Bert Klumperman

Controlled radical copolymerization of styrene and maleic anhydride and the synthesis of novel polyolefin-based block copolymers by reversible addition-fragmentation chain-transfer (RAFT) polymerization

Reversible addition–fragmentation chain transfer (RAFT) was applied to the copolymerization of styrene and maleic anhydride. The product had a low polydispersity and a predetermined molar mass. Novel, well-defined polyolefin-based block copolymers were prepared with a macromolecular RAFT agent prepared from a commercially available polyolefin (Kraton L-1203). The second block consisted of either polystyrene or poly(styrene-co-maleic anhydride). Furthermore, the colored, labile dithioester moiety in the product of the RAFT polymerizations could be removed from the polymer chain by UV irradiation.

Self-healing systems based on disulfide–thiol exchange reactions

New thermoset systems based on disulfide bonds were synthesized with self-healing capabilities. The self-healing mechanism is not related to disulfide–disulfide exchange reactions, but to thiol–disulfide exchange reactions that are pH-dependent. Stress relaxation experiments showed large relaxation for systems having PTM2 as a curing agent, which indicates that the system can rearrange its molecular structure as a mechanism to release stress. However, relaxation rates decreased for samples tested longer after production. This indicates the disappearance of thiol-groups probably caused by thiol–thiol oxidation.

Chain Transfer to Polymer and Branching in Controlled Radical Polymerizations of n-Butyl Acrylate

Chain transfer to polymer (CTP) in conventional free-radical polymerizations (FRPs) and controlled radical polymerizations (ATRP, RAFT and NMP) of n-butyl acrylate (BA) has been investigated using (13) C NMR measurements of branching in the poly(n-butyl acrylate) produced. The mol-% branches are reduced significantly in the controlled radical polymerizations as compared to conventional FRPs. Several possible explanations for this observation are discussed critically and all except one refuted. The observations are explained in terms of differences in the concentration of highly reactive short-chain radicals which can be expected to undergo both intra- and inter-molecular CTP at much higher rates than long-chain radicals. In conventional FRP, the distribution of radical concentrations is broad and there always is present a significant proportion of short-chain radicals, whereas in controlled radical polymerizations, the distribution is narrow with only a small proportion of short-chain radicals which diminishes as the living chains grow. Hence, irrespective of the type of control, controlled radical polymerizations give rise to lower levels of branching, when performed under otherwise similar conditions to conventional FRP. Similar observations are expected for other acrylates and monomers that undergo chain transfer to polymer during radical polymerization.

RAFT mediated polymerisation in heterogeneous media

Reversible addition fragmentation chain transfer (RAFT) mediated polymerisation is one of a number of living radical polymerisation processes that were developed over the last decade. The RAFT process is facilitating the synthesis of controlled macromolecular architectures radical polymerisation in homogeneous and heterogeneous media. Here we discuss the progress in the use of the RAFT process, the past, the state of the art and potential directions for the future with specific emphasis on heterogeneous reactions.

A MECHANISTIC PERSPECTIVE ON SOLVENT EFFECTS IN FREE-RADICAL COPOLYMERIZATION

1. INTRODUCTION The ability of solvents to affect the homopropagation rate of many common monomers has been widely documented. For example, Bamford and Brumby [1] showed that the propagation rate kp of methyl methacrylate (MMA) at 25°C was sensitive to a range of aromatic solvents. Burnett, Cameron, and Joiner [2] found that the kp of styrene (Sty) was depressed by increasing concentrations of benzonitrile, bromobenzene, diethyl phthalate, dinonyl phthalate, and diethyl malonate, while in other studies [3, 4], they found that the kp for MMA was enhanced by halobenzenes and naphthalene. More recent work by Zammit et al. [5] has shown that solvents capable of hydrogen bonding, such as benzyl alcohol and N-methyl pyrrolidone, have a small influence on both the activation energy Ea and preexponential factor A in Sty and MMA homopropagation reactions. These are but a few of the many instances of solvent effects in the homopolymerization reactions of two typical monomers, Sty and MMA. For these monomers, solven...

