Mechanism of electropolymerisation of methyl methacrylate and glycidyl acrylate on stainless steel

An aqueous based technique for producing uniform, thin, passive films of poly(methyl methacrylate) (PMMA) and poly(glycidyl acrylate) (PGA) on stainless steel electrodes has been developed. A cathodic free radical polymerisation mechanism is proposed based upon the results of cyclic voltammetry (CV), mechanistic electro-polymerisation and gel permeation chromatography (GPC) experiments. The polymerisation yield was increased by a synergistic relationship between sulphuric acid and potassium persulphate initiators, proposed to involve the formation of long-lived radical species. Termination reactions are believed to be inhibited by the formation of co-ordination complexes between the growing polymer chain and sulphuric acid. The mechanism accounts for the broad molecular weight distribution, cross-linking and post-electrolysis polymerisation, where polymer continued to form after the current flow ceased.     

Directional polymerisation and electronic properties of a cyanosubstituted dialkylpolyphenylenevinylene

Summary The synthesis of a monomer allowing for directional polymerisation based on the Knoevenagel condensation reaction is presented. The free running polymerisation gave a molecular weight (M _w = 24650 g mol^-1) polymer product. The polymerisation reaction could be followed by size exclusion chromatography (SEC) and the molecular weight of the polymer product could be controlled by termination of the polymerisation reaction at a suitable time. When terminated before completion a lower molecular weight product was obtained that could be separated into oligomers using preparative SEC. The polymer product and the oligomers were found to have very similar physical properties in terms of the optical band gaps, electronic energy levels and charge carrier mobilities as studied by UV-vis and pulse radiolysis time resolved microwave conductivity (PR-TRMC). Finally the positions of the filled energy levels were determined using ultraviolet photoelectron spectroscopy (UPS).This revised version was published online in September 2004. Due to technical problems, the previous version contained an incomplete PDF.     

Surface-initiated atom transfer radical polymerization of methyl methacrylate on magnetite nanoparticles

The synthesis of magnetite nanoparticles coated with a well-defined graft polymer is reported. The magnetite nanoparticles with an initiator group for copper-mediated atom transfer radical polymerization (ATRP), 2-(4-chlorosulfonylphenyl) ethyltrichlorosilane (CTCS) chemically bound on their surfaces were prepared by the self-assembled monolayer-deposition method. The surface-initiated ATRP of methyl methacrylate (MMA) was carried out with the CTCS-coated magnetite nanoparticles in the presence of free (sacrificing) initiator, p-toluenesulfonyl chloride. Polymerization proceeded in a living fashion, exhibiting first-order kinetics of monomer consumption and a proportional relationship between molecular weight of the graft polymer and monomer conversion, thus providing well-defined, low-polydispersity graft polymers with an approximate graft density of 0.7 chains/nm². The molecular weight and polydispersity of the graft polymer were nearly equal to those of the free polymer produced in the solution, meaning that the free polymer is a good measure of the characteristics of the graft polymer. The graft polymer possessed exceptionally high stability and remarkably improved dispersibility of the magnetite nanoparticles in organic solvent.     

Star oligomers for low VOC polyurethane coatings

Conclusion  Hydroxyl functional star oligomers prepared by ring-opening polycondensation have a narrow molecular weight and composition distribution. Such oligomers give a solids/viscosity advantage over linear structures at the same molecular weight and can be used in low VOC two component polyurethane coatings. The solids/viscosity advantage is a combination of the highly branched structure and the narrow molecular weight distribution. Acrylic polyols formulated at the same molecular weight/polarity/average functionality and hydroxyl value give poorer drying properties. This difference can be explained by the fact that the free radical polymerisation technique leads to polymer compositions having a broad molecular weight and functionality distribution and high fractions of polymer with a low functionality. The potlife of acrylic polyols based formulations is adversely affected by the higher fractions of high molecular weight material and with a high average functionality. In low VOC polyurethane formulations star oligomers need to be formulated within a narrow range of compositions (TG, polarity), functionality and molecular weight to get an optimum balance of drying properties and potlife.     

