Papers by swaminathan sivaram
Macromolecular Chemistry and Physics, Mar 24, 2006
Polymer Bulletin, 1984
The .reactivity ratios of styrene and acrylonitrile were computed from the t~C-NMR spectra of cop... more The .reactivity ratios of styrene and acrylonitrile were computed from the t~C-NMR spectra of copolymers prepared using cobalt acetylacetonate-triethylaluminum initiator system and compared with a free radical initiator such as AIBN. The results indicate that polymerization using the former has pronounced free radical characteristics.
Routledge eBooks, Nov 22, 2021
Activated magnesium chloride has been established as an ideal support for titanium-based high eff... more Activated magnesium chloride has been established as an ideal support for titanium-based high efficiency olefin polymerization. One of the earliest disclosed methods was to comill anhydrous magnesium chloride and titanium tetrachloride for prolonged periods either alonel or in presence of an electron donor, such as ethyl benzoate (EB).2,3 A later variant involves comilling anhydrous MgCl2 with an electron donor (typically EB) followed by treatment with TiCl4 in the liquid phase.4 In some cases prior to reaction with TiCl4, the milled MgCl2.EB complex is also treated with a second electron donor and an organoaluminum compound.5,6
Journal of molecular catalysis, Feb 1, 1989
Abstract Binuclear metal-Schiff base complexes [Mn 2 (PA 2 ppd) 2 Cl 4](I),[Mn 2 (PA 2 mpd) 2 Cl ... more Abstract Binuclear metal-Schiff base complexes [Mn 2 (PA 2 ppd) 2 Cl 4](I),[Mn 2 (PA 2 mpd) 2 Cl 4](II) and a mononuclear complex [Mn (PA 2 opd) Cl 2](III) were synthesised and characterized. The complexes IIII were used as catalysts for the epoxidation of olefins ...
Journal of Applied Polymer Science, May 15, 1993
ABSTRACT
Polymer Bulletin, 1981
Monomeric Bis-(4-hydroxybutyl) terephthalate has been synthesized and characterized. Titanium iso... more Monomeric Bis-(4-hydroxybutyl) terephthalate has been synthesized and characterized. Titanium iso-propoxide has been found to be a superior catalyst for transesterification compared to metal acetates. Further polycondensation of Bis(HBT) yields poly(l,4-butylene terephthalate). The effect of various titani~mm derived catalysts on the polycondensation of Bis(HBT) ha s been studied. The catalytic efficiency of these derivatives is ascribed to their relative hydrolytic stability and the degree of interaction between the carbonyl oxygen and the metal.
Journal of Applied Polymer Science, 2016
Polymer International, Jul 15, 2019
We provide herein a critical perspective of the burgeoning literature on microporous polymers pre... more We provide herein a critical perspective of the burgeoning literature on microporous polymers prepared using Thermal Rearrangement (TR) processes based on the learning derived from analogous chemistry involving small molecular weight compounds. TR polymers have shown interesting permeability-selectivity relationship in gas separation and, thus, have generated wide interest as potential membrane materials for industrial applications. The intractable nature of the products obtained by TR processes have precluded rigorous structural elucidation of the polymers. Based on the small molecule chemistry, we conclude that structures are likely more complex than generally depicted in the published literature. Interestingly, a simpler chemistry, namely, thermal dehydrocyclization (TCD), leads to products identical to that derived from TR, but at significantly lower temperatures. However, TCD chemistry does not involve a skeletal rearrangement of the kind purported in TR during the conversion of the imide to an oxazole ring resulting in spatially confined heterocyclic ring polymers. Yet, they show similar fractional freevolume elements as exhibited by TR polymers. This is intriguing and points out to a need for more careful examination of the factors responsible for microporosity in such materials. TR chemistry as currently practiced appears limited to only benzoxazole type structures. The ability to precisely control and reproducibly produce materials with well-defined structure and properties will be a key to large scale manufacture and industrial applications of such materials. Seen from this perspective, the TR processes leaves much to be desired and further improvements are clearly warranted. This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as
Macromolecules, Apr 15, 1999
Metal-free anionic polymerizations of alkyl (meth)acrylates using tetrabutylammonium salts of die... more Metal-free anionic polymerizations of alkyl (meth)acrylates using tetrabutylammonium salts of diethylphenylmalonate, fluorene, and 9-ethylfluorene as initiators were performed in THF at 30°C. A poor control of molecular weights, inconsistent initiator efficiencies, and broad or bimodal molecular weight distributions were obtained. The effect of counterion nature was studied from the polymerization of methyl methacrylate using the 1,1-diphenylhexyl anion with tetrabutylammonium, tetramethyldiethylguanidinium, and lithium as counterions under otherwise identical conditions. Metal-free initiators resulted in incomplete initiation which is attributed to the fact that the initiation is an equilibrium reaction. In conjunction with possible side reactions such as Hofmann elimination and transfer reactions, this leads to broad and bimodal molecular weight distributions of the resulting polymers.
