Browsing by Author "Avnish Kumar Mishra"

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(S)-2-(Ethyl propionate)-(O-ethyl xanthate) and (S)-2-(ethyl isobutyrate)-(O-ethyl xanthate)-mediated RAFT polymerization of N-vinylpyrrolidone
(2010) Vijay Kumar Patel; Avnish Kumar Mishra; Niraj Kumar Vishwakarma; Chandra Sekhar Biswas; Biswajit Ray
(S)-2-(Ethyl propionate)-(O-ethyl xanthate) (X1) and the newly synthesized (S)-2-(ethyl isobutyrate)-(O-ethyl xanthate) (X2) were used as the reversible addition-fragmentation chain transfer (RAFT) agents for the radical polymerization of N-vinylpyrrolidone (NVP). The former showed the better chain transfer ability in the polymerization at 60 °C. Kinetics study with X1 shows the psuedo-first order kinetics upto 45% monomer conversion. Molecular weight (Mn) of the resulted polymer increases linearly with increase in the monomer conversion upto around 45%. Polydispersity of the corresponding poly(NVP)s increase gradually from 1.2 to 1.9 with increase in the monomer conversion. Chain-end analysis of the resulted polymer by1H NMR shows clearly that polymerization started with radical forming out of xanthate mediator. Living nature of the polymerization was confirmed from the successful homo chain extension experiment and also the heterochain extension experiment involving synthesis of poly(NVP)-b-polystyrene amphiphilic diblock copolymer. © Springer-Verlag 2009.
(S)-2-(ethyl propionate)-(O-ethyl xanthate)- and (S)-2-(Ethyl isobutyrate)-(O-ethyl xanthate)-mediated RAFT polymerization of vinyl acetate
(2012) Vijay Kumar Patel; Niraj Kumar Vishwakarma; Avnish Kumar Mishra; Chandra Sekhar Biswas; Biswajit Ray
(S)-2-(Ethyl propionate)-(O-ethyl xanthate) (X1) and (S)-2-(Ethyl isobutyrate)-(O-ethyl xanthate) (X2) were used as the reversible addition-fragmentation chain transfer (RAFT) agents for the radical polymerization of vinyl acetate (VAc). The former showed the better chain transfer ability in the polymerization at 60°C. Kinetic study with both RAFT agents showed pseudo-first order kinetics up to around 85% monomer conversion. Molecular weight of the resulting polymer increased linearly with increase in the monomer conversion up to around 85%. The observed molecular weights calculated from 1H-NMR spectrum [M n(NMR)] are close to the corresponding theoretical molecular weights [M n(theor)]. The corresponding polydispersity index (PDI) of the resulting polymers remained almost constant at around 1.2 up to ∼ 65% monomer conversion and then increased gradually with the further increase in the monomer conversion. Chain-end analysis of the resulting polymers by 1H-NMR showed clearly that polymerization started with the radical forming out of the xanthate mediator. The negligible homo-chain extension and the hetero-chain extension involving synthesis of poly(VAc)-b-poly(NVP) diblock copolymer were occurred. © 2012 Wiley Periodicals, Inc.
Synthesis and characterization of porous poly(N-isopropylacrylamide) hydrogels prepared in ethanol-water mixtures
(2011) Chandra Sekhar Biswas; Vijay Kumar Patel; Niraj Kumar Vishwakarma; Avnish Kumar Mishra; Biswajit Ray
Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were prepared by free-radical polymerization in different ethanol-water mixtures. A scanning electron microscopy study revealed that the resulting hydrogels were macroporous. The swelling ratios of the resultant hydrogels in water at 20°C followed this order: X0.34 â X0.68 > X 0.48 > X0.09 > X0.04 > X0, where Xa denotes a gel prepared in an ethanol-water solvent mixture with an ethanol molar fraction of a. Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with increasing temperature. The complete collapse of the PNIPAM chain of all of these gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all of the PNIPAM gels with different molar fractions of ethanol at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X0.34 > X0.48 > X0.68 > X 0.09 > X 0.04 > X0. The reswelling rates of these hydrogels decreased in the following order: X0 > X0.04 â X0.48 > X0.09 â X0.68 > X 0.34. The freeze-drying process decreased the swelling ratios but increased the deswelling and reswelling properties of the PNIPAM gels. © 2011 Wiley Periodicals, Inc.
