Functional biohybrid materials synthesized via surface-initiated MADIX/RAFT polymerization from renewable natural wood fiber: Grafting of polymer as non leaching preservative

Crude wood fibers represent a wide class of renewable resources. The surface modification of such materials via covalent grafting of polymer offers new surface properties with non-leaching coating. The grafting of the polymer chains was achieved by surface-initiated controlled radical polymerization through a grafted xanthate chain transfer agent. Macromolecular design via interchange of xanthate (MADIX) technique was chosen to graft poly(vinyl acetate), polystyrene, poly(n-butyl acrylate) and poly(4-vinylbenzyl chloride)-polystyrene amphiphilic cationic copolymers. Water contact angle measurements highlighted the hydrophobization of the wood fiber surface with a nanoscaled polymer monolayer indicating the appropriate coverage of the fiber. X-ray photoelectron spectroscopy showed the successful grafting of the polymer after drastic washing procedure. The quaternization of the grafted polystyrene-co-poly(4-vinyl benzyl chloride) copolymers with tertiary amine allows the introduction of biocide quaternary ammonium functions while preserving the hydrophobic character of the modified wood fiber when introducing a long alkyl chain in the statistical copolymer. Finally, the cationic copolymer was subjected to Coniophora Puteana to evaluate its propensity to limit the fungi expansion.     

Ethylene polymerization with homogeneous nickel-diimine catalysts: effects of catalyst structure and polymerization conditions on catalyst activity and polymer properties

Ethylene polymerization was carried out using three nickel α-diimine catalysts ((ArNC(An)-C(An)NAr)NiBr₂ (1), (ArNC(CH₃)-C(CH₃)NAr)NiBr₂ (2) and (ArNC(H)-C(H)NAr)NiBr₂ (3); where An=acenaphthene and Ar=2,6-(i-Pr)₂C₆H₃) activated with modified methylaluminoxane (MMAO) in a slurry semi-batch reactor. We investigated the effects of ethylene pressure, reaction temperature, and α-diimine backbone structure variation on the catalyst activity and polymer properties. Changes in the α-diimine backbone structure had remarkable effect on the polymer microstructure as well as the catalyst activity. Catalyst 2 produced polymer with the highest molecular weight, while Catalyst 3 produced polymer with the lowest molecular weight. In addition, Catalyst 2 produced polymer with the lowest melting point, while Catalyst 3 produced the highest melting level exhibiting a melting behavior typical of high-density polyethylene (HDPE). With all the three catalysts, polymer molecular weight tended to decrease with increasing polymerization temperature due to the increase in chain transfer rates. In general, there was no clear and consistent trend observed for the effects of ethylene pressure on the polymer molecular weight. However, in polyethylene produced with Catalyst 2, the molecular weight was independent of ethylene pressure suggesting that chain transfer to ethylene may be a dominant mechanism for this catalyst.     

Effects of molecular weight on liquid-crystalline behavior of a mesogen-jacketed liquid crystal polymer synthesized by atom transfer radical polymerization

The synthesis of poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) with different molecular weight and low polydispersity was achieved by atom transfer radical polymerization in methoxybenzene solution using 1-bromoethylbenzene as an initiator and CuBr/sparteine complex as a catalyst. The concentration of the living centers throughout the polymerization was found to be constant. The liquid-crystalline behavior of the polymers with M_n ranging from 3800 to 17,400 g/mol was studied using DSC and POM. Only the polymers with M_n beyond 10,200 g/mol formed a liquid-crystalline phase, which was quite stable with a high clearing point (higher than the decomposition temperature of the polymer).     

