@article { ISI:000231000700013, title = {Synthesis of poly(1-hexene)s end-functionalized with phenols}, journal = {Polymer International}, volume = {54}, number = {9}, year = {2005}, month = {SEP}, pages = {1310-1313}, publisher = {JOHN WILEY \& SONS LTD}, type = {Article}, address = {THE ATRIUM, SOUTHERN GATE, CHICHESTER PO19 8SQ, W SUSSEX, ENGLAND}, abstract = {

Electrophilic alkylations of phenol/2,6-dimethylphenol were performed with vinylidene-terminated poly(1-hexene)s using BF3-OEt2 catalyst. Vinylidene-terminated poly(1-hexene)s with M. varying from 400 to 10000 were prepared by bulk polymerization of 1-hexene at 50 to -20 degrees C using Cp2ZrCl2/MAO catalysts. The phenol/2,6-dimethylphenol-terminated poly(1-hexene)s was characterized by NMR (H-1, C-13), UV, IR and vapor phase osmometer (VPO). The isomer distribution (ortho, para and ortholpara) was determined by P-13 NMR using a phosphitylating reagent, namely 2-chloro-1,3,2-dioxaphospholane. The number-average degree of functionality (F-n) \> 0.9 with \> 95\% para selectivity could be achieved using low-molecular-weight oligomers of poly(1-hexene)s. (c) 2005 Society of Chemical Industry.

}, keywords = {Alkylation, chain-end functionalization, functional poly(olefin)s, metallocene catalysts}, issn = {0959-8103}, doi = {10.1002/pi.1848}, author = {Yanjarappa, Mallinamadugu J. and Sivaram, Swaminathan} } @article { ISI:000238629400001, title = {NaIO4/KI/NaCl: a new reagent system for iodination of activated aromatics through in situ generation of iodine monochloride}, journal = {Tetrahedron Letters}, volume = {47}, number = {28}, year = {2006}, month = {JUL}, pages = {4793-4796}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, type = {Article}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

A new reagent system consisting of NaIO4/KI/NaCl in aq AcOH has been found to be effective in iodinating a variety of activated aromatic substrates via in situ-generated iodine monochloride, to furnish iodoaromatics in excellent yields. This iodination procedure has been applied successfully for a cost-effective synthesis of 3,3{\textquoteright}-diaminobenzidine, a key intermediate for preparing proton conducting membranes for fuel cell applications, with high yield and a purity of 99.7\%. (c) 2006 Elsevier Ltd. All rights reserved.

}, issn = {0040-4039}, doi = {10.1016/j.tetlet.2006.05.062}, author = {Emmanuvel, Lourdusamy and Shukla, Ravi Kant and Sudalai, Arumugam and Gurunath, Suryavanshi and Sivaram, Swaminathan} } @article { ISI:000239224100005, title = {Silica-supported bis(imino)pyridyl iron(II) catalyst: nature of the support-catalyst interactions}, journal = {Polymer International}, volume = {55}, number = {8}, year = {2006}, month = {AUG}, pages = {854-861}, publisher = {JOHN WILEY \& SONS LTD}, type = {Article}, address = {THE ATRIUM, SOUTHERN GATE, CHICHESTER PO19 8SQ, W SUSSEX, ENGLAND}, abstract = {

Ethylene polymerizations were performed using silica-supported 2,6-bis[1-(2,6-diisopropylphenylimino) ethyl] pyridine iron(II) dichloride with methylaluminoxane (MAO) as co-catalyst. Silica was calcined at 600, 400 and 200 degrees C under vacuum for 8 h. The effect of calcination temperature of silica on the polymerization activity and the properties of the polymers obtained were examined. Catalyst-support interactions were examined by both a chemical method and XPS. It was observed that upon supporting the catalyst on the surface of silica, there is an increase in the binding energy of the metal center. However, no change in the metal binding energy was observed on supporting the catalyst to silica calcined at different temperatures. Ethylene polymerizations were performed using MAO as co-catalyst. Catalysts were also prepared by first pretreating silica with NIAO, followed by addition of the Fe(II) catalyst and contacting a complex of Fe(II) catalyst-MAO with silica previously calcined at 400 degrees C for 8 h. The results indicate that there is no chemical bonding between the support and the catalyst. (C). 2006 Society of Chemical Industry.

