Nikhil K. Singha

Homogeneous catalytic Hydrogenation of natural rubber using RhCl(PPh3)3

Hydrogenation is an important method of chemical modification, which improves the physical, chemical, and thermal properties of diene elastomers. It is also a useful method for preparation of polymers with unusual monomer sequences. Natural rubber (NR) could be quantitatively hydrogenated to a strictly alternating ethylene-propylene copolymer using a homogeneous RhCl(PPh3)3 catalyst. The effect of concentration of rubber, catalyst and triphenyl phosphine, temperature, pressure, and solvent on the course of hydrogenation were evaluated. The thermal properties of the hydrogenated NR are compared with NR.

Effect of a Nanoclay on the Mechanical, Thermal and Flame Retardant Properties of Rigid Polyurethane Foam

Water blown rigid polyurethane foams (PUF) with organoclay/organically modified nanoclay (ONC) were prepared and their properties such as density, mechanical, morphological, insulation, thermal and flame retardant properties were studied. In this investigation, the ONC content was varied from 1 to 10 parts per hundred of polyol (php) by weight. It was observed that the compressive strength of ONC filled PUF increased up to 3 php of ONC loading and then it decreased. Wide angle X-ray diffraction and transmission electron microscopy studies indicated the exfoliated dispersion of ONC in PUF. The thermal conductivity of ONC filled PUF decreases up to 5 php and then increases. The glass transition temperature (Tg) of PUF decreases on loading of ONC. The TGA analysis shows that there is slight increase in degradation temperature with increase in ONC loading. The flame retardant properties (LOI and flame spread rate) are improved slightly on addition (3 php) of ONC filled PUF.

Mechanical, morphological and thermal properties of rigid polyurethane foam : Effect of the fillers

Rigid polyurethane foam (PUF) having different fillers such as precipitated silica (SiO2), precipitated calcium carbonate (CaCO3) and glass powder (GP) were prepared by blowing with distilled water. The effect of filler loading on different properties of PUF was studied. In this investigation, the filler content was varied from 5 to 50 parts per hundred of polyol (phr) by weight. The properties such as density, mechanical, morphological, water absorption, thermal conductivity and thermal properties of the filled PUF were compared with the neat PUF. The density of silica filled PUF decreases with an increase in the filler loading. In case of calcium carbonate and glass powder the density initially decreases with filler loading, but after a certain concentration of fillers there is an increase in density with filler content. The mechanical properties such as compressive stress at 10% strain, compressive modulus and hardness of the filled PUF decrease in comparison with the neat PUF, due to the reaction between isocyanate and surface functional group present in filler. In all cases, the water absorption of the PUF increases with the increase in filler loading, due to the decrease in the closed cell content. The thermal conductivity analysis of PUF shows that the insulation properties decrease with the increase in silica as well as CaCO3 loading. This is mainly due to formation of open and damaged cell structure. However, when glass powder is used as filler the thermal conductivity first decreases, but later increases with filler loading.

A NEW METHOD TO HYDROGENATE NITRILE RUBBER IN THE LATEX FORM

Abstract A water soluble analog of Wilkinson catalyst — chloro-tris-(sodium diphenylphosphino-benzene-m-sulfonate) rhodium(I), CAS 67178-14-7, i.e. RhCl(DPM)3— has been found to hydrogenate NBR latex. More than 60 mol% hydrogenation can be achieved at 75°C and 1 atmosphere hydrogen pressure. Hydrogenation was accompanied by an increase in gel content of the latex.

Copper-mediated controlled radical ring-opening polymerization (RROP) of a vinylcycloalkane

This investigation reports controlled ring-opening polymerization of a vinylcyclopropane via copper-mediated atom transfer radical polymerization which leads to predominantly 1,5 ring-opening polymerization.

Mechanical, Morphological and Thermal Properties of Rigid Polyurethane Foam : Effect of Chain Extender, Polyol and Blowing Agent

The properties of rigid polyurethane foams can be modified over a wide range depending on the raw materials used for its synthesis. The polyols, chain extender and blowing agent have major impact on the properties of the PUF. This investigation reports the effect of polyol and its blends, chain extender such as 1, 4-butanediol (1, 4-BD) and blowing agents [chemical as well as physical; such as distilled water and n-pentane (n-C5), hydrochlorofluorocarbon (HCFC)] on the properties of rigid PUF. Addition of the chain extender improves the mechanical properties initially but then it decreases the properties on further addition of the same. The thermal conductivity of the chain extended and that of the physically blown PUF was lower than the water blown PUF. Higher loading of chain extender and blended polyol decreased the glass transition temperature (Tg) of the PUF due to the decrease in cross-link density because of low –OH functionality in the presence of linear diols like hydroxyl terminated polybutadiene (HTPB). It was observed that there is no significant change in degradation temperature of the chain extended, physically blown and blended system except that observed in the case of HTPB filled PUF.

