Showing papers by "Nikhil K. Singha published in 2014"

Tailor-made polymethacrylate bearing bicyclo-alkenyl functionality via selective ATRP at ambient temperature and its post-polymerization modification by ‘thiol–ene’ reaction

Abstract: This investigation reports a facile synthetic route for the preparation of tailor-made polymers bearing reactive pendant bicyclo-alkenyl functionality via selective atom transfer radical polymerization at ambient temperature (AT-ATRP). In this case dicyclopentenyloxyethyl methacrylate (DCPMA) was polymerized at ambient temperature (30 °C) using CuBr or CuCl as the catalyst in combination with different ligands, such as N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) and 4,4′-di(5-nonyl)-2,2′-bipyridine (dNbpy). The polymerization was very fast and very high conversion (∼90%) was achieved in 2 min. 1H NMR and MALDI-TOF-MS analysis confirmed the presence of a bicyclic alkenyl pendant group in the polymer prepared by ATRP. This alkenyl functionality was successfully modified by the ‘thiol–ene’ reaction, as evidenced by 1H NMR and FT-IR analysis.

Thermal stability and fire retardancy of polyurea and epoxy nanocomposites using organically modified magadiite

Abstract: The purpose of this study is to investigate the effect of the surface modification of a layered silicate (magadiite) on the flammability of both polyurea and amine-cured epoxy resin. Based on the surface chemistry of magadiite, both quaternary alkyl ammonium and silane modifier can be employed for the organo-modification. Nanocomposites of both polymers were prepared via ultrasound-assisted in situ polymerization. Dispersion of magadiite was investigated through X-ray diffraction and high-resolution transmission electron microscopy. Thermal stability and flammability were evaluated by thermogravimetric analysis and cone calorimetry, respectively. The addition of small amount of magadiite resulted in significant improvements in flame resistance with not much change in thermal stability for both polymers. Ammonium-modified magadiite improves the flame resistance, whereas silane modification helps to increase time to ignition of both polymers.

EPDM Nanocomposites using Polyimide as Ablator: Morphology and Thermophysical Properties

Abstract: Launching of space craft liberates intense heat and in order to protect the rocket system from immense temperature and pressure during launching, multilayered insulation is necessary on solid rocket motor case. Elastomer, being better candidates for heat and electrical insulation are used over the metal casing in rocket motor system. The development of light weight EPDM insulation compound with suitable nanofillers can change the conventional insulation technology. The present work deals with an introduction of thermally stable polyimide based EPDM nanocomposites of different formulations for insulation in space applications. The insulators are prepared by melt mixing of polyimide (PI) powder and different nanofillers (nanosilica, nanoclay and carbon nanofiber) in ethylene propylene diene elastomer (EPDM) matrix. Polyimide provides good ablative properties and nanofillers provide good reinforcement as well as optimum thermal properties. In this study EPDM was compounded with polyimide and nanosilica/nanoclay/carbon nano fiber in Haake mixer followed by mixing of curatives and accelerator in a two roll open mill. The degradation of the elastomeric insulator has been investigated by thermogravimetric analysis (TGA). Glass transition temperature and specific heat were determined by differential scanning calorimetry (DSC) analysis. Apart from physical and mechanical properties, thermal conductivity, FTIR analysis and XRD studies were also carried out. Morphology and the study of dispersion of nanofillers in EPDM matrix were analyzed by SEM and HR-TEM.

Carbon nanofiber composite with epdm and polyimide for high-temperature insulation

Abstract: Elastomers and their composites are extensively used as a thermal insulation system in heat treatment, power generation, fire protection, and aerospace. Among different elastomers, low-density ethylene propylene diene terpolymer (EPDM) has interesting properties, such as excellent resistance to aging and oxidative degradation due to its saturated back bone. Furthermore, introduction of polyimide (PI) to the base elastomer increases its thermal stability. On the other hand, carbon nanofiber (CNF) reinforces the matrix to enhance the mechanical properties with an additional advantage of better char yield. To achieve better rubber-filler compatibilization, modification of EPDM was carried out by grafting with maleic anhydride (MAH). Morphological studies by scanning electron microscopy and high-resolution transmission electron microscopy exhibited uniform dispersion of nanofillers throughout MAH grafted EPDM matrix. Thermal properties of the EPDM/PI nanocomposites were characterized by thermogravime...

