Synthesis of amphiphilic copolymer brushes possessing alternating poly(methyl methacrylate) and poly(N‐isopropylacrylamide) grafts via a combination of ATRP and click chemistry

We report on the synthesis of well‐defined amphiphilic copolymer brushes possessing alternating poly(methyl methacrylate) and poly(N‐isopropylacrylamide) grafts, poly(PMMA‐alt‐PNIPAM), via a combination of atom transfer radical polymerization (ATRP) and click reaction (Scheme 1 ). Firstly, the alternating copolymerization of N‐[2‐(2‐bromoisobutyryloxy)ethyl]maleimide (BIBEMI) with 4‐vinylbenzyl azide (VBA) affords poly(BIBEMI‐alt‐VBA). Bearing bromine and azide moieties arranged in an alternating manner, multifunctional poly(BIBEMI‐alt‐VBA) is capable of initiating ATRP and participating in click reaction. The subsequent ATRP of methyl methacrylate (MMA) using poly(BIBEMI‐alt‐VBA) as the macroinitiator leads to poly(PMMA‐alt‐VBA) copolymer brush. Finally, amphiphilic poly(PMMA‐alt‐PNIPAM) copolymer brush bearing alternating PMMA and PNIPAM grafts is synthesized via the click reaction of poly(PMMA‐alt‐VBA) with an excess of alkynyl‐terminated PNIPAM (alkynyl‐PNIPAM). The click coupling efficiency of PNIPAM grafts is determined to be ～80%. Differential scanning calorimetry (DSC) analysis of poly(PMMA‐alt‐PNIPAM) reveals two glass transition temperatures (T_g). In aqueous solution, poly(PMMA‐alt‐PNIPAM) supramolecularly self‐assembles into spherical micelles consisting of PMMA cores and thermoresponsive PNIPAM coronas, which were characterized via a combination of temperature‐dependent optical transmittance, micro‐differential scanning calorimetry (micro‐DSC), dynamic and static laser light scattering (LLS), and transmission electron microscopy (TEM). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2608–2619, 2009     

Synthesis and gas permeation properties of poly(vinyl chloride)‐graft‐poly(vinyl pyrrolidone) membranes

A series of amphiphilic graft copolymers consisting of poly(vinyl chloride) (PVC) main chains and poly(vinyl pyrrolidone) (PVP) side chains, i.e. PVC‐g‐PVP, was synthesized via atom transfer radical polymerization (ATRP), as confirmed by ¹H NMR, FT‐IR spectroscopy, and gel permeation chromatography (GPC). Transmission electron microscope (TEM) and small angle X‐ray scattering (SAXS) analysis revealed the microphase‐separated structure of PVC‐g‐PVP and the domain spacing increased from 21.4 to 23.9 nm with increasing grafting degree. All the membranes exhibited completely amorphous structure and high Young's modulus and tensile strength, as revealed by wide angle X‐ray scattering (WAXS) and universal testing machine (UTM). Permeation experimental results using a CO₂/N₂ (50/50) mixture indicated that as an amount of PVP in a copolymer increased, CO₂ permeability increased without the sacrifice of selectivity. For example, the CO₂ permeability of PVC‐g‐PVP with 36 wt% of PVP at 35°C was about four times higher than that of the pristine PVC membrane. This improvement resulted from the increase of diffusivity due to the disruption of chain packing in PVC by the grafting of PVP, as confirmed by WAXS analysis. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of amphiphilic copolymer brushes: Poly(ethylene oxide)‐graft‐polystyrene

