Stability of growing polymer chain ends for nitroxide-mediated photo-living radical polymerization

The stability of the growing polymer chain ends for the nitroxide-mediated photo-living radical polymerization of methyl methacrylate (MMA) was explored through block copolymerization with isopropyl methacrylate ( ⁱ PMA). The block copolymerization of ⁱ PMA was performed with the PMMA prepolymer prepared by the photopolymerization of MMA using the racemic-(2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) (r-AMDV) as the initiator, 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (MTEMPO) as the mediator, and (4-tert-butylphenyl)-diphenylsulfonium triflate ( ^t BuS) as the photo-acid generator. When the polymerization of MMA was carried out for 6.5 h, the resulting block copolymer showed a bimodal GPC due to the deactivation of part of the growing chain ends of the prepolymer. On the other hand, when the MMA polymerization was shortened to 5 h, the unimodal block copolymer was obtained without deactivation of the prepolymer.     

Preparation of end-grafted polymer brushes by nitroxide-mediated free radical polymerization of vaporized vinyl monomers

In this work, we report a gas-phase polymerization approach to create end-grafted vinyl based polymer films on silicon oxide based substrates. The "surface-initiated vapor deposition polymerization" (SI-VDP) of vaporized vinyl monomers, via the nitroxide-mediated free radical polymerization mechanism, was developed to fabricate various homo- and block copolymer brushes from surface-bound initiators, 1-(4'-oxa-2'-phenyl-12'-trimethoxysilyldodecyloxy)-2,2,6,6-tetra-methylpiperidine ("TEMPO"). The resulting polymer thin films were characterized by the Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, and contact angle goniometry, respectively, to identify the surface composition, film thickness, surface coverage, and water contact angles. Through the SI-VDP, end-grafted polymer films of polystyrene (PSt), poly(acrylic acid) (PAAc), poly(N-(2-hydroxypropyl) methacrylamide) (PHPMA), and poly(N-isopropylacrylamide) (PNIPAAm) with 10-200 nm thicknesses were fabricated. Furthermore, the block copolymer films of PAAc (1st block)-b-PSt (2nd block), PSt (1st block)-b-PAAc (2nd block), and a triblock copolymer film of PAAc (1st)-b-PSt (2nd)-b-PHPMA (3rd), were also fabricated, suggesting the "renewability" of the TEMPO-initiated polymerization in the SI-VDP scheme. It is also noticed that the SI-VDP is more efficient than the conventional solution phase polymerization in producing functional polymer brushes such as PNIPAAm, PAAc, or PAAc-b-PSt end-grafted films. In summary, our studies have shown clear advantages of the SI-VDP setup for the nitroxide-mediated polymerization scheme in controlling synthesis of end-grafted homo- and copolymer thin films.     

Peptide–polymer vesicles prepared by atom transfer radical polymerization

The peptide Ac‐Ser‐Ala‐Gly‐Ala‐Gly‐Glu‐Gly‐Ala‐Gly‐Ala‐Gly‐Ser‐Gly‐OH was prepared with solid‐phase peptide chemistry. Before the removal of the peptide from the solid support, the alcohol side groups of the two serines were functionalized with an α‐bromo ester moiety to create a bifunctional initiator. This peptide‐based initiator was used in solution for the atom transfer radical polymerization of methyl methacrylate to yield a well‐defined ABA triblock copolymer, in which the poly(methyl methacrylate) end blocks had a number‐average molecular weight of 1.1 kg/mol (based on ¹H NMR spectroscopy) and a polydispersity of 1.17. The aggregation behavior of this amphiphilic triblock copolymer was then investigated. Upon the suspension of the polymer in a mixture of tetrahydrofuran and water, followed by the removal of tetrahydrofuran, spherical aggregates were formed. By the application of different electron microscopy techniques, it was determined that these aggregates were polymersomes, presumably coexisting with large compound micelles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6355–6366, 2005     

Proton‐conductive polymer nanocomposite membranes prepared from telechelic fluorinated polymers containing perfluorosulfonic acid side chains

