOH to acrylic acid and were analyzed in terms of acid-basis titrimetry, turbidimetry, rheology, and tensiometry. Titrimetry, turbidimetry and rheometry were used to analyze factors such as carboxyl group availability and particle solubilisation, tensiometry monitoring the influence of carboxyl neutralisation on polymer-surfactant interactions. For the acrylic acid content used in this work (20 wt%), the results indicated that as carboxyl groups distribution became more homogeneous, the process of latex thickening became more effective. 39 refs. Copyright (c) 2007 Elsevier Ltd.

Nano-matrix structure was formed by graft-copolymerization of styrene onto urea-deproteinised natural rubber (U-DPNR) latex. The grafted U-DPNR was characterized by FT-IR spectroscopy, 1H NMR spectroscopy and transmission electron microscopy. Conversion and grafting efficiency of styrene were more than 90% under the best condition of the graft-copolymerization. In transmission electron micrograph of film specimen stained by OsO"4, it was found that natural rubber particle of about 0.5 micrometre in diameter was dispersed in polystyrene matrix of about 15 nm in thickness. The conversion and grafting efficiency for the grafted U-DPNR were compared with those for a control sample prepared from enzymatic deproteinised natural rubber (E-DPNR) with styrene. 24 refs. Copyright (c) 2007 Elsevier Ltd.

The photo-oxidation of cast self-supporting films of a carboxylated styrene butadiene random copolymer (c-SBR) containing talc and TR92 (coated rutile) (both separately and together) has been investigated using ATR-FTIR, toluene swelling measurements and DSC (for T"g determination). An imaging chemiluminescence (ICL) method was also used to depth profile the oxidation. Both the wavelength of the UV source and the presence of filler and pigment were found to affect the major degradation products and the propensity for surface crosslinking. At relatively low levels (<50 phr) talc showed an optimum UV stabilising effect at the irradiated surface (as measured by ATR-FTIR determination of carboxylic acid carbonyl index), though, due to iron impurities in the talc, higher loadings impaired the stabilisation performance. However, due to a physical barrier effect (verified using ICL), T"g measurements indicated a progressive increase in overall stabilisation with increasing talc loading. As expected, TR92 significantly retarded surface photo-oxidation and was manifested as slow growth of the carbonyl absorption bands. Carboxylic acid was by far the major component of the latter bands throughout the entire exposure period. Even at advanced stages of oxidation, alphabeta-unsaturated carbonyl species were the major surface photo-oxidation products in samples containing talc. Interestingly talc also led to significant surface crosslinking whilst the TR92 did not. 21 refs. Copyright (c) 2007 Elsevier Ltd.

Silver nanoparticles are formed in natural rubber matrix via photo reduction of film cast from natural rubber latex (NRL) containing silver salt. The resulting NR-Ag nanocomposite is characterized using TEM, XRD and UV spectroscopic techniques. The nanoparticles, diameter ranging between 4 and 10nm, are dispersed within distinct interfaces which correspond to the inter-particle boundaries of the NRL particles that form the matrix. The average width of the interfaces is 8nm. X-ray diffraction (XRD) analysis confirms the nanoparticles as metallic silver of the face-centred cubic type. UV-vis absorption spectra show peaks characteristic of the surface plasmon resonance of nano-sized silver. A comparison with the results of formation of silver, obtained under similar reduction condition, in a series of matrices namely de-proteinised natural rubber latex (DNRL), NRL containing sodium dodecyl sulphate (SDS), aqueous solutions of bovain serum albumin and SDS, suggests that the protein in natural rubber is responsible for the formation of stable silver nanoparticles in the natural rubber (NR) matrix. 34 refs. Copyright (c) 2007 Elsevier B.V.

A new crosslinker for polyurethane, N-[(1,1-dimethyl-2-acetyl)ethyl]-beta- dihydroxy ethylamino propanamide (DDP), was synthesised by Michael reaction using diethanolamine (DEA) and diacetone acrylamide (DAAM). DDP is a dihydroxyl-containing compound with ketone moiety, which crosslinks during film formation through a reaction between ketone of DDP and hydrazide in water-soluble dihydrazide compound, added upon preparation of waterborne polyurethane. The optimal ratio of DEA/DAAM for Michael reaction, determined by gas chromatography (GC), was of 1.05mol; highest yields (80%) were obtained with this ratio when the reaction was carried out at 90 deg.C with 12h of reaction time using acetonitrile as solvent. Experimental conditions of DDP separation from the reaction mixture were predetermined first through thin-layer chromatography, and DDP separation was conducted by column chromatography. DDP with 97% of purity or higher was obtained. The structure of DDP was fully characterized by IR and NMR. The elemental composition and molecular weight of DDP were confirmed by high resolution GC-MS and HPLC-MS, respectively. Polyurethane latexes with DDP and post-added dihydrazide were prepared, and polymer film properties compared with DDP-free latex film. Tensile strength increased with a decrease in elongation in crosslinked polymers. Higher performance in water and solvent adsorptions was also detected. 16 refs. Copyright (c) 2007 Elsevier B.V.

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