Showing papers by "Nikhil K. Singha published in 2013"

Tailor-made polyfluoroacrylate and its block copolymer by RAFT polymerization in miniemulsion; improved hydrophobicity in the core–shell block copolymer

Abstract: Controlled/living radical polymerization (CRP) of a fluoroacrylate was successfully carried out in miniemulsion by Reversible Addition Fragmentation chain Transfer (RAFT) process. In this case, 2,2,3,3,4,4,4-heptafluorobutyl acrylate (HFBA) was polymerized using 2-cyanopropyl dodecyl trithiocarbonate (CPDTC) as RAFT agent, Triton X-405 and sodium dodecyl sulfonate (SDS) as surfactant, and potassium persulphate (KPS) or 2,2'-azobis isobutyronitrile (AIBN) as initiator. Being compatible with hydrophobic fluoroacrylate, this RAFT agent offered very high conversion and good control over the molecular weight of the polymer. The miniemulsion was stable without any costabilizer. The long chain dodecyl group (-C12H25) (Z-group in the RAFT agent) had beneficial effect in stabilizing the miniemulsion. When 2-cyano 2-propyl benzodithioate (CPBD) (Z=-C6H5) was used as RAFT agent, the conversion was less and particle size distribution was very broad. Block copolymerization with butyl acrylate (BA) using PHFBA as macro-RAFT agent showed core-shell morphology with the aggregation of PHFBA segment in the shell. GPC as well as DSC analysis confirmed the formation of block copolymer. The core-shell morphology was confirmed by TEM analysis. The block copolymers (PHFBA-b-PBA) showed significantly higher water contact angle (WCA) showing much better hydrophobicity compared to PHFBA alone.

Synthesis and characterization of elastomeric polyurethane and PU/clay nanocomposites based on an aliphatic diisocyanate

Abstract: This investigation reports preparation of polyurethane and polyurethane/clay nanocomposites based on polyethylene gly- col, isophorone diisocyanate (IPDI), an aliphatic diisocyanate and 1,4- Butanediol as chain extender by solution polymerization. In this case PU/clay nanocomposites were prepared via ex-situ method using 1, 3, and 5 wt % of Cloisite 30B. Thermogravimetric analy- sis showed that the maximum decomposition temperature (Tmax) of the PU/clay nanocomposite is much higher than the pristine PU. The tensile properties improved upon increasing the organoclay (Cloisite 30B) content upto 3 wt %, and then decreased to some extent upon further increasing the nanoparticle loading to 5 wt %. Optical properties of the nanocomposites were studied by UV-vis spectrophotometer. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to study the morphology of the nanocomposites. It was observed that with the incorporation of 3 wt % nanoclay the crystallinity in PU nanocomposite increases, then diminishes with further loading. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 000: 000-000, 2013

Thermally amendable tailor‐made functional polymer by RAFT polymerization and “click reaction”

Abstract: This investigation reports the preparation and char- acterization of thermally amendable functional polymer bearing furfuryl functionality via reversible-addition fragmentation and chain transfer (RAFT) polymerization and Diels-Alder (DA) reac- tion. In this case, furfuryl methacrylate (FMA) was polymerized using 4-cyano-4-((dodecylsulfanylthiocarbonyl)sulfanyl) penta- noic acid as RAFT reagent and 4,4 0 -azobis(4-cyanovaleric acid) as thermal initiator. 1 H NMR, 13 C NMR, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis showed that furfuryl group in poly(furfuryl methacrylate) (PFMA) was not affected during RAFT polymerization and the tailor-made polymer had RAFT end group. The DA reaction was successfully carried out between the reactive furfuryl functional- ity of PFMA and different bismaleimides. The thermoreversible property of these DA polymers was characterized by FT-IR and DSC analysis. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3365-3374

Electrochemical synthesis of nanostructured polyaniline: Heat treatment and synergistic effect of simultaneous dual doping

Abstract: Different nanostructured polyaniline (PAni) has been synthesized via facile template-free electrochemical synthesis approach in aqueous medium. Instead of conventionally used aniline, aniline sulphate was used in electrochemical polymerization. The synthesis process involves simultaneous doping with combination of inorganic and organic acid, i.e., sulfuric acid (H2SO4) and p-toluenesulfonic acid (PTSA) at different ratios keeping total dopant concentration constant. Synergistic increase in conductivity is observed and the best conductivity is achieved at 3:1 ratio of [H2SO4]:[PTSA]. Different nanostructures of PAni are revealed through morphological analysis consisting of nanosphere, nanorod, and clustered particles among which finer nanorods show the best electrical conductivity. Upon controlled heat treatment followed by further cooling, resistivity increases, but after one day it decreases again and in the optimized dual doped PAni, it approaches approximately the same value of initial resistance. Lattice strain and benzenoid to quinonoid ratio increases with heat treatment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Copper catalyzed ring opening copolymerization of a vinyl cyclopropane and methyl methacrylate

