Chain-length dependence of the antifouling characteristics of the glycopolymer-modified polypropylene membrane in an SMBR

Membrane-bioreactor processes have increased considerably in recent years. However, the natural disadvantages of common membrane materials, such as hydrophobic surface, cause membrane fouling and cumber further extensive applications. In this work, hydrophilic surface modification of polypropylene microporous membranes was carried out by the sequential photoinduced graft polymerization of d-gluconamidoethyl methacrylate (GAMA) to meet the requirements of wastewater treatment and water reclamation applications. The grafting density and grafting chain length were controlled independently in the first and second step, respectively. Attenuated total reflection–Fourier transform infrared spectroscopy (FT-IR/ATR) and X-ray photoelectron spectroscopy (XPS) were employed to confirm the surface modification on the membranes. Water contact angle was measured by the sessile drop method. Results of FT-IR/ATR and XPS clearly indicated that GAMA was grafted on the membrane surface. It was found that the grafting chain length increased reasonably with the increase of the UV irradiation time. Water contact angle on the modified membrane decreased with the increase of the grafting chain length, and showed a minimum value of 43.2°, approximately 51.8° lower than that of the unmodified membrane. The pure water fluxes for the modified membranes increased systematically with the increase of the grafting chain length. The effect of the grafting chain length on the antifouling characteristics in a submerged membrane-bioreactor for synthetic wastewater treatment was investigated. After continuous operation in the submerged membrane-bioreactor for about 70 h, reduction from pure water flux was 90.7% for the virgin PPHFMM, and ranged from 80.8 to 87.2% for the modified membranes, increasing with increasing chain length. The flux of the virgin PPHFMM membrane after fouling and subsequent washing was 31.5% of the pure water flux through the unfouled membrane; for the modified membranes this ranged from 27.8 to 16.3%, decreasing with increasing chain length. These results demonstrated that the antifouling characteristics for the glucopolymer-modified membranes were improved with an increase in GAMA chain length.     

The synthesis of P(MAn-co-St)-b-PS-b-P(MAn-co-St) block copolymers by RAFT polymerization and the nanostructure of their self-assembly aggregates

A series of block copolymers of styrene, maleic anhydride and acrylic acid were synthesized by the reverse addition–fragmentation chain transfer (RAFT) process. The structure, molecular weight and polydispersity index were determined by FTIR, ¹H NMR, SEC&MALLS and DSC analysis. The results showed that the polymerization occurred in a living and controlled manner. Multiple self-assembled nanostructures of these block copolymers were investigated by transmission electron microscopy (TEM). Tetrahydrofuran (THF), N,N-dimethylformamide (DMF) and 1,4-dioxane were used as the common solvents and twice-distilled water as the selective solvent to clarify the effects of the solvent. The results revealed that with the increase of the extension degree of the core, non-spherical aggregates were easily formed, the composition of the copolymers influences the aggregation behavior, and other factors also influence the self-assembly, such as hydrolysis, temperature, annealing time, molecular architecture etc. A mechanism is proposed to illustrate the formation of the various aggregates of P(MAn-co-St)-b-PS-b-P(MAn-co-St) copolymer, which were confirmed by TEM results.     

Addition–fragmentation chain transfer: Molecular weight distributions and retardation in the system methyl methacrylate/methyl α‐(bromomethyl)acrylate

A detailed investigation of addition–fragmentation chain transfer (AFCT) in the free‐radical polymerization of methyl methacrylate (MMA) in the presence of methyl α‐(bromomethyl)acrylate (MBMA) was carried out to elucidate mechanistic details with efficient macromonomer synthesis as an underlying goal. Advanced modeling techniques were used in connection with the experimental work. Curve fitting of simulated and experimental molecular weight distributions with respect to the rate coefficient for addition of propagating radicals to MBMA (k_add) over 60–120 °C resulted in E_add = 21.7 kJ mol^?1 and A_add = 2.18 × 10⁶ M^?1 s^?1 and a very weak temperature dependence of the chain‐transfer constant (E_add ≈ E_p). The rate coefficient for fragmentation of adduct radicals at 60 °C was estimated as k_f ≈ 39 s^?1 on the basis of experimental data of the MMA conversion and the concentration of 2‐carbomethoxy‐2‐propenyl end groups. The approach developed is generic and can be applied to any AFCT system in which copolymerization does not occur and in which the resulting unsaturated end groups do not undergo further reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2640–2650, 2004     