New classes of fluorinated polymer–polysilsesquioxane nanocomposites have been designed and synthesized. The synthesis method includes radical polymerization using the functional benzoyl peroxide initiator for the telechelic fluorinated polymers with perfluorosulfonic acids in the side chains and a subsequent in situ sol–gel condensation of the prepared triethoxylsilane‐terminated fluorinated polymers with oxide precursors. The telechelic polymer and nanocomposites have been carefully characterized by ¹H and ¹⁹F NMR, FTIR, TGA, and TEM. The ion‐exchange capacity (IEC), water uptake, the state of the absorbed water, and transport properties of the composite membranes have been extensively studied as a function of the content and structure of the fillers. Unlike the conventional Nafion/silica composites, the proton conductivity of the prepared membranes increases steadily with the addition of small amounts of the polysilsesquioxane fillers. In particular, the sulfopropylated polysilsesquioxane‐based nanocomposites display proton conductivities greater than Nafion. This is attributed to the presence of pendant sulfonic acids in the fillers, which increases IEC and offers continuous proton transport channels between the fillers and the polymer matrix. The methanol permeability of the prepared membranes has also been examined. Lower methanol permeability and higher electrochemical selectivity than those of Nafion have been demonstrated in the polysilsesquioxane‐based nanocomposites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis of dendronized polymer brushes containing metallo‐supramolecular polymer side chains

A new kind of dendronized polymer brush with metallo‐supramolecular polymer side chains was fabricated by a combination of macromonomer and graft‐to approach. The alternating copolymers of maleic anhydride and styryl macromonomers pendant with Fréchet‐type dendrons of three generations were reported previously. In this article, terpyridine groups were introduced along the backbone of the dendronized polymers through the amidolysis of anhydride groups. The terpyridine functionalized PEO linear chains were then incorporated through the complexation of terpyridine and Ru(II) ion. Thus, dendronized polymer brushes with amphiphilic properties were synthesized. AFM analysis showed worm‐like single molecular morphologies of the polymers of three generations, and ¹H NMR analysis indicated that such molecular brushes had an amphiphilic nature in solution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3303–3310, 2007     

Synthesis and characterization of surface-initiated polymer brush prepared by reverse atom transfer radical polymerization

Surface-initiated reverse atom transfer radical polymerization (reverse ATRP) technique was used to synthesize well-controlled nanostructure of polymer brushes from silicon wafer. Kinetic studies revealed a linear increase in polymer film thickness with reaction time, indicating that chain growth from surface was a controlled process with a “living” characteristic. This technique provides a simple and efficient approach to create various nanostructures of polymer brushes potentially used for designing nanodevices. Analysis of the polymer brush layers was conducted using ellipsometry, XPS, AFM and contact angle measurements, respectively.     

Siloxane-terminated solubilizing side chains: bringing conjugated polymer backbones closer and boosting hole mobilities in thin-film transistors

We introduce a novel siloxane-terminated solubilizing group and demonstrate its effectiveness as a side chain in an isoindigo-based conjugated polymer. An average hole mobility of 2.00 cm(2) V(-1) s(-1) (with a maximum mobility of 2.48 cm(2) V(-1) s(-1)), was obtained from solution-processed thin-film transistors, one of the highest mobilities reported to date. In contrast, the reference polymer with a branched alkyl side chain gave an average hole mobility of 0.30 cm(2) V(-1) s(-1) and a maximum mobility of 0.57 cm(2) V(-1) s(-1). This is largely explained by the polymer packing: our new polymer exhibited a π-π stacking distance of 3.58 ?, while the reference polymer showed a distance of 3.76 ?.     