Abstract: Vinyl cyclopropanes are an important class of monomers which on radical ring opening polymerization (RROP) lead to polymers having cyclic moieties, carbon-carbon unsaturation and different other functional groups inside its backbone as in the pendant group. This investigation reports controlled radical ring opening polymerization (CRROP) of 1,1-bis (ethoxy carbonyl)-2-vinylcyclopropane (BCVCP) catalyzed by Cu catalyst. In this case homo and co-polymerization of BCVCP was carried out via ATRP using ethyl-2-bromoisobutyrate as initiator and CuBr as catalyst in combination with Me6-TREN ligand. Radical polymerization of BCVCP and its copolymerization with methyl methacrylate (MMA) via ATRP led to predominantly 1,5 ring opening polymerization leading to linear polymers with >CC< in the main chain of the polymer. Conventional free radical co-polymerization of BCVCP and MMA led to polymers predominantly with cyclic rings in the main chain. The polymers were characterized by NMR, FT-IR, GPC, DSC and TGA analysis.

Atom Transfer Radical Polymerization of Glycidyl Methacrylate (GMA) in Emulsion

Abstract: This investigation reports atom transfer radical polymerization (ATRP) of glycidyl methacrylate (GMA) and its copolymerization with butyl methacrylate (BMA) in emulsion. Poly(glycidyl methacrylate) (PGMA) was prepared in emulsion using copper bromide (CuBr) as catalyst in combination with 2,2′-bypyridine (bpy) as ligand and methyl 2-bromopropionate (MBrP) as initiator. Different surfactants of Triton series (such as Triton X-100, Triton X-405) were used as emulsifier in these cases. The copolymerization of GMA with BMA was also performed successfully in emulsion via ATRP using the same reaction conditions used for the preparation of PGMA. The stability of the latexes prepared via emulsion ATRP was examined. TEM analysis was carried out to examine the particles sizes of polymer in the latex. Molecular weights and molecular weight distributions of the polymers were determined by GPC analysis. The FT-IR and 1H-NMR analyses indicated that the pendant glycidyl group of PGMA was unaffected during emulsion ATRP....

Synthesis and characterization of poly(2-ethylhexyl acrylate) prepared via atom transfer radical polymerization, reverse atom transfer radical polymerization and radical polymerization

Abstract: This investigation reports a comparative study of poly(2-ethylhexyl acrylate) (PEHA) prepared via atom transfer radical polymerization (ATRP), reverse atom transfer radical polymerization (RATRP) and conventional free radical polymerization (FRP). The molecular weights and the molecular weight distributions of the polymers were measured by gel permeation chromatography (GPC) analysis. Structural characterization of the polymers was carried out by 1H NMR and MALDI-TOF-MS analyses. Thermal properties of the polymers were evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The polymerization results and the thermal properties of PEHAs prepared via ATRP, RATRP and FRP were compared.

Aging of low-density polyethylene in natural weather, underground soil aging and sea water: Effect of a starch-based prodegradant additive

Abstract: This article reports the results of studies on the degradation of the blend of low-density polyethylene (LDPE) with a starch based prodegradant additive, named commercially as Polystarch plus H and abbreviated as PSH, under natural weather, underground soil aging, and sea water aging in Dhahran, Saudi Arabia. The work includes measurements of tensile properties, thermal behavior, and scanning electron microscopic (SEM) studies on the unaged and aged LDPE and the LDPE/PSH blend having 25% (w/w) of PSH. Results of the preliminary experiments showed that changes in properties are not prominent at lower loadings of PSH. In the case of the blend, incorporation of the additive PSH caused a reduction in elongation at break, which is accentuated under aging. The effectiveness of the prodegradant additive in the degradation behavior follows the order, natural aging > underground soil aging > sea water aging. It is believed that the prodegradant additive is effective in chain scission in sunlight under natural weathering conditions, in contrast to underground soil aging and sea water. POLYM. ENG. SCI., 53:2389–2397, 2013. © 2013 Society of Plastics Engineers

Natural weather, soil burial and sea water ageing of low‐density polyethylene: Effect of starch/linear low‐density polyethylene masterbatch

Abstract: Degradation of the blends of low-density polyethylene (LDPE) with a starch-based additive namely, polystarch N was studied under various environmental conditions such as natural weather, soil and sea water in Saudi Arabia. Stress-strain properties and thermal behavior were investigated for the LDPE and LDPE/polystarch N blend having 40% (w/w) of polystarch N. Environmen- tal ageing resulted in the reduction of percentage of elongation and crystallinity for the blend. Rheological studies and scanning electron microscope photomicrographs of the polymer samples retrieved after ageing showed that addition of polystarch N enhanced the degradation of LDPE. This is ascribed to high extent of chain scission and leaching out of starch present in polystarch N, which was corroborated by the results of morphology and Fourier transform infrared spectroscopy analyses. In the case of underground soil ageing, microbes present in the soil consume the starch in the blend, thus accelerating the degradation process. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 129: 449-457, 2013