Thin-film composite crosslinked polythiosemicarbazide membranes for organic solvent nanofiltration (OSN)

In this work we report a new class of solvent stable thin-film composite (TFC) membrane fabricated on crosslinked polythiosemicarbazide (PTSC) as substrate that exhibits superior stability compared with other solvent stable polymeric membranes reported up to now. Integrally skinned asymmetric PTSC membranes were prepared by the phase inversion process and crosslinked with an aromatic bifunctional crosslinker to improve the solvent stability. TFC membranes were obtained via interfacial polymerization using trimesoyl chloride (TMC) and diaminopiperazine (DAP) monomers. The membranes were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and contact angle measurement.The membranes exhibited high fluxes toward solvents like tetrahydrofuran (THF), dimethylformamide (DMF) and dimethylsulfoxide (DMSO) ranging around 20 L/m² h at 5 bar with a molecular weight cut off (MWCO) of around 1000 g/mol. The PTSC-based thin-film composite membranes are very stable toward polar aprotic solvents and they have potential applications in the petrochemical and pharmaceutical industry.     

One‐pot synthesis of self‐stabilized and carboxyl‐functionalized fluorescent poly(methyl methacrylate) microspheres covalently dyed with tris(8‐hydroquinolinato)aluminium by dispersion polymerization

The dispersion polymerization of methyl methacrylate (MMA) with fluorescent monomer tris[2‐((8‐hydroxyquinolin‐5‐yl)methoxy)ethyl methacrylate]aluminium (Al‐HQHEMA) was investigated to obtain fluorescent microspheres under varying conditions (such as composition of dispersion medium, and content of stabilizer polyvinylpyrrolidone (PVP) and Al‐HQHEMA) in methanol–water at 70 °C with 2,2′‐azoisobutyronitrile as the initiator. Fluorescent microspheres with particle size of 2.039 µm and uniformity of 0.171 were obtained under the following conditions: methanol–water, 7:3 (v/v); PVP, 15 wt% of MMA; Al‐HQHEMA solution, 1.5 mL. Maleic monoester of monomethoxyl poly(ethylene glycol) (Mal‐MPEG) was used as a comonomer to simultaneously incorporate carboxyl groups and PEG chains. With Mal‐MPEG, no aggregation was observed in the measurements of particle size and size distribution for the obtained microspheres after cleaning off PVP, indicating that self‐stabilized fluorescent microspheres were obtained. While without Mal‐MPEG, obvious aggregation was observed. The determination of surface carboxyl content using aqueous acid–base titration showed that most of the carboxyl groups of Mal‐MPEG were located on the surface of the microspheres. © 2015 Society of Chemical Industry     

Polydimethylsiloxane macromonomer bearing N‐vinylcaprolactam as end group: thermosensitive graft copolymers via free radical polymerization

A polydimethylsiloxane macromonomer was synthesized via anionic ring‐opening polymerization of hexamethylcyclotrisiloxane using N‐vinylcaprolactam anion as initiator and trimethylsilyl chloride as terminating agent. The polydimethylsiloxane macromonomer was copolymerized with N‐vinylcaprolactam in different molar ratios via a free radical mechanism. The new class of graft copolymers thus obtained shows cloud points in water because of an excess of N‐vinylcaprolactam units in the polymer chain. These cloud points can be shifted using randomly methylated β‐cyclodextrin as complexing agent. © 2015 Society of Chemical Industry     

Improved dispersibility of multi‐wall carbon nanotubes with reversible addition–fragmentation chain transfer polymer modification

A non‐covalent approach is used to modify multi‐wall carbon nanotubes (MWCNTs) via a block polymer that can be synthesized in aqueous solvent through reversible addition–fragmentation chain transfer polymerization. The block polymer consists of oligo(ethylene glycol) methyl ether acrylate and acrylic acid. The hydrophobic backbone is significantly adsorbed on hydrophobic MWCNT surfaces, which is verified using transmission electron microscopy, thermogravimetric analysis and X‐ray photoelectron spectroscopy. The coated block polymer can prevent the aggregation of MWCNTs and improve their dispersibility in water. The MWCNTs after modification are stable in water even after standing in a long‐term test. © 2015 Society of Chemical Industry     

