Showing papers by "Nikhil K. Singha published in 2006"

Controlled Radical Polymerization of Furfuryl Methacrylate

Abstract: Atom transfer radical polymerization provides a new method of controlled radical polymerization. The most important advantage of ATRP is that it is tolerant to the different functional groups present in the initiator as well as in the monomer. Furfuryl Methacrylate (FMA) is a specialty monomer, which has applications in coatings, adhesives and in biomedicals. Conventional radical polymerization of FMA leads to excessive gel formation, which limits its applications. In this investigation homo and co-polymerization of FMA has been carried out via ATRP. ATRP of FMA was carried out using CuBr as catalyst and i, 1, 4,7,10,10 hexamethyltriethylenetetramine (HMTETA) as ligand. There was no gel formation during the polymerization. ATRP of FMA was well controlled with a linear increase of molecular weight (Mn) with monomer conversion. The polymers were characterized by using 1 HNMR, FT-IR and GPC analysis. Interestingly, it was observed that the furfuryl ring was not affected during polymerization.

Waste natural gum as a multifunctional additive in rubber

Abstract: Bahera gum, extracted from the bark of Ter- minalia bellerica, is a waste material. The present study involves the use of this natural gum as a multifunctional additive in natural rubber (NR) and brominated isobuty- lene-co-paramethyl styrene (BIMS). Fourier transform infra- red (FTIR) analysis was employed to study the functional groups present in the gum. It was found that fatty acids/ esters in the gum act as accelerator activator and can replace stearic acid in rubber formulations. Polyphenols in the gum act as antioxidant and the action is comparable with the commercial antioxidant 2,2,4-trimethyl-1,2-dihy- droquinoline (TQ) in natural rubber. The gum improves the tack strength of the rubbers (21% at 2.5 phr loading for NR and 54% at 10 phr loading for BIMS). The gum imparts plasticization effect which is reflected in the reduc- tion in k and enhancement in n values, the exponents in the power law equation, with increasing gum concentra- tion. The activation energy of flow is also reduced with the addition of the gum. Moreover, it decreases the elastic memory of the system which causes reduction in die swell. 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4897- 4907, 2006

Atom Transfer Radical Polymerization (ATRP) of Ethyl Acrylate: Its Mechanistic Studies

Abstract: Atom transfer radical polymerization (ATRP) of ethyl acrylate was carried out in bulk using ethyl 2-bromoisobutyrate as initiator, CuBr as well as CuCl as catalyst in combination with different ligands e.g., 2,2' bipyridine (bpy)andN,N, N',N,N-pentamethyldiethylenetriamine (PMDETA). In most of the cases very high conversion (72-98%) was achieved. The polymerization was well controlled with a linear increase of molecular weight (M n SEC ) with conversion and relatively narrow molecular weight distributions (polydispersity index 1.2-1.3). Use of PMDETA as the ligand resulted in faster polymerization rate (98% conversion in 1 h) than those using bipyridine (72% conversion in 5 h). The MALDI-TOF-MS analysis of poly (ethyl acrylate) (PEA) prepared by using bpy as ligand showed the presence of halogen as the end group. On the contrary, when PMDETA was used as the ligand, the mass analysis showed no trace of this end group.

Grafting of butyl acrylate and methyl methacrylate on butyl rubber using electron beam radiation

Abstract: Being nonpolar in nature, butyl rubber (IIR) has poor compatibility toward polar polymers and fillers. It can be improved by grafting polar substrates on the butyl elastomer. Radiation-induced polymer processing is getting increasing interest, as it leads to new and improved polymers with desirable and interesting properties. In this investigation, electron beam radiation has been used to graft methyl methacrylate (MMA) and butyl acrylate (BA) on IIR. This process has several advantages over conventional grafting processes such as cationic polymerization (which needs very low temperature and stringent reaction conditions) and solution radical polymerization (which often needs solvent removal and recycling). The grafted polymers were characterized by using 1H NMR, IR, TGA, and SEM analysis. The degree of grafting increases with a decrease in irradiation dose as well as with an increase in monomer concentration. It was observed that there was a decrease in intrinsic viscosity in irradiated IIR samples, indicating the chain scission. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1340–1346, 2006