A well‐defined amphiphilic copolymer brush with poly(ethylene oxide) as the main chain and polystyrene as the side chain was successfully prepared by a combination of anionic polymerization and atom transfer radical polymerization (ATRP). The glycidol was first protected by ethyl vinyl ether to form 2,3‐epoxypropyl‐1‐ethoxyethyl ether and then copolymerized with ethylene oxide by the initiation of a mixture of diphenylmethylpotassium and triethylene glycol to give the well‐defined polymer poly(ethylene oxide‐co‐2,3‐epoxypropyl‐1‐ethoxyethyl ether); the latter was hydrolyzed under acidic conditions, and then the recovered copolymer of ethylene oxide and glycidol {poly(ethylene oxide‐co‐glycidol) [poly(EO‐co‐Gly)]} with multiple pending hydroxymethyl groups was esterified with 2‐bromoisobutyryl bromide to produce the macro‐ATRP initiator [poly(EO‐co‐Gly)_(ATRP). The latter was used to initiate the polymerization of styrene to form the amphiphilic copolymer brushes. The object products and intermediates were characterized with ¹H NMR, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, Fourier transform infrared, and size exclusion chromatography in detail. In all cases, the molecular weight distribution of the copolymer brushes was rather narrow (weight‐average molecular weight/number‐average molecular weight < 1.2), and the linear dependence of ln[M₀]/[M] (where [M₀] is the initial monomer concentration and [M] is the monomer concentration at a certain time) on time demonstrated that the styrene polymerization was well controlled. This method has universal significance for the preparation of copolymer brushes with hydrophilic poly(ethylene oxide) as the main chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4361–4371, 2006     

Polymer Brushes via ATRP: Role of Activator and Deactivator in the Surface‐Initiated ATRP of Styrene on Planar Substrates

The role of activator and deactivator species in the surface‐initiated atom‐transfer radical polymerization of styrene using CuBr/CuBr₂/pentamethyldiethylenetriamine as a model system is described. The influence of initially added deactivator with respect to the degree of controlling the layer growth and thickness is studied. Variation of the activator concentration results in changes of the kinetics as well as brush thicknesses consistent with the well‐known rate laws of ATRP.     

Incorporation of poly(2‐acrylamido‐2‐methyl‐N‐propanesulfonic acid) segments into block and brush copolymers by ATRP

2‐Acrylamido‐2‐methyl‐N‐propanesulfonic acid (AMPSA) was successfully polymerized via atom transfer radical polymerization (ATRP) using a copper chloride/2,2′‐bipyridine (bpy) catalyst complex after in situ neutralization of the acidic proton in AMPSA with tri(n‐butyl)amine (TBA). A 5 mol % excess of TBA was required to completely neutralize the acid and prevent protonation of the bpy ligand, as well as to avoid side reactions caused by large excess of TBA. The use of activators generated by electron transfer (AGET) ATRP with ascorbic acid as reducing agent resulted in both increased conversion of the AMPSA monomer during polymerization (up to 50% with a 0.8 [ascorbic acid]/[Cu(II)] ratio) and much shorter polymerization times (<30 min). Block copolymers and molecular brushes containing AMPSA side chains were prepared using this method, and the solution and surface behavior of these materials were investigated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5386–5396, 2009     

Utilization of poly(vinylchloride) and poly(vinylidenefluoride) as macroinitiators for ATRP polymerization of hydroxyethyl methacrylate: Electroanalytical and graft‐copolymerization studies

The utilization of poly(vinylchloride) (PVC) and poly(vinylidenefluoride) (PVDF) as macroinitiators for atom transfer radical polymerization (ATRP) of hydroxyethyl methacrylate (HEMA) was studied performing electroanalytical investigations and “grafting from” experiments to evaluate the potential modification of such commercial polymers by ATRP. The study was performed changing various operating parameters such as the nature of the copper salt, the ligand, the solvent, the temperature, and the reaction time. Electroanalytical data suggest that PVC can be easily activated by both CuCl/Tris(2‐pyridylmethyl)amine (TPMA) and CuCl/Tris[2‐(dimethylamino)ethyl]amine (Me₆TREN), two catalytic systems widely adopted for ATRP reactions, in a wide range of operating conditions. PVDF is more difficult to be activated, due to the higher strength of the C? F bond. In particular, the utilization of high temperature and of a more reductant redox couple such as Cu(I)Me₆TREN/Cu(II)Me₆TREN was needed to achieve a significant degree of grafting. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2524–2536     