Journal of Controlled Release, Apr 1, 1991
St-UF, starch crosslinked by urea-formaldehyde prepolymer, has been previously established as an ... more St-UF, starch crosslinked by urea-formaldehyde prepolymer, has been previously established as an effective matrix for controlled release of the systemic pesticide carbofuran for broadcast application to soil against various pests in agriculture. The water uptake and carbofuran release of this system fits in with the generalized equation M,/iW,-kt" applicable to controlled release systems involving swelling. The St-UF matrix shows an inverse relationship between rate of release and extent of crosslinking. The release rate at a particular crosslinking value is not affected by the extent of loading at low levels (3-10%), but increases at higher loading levels (20%) due to increase in porosity. The release rates were studied in mixtures of water and methanol at 0, 50,70 and 100% methanol levels, thereby varying the solubility of carbofuran in the medium from 1.2 x 10' to 100 x 1 O3 ppm. The release rates increase with solubility in a linear manner, indicating the porous nature of the matrix. Single particle release studies were conducted by a novel procedure for the first time for a matrix dispersed system of irregular shape. The results establish that the mechanism of release is non-Fickian (anomalous).
Energy technology, Apr 26, 2019
Improvement in electrical energy storage systems is one of the most contemporary research topics ... more Improvement in electrical energy storage systems is one of the most contemporary research topics of great academic and industrial interest. Rechargeable batteries appear to be one of the most viable options for humans to migrate to a low carbon intensity mobility solution. Lithium-sulfur battery system offers a theoretical energy density that is an order of magnitude larger than the popular lithium-ion batteries. The principle of working, inherent challenges in utilizing this system for commercial application and the various approaches taken to address these challenges are discussed in detail in this article. Polysulfide shuttle effect is a major concern that deteriorates electrochemical performance in this battery system. In the recent past, electrodes have been intricately engineered to tackle the problem of polysulfide shuttle. However, more recently the focus has shifted to the critical role of the separator. Modifying conventional separators or fabricating novel structures to enhance the cell performance appears to be a more feasible option. In this article we elaborate some design principles which are critical to the functioning of a separator in lithium-sulfur battery, namely, physisorption, chemisorption and electrostatic repulsion Many recent papers propose novel cell configurations with specifically designed functional separators for lithium-sulfur batteries. These reports are classified according to the three design principles, analyzed critically and compared with a view to assess their relative merits and efficacy. A few thoughts on the future directions in the development of an efficient separator are described.
