Thermoresponsive hydrogel of poly(glycidyl methacrylate‐co‐N‐isopropylacrylamide) as a nanoreactor of gold nanoparticles

The synthesis of a thermoresponsive hydrogel of poly(glycidyl methacrylate‐co‐N‐isopropylacrylamide) (PGMA‐co‐PNIPAM) and its application as a nanoreactor of gold nanoparticles are studied. The thermoresponsive copolymer of PGMA‐co‐PNIPAM is first synthesized by the copolymerization of glycidyl methacrylate and N‐isopropylacrylamide using 2,2′‐azobis(isobutyronitrile) as an initiator in tetrahydrofuran at 70 °C and then crosslinked with diethylenetriamine to form a thermoresponsive hydrogel. The lower critical solution temperature (LCST) of the thermoresponsive hydrogel is about 50 °C. The hydrogel exists as 280‐nm spheres below the LCST. The diameter of the spherical hydrogel gradually decreases to a minimum constant of 113 nm when the temperature increases to 75 °C. The hydrogel can act as a nanoreactor of gold nanoparticles because of the coordination of nitrogen atoms of the crosslinker with gold ions, on which a hydrogel/gold nanocomposite is synthesized. The LCST of the resultant hydrogel/gold nanocomposite is similar to that of the hydrogel. The size of the resultant gold nanoparticles is about 15 nm. The hydrogel/gold nanocomposite can act as a smart and recyclable catalyst. At a temperature below the LCST, the thermoresponsive nanocomposite is a homogeneous and efficient catalyst, whereas at a temperature above the LCST, it becomes a heterogeneous one, and its catalytic activity greatly decreases. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2812–2819, 2007     

Synthesis and characterization of polyethylene/clay–silica nanocomposites: A montmorillonite/silica‐hybrid‐supported catalyst and in situ polymerization

A novel approach to the preparation of polyethylene (PE) nanocomposites, with montmorillonite/silica hybrid (MT‐Si) supported catalyst, was developed. MT‐Si was prepared by depositing silica nanoparticles between galleries of the MT. A common zirconocene catalyst [bis(cyclopentadienyl)zirconium dichloride/methylaluminoxane] was fixed on the MT‐Si surface by a simple method. After ethylene polymerization, two classes of nanofillers (clay layers and silica nanoparticles) were dispersed concurrently in the PE matrix and PE/clay–silica nanocomposites were obtained. Exfoliation of the clay layers and dispersion of the silica nanoparticles were examined with transmission electron microscopy. Physical properties of the nanocomposites were characterized by tensile tests, dynamic mechanical analysis, and DSC. The nanocomposites with a low nanofiller loading (<10 wt %) exhibited good mechanical properties. The nanocomposite powder produced with the supported catalyst had a granular morphology and a high bulk density, typical of a heterogeneous catalyst system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 941–949, 2004     

Efficient synthesis of 5‐substituted tetrazoles catalysed by palladium–S‐methylisothiourea complex supported on boehmite nanoparticles

An efficient and general method is reported for the synthesis of 5‐substituted 1H ‐tetrazole derivatives in the presence of S ‐methylisothiourea complex of palladium immobilized on boehmite nanoparticles (Pd‐SMTU@boehmite) as an efficient and recyclable nanocatalyst. Boehmite nanoparticles were not sensitive to air or moisture and were prepared without inert atmosphere in water at room temperature. Then a novel type of phosphine‐free palladium complex was immobilized on these nanoparticles. This catalyst was characterized using Fourier transform infrared, thermogravimetric, Brunauer–Emmett–Teller, transmission and scanning electron microscopic, energy‐dispersive X‐ray spectroscopic, X‐ray diffraction and inductively coupled plasma optical emission spectroscopic techniques. The catalyst was reused several times without palladium leaching or change in its structure.     

Conductive ATO‐acrylate nanocomposite hybrid coatings: Experimental results and modeling

The electrical volume conductivity σ of antimony‐doped tin oxide (ATO)–acrylate nanocomposite hybrid coatings was investigated. The relation between σ and the volume filler fraction p was analyzed for the ATO‐acrylate coatings containing ATO nanoparticles grafted with different amounts of 3‐methacryloxy‐propyl‐trimethoxy‐silane coupling agent. Percolation thresholds were observed at very low filler fractions (1–2 vol %) for the coatings containing ATO nanoparticles with a low amount of surface grafting. A modified effective medium approximation (EMA) model was introduced. This model takes into consideration different distances between adjacent semiconductive particles in the particle network. The model elucidates how self‐arrangement of the particles influences the location of the percolation threshold in the log σ ? p plot. The modified EMA model can successfully explain the multiple transition behavior and the variable percolation thresholds found for the ATO‐acrylate nanocomposite hybrid coatings. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2147–2160, 2007     