Nanomorphology control in aqueous coatings

Using catalytic chain transfer polymerisation (CCTP) in emulsion polymerisation results in efficient molecular weight reduction. An additional benefit of polymers prepared with CCTP is that they have a chain terminal unsaturated group that can be used in a subsequent graft copolymerisation to yield comb-shaped polymer chains. By careful optimisation of the polymer parameters, film properties can be optimised to yield coatings with very interesting combinations of properties.     

Exploratory experiments on the fast anionic polymerisation of styrene

The limitations in the rates of polymerisation associated with the free radical process do not arise when styrene is polymerised by an anionic catalyst such as butyl lithium. However, if anionic catalysts are directly applied to pure styrene a thermal explosion follows. Some experiments are described in which sufficient low molecular weight polystyrene resin was added to the styrene to prevent boiling and the polymerisation was completed with butyl lithium. In spite of the dilution by low viscosity polymer, average molecular weights were obtained approaching those required for commercial polymer. Although purification criteria would have to be met there seems to be no fundamental obstacle to the development of small, high output polymerisation plants for making polystyrene.     

Polymerisation of butadiene in the presence of carbon tetrabromide

Studies of the polymerisation of butadiene in the presence of carbon tetrabromide in bulk and emulsion systems have shown that in both systems telomers are the first products of reaction. These consist of between 4–10 butadiene units with terminal allylic bromine and tribromomethyl groups. However, the fact that the telomers function as chain transfer agents through the terminal tribromomethyl group to produce diallylic bromine terminated low molecular weight polymers is unique to the emulsion system. Telomers prepared in bulk and emulsion have been isolated, characterised and the kinetics of their formation studied. Kinetic analysis has indicated that at low molecular weights an increase in polymerisation rate with increasing carbon tetrabromide concentration is predicted, but it is postulated that the telomer itself can initiate polymerisation. Telomers formed in either bulk or emulsion have been studied as chain transfer agents in the polymerisation of butadiene in emulsion at 60°C. Polymerisation rate decreases with increasing amount of chain transfer and it is postulated that degradative chain transfer plays a role in the polymerisation. A simplified kinetic scheme for retarded polymerisation has been developed to analyse the results. It is postulated that radical termination is by cross termination of growing polymer radicals with telomer radicals.     

PEO-functionalized polystyrene as polymeric support in metallocene catalysed olefin polymerisation

Summary A new catalyst system based on easily accessible cross-linked (by Diels-Alder reaction) polymeric supports, functionalized with nucleophilic polyethyleneoxide-monomethylether (PEO-M) is presented. The metallocene-MAO complex is noncovalently bonded to the support, avoiding a complicated polymer analogous metallocene synthesis. The polymerisation of propene and ethene with Me₂Si(2MeBenzInd)₂ZrCl₂ as metallocene is performed using this support. The resulting polymers have high molecular weights and melting points and narrow molecular weight distribution. Polypropene is produced with 95% isotacticity similar to that from homogeneous catalysis. The productivities of up to 8600 for polypropene and 1300 for polyethene ( kg polymer / mol Zr h bar ) are comparably high. The product beads exhibit a good morphology, which can be explained by fragmentation processes of the support due to the reversibility of the network formation. Received: 21 February 2001/Revised version: 2 November 2001/ Accepted: 6 November 2001     

Precipitation polymerisation of vinylidene fluoride in supercritical CO2 and real-time calorimetric monitoring

Vinylidene fluoride was polymerised in supercritical carbon dioxide. Power compensation calorimetry was used to monitor the polymerisation process on-line. The polymer product was found to have a low apparent-density, leading to an observed high solid content in the autoclave at low yields. In situ calorimetry showed a sharp transition of the heat transfer in the reactor, leading to a useful parameter for monitoring the polymerisation process. The stirring rate was found to have no effect on the molecular weight, but did modify the calorimetric traces and the morphology of the polymer. The polymerisation at a lower pressure resulted in a lower molecular weight product and a lower polymerisation rate.     