Tailor-made thermoreversible functional polymer via RAFT polymerization in an ionic liquid: a remarkably fast polymerization process

Tailor-made poly(furfuryl methacrylate) (PFMA) was prepared via RAFT polymerization of furfuryl methacrylate (FMA) using ionic liquid (IL) as a solvent and 2-cyano-2-propyl dodecyl trithiocarbonate (CPDTC) as a RAFT reagent. The polymerization reaction was much faster in IL than the same reaction carried out in toluene. After the polymerization, the IL was recovered from the reaction mixture and recycled IL was successfully reused for the RAFT polymerization of FMA. The polymers were characterized by GPC, 1H-NMR and MALDI-TOF-MS analyses. A thermoreversible functional polymer was prepared via the Diels–Alder (DA) and reverse (rDA) reaction between the PFMA and POSS maleimide isobutyl (POSS-M) and was studied by FT-IR and 1H-NMR analyses. The DA polymer product showed a higher water contact angle (WCA) value of 103.1° reflecting the presence of hydrophobic POSS moieties and demonstrating hydrophobic characteristics of the modified functional polymer.

Fluorinated amphiphilic block copolymers via RAFT polymerization and their application as surf-RAFT agent in miniemulsion polymerization

This investigation reports the preparation of amphiphilic block copolymer (Am-BCP) based on poly(ethylene glycol) methyl ether methacrylate (PEGMA) and 2,2,3,3,4,4,4-heptafluorobutyl acrylate (HFBA) via RAFT polymerization. In this case poly(PEGMA) (PPEGMA) was prepared using 2-cyano-2-propyl dithiobenzoate (CPBT) as a RAFT agent. This PPEGMA was later used as a macro-RAFT agent for the polymerization of HFBA to prepare well-defined block copolymers (BCPs), (PPEGMA-b-PHFBA) of varied lengths and compositions. The BCPs self-assembled in aqueous solution to produce spherical micelles consisting of hydrophobic block PHFBA as a core and a hydrophilic block of PPEGMA as a flexible corona. This Am-BCP formed micelles of different sizes, as characterized by dynamic light scattering (DLS) and TEM analyses. The Am-BCP was later used as a surf-RAFT agent i.e. as a surfactant as well as a macro-RAFT agent for the miniemulsion polymerization of styrene. TEM analysis showed that the synthesized polystyrene emulsion had a core–shell morphology. The particle size and particle size distributions of the polystyrene latex were determined by DLS analysis.

Modified chitosan encapsulated core-shell Ag Nps for superior antimicrobial and anticancer activity.

This investigation reports a one pot synthesis of silver nanoparticles (Ag Nps) using aqueous solution of chitosan-graft-poly(acrylamide) (Cts-g-PAAm) as a reducing agent and polyethylene glycol (PEG) as a stabilizing agent. The as synthesized Ag Nps was characterized by ultra violet-visible (UV-vis), Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis. Field emission scanning electron microscopy (FESEM), dynamic light scattering (DLS) and transmission electron microscopy (TEM) showed that Ag Nps, which were stable upto more than 60 days, were spherical in shape and the particle size was in the range of 5-50 nm. Atomic force microscopy (AFM) image also supported the above obtained result. The prepared Ag Nps exhibited strong antimicrobial activity against different gram positive bacteria (Alkaliphilus, Bascillus substillis, Lysinibascillus) and gram negative bacteria (Enterobacter aerogenus, Vivbrio vulnificus and Escherichia coli) and haemolytic assay revealed its blood compatible nature. The synthesized Ag Nps showed significant cytotoxicity over human cervical HeLa cancer cells and it was found that the inhibitory concentration for 50% cell death (IC50) was 8 μg/ml.

Homogeneous catalytic hydrogenation of poly(styrene-co-butadiene) using a ruthenium based Wilkinson catalyst

SummaryPoly(Styrene-co-butadiene) can be quantitatively hydrogenated using tris(triphenyl phosphine) ruthenium(II) chloride, RuCl2(PPh3)3 as catalyst. The effect of temperature, pressure and catalyst concentration on both the rate and degree of hydrogenation have been studied. The hydrogenated elastomers have been characterized by IR, 1H NMR and TGA.