}, keywords = {bis(imino) pyridyl iron(II) complex, Polyethylene, silica, supported catalyst, XPS}, issn = {0959-8103}, doi = {10.1002/pi.2020}, author = {Ray, Saptarshi and Sivaram, Swaminathan} } @article { ISI:000244614500012, title = {Kinetics of hexene-1 polymerization using [(N,N {\textquoteleft}-diisopropylbenzene)-2,3-(1,8-napthyl)-1,4-diazabutadiene] dibromonickel/methylaluminoxane catalyst system}, journal = {Journal of Polymer Science Part A-Polymer Chemistry}, volume = {45}, number = {6}, year = {2007}, month = {MAR}, pages = {1093-1100}, publisher = {JOHN WILEY \& SONS INC}, type = {Article}, address = {111 RIVER ST, HOBOKEN, NJ 07030 USA}, abstract = {

{Kinetics of hexene-1 polymerization was investigated using [(N,N{\textquoteright}-diiso-propylbenzene)2,3-(1,8-napthly)-1,4-diazabutadiene]/dibro monickel/methylaluminoxane catalyst. Experiments were performed at varying catalyst and monomer concentrations in the temperature range of -10 to 35 degrees C. First order time-conversion plot shows a downward curvature at temperatures of 20 degrees C and 35 degrees C indicating the presence of finite termination reactions. A nonlinear plot of degree of polymerization (P-n) with respect to conversion indicates occurrence of transfer reactions and slow initiation. The experimental molar masses are higher than predicted, which implies that a fraction of catalyst species could not be activated or is deactivated at the early stages of the reactions. The efficiency of the catalyst (Cat(eff)) varies from 0.77 to 0.89. The observed polydispersity of the poly(hexene-1) s is in the range of 1.18-1.48. The reaction order was found to be 1.11 with respect to catalyst. The Arrhenius plot obtained using the overall propagation rate constant, k(p), at five different temperatures (-10, 0, 10, 20, and 35 degrees C) was found to be linear with an activation energy

}, keywords = {Activation energy, chain transfer, degree of polymerization, hexene-1, kinetics (polym.), nickel (alpha-diimine)}, issn = {0887-624X}, doi = {10.1002/pola.21852}, author = {Subramanyam, Ummadisetty and Sivaram, Swaminathan} } @article { ISI:000243242700003, title = {Synthesis and characterization of poly(higher-alpha-olefin)s with a nickel(alpha-diimine)/methylaluminoxane catalyst system: effect of chain running on the polymer properties}, journal = {Journal of Polymer Science Part A-Polymer Chemistry}, volume = {45}, number = {2}, year = {2007}, month = {JAN}, pages = {191-210}, publisher = {JOHN WILEY \& SONS INC}, type = {Article}, address = {111 RIVER ST, HOBOKEN, NJ 07030 USA}, abstract = {

Homopolymerization of octadecene-1 at different reaction conditions has been studied. Significant chain running can be seen at higher polymerization temperatures. Interestingly, insertion of octadecene-1 into a sterically hindered nickel-cation/carbon (secondary) bond is observed. The microstructure of the polymer was established using NMR spectroscopy. The effects of chain running on polymer melting, crystallization behavior, and dynamic mechanical thermal properties were studied using DSC and DMTA. The extent of chain running (i.e., 2 omega-, 1,omega-enchainments) decreases with an increase in the carbon number of alpha-olefins. (c) 2006 Wiley Periodicals, Inc.

}, keywords = {chain running, Crystallization, glass transition, melt transition, nickel (alpha-diimine), NMR, poly(alpha-olefin)s}, issn = {0887-624X}, doi = {10.1002/pola.21783}, author = {Subramanyam, Ummadisetty and Sivaram, Swaminathan} } @article { ISI:000254135200020, title = {Synthesis of amphiphilic poly(methyl methacrylate-b-ethylene oxide) copolymers from monohydroxy telechelic poly(methyl methacrylate) as macroinitiator}, journal = {Journal of Polymer Science Part A-Polymer Chemistry}, volume = {46}, number = {6}, year = {2008}, month = {MAR}, pages = {2132-2144}, publisher = {JOHN WILEY \& SONS INC}, type = {Article}, address = {111 RIVER ST, HOBOKEN, NJ 07030 USA}, abstract = {