Forgotten monomers: isotactic polymers from N‐benzyl‐3‐methylenepyrrolidin‐2‐one via free radical polymerization

N‐Benzyl‐3‐methylenepyrrolidin‐2‐one ( 3 ) was synthesized and homopolymerized under free radical conditions. The configurational microstructure of poly(N‐benzyl‐3‐methylenepyrrolidin‐2‐one) ( 4 ) is isotactic with a minor tendency to syndiotacticity. Monomer 3 was also homopolymerized in water in the presence of methylated β‐cyclodextrin. The glass transition temperature of 4 of 124 °C was compared with the lower value of 61 °C of the ring‐opened analogue poly(N‐benzyl‐N‐ethylacrylamide). © 2015 Society of Chemical Industry     

Reverse iodine transfer polymerization of vinyl acetate and vinyl benzoate: synthesis and characterization of homo‐ and copolymers

Homo‐ and copolymers of vinyl esters including vinyl acetate (VAc) and vinyl benzoate (VBz) were synthesized via the reverse iodine transfer radical polymerization technique. Polymerization was carried out in the presence of iodine as the in situ generator of the transfer agent and 2,2′‐azobis(isobutyronitrile) as the initiator at 70 °C. Reverse iodine transfer radical homopolymerization of VAc and VBz led to conversions of 76 and 57%, number‐average molecular weights of 8266 and 9814 g mol^?1 and molecular weight distributions of 1.58 and 1.49, respectively. The microstructure of the synthesized polymers was investigated in detail using gel permeation chromatography, ¹H NMR, ¹³C NMR and distortionless enhancement of polarization transfer (135° decoupler pulse) techniques. Relatively narrow molecular weight distribution and controlled and predictable trend of molecular weight versus conversion were observed for the synthesized polymers, showing that reverse iodine transfer radical homo‐ and copolymerization of VAc and VBz proceeded with controlled characteristics. Results of molecular weight and its distribution along with the ¹H NMR spectra recorded for homo‐ and copolymers indicated that side reactions can occur during the course of polymerization with a significant contribution when VAc, even in a small amount, was present in the reaction mixture. This can result in polymer chains with aldehyde dead end and broadening of the molecular weight distribution. © 2015 Society of Chemical Industry     

Synthesis and characterization of copolymers with the same proportions of polystyrene and poly(ethylene oxide) compositions but different connection sequence by the efficient Williamson reaction

The AB type diblock PS‐b‐PEO and ABA type triblock PS‐b‐PEO‐b‐PS copolymers containing the same proportions of polystyrene (PS) and poly(ethylene oxide) (PEO) but different connection sequence were synthesized and investigated. Using the sequential living anionic polymerization and ring‐opening polymerization mechanisms, diblock PS‐b‐PEO copolymers with one hydroxyl group at the PEO end were obtained. Then, using the classic and efficient Williamson reaction (realized in a ‘click’ style), triblock PS‐b‐PEO‐b‐PS copolymers were achieved by a coupling reaction between hydroxyl groups at the PEO end of PS‐b‐PEO. The PS‐b‐PEO and PS‐b‐PEO‐b‐PS copolymers were well characterized by ¹H NMR spectra and SEC measurements. The critical micelle concentration (CMC) and thermal behaviors were also investigated by steady‐state fluorescence spectra and DSC, respectively. The results showed that, because the PEO segment in triblock PS‐b‐PEO‐b‐PS was more restricted than that in diblock PS‐b‐PEO copolymer, the former PS‐b‐PEO‐b‐PS copolymer always gave higher CMC values and lower crystallization temperature (T_c), melting temperature (T_m) and degree of crystallinity (X_c) parameters. © 2015 Society of Chemical Industry     