Journal of Polymer Science Part A, Jul 30, 1997
ABSTRACT
Macromolecular Chemistry and Physics, Mar 1, 1998
Group transfer polymerization (GTP) of methyl methacrylate (MMA) and butyl acrylate (BA) in tetra... more Group transfer polymerization (GTP) of methyl methacrylate (MMA) and butyl acrylate (BA) in tetrahydrofuran with (1-methoxy-2-methyl-l-propenyloxy)trimethylsilane (MTS) as initiator and tetrabutylammonium 3-chlorobenzoate, tetrabutylammonium bi-3-chlorobenzoate and tetrabutylammonium bibenzoate as catalysts was investigated. It was found, that the reaction of MTS with all catalysts in the absence of monomers yields the same reaction products as common GTP catalysts. Furthermore, the time-conversion curves of MMA and BA exhibit induction periods proving the assumption, that the first addition step of the monomer to the initiator is slower than the propagation reaction. With respect to molecular-weight control, oxy anions are superior to tetrabutylammonium cyanide (TBACN) due to the missing capability of oxy anions to initiate an anionic polymerization, and bibenzoates are to be preferred to monobenzoates. It is discussed, that the reaction behaviour of oxy anions in GTP can also be understood on the basis of enolate anions as active polymerization species.
Journal of Polymer Science Part A: Polymer Chemistry, 2018
We have explored two novel comonomers, namely, 4,16-dicarboxyl[2.2]paracyclophane and 5,5 0 ,6,6 ... more We have explored two novel comonomers, namely, 4,16-dicarboxyl[2.2]paracyclophane and 5,5 0 ,6,6 0-tetraamino-3,3,3 0 ,3 0-tetramethyl-1,1 0-spirobi[indane], for the synthesis of co-polybenzimidazoles (co-PBIs) with intrinsic porosity. Both these monomers possess twisted structures that can lead to "awkward" macromolecular shapes that cannot pack efficiently. The consequences of introducing these two monomers on the structure and properties of PBIs are reported. The random copolymers synthesized are amorphous and possess glass transition temperatures (T g s) greater than 400 8C. T g decreases with increasing comonomer content indicating an increase in fractional free volume. The copolymers have low surface area. TEM and BET measurements show evidence of mesopore formation. The copolymers show significant carbon dioxide adsorption. Single chain molecular dynamics simulation of 24-mer repeat units shows intramolecular void spaces arising as a result of distorted polymer chain with reduced conformational mobility. These studies define a new synthetic strategy for "bottoms-up" synthesis of PBIs with intrinsic porosity. V
Macromolecular Chemistry and Physics, Mar 1, 1998
Group transfer polymerization (GTP) of methyl methacrylate (MMA) and butyl acrylate (BA) in tetra... more Group transfer polymerization (GTP) of methyl methacrylate (MMA) and butyl acrylate (BA) in tetrahydrofuran with (1-methoxy-2-methyl-l-propenyloxy)trimethylsilane (MTS) as initiator and tetrabutylammonium 3-chlorobenzoate, tetrabutylammonium bi-3-chlorobenzoate and tetrabutylammonium bibenzoate as catalysts was investigated. It was found, that the reaction of MTS with all catalysts in the absence of monomers yields the same reaction products as common GTP catalysts. Furthermore, the time-conversion curves of MMA and BA exhibit induction periods proving the assumption, that the first addition step of the monomer to the initiator is slower than the propagation reaction. With respect to molecular-weight control, oxy anions are superior to tetrabutylammonium cyanide (TBACN) due to the missing capability of oxy anions to initiate an anionic polymerization, and bibenzoates are to be preferred to monobenzoates. It is discussed, that the reaction behaviour of oxy anions in GTP can also be understood on the basis of enolate anions as active polymerization species.
Polymer, Mar 1, 1997
A polymeric hindered amine light stabilizer (HALS), wherein the HALS functionality was attached t... more A polymeric hindered amine light stabilizer (HALS), wherein the HALS functionality was attached to the terminal chain end of an alternating ethylene-propylene copolymer has been synthesized by terminating the living anionic polymerization of isoprene with 4(2,3-epoxy propoxy)-1,2,2,6,6-pentamethylpiperidine followed by hydrogenation of the resulting polymer using Ziegler type catalyst. The solubility and diffusion coefficient of this polymeric HALS have been studied
Macromolecular Symposia, Oct 1, 2003
Chemischer Informationsdienst, Apr 5, 1983
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Papers by swaminathan sivaram