Functionalization of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) films via surface‐initiated atom transfer radical polymerization: Comparison with the conventional free‐radical grafting procedure

We modified hydrophobic poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBHV) films with hydrophilic chains to control their surface properties. We designed and investigated surface‐initiated atom transfer radical polymerization (SI‐ATRP) to modify the PHBHV films by grafting poly(2‐hydroxyethyl methacrylate) (PHEMA) from the surface. This method consisted of two steps. In the first step, amino functions were formed on the surface by aminolysis; this was followed by the immobilization of an atom transfer radical polymerization initiator, 2‐bromoisobutyryl bromide. In the second step, the PHEMA chains were grafted to the substrate by a polymerization process initiated by the surface‐bound initiator. The SI‐ATRP technique was expected to favor a polymerization process with a controlled manner. The experimental results demonstrate that the grafting density was controlled by the reaction conditions in the first step. The grafted films were analyzed by Fourier transform infrared spectroscopy, contact angle testing, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy. The results show that grafted chains under the SI‐ATRP method were preferentially located on the surface for surface grafting and in the bulk for conventional free‐radical polymerization initiated by benzoyl peroxide. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of end-functional polymers on silica nanoparticles via a combination of atom transfer radical polymerization and click chemistry

This article describes a divergent strategy to prepare grafted polymer chains with functional end groups for surface modification of nanoparticles with other functional groups. This preparation is achieved through a combination of surface-initiated atom transfer radical polymerization (ATRP) and click chemistry. First, the surface of the silica nanoparticles was modified with polystyrene (PSt) brushes via the “grafting from” approach. The terminal bromides of PSt-grafted silica nanoparticles were then substituted with azido groups. These azido-terminated PSt brushes on the nanoparticle surface were reacted with various alkyne-terminated functional end groups via click reactions. In all cases, FTIR and ¹H NMR spectra indicated quantitative transformation of the chain ends of polystyrene brushes on silica nanoparticles into the desired functional group.     

Synthesis of poly(styrene-co-acrylonitrile) copolymer brushes on silica nanoparticles through surface-initiated polymerization

In the present investigation, silica nanoparticles have been coated with poly(styrene-co-acrylonitrile) (SAN) copolymer brushes synthesized via surface-initiated atom transfer radical polymerization (ATRP). In the initial step, silica nanoparticles were functionalized with triethoxysilane-based ATR initiator, 6-(2-bromo-2-methyl) propionyloxy hexyl triethoxysilane. Successful formation of the covalent linkages between ATRP initiator and silica nanoparticles is further corroborated using thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The surface initiated ATRP of the styrene and the acrylonitrile mediated by a copper complex was carried out using the initiator fixed silica nanoparticles in the presence of a sacrificial (free) initiator. The polymerization is preceded in a living manner in all examined cases, producing nanoparticles coated with well-defined poly(styrene-co-acrylonitrile) (SAN) brushes with molecular weight in the range of 12–22 kDa. SAN-grafted silica nanoparticles were characterized using TGA which showed significant weight loss in the temperature range of 340–420 °C confirming the formation of the polymer brushes on the surface with graft densities in the range of 0.109–0.190 chains/nm². Successful formation of the SAN copolymer brushes are further characterized by FTIR and proton nuclear magnetic resonance spectroscopy techniques. Differential scanning calorimetric studies revealed that the SAN copolymer grafted onto silica nanoparticles exhibits higher glass transition temperatures than free SAN copolymers. Transmission electron microscopy and dynamic light scattering studies revealed that the SAN copolymer-grafted silica nanoparticles showed relatively fine dispersion in organic solvents such as tetrahydrofuran, when compared to bare silica nanoparticles.     