The synthesis of well-defined poly(methyl methacrylate)-block-poly(ethylene oxide) (PMMA-b-PEO) dibock copolymer through anionic polymerization using monohydroxy telechelic PMMA as macroinitiator is described. Living anionic polymerization of methyl methacrylate was performed using initiators derived from the adduct of diphenylethylene and a suitable alkyllithium, either of which contains a hydroxyl group protected with tert-butyldimethylsilyl moiety in tetrahydrofuran (THF) at -78 degrees C in the presence of LiClO4. The synthesized telechelic PMMAs had good control of molecular weight with narrow molecular weight distribution (MWD). The H-1 NMR and MALDI-TOF MS analysis confirmed quantitative functionalization of chain-ends. Block copolymerization of ethylene oxide was carried out using the terminal hydroxyl group of PMMA as initiator in the presence of potassium counter ion in THF at 35 degrees C. The PMMA-b-PEO diblock copolymers had moderate control of molecular weight with narrow MWD. The H-1 NMR results confirm the absence of trans-esterification reaction of propagating PEO anions onto the ester pendants of PMMA. The micellation behavior of PMMA-b-PEO diblock copolymer was examined in water using H-1 NMR and dynamic light scattering. (C) 2008 Wiley Periodicals, Inc.

}, keywords = {Anionic polymerization, block copolymers, synthesis}, issn = {0887-624X}, doi = {10.1002/pola.22548}, author = {Dhara, Mahua Ganguly and Baskaran, Durairaj and Sivaram, Swaminathan} } @article {39}, title = {Synthesis of hydroxy-functional PMMA macromonomers by anionic polymerization}, journal = {Journal of Macromolecular Science Part A-Pure and Applied Chemistry}, volume = {46}, number = {10}, year = {2009}, month = {SEP}, pages = {PII 914494634}, publisher = {TAYLOR \& FRANCIS INC}, type = {Article}, address = {325 CHESTNUT ST, SUITE 800, PHILADELPHIA, PA 19106 USA}, abstract = {

Living anionic polymerization has been utilized to synthesize hydroxy end-functionalized PMMA macromonomers with styryl or allyl functionalities as the polymerizable end-groups. Protected hydroxy-functionalized alkyl lithium initiators have been used to initiate anionic polymerization of MMA. Subsequently the living chains with protected hydroxyl function have been terminated using 4-vinylbenzyl chloride (4-VBC) or allyl methacrylate (ALMA) to form -hydroxy{\textendash}styryl and -hydroxy{\textendash}allyl PMMA, respectively. These protected hydroxy-functionalized PMMA macromonomers have been characterized by GPC and 1H-NMR. Termination using 4-VBC led to 50\% functionalization, whereas that using allyl methacrylate led to 100\% functionalization of the hydroxy-PMMA.

}, keywords = {Anionic polymerization, functionalized initiator, Macromonomer}, issn = {1060-1325}, doi = {10.1080/10601320903158610}, author = {Dhara, Mahua Ganguly and Sivaram, Swaminathan and Bhonde, Ramesh R. and Bhagavatula L. V. Prasad} } @article { ISI:000267110100003, title = {Synthesis of hydroxy-functionalized star-branched PMMA by anionic polymerization}, journal = {Polymer Bulletin}, volume = {63}, number = {2}, year = {2009}, month = {AUG}, pages = {185-196}, publisher = {SPRINGER}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Living anionic polymerization has been exploited to synthesize hydroxy end-functionalized PMMA star-branched polymers. Protected hydroxy-functionalized alkyl lithium initiators have been used to initiate anionic polymerization of MMA. Subsequently the living chains with protected hydroxyl function have been used to cross-link ethylene glycol dimethacrylate (EGDMA) in order to form star-branched polymers with cross-linked EGDMA core via {\textquoteleft}arm-first{\textquoteright} method. The linear arms and the star molecules have been characterized by (1)HNMR, GPC, and light scattering. Variation in the number of arms with arm molecular weight and cross-linker loading has been studied. Star-branched PMMA-OH with as many as similar to 10 arms could be successfully made. Increased molecular weight of PMMA-OH led to decrease in the number of arms incorporated due to increased steric hindrance on the core. Increase in EGDMA concentration slightly increased the arm incorporation.