Esterification of hydroxylated polymers with 2-sulfobenzoic acid cyclic anhydride: A facile approach for the synthesis of near-monodisperse strong acid homopolymers and diblock copolymers

A convenient two-step route was developed to prepare a range of low polydispersity strong acid homopolymers and several examples of well-defined diblock copolymers. Atom transfer radical polymerization (ATRP) of either 2-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate or glycerol monomethacrylate afforded the corresponding near-monodisperse hydroxylated homopolymers, while several diblock copolymer precursors were prepared by either (1) the one-pot ATRP of 2-hydroxypropyl methacrylate and 2-(diethylamino)ethyl methacrylate using sequential monomer addition or (2) the ATRP of either 2-hydroxypropyl methacrylate or glycerol monomethacrylate using a poly(ethylene oxide)-based macro-initiator. Excess 2-sulfobenzoic acid cyclic anhydride was used to fully esterify the hydroxy groups of these homopolymers and diblock copolymers under mild conditions. The resulting zwitterionic diblock copolymers undergo micellar self-assembly on adjusting the pH of the solution, while one of the anionic poly(ethylene oxide)-based diblock copolymers formed colloidal polyelectrolyte complexes in aqueous solution when mixed with a cationic poly(ethylene oxide)-based diblock copolymer.     

K–V–Ca catalysts supported on porous alumina ceramic substrate for soot combustion: Preparation and characterization

The KCl, KNO₃, CaCl₂, Ca(NO₃)₂, V–Ca and K–V–Ca catalysts supported on alumina ceramic substrates have been prepared. X-ray diffraction and thermogravimetry/differential scanning calorimetry were used to characterize the catalysts, and their catalytic activities were evaluated by a soot oxidation reaction using the temperature-programmed reaction system. The catalytic activity of KNO₃ is higher than KCl, and the catalytic activity of Ca(NO₃)₂ is as much as that of CaCl₂. The catalyst containing a higher KNO₃ content exhibits CO₂ adsorption, whereas higher CaCl₂ and Ca(NO₃)₂ content can restrain the adsorption of CO₂. The K–V–Ca catalyst with a molar ratio of 6:1:1 had the lowest soot onset combustion temperature. The melting and oxidation–reduction of KNO₃, oxygen content of catalyst surface, and formation of some eutectic phase may be the key factors in improving catalytic activity of catalysts.     

Kinetics of nitroxide-controlled radical polymerization during the non-stationary state

The activation-deactivation equilibrium of nitroxide-controlled radical polymerization of styrene at 123 °C was investigated. For this purpose the reaction solution was examined time dependently during the initial phase of the polymerization by using an SEC column combination providing a very good separation of the low-molecular weight species. By time-dependent measurement of the alkoxyamine concentration the activation rate of the alkoxyamines PhEt-TIPNO (N-tert-butyl-N-(2-methyl-1-phenyl-propyl)-O-(1-phenyl-ethyl)-hydroxylamine) k_act = 3.2 × 10⁻³ s⁻¹ and PhEt-BIPNO (N-tert-butyl-N-(1-isopropyl-2-methyl-propyl)-O-(1-phenyl-ethyl)-hydroxylamine) k_act = 6.4 × 10⁻³ s⁻¹ can be determined directly.Considering the Persistent Radical Effect theory, the measurement of the free nitroxide concentration allows to determine the pseudo-equilibrium constant of dissociation/combination between dormant and active species for polystyryl-TIPNO and polystyryl-BIPNO, K = 7.5 × 10⁻⁹ mol/L and 1.08 × 10⁻⁸ mol/L, respectively.     

Alkylation of polyethyleneimine for homogeneous ligands in ATRP

Ethylated and butylated polyethyleneimine ligands were synthesized and employed in copper catalyzed atom transfer radical polymerization of styrene and methyl methacrylate with suitable initiators in order to obtain homogeneous polymerizations, resulting in well defined polymers with low polydispersities. Linear curves drawn from kinetics and conversion-molecular weight plots indicate that all the polymerizations were successfully controlled. In ATRP reactions of S and MMA, the apparent rate of polymerization, k_p^app, exhibits a plateau at [Ligand]/[CuBr] ≥ 0.5 ratio for both ligands. The apparent rate constant also decreases by increasing the alkyl chain length of the alkylated polyethyleneimine ligand. Ethylated and butylated polyethyleneimine ligands in ATRP of S and MMA were found to be faster than the existing ATRP ligands.     

