Dispersion of alumina suspension using comb-like and diblock copolymers produced by RAFT polymerization of AMPS and MPEG

Synergistic Effect of Polycarboxylate Superplasticiser and Protein Retarders in Cementitious Materials Containing Na- Montmorillonite: Effect of Addition Methods

Polycarboxylate superplasticiser (PCE) is notably sensitive towards Na-Montmorillonite (Na-Mmt), an impurity generated from the manufacturing of concrete aggregate due to the chemical intercalation and poor surface adsorption. In order to improve the poor compatibility of PCE, the protein-based retarders were applied as the sacrificial agents, and its synergetic effects in cementitious materials containing Na-Mmt were investigated. The protein-based retarders were applied as the sacrificial agents and its synergetic effects in cementitious materials containing Na-Mmt were investigated. In addition to test rheology, minislump, and setting time, the adsorption behaviour and intercalation were characterised via Total Organic Carbon, X-ray photoelectron spectroscopy, and X-ray diffraction. The results revealed that the incorporation of protein-retarders improved the performance of PCE in terms of workability, and the rheological behaviour of cement with Na-Mmt. Moreover, compared to simultaneous addition, the application of separate addition further increased the workability and improved workability retention, with best dispersion performance obtained by prior adding the retarders, which could be due to the lessened intercalation between the layers of Na-Mmt.

Direct synthesis via RAFT of amphiphilic diblock polyelectrolytes facilitated by the use of a polymerizable ionic liquid as a monomer

A novel method to prepare amphiphilic block polyelectrolytes with a strongly hydrophobic block under homogeneous conditions is presented here.

Achieving molecular weight distribution shape control and broad dispersities using RAFT polymerizations

Metered additions of chain transfer agents are used to control molecular weight distribution (MWD) features in reversible addition-fragmentation chain-transfer polymerizations, giving polymers with tailored MWD shapes and dispersities as high as 6.2.

Liquid Crystalline Copolymers Containing Sulfonic and Light-Responsive Groups: From Molecular Design to Conductivity

In the search for novel smart multifunctional liquid crystalline materials, we report the synthesis, thermal and structural characterisation, and the conductivity, of a set of new block and statistical copolymers, containing light-responsive mesogenic groups (MeOAzB), polar sulfonic acids (AMPS), and methyl(methacrylate) groups (MMA). By using a cascade of reversible addition-fragmentation chain polymerisations, RAFT, we have tailored different side-chain polymeric structures by controlling monomer composition (MeOAzB/AMPS/MMA) and configuration. We have yielded simultaneous liquid crystalline behaviour and appreciable conductivity in polymers with low concentrations of polar acid groups, by the formation of smectic phases in narrow aggregates. The light-responsiveness of the polymers, via reversible trans-to-cis photoisomerization of azobenzene groups, and the local activation of conductivity at relatively low temperatures, opens the possibility to prepare polymer electrolytes for energy conversion and storage, whose conductivity could be controlled and optimised by external stimuli, including light irradiation.

Structure-property relationships for polycarboxylate ether superplasticizers by means of RAFT polymerization

HYPOTHESIS

Polycarboxylate ether (PCE) comb-copolymers are widely used as water reducing agents in the concrete industry while maintaining a high fluidity via the polymer adsorption to the cement particles. PCE copolymers with a broad range of structures are well established by Free radical polymerization, however, understanding the structure-property relationship is still complex due to the high polydispersity of PCE copolymers prepared by conventional polymerization. The influence of different structural parameters using well-defined polymeric structures is yet to be explored.

EXPERIMENTS

In this study, two different types of comb-like random copolymers, namely polycarboxylate ether (PCE; poly(oligo(ethylene glycol) methyl ether methacrylate/methacrylic acid)) and polysulfonate ether (PSE; poly(oligo(ethylene glycol) methyl ether acrylate/sodium 4-styrenesulfonate)), were synthesized by RAFT polymerization to enable the synthesis of polymers with controlled features. The effect of charge types and side chain lengths on the adsorption, rheology, and dispersing ability of cement pastes have been studied.

