Reversible Addition-fragmentation Chain Transfer Grafting Research Articles

High‐efficient surface tailoring via reverse atom transfer radical polymerization and reversible addition‐fragmentation chain‐transfer polymerization in an aqueous system initiated by a monocenter redox pair

AbstractThe commonly used multi‐center initiation methods always lead to the formation of quantities of homopolymer in the surface tailoring based on reverse atom transfer radical polymerization (ATRP) and reversible addition‐fragmentation chain‐transfer (RAFT) polymerization. In this study, a monocenter redox pair constructed of silica bearing tert‐butyl hydroperoxide groups and ascorbic acid (SiO2‐TBHP/AsAc) was applied to substitute the commonly used initiation method of R‐supported RAFT grafting polymerization. All the propagating radicals were restricted on the surface of solid particles during the whole procedure theoretically, resulting in a higher grafting efficiency of 95.1% combined with the “controllable” feature at 10 h. This redox pair was also used to initiate the reverse ATRP in miniemulsion successfully with a grafting efficiency of 86.3% at 10 h. The grafting efficiency obtained under this monocenter initiation method was significantly higher than that of the frequently reported surface modification by reverse ATRP and RAFT polymerization. In addition, the high‐efficient surface tailoring was traced and confirmed by nuclear magnetic resonance, Fourier transform infrared, X‐ray photoelectron spectroscopy, thermogravimetric analysis, transmission electron microscopy, and other analysis tests. The advantage of this monocenter redox pair will open a new avenue for the potential “high‐efficient” surface tailoring of various materials.

Preparation of Magnetic Temperature-Sensitive Polymer Composite Carrier and Study on Immobilized Penicillin G Acylase

This work designed and prepared a novel type of carrier for immobilization of penicillin G acylase (PGA), and then the performances of the immobilized PGA were studied in detail. The process is presented as follows: First, dopamine (DA), an adhesive biological secondary metabolite, was adopted to form a polydopamine (PDA) coating on the surface of Fe3O4nanoparticles (NPs) prepared by the inverse microemulsion method to generate Fe3O4@PDA NPs through in-situ polymerization. After that, the obtained Fe3O4@PDA NPs were modified by reversible addition fragmentation chain transfer (RAFT) reagent containing carboxyl groups on its surface. Then, taking N,N diethyl acrylamide (DEA) as the temperature-sensitive monomer, [Formula: see text]-hydroxyethyl methacrylate (HEMA) as the hydrophilic monomer, glycidyl methacrylate (GMA) as the target monomer and methyl methacrylate (MMA) as the monomer controlling the distance between targets, through the “Grafting from” strategy and the RAFT polymerization method, the magnetic temperature-sensitive polymer composite, Fe3O4@PDA-g-PDEA-b-PHEMA-b-P(MMA-co-GMA) NPs with different feeding ratios of MMA/GMA, was prepared to realize the immobilization of penicillin G acylase (PGA). Based on samples prepared at each stage of the carrier, the structure and performances were characterized by Fourier Infrared Spectroscopy (FTIR), Transmission Electron Microscope (TEM), X-ray Diffraction (XRD), and Vibration Specimen Magnetometer (VSM), respectively. Besides, the content of RAFT graft Fe3O4@PDA was also quantitatively characterized by ICP, and the molecular weight of the polymer was characterized by mass spectrometry. Result showed that the target space influenced enzyme load capacity (ELC), enzyme activity (EA) and enzyme activity recovery rate (EAR) at a large degree, and there was no positive relationship between ELC to EA and EAR. Last, performances of the immobilized PGA, including relative enzyme activity ([Formula: see text]) of immobilized PGA, were 83.9% after storing for 90 days, and 90.3% of the initial activities were still retained after 12 times of repeated use, and the catalytic stability (temperature, pH) and Michaelis–Menten const [Formula: see text] were investigated with free PGA as control if operation was allowed.

Green modification of cellulose-based natural materials by HRP-initiated controlled “graft from” polymerization

Considerable attention has been focused on the application of natural cellulosic materials due to the cost-effectiveness, renewability, and biodegradability of cellulose. However, gaps between cellulose-based and petroleum-based materials still exist. In this study, a green, environmental modification method for cellulose by enzyme-initiated reversible addition fragmentation chain transfer (RAFT) graft polymerization was reported. First, the grafting of acryloyl chloride (AC) provided reaction sites on cellulosic fiber surfaces, followed by the enzymatic RAFT graft polymerization of acrylamide (AM). The grafting of well-controlled polyacrylamide (PAM) chains on the cellulosic material surface was verified by Fourier transform infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS), and the controlled grafting ratio was also estimated. The transition of wetting behaviors after the modification of AC and PAM also provided evidence for successful grafting on cellulosic materials. In addition, this method can be well applied for the preparation of various functional cellulosic materials.