Copper mediated controlled radical copolymerization of styrene and 2-ethylhexyl acrylate and determination of their reactivity ratios.

Abstract: Copolymerization is an important synthetic tool to prepare polymers with desirable combination of properties which are difficult to achieve from the different homopolymers concerned. This investigation reports the copolymerization of 2-ethylhexyl acrylate (EHA) and styrene using copper bromide (CuBr) as catalyst in combination with N,N,N’,N”,N”- pentamethyldiethylenetriamine (PMDETA) as ligand and 1-phenylethyl bromide (PEBr) as initiator. Linear kinetic plot and linear increase in molecular weights versus conversion indicate that copolymerization reactions were controlled. The copolymer composition was calculated using 1H NMR studies. The reactivity ratio of styrene and EHA (r1 and r2) were determined using the Finemann-Ross (FR), inverted Finemann-Ross (FR) and Kelen-Tudos (KT) methods. Thermal properties of the copolymers were also studied by using TGA and DSC analysis.

LDPE Filled with LLDPE/Starch Masterbatch: Rheology, Morphology and Thermal Analysis

Abstract: This paper reported the effect of starch-based additive (PSN), on the rheology, morphology and thermal behavior of low-density polyethylene (LDPE). PSN was a commercial masterbatch of corn starch and linear low-density polyethylene (LLDPE) in the ratio of 45/55. Compositions of LDPE/PSN blend ratios at 100/0, 80/20, 70/30 and 60/40 were prepared by melt blending. It was found that addition of PSN to LDPE decreased its storage modulus (G′), loss modulus (G′′) and dynamic viscosity (η′) especially at low frequency. Results of the loss tangent (tan δ) measurements indicated a tendency of forming a maximum in the low-frequency region for the samples with high PSN content. Effect of temperature on the viscosity indicated that Arrhenius-type relation with a single slope was followed by neat LDPE, while the LDPE filled with PSN followed a non-Arrhenius-type relation with multiple slopes. Differential scanning calorimeter results indicated that the blend was partially compatible. Thermogravimetric measurement results confirmed that no degradation could happen at the temperature of rheology tests. Scanning electron microscopy studies revealed that starch was uniformly distributed in the blend of LDPE and LLDPE.

Natural weather aging of low density polyethylene: effect of prodegradant additive

Abstract: The present paper reports the results of studies on the effect of a prodegradant additive, named commercially as PDQ-H, on the natural weather aging in Saudi Arabia of low density polyethylene (LDPE), with special reference to the stress–strain properties, thermal behaviour, morphology and rheological properties. Incorporation of the additive caused a sharp fall in the elongation at break of LDPE on aging. Results of rheological and Fourier transform infrared spectroscopy (FTIR) spectroscopic studies and scanning electron microscope (SEM) analysis of the blends retrieved after aging showed that addition of the prodegradant enhanced the degradation of LDPE. Results of FTIR and gel permeation chromatography studies show that the degradation occurs due to chain scission, which is presumably followed by crosslinking. These findings are corroborated by the SEM images.

Thermoreversible Block Copolymer/Clay Nanocomposite via Surface Initiated ATRP (SI-ATRP) and "Click Reaction" in Clay Surface

Abstract: This investigation reports the preparation and characterization of a reactive block copolymer/clay nanocomposite from nanoclay surface via SI-ATRP and its post polymerization modification to prepare thermoreversible polymer via Diels-Alder (DA) and retro-DA (rDA) reaction. In this case, the block copolymer of 2-ethylhexylacrylate (EHA) and furfuryl methacrylate (FMA), a reactive methacrylate was prepared from suitably modified nanoclay surface via SI-ATRP. The furfuryl group of PFMA unit of block copolymer PEHA-bPFMA/clay nanocomposite (BCP/clay) was used as a diene in DA reaction with bismaleimide (BM) as dienophile. This DA cross-linked block copolymer/clay composite had successfully undergone retro-DA reaction at higher temperature showing reversible characteristics. The block copolymer was characterized by 1H-NMR, GPC, TEM, TGA, DSC analysis. The thermoreversible properties of block copolymer/clay nanocomposite were characterized by FT-IR and DSC analysis.