Critical retention behaviour of polymers a study on the influence of some practical parameters

Liquid chromatography under critical conditions is an important tool for the microstructural characterization of telechelic polymers and block copolymers. Until now, only little information on the practical aspects of this technique is available. The influence of some important practical parameters was investigated, using polystyrene. Critical conditions depend strongly on the type of column packing. The solubility of polymers under critical conditions for different solvent-non-solvent combinations differs to a great extent. For different solvent-non-solvent pairs on reversed-phase systems, a roughly constant eluent strength in terms of the Hildebrand solubility parameter, under critical conditions is found. Temperature can be a useful tool for fine-tuning critical conditions. On normal-phase systems, however, the retention of polystyrene changes non-monotonously with temperature, which limits the use of temperature variations. It is not possible to obtain exact molecular mass independence on any of the investigated systems, which can not be ascribed to chemical differences. This makes the validity of the current theories on critical conditions questionable. Especially for the higher-molecular-mass polystyrenes, peak broadening increases significantly when going from size exclusion conditions to critical conditions. This phenomenon can limit the application of liquid chromatography under critical conditions to a certain molecular mass range. The composition of the solvent in which polystyrenes are dissolved prior to injection, has to be exactly the critical solvent composition, in order to suppress zone splitting as much as possible. For higher-molecular-mass polystyrenes this effect cannot be completely prevented.

Polymer–protein conjugates from ω-aldehyde endfunctional poly(N-vinylpyrrolidone) synthesised via xanthate-mediated living radical polymerisation

Aldehyde omega-endfunctional poly(N-vinylpyrrolidone) was synthesised via quantitative conversion of a xanthate endfunctional precursor obtained via RAFT-mediated polymerisation.

Release of bacteriocins from nanofibers prepared with combinations of poly(D,L-lactide) (PDLLA) and poly(ethylene oxide) (PEO)

Plantaricin 423, produced by Lactobacillus plantarum, and bacteriocin ST4SA produced by Enterococcus mundtii, were electrospun into nanofibers prepared from different combinations of poly(d,l-lactide) (PDLLA) and poly(ethylene oxide) (PEO) dissolved in N,N-dimethylformamide (DMF). Both peptides were released from the nanofibers with a high initial burst and retained 88% of their original antimicrobial activity at 37 °C. Nanofibers have the potential to serve as carrier matrix for bacteriocins and open a new field in developing controlled antimicrobial delivery systems for various applications.

Interpreting the copolymerization of styrene with maleic anhydride and with methyl methacrylate in terms of the bootstrap model

Abstract The bootstrap model was proposed by Harwood to explain copolymer sequence distribution which is dependent only on copolymer composition in solvents which cause changes in the apparent reactivity ratios for a number of pairs of monomers. This work presents an explicit formulation of the equations describing copolymer composition and sequence distribution in terms of the bootstrap model for both the simple Mayo-Lewis model and the penultimate unit model. Inspection of these equations reveals the necessary and sufficient conditions for sequence distribution to be a function only of copolymer composition. The results of copolymerizations of styrene with methyl methacrylate and with maleic anhydride under various conditions are interpreted in terms of the bootstrap model.

Determination of the chemical composition distribution of copolymers of styrene and butadiene by gradient polymer elution chromatography

Abstract In order to determine the chemical composition distribution (CCD) of styrene-butadiene copolymers, gradient polymer elution chromatography has been performed. The separation is mainly based on differences in solubility among the copolymer molecules with different chemical composition. The solubility of a copolymer is dependent on the following parameters: temperature, type of solvent/non-solvent mixture, molecular mass of the polymer and the chemical composition of the polymer. The resolution of the gradient polymer elution chromatographic separation and the molecular mass dependency are influenced by the solvent/non-solvent combination. In order to obtian a reliable separation according to chemical composition, the differences in solubility must be sufficientyl high and the molecular mass dependence must be negligible. In order to separate styrene-butadiene copolymers, synthesized by emulsion polymerization, a tetrahydrofuran-acetonitrile gradient was used. After calibration of the chromatographic system with styren-butadiene copolymer standards, the CCD of styrene-butadiene copolymers could be calculated.