Johan P. A. Heuts

Polymer Encapsulated Gibbsite Nanoparticles: Efficient Preparation of Anisotropic Composite Latex Particles by RAFT-Based Starved Feed Emulsion Polymerization

Anisotropic polymer-inorganic composite latex particles were synthesized by using a RAFT-based encapsulation approach on cationic gibbsite platelets. By using the RAFT agent dibenzyl trithiocarbonate, a series of amphipatic living random RAFT copolymers with different combinations of acrylic acid and butyl acrylate units were synthesized. These RAFT copolymers were used as living stabilizers for the gibbsite platelets and chain extended to form a polymeric shell by starved feed emulsion polymerization. Cryo-TEM characterization of the resulting composite latexes demonstrates the formation of anisotropic composite latex particles with mostly one platelet per particle. Monomer feed composition, chain length, and hydrophilic-lipophilic balance of the RAFT copolymer were found to be important factors for the overall efficiency of the encapsulation. Good control over platelet orientation and high encapsulation efficiency were achieved via this route.

Catalytic chain transfer and its derived macromonomers

An overview is given of cobalt-catalyzed chain transfer in free-radical polymerization and the chemistry and applications of its derived macromonomers. Catalytic chain transfer polymerization is a very efficient and versatile technique for the synthesis of functional macromonomers. Firstly the mechanism and kinetic aspects of the process are briefly discussed in solution/bulk and in emulsion polymerization, followed by a description of its application to produce functional macromonomers. The second part of this review briefly describes the behavior of the macromonomers as chain transfer agents and/or comonomers in second-stage radical polymerizations yielding polymers of more complex architectures. The review ends with a brief overview of post-polymerization modifications of the vinyl endfunctionality of the macromonomers yielding functional polymers with applications ranging from initiators in anionic polymerization to end-functional lectin-binding glycopolymers.

Effect of glycounits on the antimicrobial properties and toxicity behavior of polymers based on quaternized DMAEMA

Polymers with quaternary ammonium groups such as quaternized poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMAQ) have been used as antimicrobial agents because of their demonstrated good antimicrobial activities against a huge number and types of microbes, although their cytotoxicity is also well-known. In this work block copolymers based on PDMAEMAQ were synthesized containing hydrophobic segments of poly(butyl methacrylate) to improve the antimicrobial activity and glycomonomer units with the aim of decreasing the cytotoxicity of the polymers. Hydrophobic butyl methacrylate (BMA) blocks were chain extended by statistical and block copolymers of DMAEMA and 2-{[(d-glucosamin-2-N-yl)carbonylethyl methacrylate (HEMAGl) glycomonomer of different compositions. In order to find the balance between antimicrobial activity and cytotoxicity, the selectivity index of each polymer was obtained from minimum inhibitory concentrations (MIC) and white and red blood cells toxicity measurements.

Free-radical copolymerization of styrene and itaconic acid studied by 1H NMR kinetic experiments

The free-radical copolymerization of itaconic acid (IA) and styrene in solutions of dimethylformamide and d(6)-dimethyl sulfoxide (50 wt %) has been studied by H-1 NMR kinetic experiments. Monomer conversion versus time data were used to estimate the ratio k(p).k(t)(-0.5) for various comonomer mixture compositions. The ratio K-p.k(t)(-0.5) varies from 5.2.10(-2) for pure styrene to 2.0.10(-2)mol(0.5)L(-0.5)s(-0.5) for pure IA, indicating a significant decrease in the rate of polymerization. Individual monomer conversion versus time traces were used to map out the comonomer mixture-composition drift up to overall monomer conversions of 60%. Within this conversion range, a slight but significant depletion of styrene in the monomer feed can be observed. This depletion becomes more pronounced at higher levels of IA in the initial comonomer mixture. The kinetic information is supplemented by molecular weight data for IA/ styrene copolymers obtained by variation of the comonomer mixture composition. A significant decrease in molecular weight of a factor of 2 can be observed when increasing the mole fraction of IA in the initial reaction mixture from 0 to 0.5

Atom transfer radical copolymerization kinetics

Starting from the basic radical mechanism of atom transfer radical polymerization (ATRP), simple expressions are derived for the description of atom transfer radical copolymerization kinetics. It is shown that kinetic parameters are interchangeable between atom transfer and conventional free-radical copolymerization, which is important for two reasons. Firstly, it enables the prediction of the average equilibrium constant (and hence average rate of polymerization) in an ATRP system with two monomers if the corresponding conventional kinetic parameters are known. Secondly, it enables the determination of the relative fractions of propagating radicals by a detailed ATRP study.

Enhanced Selectivity for the Hydrolysis of Block Copoly(2-oxazoline)s in Ethanol–Water Resulting in Linear Poly(ethylene imine) Copolymers

The ability of merging the properties of poly(2-oxazoline)s and poly(ethylene imine) is of high interest for various biomedical applications, including gene delivery, biosensors, and switchable surfaces and nanoparticles. In the present research, a methodology for the controlled and selective hydrolysis of (co)poly(2-oxazoline)s is developed in an ethanol-water solvent mixture, opening the path toward a wide range of block poly(2-oxazoline-co-ethylene imine) (POx-PEI) copolymers with tunable properties. The unexpected influence of the selected ethanol-water binary solvent mixture on the hydrolysis kinetics and selectivity is highlighted in the pursue of well-defined POx-PEI block copolymers.

