Conventional Free Radical Polymerization Research Articles

One Pot Synthesis of Surface PEGylated Core–Shell Microparticles by Suspension Polymerization with Surface Enrichment of Biotin/Avidin Conjugation

Core-shell microparticles that consist of poly(vinyl neodecanoate) (VND) crosslinked with poly(ethylene glycol dimethacrylate) (EGDMA) as the core and poly(ethylene glycol methacrylate) (PEGMA) (Mn = 360 or Mn = 526 g . mol(-1)) as the shell have been synthesized using suspension polymerization by a conventional free radical polymerization process. Interfacial tension and stability tests show that PEGMA acts as an amphiphilic macromonomer and is located on the oil/water interface of the suspension system, thus forming an outer layer during the polymerization. Kinetic studies of the monomers' conversion of VND, EGDMA, and PEGMA have been carried out using (1)H NMR spectroscopy. EGDMA and PEGMA were found to have faster reaction rates compared to VND. Moreover, scanning electron microscopy showed that the polymerization of these particles starts from the shell and finishes towards the core. Consequently, the resulting microsphere is found to have a multi-layer structure. Biotin was covalently bound to the surface by the PEGMA hydroxy groups. Conjugation of biotin with streptavidin PE (phycoerythrin) was subsequently carried out. Confocal microscopy was used to confirm the presence of fluorescing streptavidin. The amount of avidin conjugated to the microspheres was calculated by the release of a 2-(4-hydroxyphenylazo)benzoic acid/avidin complex using UV/vis spectroscopy. One avidin molecule was found to occupy 7 nm(2) on the surface of the microspheres.

Core‐shell particles with glycopolymer shell and polynucleoside core via RAFT: From micelles to rods

AbstractAmphiphilic block copolymers were synthesized via the reversible addition fragmentation chain transfer (RAFT) copolymerisation of 2‐methacrylamido glucopyranose (MAG) and 5′‐O‐methacryloyl uridine (MAU). Homopolymerisations of both monomers using (4‐cyanopentanoic acid)‐4‐dithiobenzoate (CPADB) proceeded with pseudo first order kinetics in a living fashion, displaying linear evolution of molecular weight with conversion and low PDIs. A bimodal molecular weight distribution was observed for PMAU at low conversions courtesy of hybrid behavior between living and conventional free radical polymerization. This effect was more pronounced when a PMAG macroRAFT agent was chain extended with MAU, however, in both cases, good control was attained once the main RAFT equilibrium was established. A stability study on PMAU found that its hydrolysis is diffusion controlled, and is accelerated at physiological pH compared with neutral conditions. Self‐assembly of four block copolymers with increasing hydrophobic (PMAU) block lengths produced micelles, which demonstrated an increased tendency to form rods as the PMAU block length increased. Interestingly, none of the block copolymers were surface‐active. An initial assessment of PMAU's ability to bind the nucleoside adenosine through base pairing was highly promising, with DSC measurements indicating that adenosine is fully miscible in the PMAU matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1706–1723, 2009

Monte Carlo modelling of living branching copolymerisation of monovinyl and divinyl monomers: comparison of simulated and experimental data for ATRP copolymerisation of methacrylic monomers

Branching copolymerisation of a monovinyl monomer with a small amount of a divinyl monomer under pseudo-living conditions has been modelled using a Monte Carlo program written in C# code. Molecular weights, polydispersities and the distribution of primary linear chains amongst the branched copolymer molecules can be modelled as a function of conversion. The effect of varying reactivities can be modelled by assigning different probabilities for the reaction of the double bonds of the monovinyl monomer, the unreacted divinyl monomer and the half-reacted divinyl monomer. The predictions of this Monte Carlo model have been compared with experimental data previously obtained for the ATRP of 2-hydroxypropyl methacrylate with ethylene glycol dimethacrylate (I. Bannister et al., Macromolecules, 2006, 39, 7483–7492). The model predicts higher molecular weights and polydispersities than are actually observed experimentally, probably because branching becomes diffusion controlled in real reactions at high conversion and because the model allows couplings between chains which would be spatially constrained in the real system. The model predicts (i) formation of a proportion of residual linear primary chains if the proportion of divinyl monomer is low and (ii) only very low levels of intramolecular (primary) cyclisation to form loops. Comparison of experimental and predicted molecular weight vs. conversion data confirms that the experimentally determined onset of rapid molecular weight rise can be modelled assuming random addition of double bonds of equal reactivity, leading to statistical branching and more homogeneous structures than are obtained by conventional free-radical polymerisation.

