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A. Ramakrishnan

Bio: A. Ramakrishnan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Radical polymerization & Chain transfer. The author has an hindex of 2, co-authored 2 publications receiving 24 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, a block copolymer of styrene and 2-vinylpyridine with narrow molecular weight distribution is reported, where the transformation of the polymerization mechanism from living anionic to controlled/living radical polymerization (ATRP) is described.
Abstract: A novel and simple method of preparation of a block copolymer of styrene and 2-vinylpyridine with narrow molecular weight distribution is reported. The novelty lies in the transformation of the polymerization mechanism from living anionic to controlled/“living” radical polymerization (ATRP). Thus, anionic polymerization of styrene is carried out in benzene using sec-butyllithium as the initiator followed by termination with ethylene oxide to prepare hydroxy-terminated polystyrene (PS-OH). PS-OH is converted to chloride-terminated polystyrene (PS-Cl) by a displacement reaction involving thionyl chloride and pyridine in benzene. PS-Cl is used to initiate the heterogeneous ATRP of 2-vinylpyridine in p-xylene with CuCl/2,2′-bipyridine system. The polymers synthesized are characterized by gel permeation chromatography (GPC), thin layer chromatography (TLC), IR and proton NMR spectroscopies.

18 citations

Journal ArticleDOI
TL;DR: A binol ester initiator was used as a bifunctional ATRP initiator in combination with PMDETA/copper bromide catalyst system in DMF to synthesize n-butyl acrylate macroinitiator at 50°C.
Abstract: A binol ester initiator was used as a bifunctional ATRP initiator in combination with PMDETA/copper bromide catalyst system in DMF to synthesize n‐butyl acrylate macroinitiator at 50°C. The resulting macroinitiator was used for a detailed investigation of the ATRP of methyl methacrylate (MMA) with CuCl/N,N,N′,N′,N″‐pentamethyldiethy‐lenetriamine (PMDETA) catalyst system in anisole at 30°C. Thus, the MMA polymerization is shown to proceed with first order kinetics, with predicted molecular weight and narrow polydispersity indices. Gel permeation chromatography (GPC) and NMR were used for the characterization of the polymers synthesized.

8 citations


Cited by
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Reference EntryDOI
15 Jul 2004
TL;DR: In this article, the synthesis and solution characteristics of both natural and synthetic polymers are discussed, focusing on polynucleotides, polypeptides, and polysaccharides for naturally occurring polymers.
Abstract: Water-soluble (co)polymers represent a diverse class of macromolecules ranging from naturally occurring biopolymers such as polysaccharides and most polypeptides to wholly man-made materials. Such materials have found a wide-range of applications. In this article we detail the synthesis and solution characteristics of both natural and synthetic polymers. Emphasis is placed on polynucleotides, polypeptides, and polysaccharides for naturally occurring polymers, while the discussion regarding synthetic materials is divided into sections dealing with neutral, anionic, cationic, and zwitterionic species. Special attention is given to recent advances in synthetic methodologies which now allow the tailoring of synthetic materials with precisely controlled microstructures, predetermined molecular weights, narrow molecular weight distributions, and complex topologies. Finally, we detail some of the self-assembly characteristics of both high molecular weight statistical copolymers and lower molecular weight block copolymers in aqueous media with an emphasis on those materials which undergo phase transitions and/or conformational changes in response to an applied stimulus. Keywords: water-soluble polymers; naturally occurring polymers; polynucleotides; polypeptides; proteins; polysaccharides; nonionic polymers; polyelectrolytes; polyzwitterions; polyampholytes; polybetaines

346 citations

Journal ArticleDOI
TL;DR: In this paper, a review of transformation reactions involving living and controlled/living polymerization methods is presented, including step-growth, conventional and controlled free radical, cationic, anionic, group transfer, activated monomer Ziegler-Natta and metathesis reactions.

314 citations

Patent
22 Feb 2011
TL;DR: In this article, the ORI/Ti molar ratio in the range 0.1-1.5 was used for the polymerization of MWD crystalline ethylene polymers.
Abstract: Catalyst components for the(co)polymerization of ethylene comprising Ti, Mg, halogen, ORI groups, where RI is a C1-C12 hydrocarbon group optionally containing heteroatoms, having ORI/Ti molar ratio in the range 0.1-1.5, a Mg/Ti molar ratio of less than 8, an amount of titanium, with respect to the total weight of said solid catalyst component, higher than 4% by weight characterized by a specific SS-NMR pattern are particularly useful for preparing narrow MWD crystalline ethylene polymers.

201 citations

Journal ArticleDOI
TL;DR: In this article, the authors reported the polymerization of N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA) directly in aqueous media utilizing 4-cyanopentanoic acid dithiobenzoate (CTP) as the chain transfer agent.
Abstract: Controlled radical polymerization (CRP) combines the benefits of the robust nature of conventional radical polymerization with the ability to prepare advanced macromolecular architectures common to living polymerization techniques. Of the major CRP techniques, the reversible addition−fragmentation chain transfer (RAFT) technique appears to be the most tolerant of aqueous reaction conditions and a variety of monomer functionalities. To date, however, there have been no reports of the RAFT polymerization of a cationic (meth)acrylamido monomer directly in aqueous media. Herein we report the polymerization of N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA) directly in aqueous media utilizing 4-cyanopentanoic acid dithiobenzoate (CTP) as the chain transfer agent (CTA). Polymerization in water at neutral pH allowed a moderate level of control over the polymerization up to 50% conversion. Polymerization in an aqueous buffer (pH = 5), on the other hand, afforded excellent control up to 98% conversion (Mn = 38 ...

125 citations