Living radical miniemulsion polymerization by RAFT in the presence of beta-cyclodextrin

Living radical polymerization of styrene in a miniemulsion by reversible addition–fragmentation chain transfer (RAFT) was successfully realized in the presence of beta-cyclodextrin (CD), using sodium dodecyl sulfate and hexadecane as surfactant and costabilizer, respectively. The drawback of instability (red layer formation) encountered in the living radical polymerization in emulsion or miniemulsion was overcome. The linear relationship between the monomer conversion and the molecular weight, as well as lower molecular weight distribution (MWD), shows that the polymerization process was under control. The addition of CD was found to have little influence on the polymerization rate. However, MWD of the polymer synthesized is obviously decreased. The mechanism of stability and controllability improvement in the presence of CD proposed that the complex formation between CD and RAFT agent or RAFT agent-ended oligomer increased their diffusion ability from monomer droplet to polymerization locus and improved the homogeneity of the RAFT agent level among the polymerization loci.     

Synthesis of tetracycline‐imprinted polymer microspheres by reversible addition–fragmentation chain‐transfer precipitation polymerization using polyethylene glycol as a coporogen

Tetracycline (TC)‐imprinted microspheres have been synthesized by reversible addition–fragmentation chain‐transfer precipitation polymerization using PEG as a coporogen. In the synthesis, methacrylic acid and ethylene dimethacrylate were used as the functional monomer and cross‐linker, respectively. 2,2′‐Azobisisobutyronitrile was the initiator, and cumyl dithiobenzoate was the chain‐transfer reagent. Although monodispersed microspheres were obtained using acetonitrile as porogen, the particles cannot be used in the column extraction because of the high backpressure. To increase the porosity of the material, PEG was introduced as a coporogen. The influence of the molecular weight and concentration of PEG on the morphology, binding affinity, and porosity of the molecularly imprinted polymers (MIPs) have been studied. The results demonstrated that PEG as a macroporogen increased the porosity of the polymers. Meanwhile, the column backpressure was reduced using the MIPs with higher porosity. The binding affinity of the MIPs was increased when a low concentration of PEG was employed, while it was decreased when the ratio of PEG 12 000/monomers was >0.8%. Under the optimized conditions, TC‐imprinted microspheres with good selectivity and size uniformity have been obtained, which facilitates its application in the column extraction for TC determinations.     

Facile synthesis of comb,star, and graft polymers via reversible addition–fragmentation chain transfer (RAFT) polymerization

Reversible addition–fragmentation chain transfer (RAFT) polymerization has been shown to be a facile means of synthesizing comb, star, and graft polymers of styrene. The precursors required for these reactions were synthesized readily from RAFT‐prepared poly(vinylbenzyl chloride) and poly(styrene‐co‐vinylbenzyl chloride), which gave intrinsically well‐defined star and comb precursors. Substitution of the chlorine atom in the vinylbenzyl chloride moiety with a dithiobenzoate group proceeded readily, with a minor detriment to the molecular weight distribution. The kinetics of the reaction were consistent with a living polymerization mechanism, except that for highly crowded systems, there were deviations from linearity early in the reaction due to steric hindrance and late in the reaction due to chain entanglement and autoacceleration. A crosslinked polymer‐supported RAFT agent was also prepared, and this was used in the preparation of graft polymers with pendant polystyrene chains. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2956–2966, 2002     

Kinetics of methyl methacrylate and n‐butyl acrylate copolymerization mediated by 2‐cyanoprop‐2‐yl dithiobenzoate as a RAFT agent

The RAFT (co)polymerization kinetics of methyl methacrylate (MMA) and n‐butyl acrylate (BA) mediated by 2‐cyanoprop‐2‐yl dithiobenzoate was studied with various RAFT concentrations and monomer compositions. The homopolymerization of MMA gave the highest rate. Increasing the BA fraction f_BA dramatically decreased the copolymerization rate. The rate reached the lowest point at f_MMA ～ 0.2. This observation is in sharp contrast to the conventional RAFT‐free copolymerization, where BA homopolymerization gave the highest rate and the copolymerization rate decreased monotonously with increasing f_MMA. This peculiar phenomenon can be explained by the RAFT retardation effect. The RAFT copolymerization rate can be described by 〈R_p〉/〈R_p〉₀ = (1 + 2(〈k_c〉/〈k_t〉)〈K〉)[RAFT]₀)^?0.5, where 〈R_p〉₀ is the RAFT‐free copolymerization rate and 〈K〉 is the apparent addition–fragmentation equilibrium coefficient. A theoretical expression of 〈K〉 based on a terminal model of addition and fragmentation reactions was derived and successfully applied to predict the RAFT copolymerization kinetics with the rate parameters obtained from the homopolymerization systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3098–3111, 2007     