The characterisation of polycarbonate-containing graft copolymers and the kinetics of graft polymerisation

This paper examines several procedures for selective degradation of the preformed polymer component (polycarbonate) of certain types of graft copolymers. A procedure based on a two-phase alkaline hydrolysis of the polycarbonate is identified as the preferred technique because it provides a clean system for the quantitative recovery and subsequent characterisation of the grafts. The application of the technique to a series of polycarbonate/polystyrene graft copolymers is reported. The kinetics of free-radical graft polymerisation of styrene and the molecular weight distributions of the polystyrene grafts are compared with those for styrene homopolymerisation performed at the same rates of initiation. This comparison allows several differences between the kinetics of graft and homopolymerisation to be identified, both prior to and after gelation. These factors are interpreted in terms of modifications to the rate coefficient for bimolecular termination of the propagating grafts. Two (possibly three) factors are identified which influence the polymerisation kinetics prior to gelation; their influences are contrary and their relative importances depend on the rate of initiation. After gelation an additional effect, termed the network effect, comes into force and dominates both the rates of graft polymerisation and the molecular weight distributions of the grafts.     

Synthesis, characterization, and electrospinning of zwitterionic poly(sulfobetaine methacrylate)

Poly(sulfobetaine methacrylate) (PSBMA) can be potentially utilized in filtration and wound dressing applications for which nanofibers structures are highly desirable. In this work, a series of PSBMAs with different molecular weights were synthesized, characterized, and electrospun into nanofibers. The polymer molecular weight was controlled by varying the amount of redox initiators in the free radical polymerization of SBMA, with the highest molecular weight achieved at an intermediate initiator concentration. From the intrinsic viscosity measurements, the Mark-Houwink parameters for PSBMA (at 21 °C in 0.2 M NaCl solution) was determined as a = 0.4071 and k = 2.06 × 10⁻³. Thermogravimetric (TGA) analysis shows that the PSBMAs were thermally stable up to at least 250 °C. Fourier transform infrared (FTIR) spectra indicate major structural changes of both polymer backbone and pendant groups by thermal degradation. Results from differential scanning calorimetry (DSC), TGA, and FTIR characterizations all demonstrate the existence of water strongly bound in PSBMA. DSC analysis also indicates different degrees of crystallinity for the PSBMAs of different sizes. Viscosity of the PSBMA solutions, a critical parameter for electrospinning, increased with the solution concentration and the polymer molecular weight. For the electrospinning of PSBMA, it was found that high solution concentration and high molecular weight favored the formation of smooth fibers while low solution concentration or low molecular weight led to the formation of beaded fibers or beads. Fiber diameters ranging from 200 to 570 nm were achieved by controlling solution concentration and polymer molecular weight. The characterization data and electrospinning results were finally correlated to explore the relationships between fiber formation, viscosity, molecular weight, and concentration.     

Synthesis,characterisation and flame,thermal and electrical properties of poly (<Emphasis Type="Italic">n</Emphasis>-butyl methacrylate)/titanium dioxide nanocomposites

Nanocomposites based on poly (n-butyl methacrylate) (PBMA) with various concentrations of titanium dioxide (TiO₂) nanoparticles were synthesised by in situ free radical polymerisation method. The formation of nanocomposite was characterised by FTIR, UV, XRD, DSC, TGA, impedance analyser and flame retardancy measurements. FTIR and UV spectrum ascertained the intermolecular interaction between nanoparticles and the polymer chain. The XRD studies indicated that the amorphous region of PBMA decreased with the increase in content of metal oxide nanoparticles. The SEM revealed the uniform dispersion of nanoparticles in the polymer composite. The DSC and TGA studies showed that the glass transition temperature and thermal stability of the nanocomposites were increased with the increase in the concentration of nanoparticles. The conductivity and dielectric properties of nanocomposites were higher than pure PBMA and the maximum electrical property was observed for the sample with 7 wt% TiO₂. As the concentration of nanoparticles increased above 7 wt%, the electrical property of nanocomposite was decreased owing to the agglomeration of nanoparticles in the polymer. Nanoparticles could impart better flame retardancy to PBMA/TiO₂ composite and the flame resistance of the materials improved with the addition of nanoparticles in the polymer matrix.     