Solution behavior of polyimide‐graft‐polystyrene copolymers in selective solvents

A polyimide‐graft‐polystyrene (PI‐g‐PS) copolymer with a polyimide backbone and polystyrene side chains was synthesized by the “grafting from” method using styrene polymerization on a polyimide multicenter macroinitiator via ATRP mechanism. The side chain grafting density z = 0.86 of PI‐g‐PS is rather high for graft‐copolymers synthesized by the ATRP method. Molecular characteristics and solution behavior of PI‐g‐PS were studied in selective solvents using light scattering and viscometry methods. In all solvents, the backbone tends to avoid contact with a poor solvent. To describe the conformation and hydrodynamic properties of PI‐g‐PS macromolecules in thermodynamically good solvents for side chains and PI‐g‐PS, the wormlike spherocylinder model is used. Macromolecules of the studied graft‐copolymer are characterized by high equilibrium rigidities (Kuhn segment length >20 nm). In Θ‐conditions, PI‐g‐PS macromolecules may be modeled by a rigid prolate ellipsoid of revolution with a low asymmetry form and a collapsed backbone as the ellipsoid core. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1539–1546     

Novel C60‐Anchored Two‐Armed Poly(tert‐butyl acrylate): Synthesis and Characterization

Summary: A multistep synthetic procedure for preparing novel C₆₀‐anchored two‐armed poly(tert‐butyl acrylate) was developed. First, two‐armed poly(tert‐butyl acrylate) bearing a malonate ester core with well‐controlled molecular weight was synthesized through atom transfer radical polymerization. The effective Bingel reaction between C₆₀ and the well‐defined polymer was then carried out to yield C₆₀‐anchored polymer. GPC, ¹H NMR, and UV‐vis spectroscopy indicated that the C₆₀‐anchored polymer was a monosubstituted and ‘closed’ 6,6‐ring‐bridged methanofullerene derivative.

Schematic of a novel C₆₀‐anchored two‐armed polymer.     

Nanofiltration membranes based on poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)‐graft‐poly(styrene sulfonic acid)

Graft copolymers comprising poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) backbone and poly(styrene sulfonic acid) side chains, i.e. P(VDF‐co‐CTFE)‐g‐PSSA were synthesized using atom transfer radical polymerization (ATRP) for composite nanofiltration (NF) membranes. Direct initiation of the secondary chlorinated site of CTFE units facilitates grafting of PSSA, as revealed by FT‐IR spectroscopy. The successful “grafting from” method and the microphase‐separated structure of the graft copolymer were confirmed by transmission electron microscopy (TEM). Wide angle X‐ray scattering (WAXS) also showed the decrease in the crystallinity of P(VDF‐co‐CTFE) upon graft copolymerization. Composite NF membranes were prepared from P(VDF‐co‐CTFE)‐g‐PSSA as a top layer coated onto P(VDF‐co‐CTFE) ultrafiltration support membrane. Both the rejections and the flux of composite membranes increased with increasing PSSA concentration due to the increase in SO₃H groups and membrane hydrophilicity, as supported by contact angle measurement. The rejections of NF membranes containing 47 wt% of PSSA were 83% for Na₂SO₄ and 28% for NaCl, and the solution flux were 18 and 32 L/m² hr, respectively, at 0.3 MPa pressure. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of poly(vinyl acetate)‐graft‐polystyrene by a combination of cobalt‐mediated radical polymerization and atom transfer radical polymerization