FINDINGS

RAFT polymerization could be used to prepare PCE random copolymers with good control over the polymer molecular weight and narrow polydispersity (Đ < 1.3). Results revealed that the ζ-potential values depend on both the charge type and side chain lengths. Copolymers containing SO₃^- exhibited higher absolute negative ζ-potential values than COO^- while PCE copolymers with shorter side chains developed higher absolute negative ζ-potential values. On the other hand, the adsorption study demonstrated that decreasing the side chain lengths lead to higher adsorption of PCE copolymers while Copolymers with COO^- groups were found to be adsorbed more than SO₃^- counterparts. These results are further confirmed with the rheological studies and it is found that the shorter the side chain, the lower the yield stress and the higher the dispersion of cement pastes but to a limited effect. Additionally, the charge types have a major influence on the performance of superplasticizers. This study could make further progress in establishing superplasticizers with controlled architectures for better performance.

Synthesis and characterization of comb-shaped copolymer as a filtration reducer and comparison with counterparts

A comb-shaped copolymer of 2-acrylamide-2-methyl propane sulfonic acid (AMPS), allyl polyoxyethylene ether (APEG), N-vinyl-2-pyrrolidone (NVP) and sodium styrene sulfonate (SSS) was synthesized by free-radical polymerization. The structure of the comb-shaped copolymer was characterized by Fourier transform infrared (FTIR) spectroscopy, and its molecular weight was determined by gel permeation chromatography (GPC). FTIR measurements and environmental scanning electron microscopy (ESEM) analysis were used to characterize the working mechanism of different filtrate loss reducers. Thermogravimetry and differential scanning calorimetry (TG-DSC) results showed that thermal degradation of the copolymer was significant only after 295.24 °C. The comb-shaped copolymer helped reduce filtration, while maintaining the rheological properties of the drilling fluid at high temperature and high salinity conditions as long PEG chains sterically stabilized colloids by protruding into the suspension. The filtration control of the comb-shaped copolymer was comparable to that of the sulfonated phenolic resin (SMP) mixture and outperformed AM/AMPS/NVP/SSS (NS-1) and polymeric product PAC in terms of high-temperature resistance and rheological advantages. The morphology of the comb-shaped copolymer was found with a compact 3-D film structure due to the intramolecular and intermolecular association by hydrogen bonding in the side chains. Small curly debris at high temperature and salinity remained capable of filtration control. The NS-1 had a lower temperature resistance, as large areas of flaky films thermally degraded into a small chain structure at 180 °C. Only separated filiform and coarse lines were found in PAC with a linear structure that makes the drilling fluid more viscous. Compact and structured films were formed with the SMP mixture at high temperature and salinity.

Comb-shaped copolymer as filtration reducer for high temperature and high salinity.

Poly(carboxylate ether)-based superplasticizer achieves workability retention in calcium aluminate cement

Calcium aluminate cement (CAC) suffers from loss of workability in less than an hour (~15 minutes) after first touch of water. Current superplasticizers that are utilized to modify the viscosity of cement admixtures are designed to target ordinary Portland cement (OPC). The high affinity between these superplasticizers and cement particles were found to be detrimental in CAC systems. Utilization of a monomer that, instead, facilitates gradual adsorption of a superplasticizer provides workability retention. For the first time in literature, we report a superplasticizer that caters to the properties of CAC such as high rate of surface development and surface charge. While neat CAC was almost unworkable after 1 hour, with the addition of only 0.4% of the optimized superplasticizer, 90% fluidity retention was achieved.

Effect of structure of cationic comb copolymers on their adsorption and stabilization of titania nanoparticles

Cationic linear polymer poly([2-(methacryloyloxy)ethyl] trimethylammonium chloride) p(METAC), neutral brush polymer poly(poly(ethylene glycol) methyl ether methacrylate) p(PEO22MEMA), and cationic comb copolymers p(METAC-PEO(x)MEMA) were used for the stabilization of titania dispersions under neutral and alkaline conditions. Random comb copolymers p(METAC-PEO(x)MEMA) differing in charge density and length of PEO side chains were synthesized by RAFT. The adsorption of cationic polymers on titania nanoparticles was evaluated by thermogravimetric analysis; changes in surface potential, by measuring the zeta potential; and the stability of the treated TiO2 dispersions, by laser diffraction and DLS. Cationic linear and comb copolymers containing relatively short PEO side chains promoted the inversion of nanoparticle surface potential from strongly negative (-60 mV) to moderately positive (10-35 mV). Cationic comb copolymers containing longer PEO side chains increased the zeta potential of the treated nanoparticles but did not invert it to positive. Aqueous dispersions of titania nanoparticles stabilized by cationic comb copolymers under alkaline conditions (pH 10) were dispersed by high-energy planetary ball milling up to a primary particle size of 20 nm and were stable for at least 2 days.