Control of Particle Morphology in Ab Initio RAFT Mediated Emulsion Polymerization

Recent advances in the use of reversible addition–fragmentation chain transfer (RAFT) polymerization in dispersed phase systems have paved the way for the fine control of the morphology of latex particles that was not possible by conventional free radical polymerization techniques. With this approach, living amphiphilic block copolymers are synthesized that self-assemble to form micelles. The hydrophilic segment is formed from a water-soluble monomer which stabilizes the latex particles as polymerization proceeds and the latex particles grow. The hydrophobic ends of the RAFT diblocks ultimately grow into the polymer that forms the body of the particles. This paper presents examples of ways in which these advances can be used to engineer latex particles with unique morphologies that exhibit specific application properties.

Superhydrophobic electrospun POSS-PMMA copolymer fibres with highly ordered nanofibrillar and surface structures

A POSS-PMMA copolymer has been synthesised by conventional free-radical polymerisation reaction. Uniform electrospun fibres from this copolymer showed a water contact angle as high as 165 degrees with a sliding angle as low as 6 degrees . For the first time, we found that the electrospun fibres had a bundled nanofibril secondary structure with an ordered POSS morphology on the fibre surface.

Proton conducting polymers containing 1H‐1,2,3‐triazole moieties

AbstractPolyacrylates containing a different number of 1H‐1,2,3‐triazole groups per repeat unit have been synthesized via conventional free radical polymerization. These polymers were characterized by nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Proton conductivity measurements were made using impedance spectroscopy. Introduction of more than one triazole per repeat unit did not result in an increase in conductivity as there was an accompanying increase in glass transition temperature (Tg). A maximum conductivity of 17.5 μS/cm was obtained at 200 °C under anhydrous condition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 188–196, 2009

Combinatorial materials research applied to the development of new surface coatings XII: Novel, environmentally friendly antimicrobial coatings derived from biocide-functional acrylic polyols and isocyanates

Novel, environmentally friendly antimicrobial coatings containing tethered biocide moieties derived from the ubiquitous biocide, triclosan, were synthesized and characterized using a high-throughput workflow. Triclosan was first modified with an acrylate functionality and, subsequently, copolymerized with hydroxyethyl acrylate and butyl acrylate using conventional free radical polymerization to form an array of acrylic polyol terpolymers. The polyols were characterized using nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and gel permeation chromatography. Arrays of urethane coatings were produced from the array of acrylic polyol terpolymers and, subsequently, characterized using parallel dynamic mechanical thermal analysis, surface energy measurements, and various biological assays. The results of the biological assays showed that the coatings were effective toward inhibiting Staphylococcus epidermidis biofilm retention without leaching triclosan or other toxic components from the coating. The level of antimicrobial activity was found to increase with the content of triclosan moieties incorporated into the coating matrix. These results indicate that triclosan moieties tethered to a polymer matrix can impart antimicrobial properties via a contact-active, nonleaching (i.e., environmentally friendly) mechanism. Since S. epidermidis is one of the primary microorganisms associated with infection and failure of implanted medical devices, such as prosthetic heart valves, urinary catheters, and a variety of orthopedic implants, these coatings may have good potential for commercialization in some of these applications.

Delaying the onset of macrogelation for the synthesis of branched and star-like polymers via conventional free-radical polymerisation: Binary solvent effects and incorporation of surfmers