}, keywords = {Anionic polymerization, Star polymers, Star-branched PMMA}, issn = {0170-0839}, doi = {10.1007/s00289-009-0082-7}, author = {Dhara, Mahua Ganguly and Sivaram, Swaminathan and Baskaran, Durairaj} } @article { ISI:000280389500002, title = {Addition of a silyl ketene acetal to alpha,beta-unsaturated cyclic anhydrides}, journal = {Synthetic Communications}, volume = {40}, number = {16}, year = {2010}, month = {JUL}, pages = {PII 924771265}, publisher = {TAYLOR \& FRANCIS INC}, address = {325 CHESTNUT ST, SUITE 800, PHILADELPHIA, PA 19106 USA}, abstract = {

Addition of [1-methoxy-2 methyl-1-propenyl)-oxy] trimethylsilane (MTS) to unsymmetrical ,-unsaturated cyclic anhydrides (namely, itaconic anhydride and citraconic anhydride) as well as symmetrical anhydrides (namely, maleic anhydride and 2,3-dimethylmaleic anhydride) was investigated. Itaconic anhydride isomerizes to citraconic anhydride in the presence of MTS. In the presence of Lewis acid catalysts (Yb(OTf)3/CH2Cl2), MTS adds to itaconic anhydride at room temperature in a 1,4-fashion. 1,2-Addition is the preferred pathway with both 2,3-dimethyl maleic anhydride and citraconic anhydride.

}, keywords = {1, 2-Addition, 4-addition, cyclic anhydrides, Lewis acid, Silyl ketene acetal}, issn = {0039-7911}, doi = {10.1080/00397910903243815}, author = {Gnaneshwar, Rudhramyna and Sivaram, Swaminathan} } @article { ISI:000312940700015, title = {Chemistry in India: unlocking the potential}, journal = {Angewandte Chemie-International Edition}, volume = {52}, number = {1}, year = {2013}, month = {DEC}, pages = {114-117}, publisher = {WILEY-V C H VERLAG GMBH}, address = {BOSCHSTRASSE 12, D-69469 WEINHEIM, GERMANY}, issn = {1433-7851}, doi = {10.1002/anie.201206960}, author = {Arunan, Elangannan and Brakaspathy, Ramasamy and Desiraju, Gautam R. and Sivaram, Swaminathan} } @article { ISI:000361935600025, title = {Star telechelic poly(L-lactide) ionomers}, journal = {Macromolecules}, volume = {48}, number = {18}, year = {2015}, month = {SEP}, pages = {6580-6588}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Poly(L-lactide) (PLA), a biodegradable and biorenewable polymer, has many excellent properties that are equivalent to those of petroleum-derived plastics such as polystyrene, aromatic polyesters, etc. However, a major disadvantage of PLA which limits its processability is its poor melt elasticity. In this work we explore the possibility of improving the viscoelastic properties of PLA melt by incorporating ionic groups on the polymer. Specifically, we demonstrate the synthesis of star telechelic PLA anionomers by a three-step procedure involving synthesis of Star PIA, converting the hydroxyl end groups into carboxylic acid end groups, and finally converting these into ionic groups. Rheology data showed a dramatic increase in the elasticity of the star telechelic ionomer melts relative to the Star PLA melts. The viscoelasticity of star telechelic ionomers melts could be modulated by varying the number of ionic groups per molecule.

}, issn = {0024-9297}, doi = {10.1021/acs.macromol.5b01854}, author = {Kulkarni, Amruta and Lele, Ashish K. and Sivaram, Swaminathan and Rajamohanan, P. R. and Velankar, Sachin and Chatterji, Apratim} } @article {45655, title = {Functional additives derived from structurally well-defined poly(olefin)s: Structure - function relationships}, journal = {Abstracts of Papers of the American Chemical Society}, volume = {252}, year = {2016}, month = {AUG }, type = {Meeting Abstract}, issn = {0065-7727}, author = {Sivaram, Swaminathan} } @article { ISI:000367915800019, title = {Synthesis and characterization of well-defined random and block copolymers of epsilon-caprolactone with l-lactide as an additive for toughening polylactide: Influence of the molecular architecture}, journal = {Journal of Applied Polymer Science}, volume = {133}, number = {14}, year = {2016}, month = {APR}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