Self-assembly of water insoluble polymers into Colloidal Unimolecular Polymer (CUP) particles of 3–9 nm

Colloidal Unimolecular Polymer, CUP, particles were synthesized and characterized as a potential new and useful spheroidal polymer conformation for a variety of applications. Also known as single chain nanoparticles, these nanomaterials are gaining in popularity. The route to CUP particle formation is an innovative approach utilizing a small number of hydrophilic groups along a hydrophobic polymer backbone which transitions from a random coil conformation in organic solvent to a hard sphere in water through a slow gradient with subsequent solvent removal. The CUP particles have diameters which are proportional to their molecular weights and range typically from 3 nm to over 9 nm. These CUP particles were stable in water and free of solvent or surfactants. The sodium or potassium salts of CUP particles are spheroidal and are able to be dried then re-dissolved in water with no aggregation, unlike the original polymer. The diameters of the CUP particles correlate with the absolute number average molecular weight (M_n) and distributions from the GPC. Molecular weights from 28K to 122K are reported here and are based on an acrylic copolymer having a molar ratio of 9:1 MMA:MAA.     

Synthesis and polymerisation of polycyclic compounds with strained C—C single bonds

Ring opening polymerisation of bicyclobutanes possessing electronegative substituents (CN, COOCH₃, etc.) at one or both bridgeheads can be accomplished readily with either radical or anionic initiators. The polymer chains consist exclusively of cyclobutane rings linked through the 1,3 positions. Readily obtained in high molecular weight, they possess attractive physical properties for the formation of fibres and films. These new monomers copolymerise readily with vinyl compounds, exhibiting reactivities comparable to the latter, and provide a wide variety of new copolymers. Other bicyclic compounds containing strained C—C bonds whose polymerisation has been demonstrated include bicyclo-[2.1.0]-pentane-1-carbonitrile, 1-methyl-2,3-benzocyclopropenecarbonitrile, and 1,3-dehydroadamantane. The ability to polymerise requires a high strain energy, but a high degree of p character in the C—C single bond as well.     

Stochastic model for living radical polymerisation of styrene initiated by epoxide radical ring opening

A stochastic model was developed to simulate the polymerisation kinetics and the detailed microstructure of the resulting polymers made by the living radical polymerisation of styrene initiated by epoxide radical ring opening. The model was used to predict monomer conversion, average molecular weight, polydispersity index, and molecular weight distribution as a function of polymerisation time. Simulations were used to explore the effects of rate constant values on chain microstructures and polymer properties and validated with experimental data published in the literature. It was found that some parameters, such as the exchange rate constant, have no significant effect on the polymerisation kinetics, whereas major effects were observed when other rate constants, such as the reduction rate constant, were changed.     

Macromolecular engineering: a synthetic perspective

Abstract

It has long been a desire for both the polymer academic and industrial (production and process) communities to gain a true understanding of the effects of molecular architecture variables upon polymer properties and the implications for polymer process engineering. It has also long been realised that the greatest chance of gaining this insight is not to work with industrial grade materials, which are usually polydisperse both in terms of molecular weight and architecture, but to study model polymers, synthesised in the laboratory, usually by technically challenging methods such as anionic polymerisation. It is only by using polymers in which the molecular variables such as molecular weight, polydispersity and long chain branching are controlled with a high degree of precision, that we can hope to correlate these variables with key physical properties such as melt rheology, crystallinity and solid state properties. As polymer theoreticians develop ever more sophisticated models to predict the relationships between molecular structure and physical properties the challenge to the synthetic polymer chemist is to design and build (engineer) ever more complex yet well defined molecular structures to allow experimental validation (or otherwise) of the models. Here the author discusses how the synthetic chemist has risen to meet that challenge over the years.     