It is known that the preferential solvation and conformation of a polymer in a solvent mixture are functions of the polymer's molecular weight and the solvent qualities. This paper demonstrates that these relationships can be exploited to delay the onset of macrogelation for branched poly(methyl methacrylate/ethylene glycol dimethacrylate) (p(MMA/EGDMA)) polymers and star-like poly(methyl acrylate/ethylene glycol dimethacrylate) (p(MA/EGDMA)) polymers synthesised via conventional free-radical polymerisation (CFRP) in a binary solvent mixture (consisting of a good solvent and a precipitant for the polymer). The gelation limits of the MMA/EGDMA and MA/EGDMA polymerisations in a methyl ethyl ketone (MEK)/heptane binary solvent mixture can be extended to regions of higher monomer concentration with increases in polymer yield between 13 and 50±5 w/w% for the p(MMA/EGDMA) system and between 8 and 19±6 w/w% for the p(MA/EGDMA) system across the gelation boundary. Thus, a facile method of increasing the concentration of batch reaction mixtures by the simple addition of small amounts of precipitant into the reaction solutions is presented. Furthermore, the gelation limits of both polymerisation systems in the binary solvent mixtures were further extended with increases in polymer yield between 11 and 17±4%w/w for the p(MMA/ODA/EGDMA) system and between 8 and 20±5%w/w for the p(MA/VS/EGDMA) system by the respective incorporation of octadecyl acrylate (ODA) and vinyl stearate (VS) surfmers into the polymers, demonstrating the application of steric hinderance to shield the propagating polymers from excessive cross-linking reactions.

Tacticity control by conformational isomerization in free radical polymerization of acrylate

Contribution of conformational isomerization to polymer tacticity has been studied in free radical polymerization of (−)-menthyl 2-acetamidoacrylate with azo initiators. It has been demonstrated that the chain end of the growing polymer radical, which is generated from the s-trans and s-cis conformers of monomer, produces stereoselectively new R and S configurational quaternary carbons, respectively, for the attack of monomer. In addition, polymerization reactivity of both conformers is indistinguishable under the present conditions, and the polymerization is considered to proceed through a chain-end controlled mechanism, which excludes a penultimate unit effect on tacticity in the polymerization. The results obtained would give a clue to understand an origin of tacticity in conventional free radical polymerization of acrylates.

Compartmentalization of Reverse Atom Transfer Radical Polymerization in Miniemulsion

Compartmentalization of an atom transfer radical polymerization (ATRP) miniemulsion has been experimentally observed to reduce the overall polymerization rate, primarily by increasing the rate of deactivation due to the confined space effect, and compartmentalization was also found to improve the control over the polymerization and to reduce the final polydispersity index of the polymer. Compartmentalization of an ATRP system requires that the probability of having two active chains in one particle becomes sufficiently low that the particle size influences the number of active radicals (through segregation and confined space effects). This probability is determined by both the particle volume and the number of polymer chains within each particle. For a given number of chains, compartmentalization effects become evident only when the number of reactants (active polymeric radicals and the deactivating species CuBr2−tris[2-di(2-ethylhexyl acrylate)aminoethyl]amine (EHA6TREN)) within each particle becomes limited by decreasing particle volume. Alternatively, for a given particle volume compartmentalization effects become evident when reactants (active polymeric radicals and the deactivating species CuBr2−EHA6TREN) become limited by decreasing chain number. The difference between a conventional free radical polymerization and ATRP is highlighted by the opposing impact that compartmentalization has on the kinetics of the polymerizations. In a conventional system, segregation effects cause an increase in the polymerization rate, while the confined space effect dominates the kinetics in ATRP and results in a decrease in rate.

Preparation and evaluation of a high-strength biocompatible glass-ionomer cement for improved dental restoratives

We have developed a high-strength light-cured glass-ionomer cement (LCGIC). The polymer in the cement was composed of the 6-arm star-shape poly(acrylic acid) (PAA), which was synthesized using atom-transfer radical polymerization. The polymer was used to formulate with water and Fuji II LC filler to form LCGIC. Compressive strength (CS) was used as a screening tool for evaluation. Commercial glass-ionomer cement Fuji II LC was used as control. The results show that the 6-arm PAA polymer exhibited a lower viscosity in water as compared to its linear counterpart that was synthesized via conventional free-radical polymerization. This new LCGIC system was 48% in CS, 77% in diametral tensile strength, 95% in flexural strength and 59% in fracture toughness higher but 93.6% in shrinkage lower than Fuji II LC. An increasing polymer content significantly increased CS, whereas an increasing glass filler content increased neither yield strength nor ultimate CS except for modulus. During aging, the experimental cement showed a significant and continuous increase in yield strength, modulus and ultimate CS, but Fuji II LC only showed a significant increase in strength within 24 h. The experimental cement was very biocompatible in vivo to bone and showed little in vitro cytotoxicity. It appears that this novel LCGIC cement will be a better dental restorative because it demonstrated significantly improved mechanical strengths and better in vitro and in vivo biocompatibilities as compared to the current commercial LCGIC system.