Preparation and characterization of graft terpolymers with controlled molecular structure

Segmented terpolymers, poly(alkyl methacrylate)‐g‐poly(D ‐lactide)/poly(dimethylsiloxane) (PLA/PDMS), were prepared with a combination of the “grafting through” technique (macromonomer method) and controlled/living radical polymerization (atom transfer radical polymerization or reversible addition–fragmentation transfer polymerization). Two synthetic pathways were used. The first was a single‐step approach in which a low‐molecular‐weight methacrylate monomer (methyl methacrylate or butyl methacrylate) was copolymerized with a PLA macromonomer and a PDMS macromonomer. The second strategy was a two‐step approach in which a graft copolymer containing one macromonomer was chain‐extended by a copolymerization of the second macromonomer and the low‐molecular‐weight methacrylate. The kinetics of both synthetic approaches were investigated, showing that the polymerizations exhibited a controlled/living behavior. Furthermore, the molecular structure of the terpolymers (composition, molecular weight distribution, and microstructure) was investigated by two‐dimensional liquid chromatography. Well‐defined terpolymers with controlled branch distribution, composition (F_w,PMMA/F_w,PLA/F_w,PDMS ～ 50/30/20) molecular weight (M_n ～ 50,000 g · mol^?1), and a narrow molecular weight distribution (M_w/M_n ～ 1.3) were prepared via both pathways. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1939–1952, 2004     

Preparation and characterization of a homobifunctional silicone rubber membrane grafted with acrylic acid via plasma-induced graft copolymerization

Polyacrylic acid (PAA) was grafted onto the surface of silicone rubber membrane (SR) by plasma-induced graft copolymerization (PIP). Ar-plasma was used to activate the surface of SR. Also, a determination was made of the influences of plasma treatment power, pressure, time, grafted copolymerization reaction time, and monomer concentration on polymerization yield. The surface properties of SR were measured by ATR-FTIR, ESCA, and SIMS. In those analyses, the elemental composition and different carbon bindings on the surface of SR were examined by ESCA with the amount of O1s/C1s being approximately 0.7 at 60 s by Ar-plasma treatment (60 W, 200 mtorr). The peroxide group introduced on SR was measured via 1,1-diphenyl-2-picryhydrazyl (DPPH). The optimum amount of peroxide groups was 6.85 × 10⁻⁸ mol/cm² at 60 s of Ar-plasma treatment. The peroxide group (33D peak) was introduced onto the surface of SR by negative spectra of SIMS analysis after SR treatment by Ar-plasma. An increase was obtained in grafted polymerization yield with a region of 5 to 50% (v/v) of acrylic acid aqueous solution. Both sites of polyacrylic acid were detected after staining by toluidine blue O. That is, a homobifunctional membrane was developed via this surface modification method. © 1996 John Wiley & Sons, Inc.     

Characterization and rheological properties of model alkali‐soluble rheology modifiers synthesized by reversible addition–fragmentation chain‐transfer polymerization

Model alkali‐soluble rheology modifiers of different molar masses were synthesized by the reversible addition–fragmentation chain‐transfer polymerization of methyl methacrylate, methacrylic acid, and two different associative macromonomers. The polymerization kinetics showed good living character including well‐controlled molar mass, molar mass linearly increasing with conversion, and the ability to chain‐extend by forming an AB block copolymer. The steady‐shear and dynamic properties of a core‐shell emulsion, thickened with the different model alkali‐soluble rheology modifiers, were measured at constant pH and temperature. The steady‐shear data for latex solutions with conventional rheology modifiers exhibited the expected thickening, whereas the associative rheology modifiers showed contrasting rheology behavior. The dynamic measurements revealed that the latex solutions thickened with the conventional rheology modifiers exhibit solid‐like (dominant G′) behavior as compared with the associative rheology modifiers that give the latex solution a liquid‐like (dominant G″) character. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 223–235, 2003     