Vinyl acetate and vinyl chloroacetate were copolymerized in the presence of a bis(trifluoro‐2,4‐pentanedionato)cobalt(II) complex and 2,2′‐azobis(4‐methoxy‐2,4‐dimethylvaleronitrile) at 30 °C, forming a cobalt‐capped poly(vinyl acetate‐co‐vinyl chloroacetate). The addition of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy after a certain degree of copolymerization was reached afforded 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐terminated poly(vinyl acetate‐co‐vinyl chloroacetate) (PVOAc–MI; number‐average molecular weight = 31,000, weight‐average molecular weight/number‐average molecular weight = 1.24). A ¹H NMR study of the resulting PVOAc–MI revealed quantitative terminal 2,2,6,6‐tetramethyl‐1‐piperidinyloxy functionality and the presence of 5.5 mol % vinyl chloroacetate in the copolymer. The atom transfer radical polymerization (ATRP) of styrene (St) was studied with ethyl chloroacetate as a model initiator and five different Cu‐based catalysts. Catalysts with bis(2‐pyridylmethyl)octadecylamine (BPMODA) or tris(2‐pyridylmethyl)amine (TPMA) ligands provided the highest initiation efficiency and best control over the polymerization of St. The grafting‐from ATRP of St from PVOAc–MI catalyzed by copper complexes with BPMODA or TPMA ligands provided poly(vinyl acetate)‐graft‐polystyrene copolymers with relatively high polydispersity (>1.5) because of intermolecular coupling between growing polystyrene (PSt) grafts. After the hydrolysis of the graft copolymers, the cleaved PSt side chains had a monomodal molecular weight distribution with some tailing toward the lower number‐average molecular weight region because of termination. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 447–459, 2007     

Photopatternable substrate‐independent poly(glycidyl methacrylate‐ran‐2‐(acryloyloxy) ethyl 2‐methylacrylate) polymer films for immobilization of biomolecules

We report the synthesis and characterization of a photocrosslinkable copolymer containing reactive epoxy groups for binding biomolecules. The epoxide‐containing copolymer poly(glycidyl methacrylate‐ran‐2‐(acryloyloxy) ethyl 2‐methylacrylate) offers distinct advantages such as ease of application to various substrates, enhanced stability of the bound oligonucleotide, low autofluorescence, and the ability to be photopatterned allowing localization of the linkers. The copolymer uses pendant acryloyl groups to control the crosslinking without sacrificing the epoxide groups. The films were characterized using ellipsometry, atomic force microscopy, and fluorescence microscopy. The films on glass, silicon wafer, and stainless steel showed no appreciable degradation in water, tetrahydrofuran, and acetone for ～4 months. The surface topography for a given thickness of crosslinked film was dictated by the deposition conditions. A 16mer oligonucleotide was immobilized on the thin films. A linear relationship between the film thickness and amount of oligonucleotide immobilized was observed with a maximum signal‐to‐background ratio (S/B) of 225 for a 60‐nm‐thick film, a value 50% higher than the S/B for an epoxide monolayer. The crosslinked films maintained a high fluorescence signal following long aqueous washing which is appealing for biological microarrays, immobilizing proteins, and study of slow differentiating cells where stability of the scaffold is relevant. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5826–5838, 2008     

Thermo-responsive polymer brushes as intelligent biointerfaces: preparation via ATRP and characterization

PIPAAm-brush grafted glass substrates with various graft densities and chain lengths were prepared via surface-initiated ATRP. Temperature-dependent physicochemical properties of the surfaces were characterized by means of ATR/FT-IR spectroscopy, XPS, AFM, and contact angle measurements. ATRP conditions influence the amount of grafted PIPAAm and the surface wettability and roughness of the substrate. Fibronectin adsorption and EC adhesion increased with decreasing density of PIPAAm brushes. EC adhesion was diminished with increasing PIPAAm graft length. Thus, the preparation of PIPAAm brush surface with various graft densities and chain lengths using the surface-initiated ATRP is an effective method for modulating thermo-responsive properties of surfaces.     