Surface‐graft hyperbranched polymer via self‐condensing atom transfer radical polymerization from zinc oxide nanoparticles

We present the synthesis of hyperbranched polymer grafted zinc oxide (ZnO) hybrid nanoparticles by self‐condensing vinyl polymerization (SCVP) via surface‐initiated atom transfer radical polymerizations (SI‐ATRP) from ZnO surfaces. ATRP initiators were covalently linked to the surfaces of ZnO particles, followed by SCVP of an initiator‐monomer (“inimer”) which has both a polymerizable group and an initiating group in the same molecule. Well‐defined polymer chains were grown from the surfaces to yield hybrid nanoparticles comprised of ZnO cores and hyperbranched polymer shells having multifunctional chlorobenzyl functional end groups. The percentage of grafting (PG%) achieved 429% in 6 h, calculated from the elemental analysis results. The hybrid nanoparticles were also characterized using Fourier transform infrared spectroscopy, UV–vis absorption spectroscopy, thermogravimetric analysis, X‐ray photoelectron spectroscopy, and transmission electron microscopy. POLYM. ENG. SCI., 47:1296–1301, 2007. © 2007 Society of Plastics Engineers     

Surface‐initiated atom transfer radical polymerization (ATRP) of styrene from silica nanoparticles under UV irradiation

Diethyldithiocarbamyl‐modified silica nanoparticles were prepared and used as macroinitiator for the surface‐initiated atom transfer radical polymerization (SI‐ATRP) of styrene under UV irradiation. Well‐defined polymer chains were grown from the nanoparticle surfaces to yield particles composed of a silica core and a well‐defined, densely grafted outer PS layer with a mass ratio of styrene to silica, or percentage grafting, of 276.3% after an UV irradiation time of 5 h. Copyright © 2004 Society of Chemical Industry     

‘Graft from’ polymerization on colloidal silica particles: elaboration of alkoxyamine grafted surface by in situ trapping of carbon radicals

We report in this paper an original method for the synthesis of polybutylacrylate grafted on silica particles. First, we use the Stoeber method to synthesize silica particles with a narrow size distribution. An initiator for radical-chain controlled polymerization is then grafted on the silica surface in two steps. Trimethoxysilylpropyl methacrylate (TPM) is first grafted on silica by simple condensation. Then, a alkoxyamine initiator N-tert-butyl-N-1-diethylphosphono2,2-dimethylpropyl-0,1-methoxycarbonyl ethylhydroxylamine (MONAMS) reacts with the CC double bond of the TPM to form the grafted initiator of radical polymerization. The last step is the grafting of butylacrylate. For this, we use living free radical polymerization that allows to control the molecular weight and the polydispersity of the polybutylacrylate chains. We show that this synthesis method makes it possible to obtain a colloidal suspension of silica particles having a mean size of about 88 nm, a weak polydispersity and an important grafting density of polybutylacrylate (PBA).     

Synthesis of controlled thermoresponsive PET track‐etched membranes by ATRP method

Controlled thermoresponsive PET track‐etched membranes were synthesized by grafting N‐isopropylacrylamide (NIPAAm) onto the membrane surface via atom transfer radical polymerization (ATRP). The initial measurements were made to determine the anchoring of ATRP initiator on PET membrane surface. Thereafter, polymerization was carried out to control the mass of polymer by controlling reaction time grafted from the membrane surface and, ATR‐FTIR, grafting degree measurements, water contact angle measurements, TGA, and SEM were used to characterize changes in the chemical functionality, surface and pore morphology of membranes as a result of modification. Water flux measurements were used to evaluate the thermoresponsive capacity of grafted membranes. The results show the grafted PET track‐etched membranes exhibit rapid and reversible response of permeability to environmental temperature, and its permeability could be controlled by controlling polymerization time using ATRP method. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Inorganic silica functionalized with PLLA chains via grafting methods to enhance the melt strength of PLLA/silica nanocomposites