Poly(styrene‐b‐tetrahydrofuran)/clay nanocomposites by mechanistic transformation

Synthesis of poly(styrene‐block‐tetrahydrofuran) (PSt‐b‐PTHF) block copolymer on the surfaces of intercalated and exfoliated silicate (clay) layers by mechanistic transformation was described. First, the polystyrene/montmorillonite (PSt/MMT) nanocomposite was synthesized by in situ atom transfer radical polymerization (ATRP) from initiator moieties immobilized within the silicate galleries of the clay particles. Transmission electron microscopy (TEM) analysis showed the existence of both intercalated and exfoliated structures in the nanocomposite. Then, the PSt‐b‐PTHF/MMT nanocomposite was prepared by mechanistic transformation from ATRP to cationic ring opening polymerization (CROP). The TGA thermogram of the PSt‐b‐PTHF/MMT nanocomposite has two decomposition stages corresponding to PTHF and PSt segments. All nanocomposites exhibit enhanced thermal stabilities compared with the virgin polymer segments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2190–2197, 2009     

Terephthalic acid derived ligand‐stabilized palladium nanocomposite catalyst for Heck coupling reaction: without surface‐modified heterogeneous catalyst

A new protocol is reported for the synthesis of a heterogeneous palladium nanocomposite stabilized with a terephthalic acid‐derived ligand (N ,N ‐bis(4‐hydroxy‐3‐methoxybenzylidene)terephthalohydrazide). This is a highly insoluble ligand in common organic solvents, except dimethylformamide and dimethylsulfoxide. The resulting palladium nanocomposite acts as an efficient catalyst precursor for Mizoroki–Heck coupling reactions conducted under various reaction conditions. The spectral data suggest that the rate, yield and recycling of the catalyst are more effective for C–C coupling reactions. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of UV‐cured acrylic–silica hybrid nanocomposites from dendritic acrylic oligomer and acrylic‐functionalized silica

An acrylic–silica hybrid polymeric nanocomposite, comprising well‐distributed silica nanoparticles in acrylic matrix, has been synthesized at a markedly rapid rate from a dendritic acrylic oligomer (DAO) and an acrylic‐functionalized silica (A‐silica) via UV‐curing. A‐silica was made by functioning colloidal silica nanoparticles with 3‐methacryloxypropyltrimethoxysilane (MATMS) and DAO was formed by reacting 1,5‐diamino‐2‐methylpentane (MPMDA) with trimethylopropane triacrylate (TMPTA). The MATMS has been found either doubly or singly bonded to silica nanoparticles but not triply bonded, and the inclusion of MATMS into the siloxane network structure increases the size of silica nanoparticles. The well distribution of A‐silica and its good compatibility with DAO cause an increase in T_d of the acrylic–silica hybrid material. Silica nanoparticles are too small to cause any significant light scattering, and do not have deleterious effects on transparency. The “hybrid‐on‐polyethylene terephathalate” films exhibited satisfactory hardness and surface roughness because of silica nanoparticles. The preparation as well as the characterization of the constituting species and the final hybrid material are described in detail. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8149–8158, 2008     

Engineered mesoporous ionic‐modified γ‐Fe2O3@hydroxyapatite decorated with palladium nanoparticles and its catalytic properties in water

A new mesoporous organic–inorganic nanocomposite was formulated and then used as stabilizer and support for the preparation of palladium nanoparticles (Pd NPs). The properties and structure of Pd NPs immobilized on prepared 1,4‐diazabicyclo[2.2.2]octane (DABCO) chemically tagged on mesoporous γ‐Fe₂O₃@hydroxyapatite (ionic modified (IM)‐MHA) were investigated using various techniques. The synergistic effects of the combined properties of MHA, DABCO and Pd NPs, and catalytic activity of γ‐Fe₂O₃@hydroxyapatite‐DABCO‐Pd (IM‐MHA‐Pd) were investigated for the Heck cross‐coupling reaction in aqueous media. The appropriate surface area and pore size of mesoporous IM‐MHA nanocomposite can provide a favourable hard template for immobilization of Pd NPs. The loading level of Pd in the nanocatalyst was 0.51 mmol g^?1. DABCO bonded to the MHA surface acts as a Pd NP stabilizer and can also lead to colloidal stability of the nanocomposite in aqueous solution. The results reveal that IM‐MHA‐Pd is highly efficient for coupling reactions of a wide range of aryl halides with olefins under green conditions. The superparamagnetic nature of the nanocomposite means that the catalyst to be easily separated from solution through magnetic decantation, and the catalytic activity of the recycled IM‐MHA‐Pd showed almost no appreciable loss even after six consecutive runs.     