Design of biocompatible surface-modified polyurethane and polyurea nanoparticles

This study is focused to design systems of polyurethane and polyurea nanoparticles prepared via interfacial polycondensation in O/W nano-emulsions with biocompatible components suitable for drug delivery systems. Polyurethane and polyurea nanoparticles with a small diameter (50–90 nm) and high kinetic stability were developed from O/W nano-emulsions in aqueous solution/polysorbate 80/oil systems. The influence of several factors on the particle size and polydispersity index was studied. The monomer concentration, oil/surfactant weight (O/S) ratio, polymerisation temperature and components that can be located in the droplet interface and the dispersed phase of nano-emulsion played a key role in the formation of these nanoparticle systems. The biocompatibility of these nanoparticles was assessed using haemolysis and cell viability assays. No significant haemolysis and low effects on human endothelial cell viability were obtained after incubation with nanoparticles. Therefore, herein we provide useful information for the development of biocompatible drug carriers using polyurethanes and polyureas.     

Synthesis of poly(vinyl alcohol)s with narrow molecular weight distribution from poly(benzyl vinyl ether) precursors

Summary A series of poly(benzyl vinyl ether)s of low molecular weight (5000 to 15000 g mol^-1) and narrow molecular distribution ( ) have been synthesisedvia the cationic polymerisation of benzyl vinyl ether. Acetylation with acetic anhydride/tin (IV) chloride leads to poly(vinyl acetate), which can be hydrolysed to near-monodisperse water-soluble poly(vinyl alcohol) with an isotacticity of approximately 47%. This polymer was re-acetylated and its molecular weight distribution assessed to confirm that hydrolysis gives minimal chain scission.     

A convenient route to high molecular weight highly isotactic polystyrene using Ziegler-Natta catalysts and ultrasound

Ziegler-Natta (TiCl₄/AlEt₃) catalysts and ultrasound were used to prepare highly isotactic polystyrene (ca. 99%) with a molecular weight of 4.7×10⁶ mol g⁻¹ and low molecular weight distribution (M_w/M_n=1.6) via a convenient method. Ultrasound was most effective if applied only during an initial stage in the polymerisation, most likely permitting dispersion of catalyst particles which were subsequently coated and separated by growing polymer chains. Yields could be improved by varying the amount of catalyst and reaction time.     

Janus gold nanoparticle with bicompartment polymer brushes templated by polymer single crystals

Janus particles have attracted increasing attention from the communities of materials science, chemistry, physics and biology. While large size Janus particles are readily achieved, synthesizing Janus nanoparticles (JNP) with diameters smaller than ∼20 nm remains a challenging task. In this article, we report a systematic study on growing polymer brushes on polymer-single-crystal-immobilized 6 and 15 nm diameter gold nanoparticles (AuNPs) using atom transfer radical polymerization. JNPs with bicompartment polymer brushes, such as poly(ethylene oxide) (PEO)/poly(methyl methacrylate), PEO/poly(tert-butyl acrylate), and PEO/poly(acrylic acid), were synthesized. The grafting densities can be carefully controlled. The Janus feature of these particles was confirmed using both platinum nanoparticle decoration and UV/Vis spectroscopy analysis. The surface plasmon resonance absorbance of Janus particles exhibited a blue shift compared with that of symmetric AuNPs with either homopolymer or mixed polymer brushes. This work demonstrated that using polymer single crystal as the templates, small size (<20 nm diameter) JNPs having bicompartment polymer brushes can be readily obtained. The ability to tune grafting density and molecular weight of polymer brushes can lead to controlled particle amphiphilicity.