Well-defined multiarmed star random and block copolymers of epsilon-caprolactone with l-lactide with controlled molecular weights, low polydispersities, and precise numbers of arms were synthesized by the ring-opening polymerization of respective cyclic ester monomers. The polymers were characterized by H-1-NMR and C-13-NMR to determine their chemical composition, molecular structure, degree of randomness, and proof of block copolymer formation. Gel permeation chromatography was used to establish the degree of branching. Star-branched random copolymers exhibited lower glass-transition temperatures (T-g{\textquoteright}s) compared to a linear random copolymer. When the star random copolymers were melt-blended with poly(l-lactic acid) (PLA), we observed that the elongation of the blend increased with the number of arms of the copolymer. Six-armed block copolymers, which exhibited higher T-g{\textquoteright}s, caused the maximum improvement in elongation. In all cases, improvements in the elongation were achieved with no loss of stiffness in the PLA blends. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43267.

}, keywords = {biodegradable, copolymers, differential scanning calorimetry, mechanical properties, ring-opening polymerization}, issn = {0021-8995}, doi = {10.1002/app.43267}, author = {Deokar, Megha D. and Idage, Susheela B. and Idage, Bhaskar B. and Sivaram, Swaminathan} } @article {43645, title = {Thermally conductive thin films derived from defect free graphene-natural rubber latex nanocomposite: preparation and properties}, journal = {Carbon}, volume = {119}, year = {2017}, month = {AUG}, pages = {527-534}, abstract = {Commercially useful rubber products viz. gloves, condoms, tyres, and rubber hoses used in high temperature environments, etc., require efficient thermal conductivity, which increases the lifetime of these products. Graphene can fetch this property, if it is effectively incorporated into the rubber matrix. The great challenge in preparing graphene-rubber nanocomposites is formulating a scalable method to produce defect free graphene and its homogeneous dispersion into polymer matrices through an aqueous medium. Here, we used a simple method to produce defect free few layer (2-5) graphene, which can be easily dispersed into natural rubber (NR) latex without adversely affecting its colloidal stability. The resulting new composite showed large increase in thermal conductivity (480-980\%) along with 40\% increase in tensile properties and 60\% improvement in electrical conductivity. This study provides a novel and generalized approach for the preparation of graphene based thermally conductive rubber nanocomposites. (C) 2017 The Authors. Published by Elsevier Ltd.}, doi = {10.1016/j.carbon.2017.04.068}, author = {George, Gejo and Sisupal, Suja Bhargavan and Tomy, Teenu and Pottammal, Bincy Akkoli and Kumaran, Alaganandam and Suvekbala, Vemparthan and Gopimohan, Rajmohan and Sivaram, Swaminathan and Ragupathy, Lakshminarayanan} } @article {44614, title = {Facile, environmentally benign and scalable approach to produce pristine few layers graphene suitable for preparing biocompatible polymer nanocomposites}, journal = {Scientific Reports}, volume = {8}, year = {2018}, month = {JUL}, pages = {11228}, abstract = {

The success of developing graphene based biomaterials depends on its ease of synthesis, use of environmentally benign methods and low toxicity of the chemicals involved as well as biocompatibility of the final products/devices. We report, herein, a simple, scalable and safe method to produce defect free few layers graphene using naturally available phenolics i.e. curcumin/tetrahydrocurcumin/ quercetin, as solid-phase exfoliating agents with a productivity of similar to 45 g/batch (D/G = 0.54 and D/D{\textquoteright} \<= 1.23). The production method can also be employed in liquid-phase using a ball mill (20 g/batch, D/G \<= 0.23 and D/D{\textquoteright} \<= 1.12) and a sand grinder (10 g/batch, D/G \<= 0.11 and D/D similar to = 0.78). The combined effect of p-p interaction and charge transfer (from curcumin to graphene) is postulated to be the driving force for efficient exfoliation of graphite. The yielded graphene was mixed with the natural rubber (NR) latex to produce thin film nanocomposites, which show superior tensile strength with low modulus and no loss of \% elongation at break. In-vitro and in-vivo investigations demonstrate that the prepared nanocomposite is biocompatible. This approach could be useful for the production of materials suitable in products (gloves/condoms/catheters), which come in contact with body parts/ body fluids.