Surface Modification of Multiwalled Carbon Nanotubes with Engineered Self-Assembled RAFT Diblock Coatings

A facile method to modify the surface of multiwalled carbon nanotubes (MWCNTs) via electrostatic interactions between polyelectrolytes and oxidized MWCNTs was developed. Diblock copolymers containing poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC), a positively charged block, and poly(ethylene glycol) methacrylate (PEGMA), a neutral block, with tailored molecular weights and low polydispersities were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Acid treated-MWCNTs were coated with the RAFT diblock copolymers to improve their dispersibility in aqueous phosphate buffered saline (PBS) solution. The short positively charged PMETAC block was designed to attach the block copolymers to the surface of MWCNTs via electrostatic interactions, whereas the PEGMA block improved dispersibility of the MWCNTs in aqueous solutions. Extensive screening of the diblock copolymers with different degrees of polymerization (DP) showed that the dispersion stability of the polymer-coated MWCNTs in PBS was greatly improved with increasing chain length of the PEGMA block. In particular, the MWCNTs coated with a diblock copolymer containing PEGMA (DP = 118, the longest block investigated) showed superior dispersion stability in both water and PBS solution.

Reactive adsorption of PS-PMMA block copolymers on concave alumina surfaces

The influence of pore size, relative block size, and solvent quality on the extent of diblock copolymer adsorption on alumina surfaces was determined. To this end, the block copolymer that was chosen was poly(styrene)-b-poly(methyl methacrylate) (PS-b-PMMA), in which the PMMA block strongly chemisorbs to the surface and the PS block weakly physisorbs. Several architectures (i.e., different ratios of M(n(PMMA)) and M(n)((PS))) of the PS-b-PMMA copolymers were adsorbed from various solvents onto porous alumina membranes with various pore sizes. It was determined that the diblock copolymer coverage decreased significantly as the pore size decreased, similar to the behavior of the PMMA homopolymer under the same conditions. However, the coverage decreased as the molecular weight of the anchoring block (PMMA) increased for all pore sizes, which is in contrast to the behavior of the PMMA homopolymer under the same conditions. The dependence of the coverage on the relative block size and solvent quality is analyzed on the basis of the anchor-buoy model and the deviation from it in a nonideal system. The results presented in this work are relevant to the study of block copolymer conformation in solutions and on surfaces, adsorption chromatography, and solvent sensors and controls.

Self-assembled Polyion Complex Micelles based on PVP-b-PAMPS and PVP-b-PDMAEMA for Drug Delivery

The double hydrophilic block copolymer, poly(N-vinylpyrrolidone)-block-poly(2-acrylamido-2-methyl-1-propanesulfonic acid), was synthesized by reversible addition-fragmentation chain transfer RAFT polymerization. Gel permeation chromatography, 1H-NMR, and FTIR were used to determine the structure and composition. In aqueous media, this block copolymer spontaneously forms polyion complex (PIC) micelles with an oppositely charged block copolymer, poly(N-vinylpyrrolidone)-block-poly(N, N-dimethylaminoethyl methacrylate). Dynamic light scattering and transmission electron micrograph showed that the micelles were <200 nm in diameter and had a narrow single distribution. The release profiles of folic acid, incorporated into the micelles, showed remarkable pH responsive behavior. The PIC micelles exhibited good biocompatibility based on MTT assay with human embryonic kidney (HEK293) cells. These PIC micelles have the potential as pH-sensitive carriers for drug delivery.

Living Radical Polymerization by the RAFT Process - A Second Update

This paper provides a second update to the review of reversible deactivation radical polymerization achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition–fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379–410). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669–692). This review cites over 500 papers that appeared during the period mid-2006 to mid-2009 covering various aspects of RAFT polymerization ranging from reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses and a diverse range of applications. Significant developments have occurred, particularly in the areas of novel RAFT agents, techniques for end-group removal and transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.