Preparation and characterization of heteroarm H‐shaped terpolymers by combination of reversible addition‐fragmentation transfer polymerization and ring‐opening polymerization

Heteroarm H‐shaped terpolymers, [(poly(L ‐lactide))(polystyrene)]poly(ethylene oxide)[(polystyrene)(poly(L ‐lactide))], [(PLLA)(PS)]PEO[(PS)(PLLA)], in which PEO acts as a main chain and PS and PLLA as side arms, have been successfully prepared via combination of reversible addition–fragmentation transfer (RAFT) polymerization and ring‐opening polymerization (ROP). The first step is the synthesis of the PEO capped with one terminal dithiobenzoate group and one hydroxyl group at every chain end, [(HOCH₂)(PhC(S)S)]PEO[(S(S)CPh)(CH₂OH)] from the reaction of carboxylic acid with ethylene oxide. Then, the RAFT polymerization of styrene (St) was carried out using [(HOCH₂)(PhC(S)S)]PEO[(S(S)CPh)(CH₂OH)] as RAFT agent and AIBN as initiator, and the triblock copolymer, [(HOCH₂)(PS)]PEO[(PS)(CH₂OH)], was formed. Finally, the heteroarm H‐shaped terpolymers, [(PLLA)(PS)]PEO[(PS)(PLLA)], were produced by ROP of LLA, using triblock copolymer, [(HOCH₂)(PS)]PEO[(PS)(CH₂OH)], as macroinitiator and Sn(Oct)₂ as catalyst. The target products and intermediates were characterized by ¹H NMR spectroscopy and gel permeation chromatography. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 789–799, 2007     

Reversible addition–fragmentation chain‐transfer graft polymerization of styrene: Solid phases for organic and peptide synthesis

The γ‐initiated reversible addition–fragmentation chain‐transfer (RAFT)‐agent‐mediated free‐radical graft polymerization of styrene onto a polypropylene solid phase has been performed with cumyl phenyldithioacetate (CPDA). The initial CPDA concentrations range between 1 × 10^?2 and 2 × 10^?3 mol L^?1 with dose rates of 0.18, 0.08, 0.07, 0.05, and 0.03 kGy h^?1. The RAFT graft polymerization is compared with the conventional free‐radical graft polymerization of styrene onto polypropylene. Both processes show two distinct regimes of grafting: (1) the grafting layer regime, in which the surface is not yet totally covered with polymer chains, and (2) a regime in which a second polymer layer is formed. Here, we hypothesize that the surface is totally covered with polymer chains and that new polymer chains are started by polystyrene radicals from already grafted chains. The grafting ratio of the RAFT‐agent‐mediated process is controlled via the initial CPDA concentration. The molecular weight of the polystyrene from the solution (PS_free) shows a linear behavior with conversion and has a low polydispersity index. Furthermore, the loading of the grafted solid phase shows a linear relationship with the molecular weight of PS_free for both regimes. Regime 2 has a higher loading capacity per molecular weight than regime 1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4180–4192, 2002     

Implementing the reversible addition–fragmentation chain transfer process in PREDICI

There is currently a highly controversial debate about the nature of the reversible addition–fragmentation chain transfer (RAFT) mechanism. In this debate, kinetic computer modeling is frequently used as a powerful tool to correlate experimental data with theoretical models to deduce the rate coefficients that govern the process. Frequently, the PREDICI program package has been used as a simulation tool. Recently, the implementation and mathematical basis of the RAFT process, with respect to PREDICI, have been criticized. This communication discusses the mathematical and mechanistic implementation of the RAFT process in the PREDICI program package and elucidates the well‐founded mathematical basis of the approach. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1441–1448, 2004     

Controlled,radical reversible addition–fragmentation chain‐transfer polymerization in high‐surfactant‐concentration ionic miniemulsions

