Showing papers by "Nikhil K. Singha published in 2016"

A novel ionomeric polyurethane elastomer based on ionic liquid as crosslinker

Abstract: A novel ionic liquid crosslinked flexible polyurethane elastomer (PUIL) was successfully synthesized by a one-pot polymerization method. A variety of characterization methods was employed to study the properties of PUIL, and they were compared with those of a linear thermoplastic polyurethane elastomer (TPU) prepared using butanediol (BDO) as a chain extender. A reference chemically crosslinked polyurethane (PUTMP) was also synthesized by using trimethylolpropane (TMP) as a non-ionic crosslinker. FT-IR spectroscopy revealed that the hydrogen bonding interaction was significantly suppressed in the presence of ionic liquid crosslinker leading to a highly flexible but tough elastomer material. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) demonstrated the improved flexibility of PUIL, as the glass transition temperature (Tg) of PUIL was lower than that of TPU and PUTMP. At the same time, PUIL exhibited a significantly higher tensile strength as well as higher elongation at break, as compared to TPU and PUTMP prepared without ionic liquid crosslinker. In the SAXS profiles, both TPU and PUIL showed single and broad peak characteristics of non-uniform microphase-separated morphology, whereas no phase separation was found in PUTMP. Contact angle measurement showed that the polarity of PUIL is higher than TPU and PUTMP, but importantly, the presence of ionic liquid crosslinks improved the oil resistance property.

Synthesis of a self-healable and pH responsive hydrogel based on an ionic polymer/clay nanocomposite

Abstract: This investigation reports the preparation of a pH responsive self-healing nanocomposite hydrogel based on the in situ polymerization of 2-(acryloyloxy)ethyl trimethylammonium chloride and acrylic acid using N,N′-methylenebisacrylamide as a crosslinker and ammonium persulfate (APS) as a thermal initiator in the presence of soluble starch and organically modified montmorillonite (OMMT). The hydrogel was characterized using FTIR, SEM and TEM analyses. The influence of different parameters in swelling was investigated. The self-healing ability of the hydrogel was measured in different pH media and it was observed that it can show self-healing ability in physiological pH (pH = 7.4), in acidic pH (pH = 1.2) and in saline solution. This developed hydrogel showed excellent swelling ratio, mechanical strength, and elasticity. The hydrogel exhibited modulus values (G′, G′′) in the range of 102 Pa.

Amphiphilic functional block copolymers bearing a reactive furfuryl group via RAFT polymerization; reversible core cross-linked micelles via a Diels–Alder “click reaction”

Abstract: Amphiphilic diblock copolymers of poly(furfuryl methacrylate) (PFMA) and poly(polyethylene glycol methyl ether methacrylate) (PPEGMA) (PFMA-b-PPEGMA) were prepared via reversible addition fragmentation chain-transfer (RAFT) polymerization by using PFMA as a macro-RAFT agent. In water, the amphiphilic diblock copolymer, poly(FMA-b-PEGMA) (PFP) formed micelles with PFMA in the core and PPEGMA in the corona. Diels–Alder chemistry was carried out to crosslink the hydrophobic PFMA core by using bismaleimide in water at 60 °C. The de-crosslinking of hydrophobic PFMA core was carried out upon heating the samples at 150 °C for 30 min via retro-DA reaction which was confirmed by 1H-NMR analysis.

Nanoclay stabilized Pickering miniemulsion of fluorinated copolymer with improved hydrophobicity via RAFT polymerization

Abstract: This investigation reports the preparation of fluorinated copolymer/clay nanocomposite latex by Pickering miniemulsion polymerization using nanoclay sodium montmorillonite (NaMMT) as sole stabilizer. In this case the copolymerization of styrene (St), butyl acrylate (BA) and 2,2,3,3,4,4,4-heptafluorobutyl acrylate (HFBA) was carried out via Reversible Addition–Fragmentation chain Transfer (RAFT) process. Addition of 2-(acryloyloxy) ethyl trimethylammonium chloride (AETAC) increased the rate of polymerization. As nanoclays are negatively charged silicate layers, AETAC, a cationic monomer was introduced to increase the polymer–clay interaction via ion-exchange which has beneficial effect on the final properties of the copolymer. The copolymers had controlled molecular weights as well as narrow dispersity (Ð). Nanoclay armored morphology was observed by TEM and SEM analyses. The polymers had improved hydrophobicity and lower water uptake rate due to improved polymer–clay interaction.

Insights into the preparation of vinyl polybutadiene via cobalt-based catalyst: tuning its properties by thiol-ene modification of vinyl group

Abstract: Elastomers with pendant alkenyl functionality can be easily modified using different types of postpolymerization reactions that lead to improved properties. This investigation reports the preparation of polybutadiene (PB) with control vinyl content by Co-based catalyst followed by modification of vinyl functionality via thiol-ene reaction. In this case, the polymerization of butadiene was carried out in cyclohexane using cobalt octanoate (Co[oct]2) in combination with diethylaluminium chloride (DEAC) and triethylaluminium (TEAL) as cocatalysts. The effects of different parameters, such as the concentration of catalyst and cocatalyst, monomer concentration, and reaction temperature on polymerization of butadiene (BD), were evaluated and optimized to obtain the desired vinyl content in the polymer. The microstructures in PB were investigated by 1H nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy analyses. Molecular weights and dispersity (Ð) of the polymers were determin...