}, issn = {2045-2322}, doi = {10.1038/s41598-018-28560-1}, author = {George, Gejo and Sisupal, Suja Bhargavan and Tomy, Teenu and Kumaran, Alaganandam and Vadivelu, Prabha and Suvekbala, Vemparthan and Sivaram, Swaminathan and Ragupathy, Lakshminarayanan} } @article {44371, title = {Soluble polybenzimidazoles with intrinsic porosity: synthesis, structure, properties and processability}, journal = {56Journal of Polymer Science Part A-Polymer Chemistry}, volume = {56}, year = {2018}, month = {MAY}, pages = {1046-1057}, type = {Article}, abstract = {We have explored two novel comonomers, namely, 4,16-dicarboxyl[2.2]paracyclophane and 5,5,6,6-tetraamino-3,3,3,3-tetramethyl-1,1-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 degrees C. 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. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1046-1057}, doi = {10.1002/pola.28979}, author = {Kumar, Vikas and Chatterjee, Shyambo and Sharma, Pragati and Chakrabarty, Suman and Avadhani, Chilukuri V. and Sivaram, Swaminathan} } @article {46133, title = {Lithium speciation in the LiPF6/PC electrolyte studied by two dimensional heteronuclear overhauser enhancement and pulse field gradient diffusometry NMR}, journal = {Journal of Physical Chemistry C}, volume = {123}, year = {2019}, month = {APR}, pages = {9661-9672}, type = {Article}, abstract = {

Electrolytic dissociation of lithium hexafluorophosphate (LiPF6) in the nonaqueous cyclic propylene carbonate (PC) has been investigated in the wide range of concentration (0.05-3.5 M) by Li-7 solution-state nuclear magnetic resonance (NMR) spectroscopy. Two-dimensional heteronuclear Overhauser enhancement spectroscopy NMR experiments have not only enabled the cation solvation and ion-pairing to be directly monitored but additionally evidence anion solvent interaction at higher concentrations (\>1.2 M) of the PC electrolyte. Preliminary analysis of kinetic nOe data has been made to determine site-dependent cross-relaxation rates for the spatial interaction of the solvent with the Li+ cation and the PF6- anion. The concentration dependence of the Li-7 NMR self-diffusion coefficient (D-self), determined using very strong pulsed magnetic field gradients (similar to 1700 Gauss/cm), depicts two breaks to mark the solvation and ion-pairing events in a distinct manner. This in turn has aided the determination of solvent coordination number and average sizes of solvated and ion-paired clusters. Our results indicate that in the contact ion pair (CIP)-dominated electrolyte (\>2 M), lithium-ion mobility across the solvated and ion-paired environments appears to be inhibited which makes the spectral distinction of solvated and ion-paired environments possible. The concentration dependence of the Li-7 NMR spectral and diffusometry data is in striking correspondence with that of bulk conductivity measurements and point to the detrimental effect of CIP aggregates in impeding the ionic conductivity at high salt concentrations. These results have significance in understanding the structure and dynamics of lithium-ion solvates that are ubiquitous in the working environment of a lithium-ion battery.

}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.8b11599}, author = {Kumar, Vikas and Reddy, R. Ravikanth and Kumar, B. V. N. Phani and Avadhani, Chilukuri V. and Ganapathy, Subramanian and Chandrakumar, Narayanan and Sivaram, Swaminathan} } @article {46094, title = {Separator membranes for lithium-sulfur batteries: design principles, structure, and performance}, journal = {Energy Technology}, volume = {7}, year = {2019}, month = {JUN}, pages = {1800819}, type = {Article}, abstract = {

Improvement in electrical energy storage systems is one of the most recent research topics of great academic and industrial interest. Lithium-sulfur (Li-S) battery systems offer a theoretical energy density an order of magnitude larger than the popular Li-ion batteries. The principle of working, inherent challenges in utilizing this system for commercial applications, and the various approaches taken to address these challenges are herein discussed in detail. The polysulfide shuttle effect is a major concern that deteriorates electrochemical performance in this system. In the recent past, electrodes have been intricately engineered to tackle this problem. 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. Some design principles that are critical to the functioning of a separator in Li-S batteries, namely physisorption, chemisorption, and electrostatic repulsion, are discussed. Many recent papers proposed novel cell configurations with specifically designed functional separators. These reports are classified according to three design principles, analyzed critically, and compared with a view to assess their relative merits and efficacy. Some thoughts on the future directions in the development of an efficient separator are described.