The low melt strength greatly limits the application of PLA as biodegradable package materials produced by film blowing method. Modified silica nanoparticles are introduced into PLA matrix to solve this problem in this study. To build Poly (l-lactide) nanocomposites successfully, two kinds of convenient and efficient methods are conducted to synthesize well-defined topological PLLA grafted SiO₂ nanoparticle. One is the ring-opening of l-lactide (Grafting from), and another is nucleophilic addition reaction (Grafting to). The structure, molecular weight of grafted PLLA chains, grafting density, and the thermal decomposition behavior of the nanoparticles prepared by different methods are characterized. By varying the contents of the initiator SiO₂ and the molecular weight of the reacted PLA chains, high density-low molecular weight PLLA grafted SiO₂ are obtained in “grafting from” while high molecular weight-low grafting density PLLA grafted SiO₂ are synthesized in “grafting to”. It is exactly in good agreement with the theoretic model. The spatial distribution of nanoparticles as well as the interaction force between nanoparticles and matrix is critical important to structuring bionanocomposites with desirable properties. So the two kinds of synthesized nanoparticles are introduced into PLA matrix in our contribution to evaluate these two factors, respectively. The TEM and SEM results both reveal the uniform dispersion of nanoparticles after modified. While the extension and shear rheology results show that the long grafted chains covalently connected on the surface of the silica via “grafting to” contribute more to enhance the melt strength of PLA. Meanwhile, stabilized PLA nanocomposites films with modified silica via “grafting to” method are successfully blown base on these researches. The research in this work constitutes a robust way to design melt-strengthen PLA/SiO₂ nanocomposites.     

Modification of Silica Nanoparticles with Miktoarm Polymer Brushes via ATRP

Silica nanoparticles were successfully modified with miktoarm brushes via atom transfer radical polymerization (ATRP) using three different approaches. In the first approach: “graft onto and from”, a poly(tert-butyl acrylate) (PtBA) macroinitiator was grafted onto the surface of a monomer-modified silica nanoparticle. Then, polystyrene (PSt) brush was grafted from the surface-tethered reactive chain end. In the second approach: “two-step reverse ATRP”, the PtBA and poly(n-butyl acrylate) (PBA) brushes were consecutively grafted from initiator-modified silica particles via ATRP. The polymerization was initiated from the silica surface via a two-step controlled thermal decomposition of surface-tethered diazo initiator moieties. In the third method: “diblock first”, a diblock copolymer of poly(tert-butyl acrylate) and poly(glycidyl methacrylate) (PtBA-b-PGMA) was grafted onto amine-modified silica particles. The diblock copolymer was covalently attached to the silica surface via interaction between surface-tethered amine groups and the short reactive block containing glycidyl groups. Next, the polystyrene brushes were grafted from surface-tethered reactive chain end. The materials prepared by three different approaches were characterized using gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). The PtBA brushes were hydrolyzed under acidic conditions to form poly(acrylic acid) (PAA) brushes. The resulting materials were imaged using atomic force microscopy (AFM) and transmission electron microscopy (TEM).     

A novel method of surface-initiate atom transfer radical polymerization of styrene from silica nanoparticles for preparation of monodispersed core-shell hybrid nanospheres

A new kind of initiator, 3-(2-bromo-2-methylacryloxy)propyltriethysiliane (MPTS-Br), was prepared with a simply hydrobrominated commercial silane coupling agent (3-methacryloxy-proplytriethysilane, MPTS). It has been one-step self-assemble onto the surface of silica nanoparticles, and by using this initiator-modified nanoparticle (SiO₂-MPTS-Br) as macroinitiator for atom transfer radical polymerization (ATRP). Structurally well-defined homopolymer polystyrene (PS) and block polymer poly(styrene-b-methyl methacrylate) (PS-b-PMMA) chains were grown from the nanoparticles surface to yield individual particles composed of silica core and thick-coated polymer shell. The graft parameters could be calculated from the elemental analysis (EA) results, and linear plots of percentage of grafting (PG%) and conversion of monomer (C%) versus polymerizing time were achieved, respectively. Narrow molecular weight distribution (M_w/M_n) for the graft polymer samples were characterized by the gel permeation chromatography (GPC). The graft polymerizations exhibited the characteristics of the controlled/“living” polymerization. The glass transition temperature (T_g) of SiO₂-g-PS after polymerizing time of 24 h was found about 133 °C which was different from the polymer not grafted on the silica at 102 °C by the differential scanning calorimetry (DSC) analysis. The products were also characterized by FT-IR, XPS and TEM. The robustness and simplicity of this method may make large-scale manufacture of these polymer-coated nanospheres possible.     