Synthesis and characterizations of the four‐armed amphiphilic block copolymer S[poly(2,3‐dihydroxypropyl acrylate)‐block‐poly(methyl acrylate)]4

The polymers poly[(2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate] (PDMDMA) and four‐armed PDMDMA with well‐defined structures were prepared by the polymerization of (2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate (DMDMA) in the presence of an atom transfer radical polymerization (ATRP) initiator system. The successive hydrolyses of the polymers obtained produced the corresponding water‐soluble polymers poly(2,3‐dihydroxypropyl acrylate) (PDHPA) and four‐armed PDHPA. The controllable features for the ATRP of DMDMA were studied with kinetic measurements, gel permeation chromatography (GPC), and NMR data. With the macroinitiators PDMDMA–Br and four‐armed PDMDMA–Br in combination with CuBr and 2,2′‐bipyridine, the block polymerizations of methyl acrylate (MA) with PDMDMA were carried out to afford the AB diblock copolymer PDMDMA‐b‐MA and the four‐armed block copolymer S{poly[(2,2‐dimethyl‐1,3‐dioxolane‐4yl) methyl acrylate]‐block‐poly(methyl acrylate)}₄, respectively. The block copolymers were hydrolyzed in an acidic aqueous solution, and the amphiphilic diblock and four‐armed block copolymers poly(2,3‐dihydroxypropyl acrylate)‐block‐poly(methyl acrylate) were prepared successfully. The structures of these block copolymers were verified with NMR and GPC measurements. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3062–3072, 2001     

Elaboration of well‐defined Rasta resins and their use as supported catalytic systems for atom transfer radical polymerization

New supported catalytic systems based on the immobilization of a ligand onto supported (co)polymers were prepared, allowing copper immobilization onto a solid support during the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). These supported catalysts were elaborated by the ATRP of 2‐vinyl‐4,4‐dimethyl‐5‐oxazolone and/or styrene onto a Wang resin initiator. Two different approaches were used, involving well‐defined architectures synthesized by ATRP. First, a supported electrophilic homopolymer [Wang‐g‐poly(2‐vinyl‐4,4‐dimethyl‐5‐oxazolone)] was synthesized to obtain an azlactone ring at each repetitive unit, and a supported statistical copolymer [Wang‐g‐poly(2‐vinyl‐4,4‐dimethyl‐5‐oxazolone‐stat‐styrene)] was synthesized to introduce a distance between the azlactone rings. The azlactone‐based (co)polymers were then modified by a reaction with N,N,N′,N′‐tetraethyldiethylenetriamine (TEDETA) to create supported complexing sites for copper bromide. The ATRP of MMA was studied with these supported ligands, and a first‐order kinetic plot was obtained, but high polydispersity indices of the obtained poly(methyl methacrylate) were observed (polydispersity index > 2). On the other hand, the supported ATRP of styrene was performed, followed by the nucleophilic substitution of bromine by TEDETA (Wang‐g‐polystyrene–N,N,N′,N′‐tetraethyldiethylenetriamine) at the chain end of the grafted polystyrene chains. This strategy led the ligand away from the core bead, depending on the length of the polystyrene block (number‐average molecular weight determined by size exclusion chromatography = 1100–2250 g/mol). These supported complexes mediated a controlled polymerization of MMA, yielding polymers with controlled molar masses and low polydispersity indices. Moreover, after the polymerization, 96% of the initial copper was kept in the beads. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5316–5328, 2006     

Growth of poly(methyl methacrylate) brushes on silicon surfaces by atom transfer radical polymerization

Poly(methyl methacrylate) (PMMA) brushes are grown by surface‐initiated atom transfer radical polymerization on silicon surfaces at various polymerization temperatures. Kinetic studies show that the layer thickness scales linearly with the degree of polymerization of the polymers under some conditions, indicating a constant graft density of the surface‐attached chains. At high temperatures, the layer growth is a controlled process only for short reaction times, and after a rapid increase, the film growth levels off, and a constant thickness is obtained. At lower reaction temperatures, polymers with a lower polydispersity are obtained, but at the expense of a much slower growth rate. Accordingly, intermediate temperatures yield the highest film thickness on experimentally feasible timescales. The reinitiation of these surface‐grafted PMMA chains at room temperature to either extend the chains or grow a chemically different polyglycidylmethacrylate block demonstrates the presence of active ends and the living nature of the surface‐grafted PMMA chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1758–1769, 2006     