}, keywords = {lithium-sulfur batteries, polysulfides, rechargeable batteries, separators, shuttle effect}, issn = {2194-4288}, doi = {10.1002/ente.201800819}, author = {Gupta, Aritrajit and Sivaram, Swaminathan} } @article {46696, title = {Ultrahigh molecular weight polyethylene: catalysis, structure, properties, processing and applications}, journal = {Progress in Polymer Science}, volume = {109}, year = {2020}, month = {OCT}, pages = {101290}, type = {Review}, abstract = {

Ultrahigh molecular weight polyethylene (UHMWPE) belongs to an emerging class of high-performance specialty polymers with a unique set of properties and applications. The field has witnessed many scientific and technological advances in recent years. However, synthesis of UHMWPE is not a trivial exercise and presents several challenges. This review addresses these fundamental challenges and provides an overview of recent developments in the field of UHMWPE. The nature of catalysts, reaction conditions that favor its formation, their physical properties, methods of processing them into products, and their applications are discussed. Recent developments in formation of UHMWPE in a disentangled state by use of appropriate catalysts and reaction conditions are also discussed. This has elicited considerable interest as a means of enabling melt processing of UHMWPE. This review provides a comprehensive source of information and understanding of the multifaceted aspects of UHMWPE with specific reference to chemistry, catalysis, processes for manufacturing, and an analysis of catalyst structure-polymer property relationships. (C) 2020 Elsevier B.V. All rights reserved.

}, keywords = {Catalysts for UHMWPE, Disentangled UHMWPE, Entangled UHMWPE, polyethylene (PE), Ultrahigh molecular weight (UHMW) PE}, issn = {0079-6700}, doi = {10.1016/j.progpolymsci.2020.101290}, author = {Patel, Ketan and Chikkali, Samir H. and Sivaram, Swaminathan} } @article {48390, title = {Toughening poly(l-lactide) blends: effectiveness of sequence-controlled six-arm star-branched block copolymers of poly(L-lactide) and poly(epsilon-caprolactone)}, journal = {ACS Omega}, volume = {7}, year = {2022}, month = {MAR}, pages = {9118-9129}, type = {Article}, abstract = {

Well-defined six-arm star-branched bio-degradable block copolymers of L-lactide and epsilon-caprolactone were prepared using controlled ring-opening polymerization and a sequential monomer addition method using dipentaerythritol as the initiator core and organocatalysts at low temperatures in solution. Sequence of enchainment was changed by reversing the order of monomer addition giving, either, a crystalline PLA block or an amorphous PCL block as the outer segment. Well-defined six-arm poly(epsilon-caprolactone-b-L-lactide, 6s-PCL-b-PLA) block copolymers were obtained with a range of segment molecular weights. However, in the case of six-arm poly(L-lactide-b-epsilon-caprolactone, 6s-PLA-b-PCL), disruption of the block structure was observed on account of competing transesterification reactions accompanying a chain-growth reaction. Such sequence-controlled block copolymers showed interesting phase morphologies, as evidenced by differential scanning calorimetry (DSC) studies. 6s-PCL-b-PLA showed two glass-transition temperatures and two melting temperatures characteristic of the amorphous and crystalline blocks. 6s-PCL-b-PLA and 6s-PLA-b-PCL with different segment chain lengths were solution blended (10 wt \%) with a commercially sourced PLA. All the blends were highly transparent. The structure and properties of the blend were examined by DSC, measurement of mechanical properties, and scanning electron microscopy. The results show that a phase-separated 6s-PCL-b-PLA copolymer results in two- to three-fold improvement in tensile toughness without the loss of modulus. A possible hypothesis for the mechanism of tensile toughness in the blend has been proposed.

}, issn = {2470-1343}, doi = {10.1021/acsomega.1c04486}, author = {Deokar, Megha D. and Garnaik, Baijayantimala and Sivaram, Swaminathan} }