Thermal characterization of poly(vinyl chloride) samples prepared by living radical polymerization: Comparison with poly(vinyl chloride) prepared by free radical polymerization

AbstractPoly(vinyl chloride) (PVC) samples were synthesized by a living radical polymerization (LRP) method and compared with commercial PVC prepared by the conventional free radical polymerization (FRP). The differences were assessed, for the first time, in terms of viscosimetry parameters and thermal analysis. The LRP method used to prepare the PVC‐LRP samples is the only one available to obtain this polymer free of structural defects, being of commercial interest in a view of preparing a new generation of PVC‐based polymer with outstanding performance. The polymerization temperature selected (35°C) to prepare the LRP samples is currently used in the industry to prepare PVC‐FRP grades with moderate to high molecular weight. Since the thermal stability is a direct consequence of the polymer structure, this study is of vital importance to understand the potential of new PVC‐LRP. The thermoanalytical measurements demonstrate an enhanced thermal stability of PVC‐LRP when compared with its FRP counterpart. The PVC‐LRP sample with very low molecular weight reveals a higher thermal stability than the most stable PVC‐FRP sample. It is the first report dealing with thermal analysis of PVC prepared by LRP. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

A novel photoconductive ZnO/PVK nanocomposite prepared through photopolymerization induced by semiconductor nanoparticles

A composite of ZnO nanoparticles and poly( N-vinylcarbazole) (PVK) is prepared in this study. The ZnO nanoparticles are finely dispersed in the PVK matrix. It is found that the photoluminescence intensity of PVK matrix in the as-prepared nanocomposite is greatly reduced in comparison with the pure PVK. This change is attributed to interfacial charge transfer between PVK matrix and ZnO nanoparticles, and indicates that ZnO nanoparticles in the as-prepared composite are effective electron trappers. Photoconductivity of the device fabricated from the nanocomposite is investigated, and the results are compared to the pure PVK and the composite prepared by a conventional free radical polymerization.

Statistical copolymers of 2‐(trimethylsilyloxy)ethyl methacrylate and methyl methacrylate synthesized by ATRP

AbstractNo Abtract.

Coating of gold nanoparticles by thermosensitive poly(N-isopropylacrylamide) end-capped by biotin

Gold nanoparticles (NPs) were prepared by reduction of HAuCl4 in aqueous solution and stabilized by poly(N-isopropylacrylamide) (PNIPAM). PNIPAM was prepared by two distinct routes: (i) conventional free-radical polymerization leading to polymer without any reactive end-group, and (ii) Reversible Addition–Fragmentation chain Transfer (RAFT) polymerization with 2-dodecylsulfanylthiocarbonylsulfanyl-2-methyl propionic acid (DMP) as a RAFT agent. PNIPAM with low polydispersity was then end-capped by an α-carboxylic acid and an ω-trithiocarbonate that was converted into an ω-thiol upon hydrolysis. This hetero-telechelic polymer was analyzed by mass spectroscopy, size exclusion chromatography (SEC) and 1H NMR. Even without thiol end-group, known for chemisorption onto gold, PNIPAM was effective in stabilizing gold NPs (∼1–5nm). The thermosensitivity of PNIPAM at the surface of gold NPs was, however, dependent on the molecular weight of the chains. Finally, the α-carboxyl end-group of PNIPAM was used to anchor biotin, which is indeed known for complexation with avidin, which is a possible strategy for the coated gold NPs to be involved as building blocks in supramolecular assemblies. TEM and UV–vis spectroscopy were used to characterize the gold nanoparticles.

SYNTHESIS OF HETEROARM STAR-SHAPED POLYMER BY THE USE OF POLYFUNCTIONAL CHAIN-TRANSFER AGENT via CONVENTIONAL FREE RADICAL POLYMERIZATION

Heteroarm star-shaped polymers were synthesized by conventional free radical polymerization in two steps by the use of polyfunctional chain transfer agent. In the first step, free radical polymerization of methyl methacrylate was carried out in the presence of a polyfunctional chain transfer agent, pentaerythritol tetrakis(3-mercaptopropinate). At appropriate monomer conversions, two-arm PMMA having two residual thiol groups at the chain center or three-arm PMMA having one residual thiol group at the core were obtained. In the second step, free radical polymerization of styrene was carried out using PMMAs obtained above as macro-chain transfer agent. When styrene conversion was lower than 30%, heteroarm star-shaped polymers, (PMMA)2(PS)2 and (PMMA)3(PS), were obtained successfully.