Pendant cyclic carbonate‐polymer/Na‐smectite nanocomposites via in situ intercalative polymerization and solution intercalation

Nanocomposites of sodium smectite with polyether‐ and polystyrene‐containing pendant cyclic carbonates offer a novel approach to improving hydraulic barrier properties of Na‐smectite liners to saline leachates. The cyclic carbonate polyethers were prepared by cationic ring opening polymerization of a cyclic carbonate‐containing epoxide, whilst polystyrene polymers having pendant cyclic carbonate groups were obtained from radical photopolymerization of styrene. Na‐smectite nanocomposites of these polymers were formed via clay in situ polymerization and solution intercalation methods. X‐ray diffraction (XRD) and FT‐IR analysis confirmed that the polyether can be intercalated within the layers of smectite via in situ as well as solution intercalation of the pre‐formed polymer. The cyclic carbonate polyether nanocomposite was more resistant to leaching in 3M aqueous sodium chloride than its respective cyclic carbonate. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2421–2429     

Poly(methacrylic acid)‐grafted clay–thermoplastic elastomer composites with water‐induced shape‐memory effects

Composites with excellent water‐induced shape‐memory effects (SMEs) were successfully synthesized by first using clay as the SME‐activating phase and thermoplastic polyurethane (TPU) as the matrix. Naturally abundant clay was grafted with poly(methacrylic acid) (PMAA) to improve particle interactions, which allowed for the formation of strong percolation networks in the composites, determined by swelling tests and dynamic mechanical analysis in combination with theoretical modeling. This led to significant improvements of the polymer modulus and high water absorptions, causing reversible modulus changes of up to 30 times from the wet to the dry condition. The results from cyclic wetting‐drying‐stretching tests showed the TPU–clay composite containing 10.4 vol % PMAA‐grafted clay exhibited the best SMEs among the composites investigated, with the shape fixity and shape recovery ratios being 82% and 91%, respectively. Besides SMEs, these new polymer–clay composites were also pH‐sensitive and mechanically adaptive upon exposure to water. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1513–1522     

Synthesis and characterization of multiblock copolymers composed of poly(5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one) outer blocks and poly(L‐lactide) inner blocks

Ethylene glycol (EG) initiated, hydroxyl‐telechelic poly(L ‐lactide) (PLLA) was employed as a macroinitiator in the presence of a stannous octoate catalyst in the ring‐opening polymerization of 5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one (MBC) with the goal of creating A–B–A‐type block copolymers having polycarbonate outer blocks and a polyester center block. Because of transesterification reactions involving the PLLA block, multiblock copolymers of the A–(B–A)_n–B–A type were actually obtained, where A is poly(5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one), B is PLLA, and n is greater than 0. ¹H and ¹³C NMR spectroscopy of the product copolymers yielded evidence of the multiblock structure and provided the lactide sequence length. For a PLLA macroinitiator with a number‐average molecular weight of 2500 g/mol, the product block copolymer had an n value of 0.8 and an average lactide sequence length (consecutive C₆H₈O₄ units uninterrupted by either an EG or MBC unit) of 6.1. For a PLLA macroinitiator with a number‐average molecular weight of 14,400 g/mol, n was 18, and the average lactide sequence length was 5.0. Additional evidence of the block copolymer architecture was revealed through the retention of PLLA crystallinity as measured by differential scanning calorimetry and wide‐angle X‐ray diffraction. Multiblock copolymers with PLLA crystallinity could be achieved only with isolated PLLA macroinitiators; sequential addition of MBC to high‐conversion L ‐lactide polymerizations resulted in excessive randomization, presumably because of residual L ‐lactide monomer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6817–6835, 2006     

Surface‐modified hydroxyapatite linked by L‐lactic acid oligomer in the absence of catalyst