Well-defined polymers with acetal side chains as reactive scaffolds synthesized by atom transfer radical polymerization

The synthesis of a polymer with acetal functionalized side chains, deprotection to aldehydes, and conjugation of aminooxy-modified molecules is reported. Poly(3,3′-diethoxypropyl methacrylate) (PDEPMA) was prepared by atom transfer radical polymerization (ATRP). Kinetic investigation of the ATRP of DEPMA from ethyl 2-bromoisobutyrate in methanol with copper (I) bromide and 2,2′-bipyridine (BIPY) at ambient temperature revealed a controlled polymerization. Altering the initial monomer to initiator ratios resulted in 75–93% conversion to polymers with different molecular weights and narrow molecular weight distributions (PDIs < 1.3). Reactive aldehyde groups were produced by hydrolysis of the acetals in dilute acid. Aminooxy-functionalized oligo(ethylene glycol) and O-(carboxymethyl)hydroxylamine were conjugated to the side chains via oxime linkages. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5004–5013, 2006     

Synthesis and characterization of a new network polymer electrolyte containing polyether in the main chains and side chains

A new network polymer electrolyte matrix with polyether in the side chains and main chains was synthesized by the azo-macroinitiator method and urethane reaction. The macroinitiator, polymer and network polymer were confirmed by Fourier-transform infrared (FT-IR) spectroscopy and ¹H NMR. FT-IR was also used to study the environment of lithium ions doped in these network polymer electrolytes. Three important groups are considered: N-H, carbonyl, and ether groups. The thermal properties of the polymer electrolytes were measured by differential scanning calorimetry and thermogravimetric analysis. The T_g value of this polymer is less than that of a general comb-like polymer. Added lithium ions interact with the oxygen atoms on ether groups, causing the T_g of the polymer electrolyte to increase. Moreover, the interaction between lithium ions and ether groups decreases the decomposition temperature of the polymer. The conductivity measured by AC impedance reached a maximum of 10⁻⁴ S cm⁻¹. A plot of conductivity vs. temperature fit the Vogel-Tamman-Fulcher equation, indicating that ionic mobility in this network polymer electrolyte is coupled to segmental chain movements.     

Superparamagnetic lysozyme surface-imprinted polymer prepared by atom transfer radical polymerization and its application for protein separation

Molecular imprinting as a promising and facile separation technique has received much attention because of their high selectivity for target molecules. In this study, the superparamagnetic lysozyme surface-imprinted polymer was prepared by a novel fabricating protocol, the grafting of the imprinted polymer on magnetic particles in aqueous media was done by atom transfer radical polymerization (ATRP), and the properties of the imprinted polymer were characterized in detail. Its high selective adsorption and recognition to lysozyme demonstrated the separation ability of the magnetic imprinted material to template molecule, and it has been used for quick and direct separation of lysozyme from the mixture of standard proteins and real egg white samples under an external magnetic field. Furthermore, the elution of lysozyme from the imprinted material was achieved by PEG/sulphate aqueous two-phase system, which caused lysozyme not only desorption from the imprinted materials but also redistribution in the top and bottom phase of aqueous two-phase system. The aqueous two-phase system exhibited some of the extraction and enrichment effect to desorbed lysozyme. Our results showed that ATRP is a promising method for the protein molecularly imprinted polymer preparation.     

Synthesis and thermal behaviour of polybutadiene resins containing acetylene groups in the side chains

Two resins were synthesized containing triple bonds in the side chains. The polymers were characterized by IR and NMR spectroscopy. DSC and thermal decomposition temperatures were determined. These resins show high thermal stability.     

Amphiphilic polymer conetworks prepared by controlled radical polymerization using a nitroxide cross‐linker

Tandem atom transfer radical polymerization (ATRP) and nitroxide‐mediated radical polymerization (NMRP) were used to synthesize a polystyrene‐co‐poly(acrylic acid) (poly(St‐co‐AA)) network, in which the two components were interconnected by covalent bond. First, a specific cross‐linker, 1,4‐bis(1′‐(4″‐acryloyloxy‐2″,2″,6″,6″‐tetramethylpiperidinyloxy)ethyl)benzene (di‐AET), a bifunctional alkoxyamine possessing two acrylate groups, was copolymerized with tert‐butyl acrylate through ATRP to prepare a precursor gel. The gel was then used to initiate the NMRP of styrene to prepare poly(St‐co‐(t‐BA)) conetwork, in which the cross‐linkages are composed of polystyrene segments. Finally, the poly(St‐co‐(t‐BA)) conetwork was hydrolyzed to produce amphiphilic poly(St‐co‐AA) conetwork. The resulting gels show swelling ability in both organic solvent and water, which is characteristic of amphiphilic conetworks. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4141–4149, 2010     