亲水性环氧聚合物磁性微球的制备及其固定化青霉素酰化酶

通过设计反相悬浮聚合体系,制备了聚甲基丙烯酸缩水甘油酯（GMA）-甲基丙烯酸羟乙酯（HEMA）- N,N′-亚甲基双丙烯酰胺（MBAA）亲水性磁性聚合物GHM微球。球中的Fe₃O₄微晶呈倒立尖晶石结构,在微球表面存在着大量环氧基和亲水性的羟基及酰胺等基团,这些功能性基团为青霉素酰化酶（PGA）的固定化提供了适宜的微环境;同时,GHM微球具有的大孔结构和较高的比表面积,使其制备的固定化酶的载酶量高,这些有利因素使得固定化酶PGA/GHM在37℃下水解青霉素G钾合成6-氨基青霉烷酸的表观活性达748 IU·g^-1。 PGA/GHM经15次重复使用,其催化活性未出现明显的衰减,在使用中,固定化酶在磁场的作用下能够快速沉降与产物分离。     

Highly efficient synthesis of cylindrical polymer brushes with various side chains via click grafting-onto approach

Though much attention has been paid to synthesis of cylindrical polymer brushes, it is still not easy to prepare well-defined brushes by a general approach. Herein, well-defined cylindrical polymer brushes with various side chains were synthesized via grafting-onto approach by CuAAC click chemistry. Narrowly dispersed polymer backbones functionalized with azide groups were obtained by post-modification of poly(glycidyl methacrylate) (PGMA) which was prepared by reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerization. The alkyne-terminated side chains, polystyrene, polyacrylates, polymethacrylates and poly(N-alkyl acrylamide)s, were synthesized by RAFT mediated radical polymerization with alkyne-containing chain transfer agents (CTAs). The CuAAC reactions between the backbone and side chain polymers were conducted with an equivalent feed of alkyne-terminated side chains and azide groups under mild conditions. Influences of reaction conditions and chemical composition of polymer side chains on grafting efficiency and molecular weight distribution of the polymer brushes were investigated. It is demonstrated that the side chains of polystyrene, polyacrylates and poly(N-alkyl acylamide)s were grafted at a density above 85% while that of polymethacrylates decreased to ca. 50%. The polymer brushes synthesized under the optimized reaction conditions had well-defined chemical composition and narrow distribution of molecular weight, and their wormlike morphology was visualized by atomic force microscopy (AFM).     

Molecularly imprinted polymer nanomaterials and nanocomposites by controlled/living radical polymerization

Since the pioneering work of Wulff and Mosbach more than 30 years ago, molecular imprinting of synthetic polymers has emerged as a robust and convenient way for synthesizing polymeric receptor materials bearing specific recognition sites for target molecules. The resulting materials, molecularly imprinted polymers (MIPs), are therefore commonly referred to as ‘plastic antibodies’. They are obtained by polymerizing a scaffold around a target, or a derivate thereof, which acts as a molecular template. MIPs have been successfully applied in many areas including affinity separation, immunoassays, chemical sensing, solid-phase extraction, drug delivery, cell and tissue imaging, direct synthesis and catalysis. In terms of affinity and selectivity, MIPs are on a par with biological receptors like antibodies, and this is accompanied by a superior chemical and physical stability, compatibility with organic media, reusability, easy engineering and low cost. These advantages represent the main reasons for the wide interest raised around molecularly imprinted materials. Mainly produced by free radical polymerization (FRP) of vinyl monomers, MIPs have also taken advantage of the introduction of controlled/living radical polymerization (CRP) techniques, which have literally transformed polymer chemistry over the last decade. This review describes the advantages arising from the use of CRP in synthesizing MIPs, both in terms of sheer binding properties as well as for their remarkable potential for post-polymerization functionalization, for the synthesis of MIP nanomaterials and for the integration of MIPs into composites and hybrid materials. The benefits of using CRP are critically assessed with respect to the still largely applied FRP and guidelines are provided for choosing the most convenient technique to fit a specific targeted application of MIPs.     