Living free‐radical polymerization of methacrylate and styrenic monomers with ionic surfactants was carried out with reversible addition–fragmentation chain transfer in miniemulsion with different surfactant types and concentrations. The previously reported problem of phase separation was found to be insignificant at higher surfactant concentrations, and control of the molar mass and polydispersity index was superior to that of published miniemulsion systems. Cationic and anionic surfactants were used to examine the validity of the argument that ionic surfactants interfere with transfer agents. Ionic surfactants were suitable for miniemulsion polymerization under certain conditions. The colloidal stability of the miniemulsions was consistent with the predictions of a specific model. The living character of the polymer that comprised the latex material was shown by its transformation into block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 960–974, 2004     

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. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3596–3603, 2000     

Living free‐radical polymerization of styrene under a constant source of γ radiation

Living polymerization of styrene was observed using γ radiation as a source of initiation and 1‐phenylethyl phenyldithioacetate as a reversible addition–fragmentation chain transfer (RAFT) agent. The γ radiation had little or no detrimental effect on the RAFT agent, with the molecular weight of the polymer increasing linearly with conversion (up to the maximum measured conversions of 30%). The polymerization had kinetics (polym.) consistent with those of a living polymerization (first order in monomer) and proportional to the square root of the radiation‐dose rate. This initiation technique may facilitate the grafting of narrow polydispersity, well‐defined polymers onto existing polymer surfaces as well as allow a wealth of kinetic experiments using the constant radical flux generated by γ radiation. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 19–25, 2002     

Diene-functional macromonomers by a single-step free radical addition–fragmentation reaction. Syntheses and kinetics

A new chain transfer agent, 5-tert-butylthio-1,3-pentadiene (TBPD or 7, 7-dimethyl-6-thia-1,3-octadiene) was used in the free radical polymerization of methyl methacrylate and styrene to produce conjugated diene-end capped macromonomers by a free radical addition–fragmentation mechanism. The chain transfer was found to be degradative. A new kinetic model was proposed to describe the retarded polymerization. The kinetic parameters per-taining to transfer, reinitiation, primary radical termination, and mutual termination of the primary radicals were evaluated at different temperatures permitting precise theoretical prediction of the functionalities. The chain transfer constants, calculated using a modified Mayo's equation revealed better transfer properties for MMA. The macromonomers were synthesized by high conversion polymerization. Characterizations of the macromonomers revealed that copolymerization predominated over the fragmentation following 1,4-addition, although the former reaction is not detrimental for the chain-end functionalization. © 1995 John Wiley & Sons, Inc.     

Preparation of Forced Gradient Copolymers Using Tube‐in‐Tube Continuous Flow Reactors

The preparation of forced gradient polymers has received considerable attention using batch reactors, while the preparation of usable quantities of forced gradient copolymers using continuous flow reactors has been hampered by the need to vary the composition of the monomer feedstock continuously during the reaction. A reactor that allows for addition of a monomer feedstock continuously at all points along the length of the reactor tubing allows for the preparation of forced gradient copolymers in continuous flow reactors, allowing for the scale‐up and bulk preparation of these polymers. This study reports here the initial investigation of preparing forced gradient copolymers using the reversible addition–fragmentation chain transfer methodology in tube‐in‐tube continuous flow reactors.

     

Addition–fragmentation behavior of a capto-dative group-substituted acrylic ester in free-radical polymerization and reactivity of the derived macromonomers

Ethyl-2-(2-cyano-2-ethylthio)-ethyl-propenoate (ECEP) was synthesized and examined as free-radical addition–fragmentation chain transfer agent (AFCTA) in the bulk polymerization of methyl methacrylate (MMA) and styrene at various temperatures. A better chain transfer constant (C_tr) was observed for styrene than for MMA, projecting the potentiality of the compound as a better end-functionalizing agent for the former. In both cases, copolymerization of ECEP with the monomer predominated over fragmentation, the relative proportions of which were dependent on the monomer. The ECEP-terminated radical fragmented to an extent of 26% in the presence of MMA, whereas it was only 9.5% in the case of styrene. The relative extent of fragmentation and copolymerization was in conformation to the calculated reactivity ratios and chain transfer constants. Addition–fragmentation chain transfer resulted in the formation of methacrylic-functional macromonomers. The copolymerizability of the resultant macromonomer was found to depend on the nature of the backbone and on the comonomer. On copolymerizing with MMA, the terminal monomer moiety on polystyrene (PS)-based macromonomers preferred to undergo fragmentation, whereas that of the polymethyl methacrylate (PMMA)-based one copolymerized readily with styrene because of thermodynamic and kinetic factors. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2511–2524, 1999