Controlled surface modification of silicone rubber by gamma-irradiation followed by RAFT grafting polymerization

The formation of biofilms on the surface of some biomaterials causes problems that can have a negative impact on human health. Various studies have been carried out for the modification of polymeric biomaterials; however, with conventional methods of modifying surfaces with radiation-induced grafts, obtaining uniformly distributed grafts over the entire surface is not facilitated, so the mechanical properties are strongly affected by the modification. In this study, silicone rubber (SR) films were modified with 2-hydroxyethyl methacrylate (HEMA) and with oligo(ethylene glycol) methyl ether methacrylate, Mn = 300 g mol−1 (OEGMA300) using the oxidative pre-irradiation method with gamma-irradiation followed by reversible addition-fragmentation chain transfer (RAFT) grafting polymerization. The copolymers of SR-g-PHEMA and SR-g-poly(HEMA-co-OEGMA300) were synthesized with various grafting percentages and these could be adjusted to obtain a thin grafted layer. The grafted samples were characterized by FTIR-ATR spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), light microscopy, swelling in water, contact angle, and dynamic mechanical analysis (DMA); in addition, the non-grafted polymer formed in the RAFT copolymerization reactions was analyzed by gel permeation chromatography (GPC) and nuclear magnetic resonance spectroscopy (NMR). The results confirmed the presence of PHEMA and poly(HEMA-co-OEGMA300) on the surface of SR films, uniformly grafted by the use of a chain transfer agent (CTA). The uniform layer of hydrophilic grafts in the SR films generates a surface capable of forming a water barrier on the surface, without significantly compromising the elastic properties of the SR; furthermore, the grafted thin layer was capable of loading biologically active molecules like curcumin. Modified SR films loaded with curcumin may decrease the possibility of biofilm formation. The described approach of oxidative gamma pre-irradiation followed by RAFT controlled grafting may be of interest for the modification of biomaterials in a controlled way, in the case of silicone for instance for catheters or aesthetic implants.

The Kinetics of Surface‐Initiated RAFT Polymerization of Butyl acrylate Mediated by Trithiocarbonates

Stationary and time‐resolved electron spin resonance spectroscopy measurements are employed to investigate the kinetics of the surface‐initiated reversible addition fragmentation chain transfer (RAFT) polymerization of n‐butyl acrylate from silica nanoparticles using both R‐ and Z‐group‐attached trithiocarbonates as RAFT agents. The obtained kinetic parameters reveal that the addition rate coefficient in the main equilibrium of RAFT graft polymerizations is significantly smaller than the one for comparable RAFT polymerizations in solution phase, as translational diffusion of surface‐attached molecules is limited. In comparison to the R‐group approach, the equilibrium constants of the Z‐group approach are about one to two orders of magnitude smaller due to a stronger shielding of the RAFT moieties. image

2-(2-Cyanopropyl) Dithiobenzoate-mediated Grafting Polymerization of Methyl Methacrylate from Vinyl Modified Silica

Grafting polymerization of methyl methacrylate (MMA) from vinyl modified silica mediated by 2-(2-cyanopropyl) dithiobenzoate was first conducted. Surface radicals generated by the addition reaction of “free” polymeric radicals with surface vinyl could initiate reversible addition-fragmentation chain transfer (RAFT) grafting polymerization of MMA from silica. The RAFT grafting polymerization of MMA from silica exhibited a living character, evident from the linear relationship of grafting ratio with monomer conversion. Grafting polymerization rate appeared dependent on target molecular weight and initiator concentration because of diffusion-controlled RAFT process on silica. The PMMA-grafted silica allowed for a second-step grafting polymerization due to the existence of dithioester group on the chain ends of grafted PMMA. In this case, surface radicals were generated by the reaction of “free” polymeric radicals with the surface RAFT agents, which differed from the RAFT process of grafting polymerization from vinyl modified silica. This method could be extended to prepare a variety of block copolymers from silica.

Polypropylene membrane surface modification by RAFT grafting polymerization and TiO 2 photocatalysts immobilization for phenol decomposition in a photocatalytic membrane reactor

The main technical barriers that impede photocatalytic membrane reactor (PMR) commercialization remain on the post-recovery of the catalyst particles after water treatment. To overcome this problem, surface modification of polypropylene macroporous membrane was performed with the technique of photoinduced reversible addition-fragmentation chain transfer grafting polymerization of acrylic acid. Titanium oxide photocatalysts were introduced to the acrylic acid grafted membrane surface. Phenol decomposition was carried out under UV irradiation in a recycle batch photocatalytic membrane reactor. The normalized membrane flux reached 1.7 times that of the unmodified membrane for the PAAc modified membrane. Introducing TiO 2 photocatalysts to the membrane surface reduced the normalized membrane flux slightly. For the PMR with a grafting degree of 12.9% (wt) of PAAc on the membrane surface, the corresponding decomposition percentage was 32.5% after 6 h UV light irradiation.