Nitroxide-mediated radical polymerization of styrene in miniemulsion: model studies of alkoxyamine-initiated systems

A mathematical model has been developed to describe the behavior of the nitroxide-mediated miniemulsion polymerization (NMMP) of styrene initiated by alkoxyamine initiators. The model includes mechanisms describing reactions in the aqueous and organic phases, particle nucleation, the entry and exit of oligomeric radicals, and the partitioning of nitroxide and styrene between the aqueous and organic phases. The influence of nitroxide partitioning on the polymerization kinetics was examined by modeling systems initiated by the alkoxyamines BST and hydroxyl-BST; BST and hydroxyl-BST are benzoylstyryl radicals terminated by the nitroxides TEMPO and 4-hydroxyl-TEMPO, respectively.Predicted monomer conversions, number average molecular weights and polydispersities were in agreement with experimentally measured values. Simulations and mathematical analysis showed that the rate of styrene NMMP is not strongly influenced by the partitioning properties of TEMPO and 4-hydroxyl-TEMPO because of the complex interaction between reaction equilibrium, phase equilibrium, termination and thermal initiation. However, in the absence of styrene thermal initiation, nitroxide partitioning was found to have a significant influence on the polymerization kinetics. The model was also used to make quantitative estimates of: the population of active and dormant polymer radicals derived from both alkoxyamine initiators and thermal initiation; the population of dead polymer chains; and the number molecular weight distributions of living and dead polymer chains.     

烯烃聚合用茂金属催化剂负载化机理的研究进展

从无机载体、有机高聚物载体和有机无机杂化高聚物载体催化剂三方面综述了近年来烯烃聚合用茂金属催化剂负载化的研究进展。与多活性中心催化剂相比,茂金属催化剂具有活性高,用其所制聚合物的相对分子质量分布窄等特点,茂金属催化剂负载化克服了用均相催化剂制备的聚合物形貌不可控的缺点,并可降低助催化剂用量。目前无机载体是工业生产中最常用的载体类型,但用高聚物载体负载所具有的不需要复杂预处理、茂金属催化剂易被官能化及产物中载体成分不影响最终催化剂性能等优点,也逐渐受到关注。     

Synthesis of polymeric nanofiber and polymeric nanosphere by living free radical polymerization

Living free radical polymerizations are employed to synthesize the polystyrene copolymer. The applications of those copolymer in nanomaterials are elucidated in this research. It involves the copolymerization of styrene with 2‐hydroxyethyl methacrylate. The copolymers are reacted with cinnamoyl chloride, and then irradiated with UV light. The polymeric nanofibers are formed by solvent splitting. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3550–3558, 2006     

Water‐soluble polymer and photocatalysis for arsenic removal

In this study, the photocatalytic oxidation of hazardous arsenite (As(III)) to arsenate (As(V)) and the sequential removal of arsenate from aqueous solution by liquid‐phase polymer‐based retention (LPR) were investigated. The photocatalytic oxidation of arsenite was performed using TiO₂ (P25 Degussa, Germany) under UV‐A light. The optimal photocatalytic conditions to oxidize 10 mg L^?1 of arsenite solution were achieved using a 0.5 g L^?1 of catalyst at a pH value of 2. The As(III) oxidation reached 100% after 30 min of illumination with UV‐A light. A water‐soluble polymer containing quaternary ammonium groups, poly(3‐acrylamidopropyl)trimethylammonium chloride (P(ClAPTA)), was used as an extracting reagent in the LPR process. To obtain the optimized conditions, the removal experiments were performed at various polymer : As(V) molar ratios using 10 mg L^?1 of arsenate solutions. After the oxidation of As(III) to As(V), the removal of arsenate by P(ClAPTA) was obtained in a 99% yield using a 20 : 1 polymer : As(V) molar ratio at a pH value of 9. The results demonstrate that the combination of these methods is highly useful for potential applications related to the treatment of wastewater contaminated with As(III). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40871.     

Styrene/4-hydroxystyrene random, block and gradient copolymers modified with an organic dye: Synthesis by controlled radical polymerization and characterization of electrorheological properties

Styrene/4-hydroxystyrene block and gradient copolymers containing the organic dye Disperse Red 1 (S/HSDR) were synthesized using nitroxide-mediated controlled radical polymerization, and a random copolymer was made using conventional free radical polymerization. The three types of S/HSDR copolymer, with similar molecular weight and composition but different S/HSDR sequence distributions along each copolymer chain, were used as dispersed particles for a study of electrorheological (ER) suspensions. The characterization of each ER fluid as a function of controlled molecular structure in suspension showed different ER behaviors. In particular, the suspension of the S/HSDR gradient copolymer showed the greatest degree of enhancement in shear viscosity, by as much as a factor of 10, upon application of a 1700 kV/m electric field.     