Narrowing the size distribution of the polymer acid improves PANI conductivity

By narrowing the size distribution of the polymer acid template, polyaniline (PANI) that is subsequently template synthesized exhibits enhanced conductivity. We used poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PAAMPSA, as the polymer acid and it was synthesized by both conventional free-radical polymerization and atom transfer radical polymerization (ATRP). ATRP-derived PAAMPSA, or aPAAMPSA, has a narrower size distribution compared to conventional PAAMPSA at comparable molecular weights. In general, PANI–aPAAMPSA is two to three times as conductive as PANI–PAAMPSA. The enhanced conductivity of PANI–aPAAMPSA is strongly correlated with increases in the conjugation length and crystallinity of PANI. More surprisingly, PANI–aPAAMPSA adopts a crystal structure that is different from that of PANI–PAAMPSA, but one that is similar to that of PANI doped with a molecular acid counterpart of AAMPSA.

Preparation and proton conductivity of acid-doped 5-aminotetrazole functional poly(glycidyl methacrylate)

Proton conducting polymer membranes have become crucial due their applications in fuel cells as source of clean energy. In this work, we synthesized poly(glycidyl methacrylate) (PGMA) by conventional free radical polymerization of GMA using azobisisobutyronitrile (AIBN) as initiator. PGMA was modified with 5-aminotetrazole by ring opening of the epoxide group. The composition of the polymer was studied by elemental analysis (EA) and the structures were characterized by FT-IR and solid 13C NMR spectra. Thermogravimetry analysis (TG) and differential scanning calorimetry (DSC) were employed to examine the thermal stability and homogeneity of the materials, respectively. Polymers were doped with H 3PO 4 at several stoichometric ratios. The effect of doping on the proton conductivity was studied via impedance spectroscopy. Maximum proton conductivity of acid-doped PGMA-aminotetrazole was found to be 0.01 S/cm at 150 °C in the anhydrous state.

Development of networks in atom transfer radical polymerization of dimethacrylates

The development of networks and structural heterogeneity in the atom transfer radical polymerization (ATRP) of dimethacrylates was studied. The structural and kinetic evolutions during the polymerization were followed using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and extraction/swelling measurement. The reversible activation/deactivation equilibrium between growing radical and dormant species slowed down the polymerization process, giving rise to sufficient chain relaxation and diffusion of reactive species, which favored the formation of homogeneous networks. Compared to the networks prepared by conventional free radical polymerization that favored microgel formation, the ATRP products were more homogeneous, suggested by narrower peak width of the tanδ curve. It was also found that crosslinking density and degree of structural heterogeneity of the ATRP products increased with vinyl conversion. The loss of the living feature at high conversions did not further increase the structural heterogeneity. The ATRP of dimethacrylates with longer spacer yielded more homogeneous networks with lower crosslinking density and lower glass transition temperature.

Synthesis and Characterization of Core Cross-Linked Star Clusters by Conventional Free-Radical Polymerization

Core cross-linked star (CCS) clusters consisting of linear poly(methyl methacrylate) (PMMA) segments surrounding multiple, dispersed poly(divinylbenzene) (PDVB) cores have been synthesized by conventional free-radical polymerization via a “core-first” method. This unique macromolecular structure is akin to a cluster of several CCS polymers (a star polymer with a single, densely cross-linked core) that are covalently bonded together by linear core-to-core PMMA segments and retain excellent solubility even at very high molecular weights. This study provides evidence to the proposed “core-first” mechanism and subsequent CCS cluster formation by comparison to linear PMMA and model CCS polymers synthesized by atom transfer radical polymerization (ATRP). Characterization by UV−vis spectrophotometry, proton nuclear magnetic resonance (1H NMR), dynamic light scattering (DLS), and thermal analysis verified the formation of PMMA−PDVB CCS clusters and elucidated their macromolecular structure. Molecular weights of b...