Trithiocarbonates Containing Trimethoxysilyl Functionalities as Mediating Agents in Reversible Addition‐Fragmentation Chain Transfer (RAFT) Polymerization of Methyl Acrylate

AbstractSummary: Reversible addition‐fragmentation chain transfer (RAFT) polymerization with benzyl(3‐trimethoxylsilylpropyl)trithiocarbonate (BTPT) and 1,4‐bis(3′‐trimethoxysilylpropyltrithiocarbonylmethyl)benzene (TPTB) as mediators was performed to produce branched poly(methyl acrylate) (pMA). The deviation of the experimental number average molecular weights towards higher values and the size exclusion chromatography (SEC) traces measured at distinct time instants after polymerization indicated a coupling of the trimethoxysilyl end‐groups to form terminal‐linked pMA of high molecular weight. The trimethoxysilyl moieties also caused the unusual creation of doubly ionized pMA chains in electrospray ionization mass spectrometry (ESI‐MS). BTPT was furthermore anchored onto fumed silica to carry out a RAFT graft polymerization with benzylpropyltrithiocarbonate as additional RAFT agent in solution to afford well‐defined pMA chains fixed to silica nanoparticles. A block copolymerization of the living anchored pMA chains with styrene (Sty) produced grafted pMA‐b‐pSty chains with good agreement between experimental and theoretical molecular weights.

Effect of rate retardation in RAFT grafting polymerization from silicon wafer surface

AbstractPolystyrene and poly(butyl acrylate) were grafted from silicon wafer surface by reversible addition‐fragmentation chain transfer (RAFT) polymerization. Three RAFT agents were immobilized onto silicon wafer through their leaving/initiating groups (R group). Grafting polymerization of butyl acrylate (BA) and styrene (St) was then carried out from the immobilized RAFT agents. The immobilization of the RAFT agents and the subsequent grafting polymerization of St and BA were evaluated by ellipsometry and X‐ray photoelectron spectroscopy. It was found that type of monomer, structure of RAFT agent, and local RAFT concentration on the surface have dramatic influences on the thickness of grafted polymer layer. The grafting polymerization with more severe rate retardation effect yielded thinner polymer films on the silicon wafer. Selection of a RAFT agent with little rate retardation was critical in the grafting polymerization to achieve thick films. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 970–978, 2008

RAFT Graft Polymerization of 2-(Dimethylaminoethyl) Methacrylate onto Cellulose Fibre

Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) was grafted from cellulose by reversible addition–fragmentation chain transfer (RAFT) polymerization. The use of a free chain transfer agent in solution allowed for a better control over graft ratio, chain length of grafted polymer, monomer conversion, and homopolymer formation in solution. An increase in polymerization time or degree of polymerization led to an increase in graft ratio, as expected from a living system.

Controlled Modification of Cellulosic Surfaces via the Reversible Addition - Fragmentation Chain Transfer (RAFT) Graft Polymerization Process

Background The surface modification of the cellulose fibres through graft polymerization is of great interest to the researcher due to their wide range of potential applications. Living radical polymerization methods have been used to achieve well defined and living polymer grafts from the cellulose surface. [1] RAFT polymerization is a versatile method that allows the synthesis of polymers with complex molecular architectures, low polydispersity, and functionalizable end groups. [2] The controlled surface modification of different solid substrates (such as poly(propylene) lanterns, core-shell microspheres, silica, gold nanoparticles, carbon nanotubes, and the Merrifield resin system) via RAFT has already been reported. [3-7] RAFT graft polymerization from a solid support can be performed using both the R-group approach (the leaving and reinitiating R-group attached to the backbone) and the Z-group approach (the stabilizing group attached to the backbone).The R-group approach follows the 'grafting from' mechanism and higher graft densities can be achieved relative to that achieved using the 'grafting onto' (Z-group) approach due to fewer steric hindrance problems. [7,8] The use of a solid-supported chain transfer agent (the R-group approach) to mediate the controlled graft polymerization from the different cellulosic surfaces such as cotton fabric and filter paper has been the focus of recent studies. [9-11] Current research into RAFT polymerization is covered by two reviews. [12,13] .

Reversible addition–fragmentation chain transfer graft copolymerization of styrene and m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate from polypropylene lanterns: Solid phases for scavenging applications

AbstractThe γ‐initiated reversible addition–fragmentation chain transfer mediated free‐radical graft copolymerization of styrene and m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate (TMI) from a polypropylene (PP) solid phase was performed with cumyl phenyldithioacetate (CPDA) as the chain‐transfer agent. The initial CPDA concentration was 8 × 10−3 mol L−1. Polymerizations were performed with a dose rate of 0.18 kGy h−1 at the ambient temperature. Initial comonomer mixtures with 15, 30, and 50 mol % TMI were used. Depending on the amount of TMI in the initial comonomer mixture, the plot of the grafting ratio versus the time showed two grafting regimes (for 15 and 50 mol % TMI) or one (for 30 mol % TMI). Scavenger lanterns with 15 and 50 mol % TMI featured two isocyanate loading regimes, the second with higher loading capacities. The scavenger lanterns with 30 mol % TMI showed a linear loading capacity over the full grafting ratio. A maximum loading capacity of 110 μmol per scavenger lantern was achieved with 50 mol % TMI at a grafting ratio of approximately 60 wt %. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 857–864, 2006

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

AbstractThe 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 (PSfree) 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 PSfree 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