Effect of Pluronic F127 on the 3D pore morphology of poly(N-isopropylacrylamide-co-acrylic acid) hydrogels and their nitric oxide release from S-nitrosoglutathione

Changing the pore morphology of hydrogels can be an effective strategy to modulate their drug release profiles. Herein, Pluronic F127 was used to change the three-dimensional pore morphology of crosslinked poly(N-isopropylacrylamide-co-acrylic acid) (P[NIPAm-co-AAc]) hydrogels. F127 reduced the pore diameters from 20 ± 4 to 2.9 ± 0.4 μm and from 11 ± 1 to 1.4 ± 0.4 μm in hydrogels synthesized at 8 and 30°C, respectively. Small-angle X-ray scattering indicates that the segregation of the F127 during the polymerization process induces F127 phase transitions from unimers (at 8°C) or cubic-packed micelles (at 30°C) to a lamellar structure. P(NIPAm-co-AAc) hydrogels charged with S-nitrosoglutathione (GSNO), released nitric oxide (NO) spontaneously during hydration. The decrease in the pore diameter led to a twofold to threefold increase in the rate of water absorption and a fourfold to sixfold increase in the rate of NO release of the hydrogels. F127 can be used to change the pore morphology of P(NIPAm-co-AAc) hydrogels, with concomitant changes in their rate of hydration and NO release from GSNO, opening a new perspective for their use in topical NO delivery.     

On‐surface polymerization – a versatile synthetic route to two‐dimensional polymers

Two‐dimensional (2D) polymers are novel covalent sheet materials with promising properties, but also great synthetic challenges. The inadequacy of traditional wet chemical synthesis calls for new synthetic paradigms. In this respect, employing surfaces as inherently 2D reaction venues appears an adequate choice and has recently already yielded encouraging results. Polymerization at air ? liquid and liquid ? liquid interfaces has been reported from time to time over the last decades, whereas recent efforts on solid surfaces are less traditional. In either case, both movement and coupling of monomers are already confined in two dimensions at interfaces or on surfaces. Accordingly, this approach naturally affords low‐dimensional reaction products. To achieve 2D reticulation, monomers are functionalized with multiple reactive groups of the same or a different kind, whereby their number and stereochemical arrangement predefines the ideal structure of the resulting 2D polymer. This perspective article exemplifies different approaches, i.e. types of surfaces, coupling chemistry and activation schemes, to employ surfaces for novel synthetic routes for the bottom‐up synthesis of 2D polymers. © 2015 Society of Chemical Industry     

Intercalation structure and toughening mechanism of graphene/urea‐formaldehyde nanocomposites prepared via in situ polymerization

Based on the industrialized graphene (GN) product, a series of graphene/urea‐formaldehyde nanocomposites were synthesized via in situ polymerization by incorporation of silicon coupling agent with terminal amino groups (SA) as the compatibilizer. The results showed that addition of SA coupling agent led to much more efficient grafting of UF molecules on the GN surface with high layer thickness by formation of hydrogen bonding, and thus complete exfoliation and uniform dispersion of GN were achieved for the composites. Compared with neat UF, the addition of 1.0 wt% GN resulted in a roughly 25% increase in tensile strength and 12% increase in impact strength; meanwhile the impact fracture surfaces of the composite showed obvious ductile fracture characteristics, indicating the reinforcing and toughening effect of GN on the UF matrix. With increasing GN content, the storage modulus, glass transition temperature and crosslinking density of UF increased, while the tan δ_max decreased, suggesting that a double crosslinking network structure with GN centered crosslinking point and chemical crosslinking point of UF molecular chains formed, leading to improvement in the stiffness of the composites. The present work showed promising potential for developing high performance UF resin on an industrial scale. © 2017 Society of Chemical Industry