原子转移自由基聚合法接枝改性纳米纤维素及其功能化应用

纳米纤维素不仅具有天然纤维素的基本结构和特性,还具有纳米粒子的独特性能,使其成为众多领域的研究热点。然而,由于纳米纤维素表面存在丰富的羟基,导致表面化学性质单一,需要对其进行化学改性拓宽应用领域。原子转移自由基聚合法(ATRP)能够对纳米纤维素表面进行接枝改性,从而赋予纳米纤维素多样化的功能特性,是纳米纤维素高值化应用的重要方法。本文首先总结了传统ATRP法以及四种新型ATRP法在纳米纤维素表面接枝改性中的应用进展;随后介绍了ATRP法在纳米纤维素端基接枝改性中的应用进展;然后分别介绍了ATRP改性的纳米纤维素接枝共聚物在纳米复合增强、智能响应、环保和生物医疗等领域的应用研究;最后总结了ATRP法改性纳米纤维素存在的难点,并展望了未来ATRP法在纳米纤维素接枝改性领域的发展趋势。     

Silica/polystyrene and silica/polystyrene‐b‐polymethacryloxypropyltrimethoxysilane hybrid nanoparticles via surface‐initiated ATRP and comparison of their wettabilities

Both silica/polystyrene (SiO₂/PS) and silica/polystyrene‐b‐polymethacryloxypropyltrimethoxysilane (SiO₂/PS‐b‐PMPTS) hybrid nanoparticles were synthesized via surface‐initiated atom transfer radical polymerization (SI‐ATRP) from SiO₂ nanoparticles. The growths of all polymers via ATRP from the SiO₂ surfaces were well controlled as demonstrated by the macromolecular characteristics of the grafted chains. Their wettabilities were measured and compared by water contact angle (WCA) and surface roughness. The results show that the nanoparticles possess hydrophobic surface properties. The static WCA of SiO₂/PS‐b‐PMPTS hybrid nanoparticles is smaller than that of SiO₂/PS hybrid nanoparticles, meanwhile, the surface roughness of SiO₂/PS‐b‐PMPTS hybrid nanoparticles is yet slightly rougher than that of SiO₂/PS hybrid nanoparticles, which shows that the combination and competition of surface chemistry and roughness of a solid material can finally determine its wettability. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Surface‐initiated nitroxide‐mediated radical polymerization of 4‐vinylpyridine on magnetite nanoparticles

Poly (4‐vinylpyridine) (P4VP) brushes had been prepared by the surface‐initiated nitroxide‐mediated radical polymerization of 4‐VP on the surface of 3‐methacryloxyproyltrimethoxysilane (3‐MPS)‐modified magnetite nanoparticles with an average diameter of 30 nm. The grafting polymerization was accomplished by nitroxide‐mediated polymerization of 4‐VP, using 4‐hydroxyl‐2,2,6,6‐tetramethyl‐1‐piperidinyl‐oxy (HTEMPO·) free radical as capping agent and benzoyl peroxide (BPO) as initiator. X‐ray photoelectron spectra (XPS) measurement demonstrated that the alkoxysilane initiator layer had formed on the magnetite surface. Gel permeation chromatograph analysis and XPS measurement suggested that the amount of grafted P4VP increases with increasing grafting time. The amount of P4VP grafted on the surface could be determined to be 0.09 chains/nm² by thermogravimetric analysis. The P4VP‐grafted magnetite particles exhibited the characteristics of multidomain system, distinct from the single domain attributes of the pure magnetite particles. Atomic force‐microscopy analysis revealed the diameter of the grafted P4VP magnetic latex particles is in the range of 120 nm to 150 nm. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Comparison study of a chiral stationary phase based on cellulose derivatives prepared by “grafting from” and “grafting to” methods

