Living Radical Polymerization and Molecular Imprinting: Improving Polymer Morphology in Imprinted Polymers

Living radical polymerization (LRP) techniques and their ability to improve the morphology of crosslinked polymer networks by controlling polymer chain growth are reviewed. Recent successes in the creation of improved molecularly imprinted polymer networks are also discussed. LRP offers the ability to control molecular weight, polydispersity, and tacticity while reducing microgel formation in polymers created via free‐radical polymerization (FRP). The improved network architecture of polymers created via LRP has great potential, especially when considering imprinted networks which have traditionally been plagued by heterogeneity in network morphology and binding affinities. Using LRP can considerably improve template recognition and further delay template transport in imprinted polymers.

     

Preparation and characterization of antifouling poly(vinylidene fluoride) blended membranes

Poly(vinylidene fluoride) (PVDF) membranes have been widely used in microfiltration and ultrafiltration because of their excellent chemical resistance and thermal properties. However, PVDF membranes have exhibited severe membrane fouling because of their hydrophobic properties. In this study, we investigated the antifouling properties of PVDF blended membranes. Antifouling PVDF blended membranes were prepared with a PVDF‐g‐poly(ethylene glycol) methyl ether methacrylate (POEM) graft copolymer. The PVDF‐g‐POEM graft copolymer was synthesized by the atom transfer radical polymerization (ATRP) method. The chemical structure and properties of the synthesized PVDF‐g‐POEM graft copolymer were determined by NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography. To investigate the antifouling properties of the membranes, we prepared microfiltration membranes by using the phase‐inversion method, which uses various PVDF/PVDF‐g‐POEM concentrations in dope solutions. The pure water permeabilities were obtained at various pressures. The PVDF/PVDF‐g‐POEM blended membranes exhibited no irreversible fouling in the dead‐end filtration of foulants, including bovine serum albumin, sodium alginate, and Escherichia coli broth. However, the hydrophobic PVDF membrane exhibited severe fouling in comparison with the PVDF/PVDF‐g‐POEM blended membranes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

New fluorous bipyridine ligands for copper‐catalyzed atom transfer radical polymerization of methyl methacrylate in the thermomorphic mode

The atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) is often carried out under homogeneous conditions, so the residual metal catalyst in the polymer often influences the quality of the polymer and causes environmental pollution in the long run. Novel CuBr/4,4′‐bis(R_fCH₂OCH₂)‐2,2′‐bpy complexes (R_f = n‐C₉F₁₉, n‐C₁₀F₂₁, or n‐C₁₁F₂₃; 2,2′‐bpy = 2,2′‐bipyridine) are insoluble in toluene at room temperature yet readily dissolve in toluene at elevated temperatures to form homogeneous phases for use as catalysts in the ATRP reaction, and the Cu complexes precipitate again upon cooling. The CuBr/4,4′‐bis(n‐C₉F₁₉CH₂OCH₂)‐2,2′‐bpy system produced the best results (e.g., polydispersity index by gel permeation chromatography = 1.26–1.41), in that the residual Cu content in the polymer was as low as 19.3 ppm when the ATRP of MMA was carried out in the thermomorphic mode. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Living/controlled radical autopolymerization of styrene in the presence of CuCl2 and 2,2′‐bipyridine

The bulk autopolymerization of styrene (St) was successfully conducted in the presence of CuCl₂ and 2,2′‐bipyridine (bpy) at 110 and 130°C. We found that this polymerization was a living/controlled radical polymerization at a [St]₀/[CuCl₂]₀/[bpy]₀ ratio of 54:1:2.5. The resulting number‐average molecular weights linearly increased with conversion, and the polydispersity indices were very narrow (<1.5). The polymerization rate increased with temperature. Increasing the ratios (i.e., 129:1:2.5, 259:1:2.5, and 386:1:2.5) led to a decrease in the ability to control the autopolymerization of St, even uncontrolled polymerization (i.e., 643:1:2.5). The analysis of end groups by ¹H‐NMR indicated that the spontaneous generation of radicals from St were generated by a Mayo‐type process, and this living/controlled radical polymerization might have underwent a reverse atom‐transfer radical polymerization process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1532–1538, 2003     

活性自由基乳液聚合的研究进展

活性自由基乳液聚合是一个非常新的研究领域。介绍了目前活性自由基乳液聚合领域的3种常用的方法及应用这些方法进行乳液聚合的研究进展,包括:原子转移自由基聚合(ATRP),氮氧调节自由基聚合(NMP)和可逆加成-断裂链转移自由基聚合(RAFT)。     

Synthesis of a chiral stationary phase with poly[styrene‐b‐cellulose 2,3‐bis(3,5‐dimethylphenylcarbamate)] by surface‐initiated atom transfer radical polymerization and its chiral resolution efficiency