Synthesis of poly(ethylene‐co‐vinyl alcohol)‐g‐polystyrene graft copolymer and their applications for ordered porous film and compatibilizer

A series of new functional poly(ethylene‐co‐vinyl alcohol)‐g‐polystyrene graft copolymers (EVAL‐g‐PS) with controlled molecular weight (M_n = 38,000–94,000 g mol^?1) and molecular weight distribution (M_w/M_n = 2.31–3.49) were synthesized via a grafting from methodology. The molecular structure and component of EVAL‐g‐PS graft copolymers were confirmed by the analysis of their ¹H NMR spectra and GPC curves. The porous films of such copolymers were fabricated via a static breath‐figure (BF) process. The influencing factors on the morphology of such porous films, such as solvent, temperature, polymer concentration, and molecular weight of polymer were investigated. Ordered porous film and better regularity was fabricated through a static BF process using EVAL‐g‐PS solution in CHCl₃. Scanning electron microscopy observation reveals that the EVAL‐g‐PS graft copolymer is an efficient compatibilizer for the blend system of low‐density polyethylene/polystyrene. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 516–524     

Synthesis of Novel Rod‐Coil Amphiphilic Block Copolymers PAA‐b‐DPS with Fréchet‐Type Dendronized Polystyrene and Poly(acrylic acid)

A series of well‐defined rod‐coil PAA‐b‐DPS block copolymers, containing Fréchet‐type dendronized polystyrene (DPS) with different generation as a rod‐like hydrophobic block and poly(acrylic acid) (PAA) as a hydrophilic coil were synthesized. The procedure included the following steps: the precursor PMA‐b‐DPS copolymer was prepared through ATRP of Fréchet‐type dendritic styrene macromonomer bearing the first to the third generation (G1–G3), respectively, initiated by poly(methyl acrylate) (PMA‐Br). Then, by converting PMA into PAA by subsequent hydrolysis, the targeted amphiphilic copolymers were obtained. Moreover, by using the rod‐coil amphiphiles as building blocks, large compound micelles and vesicles were formed in a binary solvent mixture of DMF/H₂O. Morphological changes in self‐assembly showed dependence on the length of the dendronized block.

     

Comparison of surface confined ATRP and SET‐LRP syntheses for a series of amino (meth)acrylate polymer brushes on silicon substrates

A series of poly(amino (meth)acrylate) brushes, poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA), poly(2‐(diethylamino)ethyl methacrylate) (PDEAEMA), poly(2‐(dimethylamino)ethyl acrylate) (PDMAEA), poly(2‐(tert‐butylamino)ethyl methacrylate) (PTBAEMA), has been synthesized via surface‐confined controlled/living radical polymerizations using surface‐confined initiator from silane self‐assembled monolayers (SAMs) on silicon (Si) wafer substrates. Chemical methods and efficacies for two types of living radical polymerization, atom transfer radical (ATRP) and single electron transfer (SET‐LRP), are described and contrasted for the surface confined polymerization of poly(amino (meth)acrylate)s. Effects of solvent, catalyst/ligand system, and temperature on polymerization success were examined. Chemical compositions after each reaction step were characterized with FTIR spectroscopy, contact angle goniometry, and X‐ray photoelectron spectroscopy while the SAM and polymer brush thicknesses were measured with spectroscopic ellipsometry. For the first time, this study demonstrates successful surface‐confined polymerization of a series of poly(amine (meth)acrylate) brushes from Si‐SAM substrates using a copper metal electron donor catalyst. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6552–6560, 2009