Glycoparticles and bioactive films prepared by emulsion polymerization using a well-defined block glycopolymer stabilizer

A well-defined amphiphilic diblock glycopolymer of poly(2-{[(D-glucosamin-2-N-yl)carbonyl]oxy}ethyl methacrylate)-b-poly(butyl methacrylate) (PHEMAGl-b-PBMA) was synthesized via atom transfer radical polymerization (ATRP). Due to its capability to form micelles in aqueous solution, the obtained block glycopolymer was used as polymeric surfactant in the emulsion polymerization of butyl methacrylate in order to prepare glycosylated polymer particles. Core–shell particles consisting of a soft core of poly(butyl methacrylate) covered with glycopolymer bearing glucose moieties were obtained. Then these latex particles were employed to prepare polymer films with active surface. The surface bioactivity of this polymer coating was examined using the specific lectin Concanavalin A, Canavalia ensiformis. The specific and successful binding to the Concanavalin A was demonstrated by both fluorescence microscopy and spectroscopy being more intense with increasing concentration of block glycopolymer surfactant. The good accessibility of the glucose moieties at the surface of the coating makes this method a powerful tool to achieve potential materials for biomedical applications involving molecular recognition processes.

Polyethylene end functionalization using thia-Michael addition chemistry

Thiol end functionalized polyethylenes (PE-SH, Mn around 1000 g mol−1, Đ < 1.3) were used as nucleophiles in thia-Michael additions with different acrylic molecules. It was found that under commonly used practical conditions the addition to methacrylates was very difficult, whereas addition to acrylates was very efficient. First, block copolymers based on PE and poly(methyl methacrylate) (PMMA) were targeted by reaction of PE-SH with PMMA obtained by catalytic chain transfer polymerization (CCTP). The reaction however failed and detailed model experiments using butanethiol and a dimer of MMA showed that the solubilization temperature of PE-SH was an impediment to the success of the reaction. The lack of reactivity towards PMMA obtained by CCTP and methacrylate functions was advantageously used to react molecules containing both an acrylate and a methacrylate group in the presence of tributyl phosphine (PBu3) to produce methacrylate-type PE macromonomers. The presence of a hydroxyl function on 3-(acryloyloxy)-2-hydroxypropyl methacrylate induced side trans-esterification reactions catalyzed by PBu3. This was overcome by using the hydroxyl free 2-(acryloyloxy) ethyl methacrylate. With the latter, the desired PE macromonomer exhibited a functionality as high as 85%. Alternatively, 2-isocyanatoethyl methacrylate could also be reacted with PE-SH to produce a highly functionalized methacrylate type PE macromonomer (functionality 89%). Eventually, the efficiency of the thia-Michael addition of PE-SH onto poly(ethylene glycol) acrylate (PEG-acrylate) was used to synthesize the PE-b-PEG block copolymer.

Conventional and catalytic chain transfer in the free-radical polymerization of 2-phenoxyethyl methacrylate

A comparative study was conducted on chain transfer mechanisms in the free radical polymerization of a viscous methacrylate, viz. 2-phenoxyethyl methacrylate. Two chain transfer agents were subjected to investigation: n-dodecanethiol (DDM) and bis[(difluoroboryl)diphenylglyoximato]cobalt (II) (COPhBF). The chain transfer constant (Cs) for DDM was found to be 0.7 (at 60 degrees C); a value comparable with the Cs value obtained for a low viscosity methacrylate, methyl methacrylate, under similar conditions. In contrast, the Cs value for COPhBF was found to be 2 x 10(3) (at 60 degrees C) which is one order of magnitude lower than the Cs value published for methyl methacrylate. This result is explained in terms of the different chain transfer mechanisms operating in the two polymerizing systems. Radical reactions with DDM involve a chemically controlled hydrogen transfer event, whereas experimental results obtained for the reaction of methacrylate radicals with COPhBF indicate a diffusion-controlled, rate determining step in the hydrogen transfer process. Thus in the reaction of COPhBF with 2-phenoxyethyl methacrylate radicals, the high viscosity reaction medium (monomer) has a significant influence on the transfer rate

Biocompatible and thermo-responsive nanocapsule synthesis through vesicle templating

Thermo-responsive and biocompatible cross-linked nanocapsules were synthesized through dimethyldioctadecylammonium bromide (DODAB) vesicle templating. For this, firstly two random copolymers, N-vinylcaprolactam (VCL) and acrylic acid (AA), with different chain lengths but using the same monomer ratio, were synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. These anionic random copolymers were adsorbed onto cationic DODAB vesicles. Then, biocompatible and thermo-responsive nanocapsules were obtained by semicontinuous emulsion polymerization under monomer-starved conditions for both the main monomer (VCL) and the cross-linker. Although in all the cases the typical thermal behavior of PVCL-based nanocapsules was observed, hysteresis between cooling and heating cycles was observed at low temperature in the case of non-cross-linked nanocapsules. This behavior was reduced using different types and amounts of cross-linkers. In addition, transmission electron microscopy (TEM) characterization demonstrated the successful formation of nanocapsules either with short or long random copolymers. The formation of stable nanocapsules was confirmed below and above the volume phase transition temperature (VPTT) by surfactant lysis experiments through optical density and DLS measurements in all the nanocapsules synthesized. These biocompatible and thermo-responsive nanocapsules could be suitable and potentially useful as nanocarriers for drug delivery.