Chiral stationary phase (CSP) with cellulose derivatives was synthesized using the “grafting from” and “grafting to” methods. The “grafting to” method involves the bonding of a preformed end‐functionalized polymer to reactive surface amine groups on the silica gel. The “grafting from” involves the immobilization of initiator onto the aminated silica gel followed by atom transfer radical polymerization (ATRP) to generate the chiral polymer chains. The successful preparation of the CSP with cellulose derivatives prepared by ATRP was confirmed by FE‐SEM, XPS, EA, and thermal analysis. The chiral resolution of the CSP with cellulose derivatives was evaluated by high‐performance liquid chromatography using 10 racemates with various mobile phases that consisted of hexane/alcohol, hexane/THF, and hexane/chloroform. Furthermore, the CSP with cellulose derivatives prepared by “grafting from” and “grafting to” were compared and discussed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Grafting of polystyrene chains on surfaces of nanosilica particles via peroxide bulk polymerization

This article describes an in situ bulk polymerization process of styrene in the presence of silica nanoparticles. In this peroxide bulk polymerization process, two polystyrene fractions are formed: A polystyrene (PS) fraction attached to the particle's surface, which cannot be detached by hot xylene extraction, and an unattached PS fraction which dissolves in xylene. Solvent extraction and TGA measurements have confirmed the existence of grafted PS chains to the silica surfaces. FTIR measurements have indicated the existence of Si O C bonds connecting the PS grafts to the silica surface. Polypropylene (PP) was blended with the extracted PS‐g‐silica particles to produce concentrations of 1–3% nanoparticles in the PP composites. A remarkably improved dispersability of the nanoparticles was achieved, thus grafting reduces re‐agglomeration and increases the affinity of the grafted surface to the polymer matrix. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Surface grafting of polyacrylamide from polyethylene‐based copolymer film

Atom transfer radical polymerization (ATRP) was used to grow polyacrylamide from the surface of ethylene–acrylic acid copolymer (EAA) film. The surface functionalization constituted initiator immobilization and surface graft polymerization. All reaction steps were conducted at 24 ± 3°C; polymerization was done in aqueous solution. For initiator immobilization, the carboxylic acid groups on EAA film were converted to acid chloride groups; further reaction with ethanolamines gave hydroxyl groups onto which 2‐bromoisobutyryl bromide initiator was attached. ATR‐FTIR data indicated that 1.64 ± 0.09 times higher initiator density was achieved by using diethanolamine, relative to ethanolamine. Acrylamide monomer was polymerized from the initiator by ATRP to yield nondistorted, transparent films with polymerization times of up to 1 h. For films prepared using diethanolamine, 1 h polymerization time reduced the static water contact angle by more than 50°, significantly increasing the hydrophilicity of the film surface. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1589–1595, 2004     

ATRP grafting from silica surface to create first and second generation of grafts

Summary (11'-Chlorodimethylsilylundecyl)-2-chloro-2-phenylacetate 2 as an atom transfer radical polymerisation (ATRP) initiator was bound covalently to the surface of silica. ATRP grafting of styrene monomer from the silica surface was achieved and the grafts were detached from the solid particles for analysis. It is shown that after polymerisation of a first generation of grafts and work-up of the thus grafted silica the chain ends of the grafts are still active to initiate a second monomer feed to further chain growth. Received: 17 July 1999/Revised version: 12 December 1999/Accepted: 10 January 2000     