Removal of cefalexin using yeast surface‐imprinted polymer prepared by atom transfer radical polymerization

The first use of yeast as a support in the molecular imprinting field combined with atom transfer radical polymerization was described. Then, the as‐prepared molecularly imprinted polymers were characterized by Fourier transmission infrared spectrometry, scanning electron microscope, thermogravimetric analysis, and elemental analysis. The obtained imprinted polymers demonstrated elliptical‐shaped particles with the thickness of imprinting layer of 0.63 μm. The batch mode experiments were adopted to investigate the adsorption equilibrium, kinetics, and selectivity. The kinetic properties of imprinted polymers were well described by the pseudo‐second‐order kinetic equation, indicating the chemical process was the rate‐limiting step for the adsorption of cefalexin (CFX). The equilibrium data were well fitted by the Freundlich isotherm, and the multimolecular layers adsorption capacity of imprinted polymers was 34.07 mg g^?1 at 298 K. The selectivity analysis suggested that the imprinted polymers exhibited excellent selective recognition for CFX in the presence of other compounds with related structure. Finally, the analytical method based on the imprinted polymers extraction coupled with high‐performance liquid chromatograph was successfully used for CFX analysis in spiked pork and water samples.     

Dehalogenation of polymers prepared by atom transfer radical polymerization

Polymers prepared by atom transfer radical polymerization (ATRP) have well‐defined end groups, predetermined by the initiator used. A typical initiator is an alkyl halide from which the halogen is transferred to one chain end. To remove the halogen end group, dehalogenation with trialkyltin hydride has been used. Procedures for the removal of the polymer halogen end groups are described, one of them being a one‐pot reaction where the dehalogenation of the polymer chain ends occurs immediately after polymerization.     

Synthesis and characterization of an acrylate polymer containing chlorine-1,3-dioxalane groups in side chains

Poly[2-（4-chlorophenyl）-1,3-dioxolan-4-yl]methyl acrylate,poly（CPhDMA）,was synthesized with radical polymerization process using 2,2′-azobisisobutyronitrile as radical initiator in 1,4-dioxane at 60℃.The structure of poly（CPhDMA） was confirmed by means of UV-Vis,FT-IR,¹H-NMR,and ¹³C-NMR spectral techniques.The molecular weight distribution values of the polymer were determined with gel permeation chromatography（GPC）.The number-average molecular weight（M_n）,weight-average molecular weight（M_W） and polydispersity index（PDI） values of poly（CPhDMA） were determined to be 10300,21600 and 2.097,respectively.The thermal degradation kinetics of the polymer was investigated by using TG/DTG-DTA and DSC analyses at different heating rates in dynamic nitrogen atmosphere.The apparent activation energy values obtained by Flynn-Wall-Ozawa and Friedman methods were found to be 91.68 and 85.23 kJ mol^-1,respectively,for thermal decomposition of poly（CPhDMA）.Also,the thermal degradation activation energy value of poly（CPhDMA） was calculated by using the Kissinger method based on the DTG,DTA and DSC data.Then the mechanism function of it was determined by master plots method.Finally,electrical and optical properties of poly（CPhDMA） were determined by four-point probe and UV-Vis techniques,respectively.     

Effects of initiators and photo-acid generators on nitroxide-mediated photo-living radical polymerization of methyl methacrylate