A new surface modification method of hydroxyapatite nanoparticles (n‐HA) by surface grafting reaction of L ‐lactic acid oligomer with carboxyl terminal (LAc oligomer) in the absence of any catalyst was developed. The LAc oligomer with a certain molecular weight was directly synthesized by condensation of L ‐lactic acid. Surface‐modified HA nanoparticles (p‐HA) were attested by Fourier transformation infrared spectroscopy, ³¹P MAS‐NMR, and thermal gravimetric analysis (TGA). The results showed that LAc oligomer could be grafted onto the n‐HA surface by forming a Ca carboxylate bond. The grafting amount of LAc oligomer was about 13.3 wt %. The p‐HA/PLLA composites showed good mechanical properties and uniform microstructure. The tensile strength and modulus of the p‐HA/PLLA composite containing 15 wt % of p‐HA were 68.7 MPa and 2.1 GPa, respectively, while those of the n‐HA/PLLA composites were 43 MPa and 1.6 GPa, respectively. The p‐HA/PLLA composites had better thermal stability than n‐HA/PLLA composites and neat PLLA had, as determined by isothermal TGA. The hydrolytic degradation behavior of the composites in phosphate buffered saline (PBS, pH 7.4) was investigated. The p‐HA/PLLA composites lost their mechanical properties more slowly than did n‐HA/PLLA composites in PBS because of their reinforced adhesion between the HA filler and PLLA matrix. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5177–5185, 2005     

Novel fluorinated stabilizers for ring‐opening polymerization in supercritical carbon dioxide

Ring‐opening polymerization (ROP) in supercritical carbon dioxide (scCO₂) has been the subject of much recent interest, although few publications describe the development of stabilizers to produce biodegradable particles of poly(L ‐lactide) (PLLA) and polyglycolide (PGA). Here we describe the synthesis of a series of novel fluorinated diblock copolymers by the acid‐catalyzed esterification of well‐defined blocks of polycaprolactone (PCL) with Krytox 157FSL, a carboxylic acid terminated perfluoropolyether. These diblock copolymers were then tested as stabilizers in the ROP of glycolide and L ‐lactide, or a mixture of the two, in scCO₂, and this resulted in the corresponding homopolymers or random copolymers. In the absence of stabilizers, only aggregated solids were formed. When the reaction was repeated with a stabilizer, PGA and PLLA were obtained as discrete microparticles. The stabilizer efficiency increased as the length of the polymer‐philic PCL block increased. One optimized stabilizer worked at loadings as low as 3% (w/w) with respect to the monomer, demonstrating these to be extremely effective stabilizers. It was found that to produce microparticles with this process, the product polymers must be semicrystalline; amorphous polymers, such as poly(lactide‐co‐glycolide), are plasticized by scCO₂ and yield only aggregated solids rather than discrete particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6573–6585, 2005     

Facile fabrication of hybrid nanoparticles surface grafted with multi‐responsive polymer brushes via block copolymer micellization and self‐catalyzed core gelation

Poly(2‐(dimethylamino)ethyl methacrylate)‐b‐poly(γ‐methacryloxypropyl‐trimethoxysilane) (PDMA‐b‐PMPS) was synthesized via consecutive reversible addition‐fragmentation chain transfer (RAFT) polymerizations in 1,4‐dioxane. Subsequent micellization of the obtained amphiphilic diblock polymer in aqueous solution led to the formation of nanoparticles consisting of hydrophobic PMPS cores and well‐solvated PDMA shells. Containing tertiary amine residues, PDMA blocks in micelle coronas can spontaneously catalyze the sol–gel reactions of trimethoxysilyl groups within PMPS cores, leading to the formation of hybrid nanoparticles coated with PDMA brushes. Transmission electron microscopy (TEM) and laser light scattering (LLS) revealed the presence of monodisperse spherical hybrid nanoparticles, and the grafting density of PDMA chains at the surface of nanoparticle cores was estimated to be ～5.8 nm²/chain. PDMA brushes exhibit dual stimuli‐responsiveness, and the swelling/collapse of them can be finely tuned with solution pH and temperatures. The obtained multi‐responsive hybrid nanoparticles might find potential applications in fields such as smart devices, recyclable catalysts, and intelligent nanocarriers for drug delivery or gene transfection. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2379–2389, 2008     

Biochar as heterogeneous support for immobilization of Pd as efficient and reusable biocatalyst in C–C coupling reactions

Biochar is a stable and carbon‐rich solid which has a high density of carbonyl, hydroxyl and carboxylic acid functional groups on its surface. In this work, the surface of biochar nanoparticles (BNPs) was modified with 3‐choloropropyltrimtoxysilane and further 2‐(thiophen‐2‐yl)‐1H‐benzo[d]imidazole was anchored on its surface. Then, palladium nanoparticles were fabricated on the surface of the modified BNPs and further the catalytic application was studied as recyclable biocatalyst in carbon–carbon coupling reactions such as Suzuki–Miyaura and Heck–Mizoroki cross‐coupling reactions. The structure of the catalyst was characterized using scanning electron microscopy, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, thermogravimetric analysis, X‐ray diffraction and atomic absorption spectroscopy. The catalyst can be reused several times without a decrease in its catalytic efficiency. In addition to the several advantages reported, application of biochar as catalyst support for the first time is a major novelty of the present work.     