Controlled polymerization of methylmethacrylate from fumed SiO2 nanoparticles through atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) is a promising method to synthesize well‐defined polymer/inorganic nanoparticles. However, the surface‐initiated ATRP from commercially mass produced inorganic nanoparticles has seldom been studied. In this study, the surface‐initiated ATRP of methylmethacrylate (MMA) from commercially mass produced fumed silica (SiO₂) nanoparticles was investigated. Unlike the ATRP of MMA initiated from a free initiator, the controllability of ATRP of MMA from the surface of fumed silica nanoparticles was much better using ligand 2,2'‐bipyridine (bpy) than N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) as the initiator was immobilized on the surface of the SiO₂ nanoparticles and the presence of the SiO₂ nanoparticles made the CuCl/bpy catalyst system a homogeneous catalyst system and CuCl/PMDETA a heterogeneous one. The appropriate molar ratio of monomer and initiator was essential for preparing controlled PMMA/SiO₂ nanoparticles. The entire process of ATRP of MMA from the surface of SiO₂ nanoparticles was controllable when using bpy as ligand, xylene as solvent and with a monomer to initiator ratio of 300:1. The ¹H NMR results indicated that the PMMA on the surface of the SiO₂ was prepared via ATRP initiated from 4‐(chloromethyl)phenyltrimethoxysilane. The well‐defined PMMA/SiO₂ nanoparticles obtained have good thermal stability and are well dispersed in organic media as proved by TGA, dynamic light scattering and transmission electron microscopy. © 2013 Society of Chemical Industry     

Synthesis of well‐defined responsive membranes with fixable solvent responsiveness

A versatile method is described to synthesize a new family of solvent‐responsive membranes whose response states can be not only tunable but also fixable via ultraviolet (UV) irradiation induced crosslinking. The atom transfer radical polymerization (ATRP) initiator 2‐bromoisobutyryl bromide was first immobilized on the poly(ethylene terephthalate) (PET) track‐etched membrane followed by room‐temperature ATRP grafting of poly(2‐hydroxyethyl methacrylate) (PHEMA) and poly(2‐hydroxyethyl methacrylate‐co‐2‐(dimethylamino)ethyl methacrylate) (P(HEMA‐co‐DMAEMA)) respectively. The hydroxyl groups of PHEMA were further reacted with cinnamoyl chloride (a photosensitive monomer) to obtain photo‐crosslinkable PET‐g‐PHEMA/CA membrane and PET‐g‐P(HEMA/CA‐co‐DMAEMA) membrane. The length of grafted polymer chains was controllable by varying the polymerization time. X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy in attenuated total reflection and thermogravimetric analysis were employed to characterize the resulting membranes. The various membrane surface morphologies resulting from different states of the grafted chains in water and dimethylformamide were characterized by scanning electron microscopy. It was demonstrated that the grafted P(HEMA/CA‐co‐DMAEMA) chains had more pronounced solvent responsivity than the grafted PHEMA/CA chains. The surface morphologies of the grafted membranes could be adjusted using different solvents and fixed by UV irradiation crosslinking. © 2014 Society of Chemical Industry     

CdS/CdSe quantum dot co-sensitized graphene nanocomposites via polymer brush templated synthesis for potential photovoltaic applications

CdS/CdSe quantum dot (QDs) co-sensitized graphene sheets have been obtained via polymer brush templated synthesis. Firstly, the anionic functional polymer (polymethacrylate cadmium) was grafted via the surface initiated atomic transfer radical polymerization (ATRP) using a macromolecular initiator, which contains polymerized pyrene units for chemical anchoring on graphene surface and alkyl bromines to initiate ATRP. Then, the coordinated cadmium in the polymer chains can act as a source precursor for QDs. After reaction, polymer brushes can be recovered and act as the nanoreactor via the absorption of cadmium ions by carboxylate groups. So, high density QDs can be multiply uploaded onto the graphene surface by repeated steps. The as-prepared composite materials exhibited significantly enhanced visible light response compared to plain graphene, and have potential applications as the platform to build solar cell assembles.