A chiral stationary phase (CSP) with poly[styrene‐b‐cellulose 2,3‐bis(3,5‐dimethylphenylcarbamate)] was synthesized by the surface‐initiated atom transfer radical polymerization (SI‐ATRP) of cellulose 2,3‐bis(3,5‐dimethylphenylcarbamate)‐6‐acrylate after the SI‐ATRP of styrene on the surface of silicon dioxide supports in pyridine. The successful preparation of the CSP with poly[styrene‐b‐cellulose 2,3‐bis(3,5‐dimethylphenylcarbamate)] was confirmed via Fourier transform infrared spectroscopy, field emission scanning electron microscopy, X‐ray photoelectron spectroscopy, elemental analysis, and thermal analysis. The applicability for the chiral resolution of the CSP with poly[styrene‐b‐cellulose 2,3‐bis(3,5‐diphenylcarbamate)] was evaluated with high‐performance liquid chromatography with 10 racemates under various mobile phases of hexane/alcohol, hexane/tetrahydrofuran (THF), and hexane/chloroform. The results show that the CSP with poly[styrene‐b‐cellulose 2,3‐bis(3,5‐diphenylcarbamate)] could be used in THF and chloroform as eluents. The chiral resolutions of the commercial Chiracel OD, the CSP with cellulose 2,3‐bis(3,5‐dimethylphenylcarabmate), and the CSP with poly[styrene‐b‐cellulose 2,3‐bis(3,5‐dimethylphenylcarbamate)] prepared by SI‐ATRP were examined. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Dynamic Monte Carlo Simulation of Atom‐Transfer Radical Polymerization

Summary: A dynamic Monte Carlo model was developed to simulate atom‐transfer radical polymerization (ATRP). The algorithm used to describe the polymerization includes activation, deactivation, propagation, chain transfer, and termination by combination and disproportionation reactions. Model probabilities are calculated from polymerization kinetic parameters and reactor conditions. The model was used to predict monomer conversion, average molecular weight, polydispersity and the complete molecular weight distribution at any polymerization time or monomer conversion. The model was validated with experimental results for styrene polymerization and compared with simulation results from a mathematical model that uses population balances and the method of moments. The simulations agree well with experimental and theoretical results reported in the literature. We also investigated the control volume size and number of iterations to reduce computation time while keeping an acceptable noise level in the Monte Carlo results.

Comparison of the chain length distribution of polystyrene made with ATRP and conventional free radical (CFR) polymerization at 50% conversion. The initiator to monomer ratios are 1:100 (ATRP left peak), 1:500 (ATRP right peak), and 1:1000 (CFR).     

N-(n-Alkyl)-2-pyridinemethanimine mediated atom transfer radical polymerization of lauryl methacrylate: Effect of length of alkyl group

The article describes the polymerization of lauryl methacrylate (LMA) using Cu(I)Br as catalyst for atom transfer radical polymerization in conjunction with N-(n-propyl) [PPMI]/(n-hexyl) [HPMI]/(n-octyl) [OPMI]-2-pyridinemethanimine as complex ligands. The polymerization of LMA was investigated in bulk and solution (toluene as solvent) using Cu(I)Br as catalyst, N-(n-alkyl)-2-pyridinemethanimine as ligands and ethyl-2-bromo isobutyrate (EBiB) as initiator. The ratio of LMA : CuBr : Ligand : EBiB was kept constant in all the polymerizations. In bulk polymerization, the solubility of the catalyst complex increased with increasing the length of alkyl chain on the ligand from propyl to octyl and also gave polymers with narrow molecular weight distribution. The PDI was further narrowed by using OPMI as ligand and toluene was used as solvent. The kinetics of polymerization was also analyzed and it clearly shows that % conversion increased with time. Increase in molecular weight with % conversion without affecting PDI clearly show that the system is living and living nature can be controlled by increasing the length of alkyl group. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of poly(n‐butyl methacrylate)‐b‐polystyrene diblock copolymers by atom transfer radical emulsion polymerization

Poly(n‐butyl methacrylate) (PBMA)‐b‐polystyrene (PSt) diblock copolymers were synthesized by emulsion atom transfer radical polymerization (ATRP). PBMA macroinitiators that contained alkyl bromide end groups were obtained by the emulsion ATRP of n‐butyl methacrylate with BrCH₃CHCOOC₂H₅ as the initiator; these were used to initiate the ATRP of styrene (St). The latter procedure was carried out at 85°C with CuCl/4,4′‐di(5‐nonyl)‐2,2′‐bipyridine as the catalyst and polyoxyethylene(23) lauryl ether as the surfactant. With this technique, PBMA‐b‐PSt diblock copolymers were synthesized. The polymerization was nearly controlled; the ATRP of St from the macroinitiators showed linear increases in number‐average molecular weight with conversion. The block copolymers were characterized with IR spectroscopy, ¹H‐NMR, and differential scanning calorimetry. The effects of the molecular weight of the macroinitiators, macroinitiator concentration, catalyst concentration, surfactant concentration, and temperature on the polymerization were also investigated. Thermodynamic data and activation parameters for the ATRP are also reported. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2123–2129, 2005