Functionalization of multi‐walled carbon nanotubes with pramipexole for immobilization of palladium nanoparticles and investigation of catalytic activity in the Sonogashira coupling reaction

Pramipexole drug was attached to the surface of multi‐walled carbon nanotubes (MWCNTs) by reaction of acylated carbon nanotubes with pramipexole for the first time. The modified MWCNTs were characterized using Fourier transform infrared spectroscopy, transmission and scanning electron microscopies and CHNS analysis. The prepared pramipexole–MWCNTs were used for immobilization of palladium nanoparticles as a novel nanocatalyst. After characterization of the final nanocomposite, the pramipexole–MWCNTs/Pd was applied as a novel phosphine‐free recyclable heterogeneous catalyst for Sonogashira reactions. Interestingly, the novel catalyst could be recovered and recycled five times without any significant loss in activity.     

An improved preparation of mesoporous silica‐supported Pd as sustainable catalysts for phosphine‐free Suzuki–Miyaura and Heck coupling reactions

An improved and eco‐friendly procedure has been developed to generate mesoporous silica‐supported palladium nanoparticles (SiO₂@PdNP) that could be used as a sustainable heterogeneous Pd catalyst for phosphine‐free Suzuki–Miyaura and Heck coupling reactions with excellent turnover number and turnover frequency. The presence of Pd on the silica surface was detected by X‐ray diffraction and the structural morphology of SiO₂@PdNP was obtained by transmission electron microscopy. The heterogeneous catalytic system is recyclable and leaching of the metal after the reaction is not apparently observed. Copyright © 2013 John Wiley & Sons, Ltd.     

Use of an isotactic‐propylene/hexene copolymer as a new,versatile, soluble support

The use of isotactic‐poly(propylene‐co‐hexene) (iPPH) as new polymeric scaffold for synthesis as well as a phase‐selective, soluble polymer support for homogeneous catalysis is described. It was possible to functionalize olefin‐terminated iPPH using standard organic transformations. Each derivative could be isolated and purified using typical precipitations into a minimum amount of polar solvent, negating the need for wasteful work up and chromatographic procedures. Furthermore, it was demonstrated that an iPPH‐supported DMAP could serve as a recoverable, recyclable catalyst. Published 2013. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 600–605     

SBA‐15‐functionalized melamine–pyridine group‐supported palladium(0) as an efficient heterogeneous and recyclable nanocatalyst for N‐arylation of indoles through Ullmann‐type coupling reactions

SBA‐15‐functionalized melamine–pyridine group‐supported palladium(0) was found to serve as a heterogeneous and recyclable nanocatalyst for N‐arylation of indoles with aryl iodides under a low catalyst loading (0.3 mol% of Pd) through Ullmann‐type C? N coupling reactions. A variety of aryl iodides could be aminated to provide the N‐arylated products in good to excellent yields without the need of an inert atmosphere. Also, this catalyst was found to be an efficient system for the N‐arylation of other nitrogen‐containing heterocycles with aryl iodides. The heterogeneous palladium catalyst could be recovered by simple filtration of the reaction solution and reused for six cycles without significant loss in its activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Toughening of poly(L‐lactide)/multiwalled carbon nanotubes nanocomposite with ethylene‐co‐vinyl acetate

Poly(L ‐lactide)/multiwalled carbon nanotubes (PLLA/MWCNTs) nanocomposite recently attracts much attention because of its excellent comprehensive properties including improved thermostability, tensile strength, and conductivity. However, the nanocomposite exhibits similar brittleness compared with unmodified PLLA. In this work, a polar elastomer, that is, ethylene‐co‐vinyl acetate (EVA), was introduced into PLLA/MWCNTs nanocomposite. The selective distribution of MWCNTs and the effects of EVA on crystalline structure of PLLA were investigated using scanning electron microscope, transmission electron microscope, differential scanning calorimetry, and wide angle X‐ray diffraction. The results show that the presence of EVA induces the change of the distribution of MWCNTs in the nanocomposites, and consequently, the cold crystallization of PLLA is prevented. With the increase of EVA content, both the ductility and the impact resistance of PLLA/FMWCNTs are improved greatly, indicating the toughening effect of EVA on PLLA/MWCNTs nanocomposite. The decreased tensile strength and modulus can be compensated through annealing treatment. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011