Gel formation and primary chain lengths in nitroxide-mediated radical copolymerization of styrene and divinylbenzene in miniemulsion

Gelation in 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO)-mediated cross-linking copolymerization of styrene and divinylbenzene (8.2 mol%) in aqueous miniemulsion at 125 °C has been investigated. The rate of gel formation relative to monomer conversion was the same in miniemulsion and the corresponding solution polymerization when the organic phase contained 6 vol% tetradecane (TD; hydrophobe) and 48 vol% toluene. However, at 54 vol% TD and no toluene (the same total monomer concentration), the conversion at the gel point was lower in miniemulsion than in solution, consistent with our previous results describing enhanced apparent pendant reactivity related to the presence of TD in the present system. The primary chain lengths were higher in miniemulsion with 54 vol% TD than in miniemulsion with 6 vol% TD and in solution (6 and 54 vol% TD). It was deduced via application of Flory-Stockmayer gelation theory that this difference in primary chain lengths, although significant with regards to gelation, was insufficient to explain the rapid gel formation in the miniemulsion containing 54 vol% TD, which is speculated to be related to specific effects of the heterogeneity of the miniemulsion system.     

Preparation of polymer latex particles carrying salt-responsive fluorescent graft chains

We prepared the novel fluorescent polymer latex particles which can change their fluorescence intensity in response to the increasing NaCl concentration in water. Core polymer latex particles were synthesized by emulsifier-free emulsion polymerization of styrene and 2-(2-chloroisobutyroyloxy)ethyl methacrylate. Hydrophilic polymer chains containing epoxy groups were grafted from the core particles by surface-initiated atom transfer radical copolymerization of methoxy polyethyleneglycol methacrylate (MEO_xMA, x = 4 or 9) and glycidyl methacrylate in aqueous media. After azidation of epoxy groups in graft chains, a water-soluble fluorescent dansyl derivative was successfully coupled with the graft chains by copper-catalyzed azide-alkyne cycloaddition in aqueous media. The wavelength of maximum fluorescence intensity of polymer particles carrying graft chains with longer PEG side chains (x = 9) was slightly blue-shifted (7 nm) and the fluorescence intensity increased (1.35 times) with an increase in NaCl concentration as opposed to polymer particles with shorter PEG chains (x = 4).     

Aggregation behaviour of well defined amphiphilic diblock copolymers with poly(N-isopropylacrylamide) and hydrophobic blocks

Series of amphiphilic diblock copolymers with poly(N-isopropylacrylamide) as a hydrophilic block and a hydrophobic block consisting of either polystyrene or poly(tert-butyl methacrylate) were synthesised using RAFT polymerisations. Differential scanning calorimetry showed the chemically different blocks being phase separated in dry polymers. Light scattering and microcalorimetry studies were performed on aqueous solutions to investigate the phase behavior of the diblock copolymers. By carefully transferring the polymers from an organic solvent to water, either micellar particles or large aggregates were obtained depending on the relative lengths of the blocks. Large aggregates collapsed upon heating, whereas collapse occurred slowly within a broad temperature range in the case of micelle like structures. However, microcalorimetrically the collapse of the PNIPAM chains was observed to take place in all samples, suggesting that the shells of the micellar particles are crowded in a way which hinders the compression of the poly(N-isopropylacrylamide) chains.     

Controlled radical polymerization of p-(iodomethyl)styrene—a route to branched and star-like structures

p-(Iodomethyl)styrene was polymerized under the action of a radical initiator (AIBN). The polymerization proceeds with degenerative chain transfer and leads to well defined branched polymers with functional primary and secondary iodomethyl groups as revealed by NMR studies. The obtained polymer can be further used as macroinitiator for radical polymerization of styrene. This polymerization proceeds in controlled way to polystyrene star polymers with reactive groups at the end of their arms. The characterization of branched and star structures was performed by NMR and GPC with absolute molar mass detection (MALLS).