The effects of the structure of initiators and photo-acid generators on the nitroxide-mediated photo-living radical polymerization of methyl methacrylate were explored. The bulk polymerization was performed at room temperature using nine different initiators in the presence of (4-tert-butylphenyl)diphenylsulfonium triflate as the photo-acid generator. 2,2′-Azobisisobutyronitrile, 2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl 2,2′-azobis(2-methylpropionate), and 2,2′-azobis(N-butyl-2-methylpropionamide) produced the polymers with a molecular weight distribution (MWD) around 1.6, while the racemic- and meso-(2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) provided a 1.4 MWD. 2,2′-Azobis(2-methylbutyronitrile), 1,1′-azobis(cyclohexane-1-carbonitrile), and 1-(cyano-1-methylethoxy)-4-methoxy-2,2,6,6-tetramethylpiperidine produced a broad MWD over 4.0. The structure of the photo-acid generator also had an influence on the molecular weight control. The photo-acid generator of sulfonium salts supporting the alkyl, methoxy, phenoxy, methylthio, and tert-butoxycarbonylmethoxy groups, coupled with halogens with the exception of the iodide had no effect on the MWD. On the other hand, the salts containing the iodide, phenylthio, and naphthyl groups produced polymers with broad MWDs and with uncontrolled high molecular weights.     

Synthesis of novel polymer containing selenium by radical addition polymerization of 1,4-benzenediselenol to 1,4-divinylbenzene

A novel addition polymerization of 1,4-benzenediselenol (BDSe) to 1,4-divinylbenzene (DVB) was carried out with various azo radical initiators [dimethyl 2,2′-azobisisobutyrate (DAIB), 1,1′-azobis(1-acetoxy-1-phenylethane) (AAPE), and AIBN] in toluene at 65 and 75°C under a nitrogen atmosphere. The polymerization proceded without an induction period, and pale-yellowish powder polymers were obtained in 89% yields for 75 h (DAIB), 89% yields for 24 h (AAPE), and 60% yields for 8 h (AIBN). The molecular weight (M_w) of the insoluble polymers in toluene was about 4000 (IBN) to 14,000 (DAIB or AAPE) by GPC. The polymer had an alternating structure of BDSe to DVB units by ¹H-NMR, IR analyses, and selenium contents, but the polymer contained the diselenide linkage by Raman spectroscopy. By AIBN initiator, the yield of the polymers did not increase over 60% and higher molecular weight polymer was hardly obtained. According to the model addition reaction of benzeneselenol to styrene by AIBN, it was found that AIBN was consumed by the side reaction between dimethyl-N-(2-cyano-2-propyl)ketenimine derivedAppl 11 from AIBN and benzeneselenol to give the adduct C, MH⁺ 295 by DCI MS. On the other hand, DAIB and AAPE initiators, which do not form a ketenimine intermediate, gave the polymers of higher molecular weight in a higher yield. The polymer film exhibited high refractive index (n²⁵_D = 1.81) and a reversible phase transition between a transparency and an opaque by thermal mode. © 1994 John Wiley & Sons, Inc.     

Preferred spatial arrangement of the aromatic side chains in linear oligopeptides containing tyrosine.

¹H-NMR. studies of the protected linear tetrapeptides CF₃CO-Gly-Gly-L -Tyr-L -Ala-OCH₃, CF₃CO-Gly-L -Ala-L -Tyr-L -Ala-OCH₃ and CF₃CO-Gly-L -Ala-L -Tyr-Gly-OCH₃ showed that the side chain of the tyrosyl residue was in all three peptides preferentially oriented towards the amino terminus of the peptide chain. This preferred spatial arrangement of the aromatic side chain was manifested in the chemical shifts of the amino acid residue preceding tyrosine and in the vicinal spin-spin coupling constants ³J_HCαCβH of tyrosine.     

Highly selective capture of nucleosides with boronic acid functionalized polymer brushes prepared by atom transfer radical polymerization

The nucleoside or modified nucleoside level in biological fluids reflects the pathological or physiological state of the body. Boronate affinity absorbents are widely used to selectively extract nucleosides from complex samples. In this work, a novel functionalized absorbent was synthesized by attaching 4‐mercaptophenylboronic acid to gold nanoparticles on modified attapulgite. The surface of the attapulgite was modified by poly(acryloyloxyethyltrimethyl ammonium chloride) by atom transfer radical polymerization, creating many polymer brushes on the surface. The resultant material exhibited superior binding capacity (30.83 mg/g) for adenosine and was able to capture cis‐diol nucleosides from 1000‐fold interferences. Finally, to demonstrate its potential for biomolecule extraction, this boronate affinity material was used to preconcentrate nucleosides from human urine and plasma.