Synthesis and characterization of stereocontrolled poly(N -isopropylacrylamide) hydrogel prepared in the presence of Y(OTf)3 lewis acid
(2010) Chandra Sekhar Biswas; Vijay Kumar Patel; Niraj Kumar Vishwakarma; Avnish Kumar Mishra; Satyen Saha; Biswajit Ray
Macroporous poly(N-isopropylacrylamide) (PNIPAM) hydrogels have been prepared in methanol-water (1:1, v/v) mixture in the presence of 0, 0.05, 0.1, 0.15, and 0.2 M Y(OTf)3 Lewis acid concentrations. Synthesis of the corresponding linear PNIPAM homopolymers in the absence of a cross-linker keeping all other conditions the same shows that the isotacticity (meso dyad, %) and the cloud point temperature of the resulted in polymers increases and decreases, respectively, with the increase in the concentration of the Lewis acid. SEM micrographs reveal that the resulted hydrogels are highly porous. Swelling ratios of all the hydrogels in water decrease with the increase in the temperature. Moreover, swelling ratios of all the hydrogels in different methanol-water mixtures pass through a minimum in the co-nonsolvency zone, and the co-nonsolvency zone shifts toward the lower methanol-content solvent mixture with gradual increase in the Lewis acid concentration. Deswelling rate of the hydrogel prepared in methanol-water (1:1, v/v) mixture is much faster than that of the conventional hydrogel prepared in water. Moreover, the deswelling rate slightly increases with the hydrogels prepared with the increasing concentrations of Lewis acid. But, the reswelling rate of the hydrogels follows almost the reverse order. All these results have been explained on the basis of the formation of highly porous hydrogels with higher isotactic PNIPAM chain segment owing to the faster polymerization rate in the methanol-water mixture in the presence of Lewis acid and the co-nonsolvency behavior of the methanol-water (1:1, v/v) mixture toward PNIPAM chain segment in the PNIPAM hydrogel. © 2010 American Chemical Society.
Synthesis and self-assembly properties of well-defined four-arm star poly(ε-caprolactone)-b-poly(N-vinylpyrrolidone) amphiphilic block copolymers
(2013) Avnish Kumar Mishra; K. Ramesh; Tapas Kumar Paira; Divesh N. Srivastava; Tarun Kumar Mandal; Nira Misra; Biswajit Ray
Well-defined amphiphilic four-arm star diblock copolymers of poly(ε-caprolactone) (PCL) and poly(N-vinylpyrrolidone) (PNVP) have successfully been synthesized by combining the ring-opening polymerization (ROP) of ε-caprolactone (CL) and xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinylpyrrolidone (NVP). The resulting block copolymer shows the formation of spherical micelles in water as revealed by transmission electron microscopy (TEM) and supported by light-scattering study. The critical micellar concentration (cmc) value of the micelle increases with the increase in the PNVP block length. Hydrodynamic diameter distribution of the micelles decreases with the increase in the PNVP block length. The effective hydrodynamic ratio (R h) remains almost constant over the angles of scattering measurements above the corresponding cmc value. The usefulness of the synthesized star amphiphilic block copolymers was checked by the successful synthesis of silver nanoparticles. Graphical abstract: Well-defined four-arm star poly(ε-caprolactone)-b-poly(N-vinylpyrrolidone) amphiphilic block copolymers are prepared by the combination of ring opening polymerization and xanthate-mediated reversible addition-fragmentation chain transfer polymerization and their self-assembly properties are studied using 1H NMR, fluorescence spectroscopy, dynamic light scattering, and TEM. [Figure not available: see fulltext.] © 2013 Springer-Verlag Berlin Heidelberg.
Synthesis and study of the properties of stereocontrolled poly(N-isopropylacrylamide) gel and its linear homopolymer prepared in the presence of a Y(OTf) 3 Lewis acid: Effect of the composition of methanol-water mixtures as synthesis media
(2012) Chandra Sekhar Biswas; Niraj Kumar Vishwakarma; Vijay Kumar Patel; Avnish Kumar Mishra; Satyen Saha; Biswajit Ray
Poly(N-isopropylacrylamide) (PNIPAM) hydrogels and the corresponding linear homopolymers were synthesized in different methanol-water mixtures (x m = 0, 0.13, 0.21, 0.31, 0.43, 0.57, and 0.76, where x m is the mole fraction of methanol) in the presence of 0.1 M Y(OTf) 3 Lewis acid. The isotacticity (meso dyad (m), %) and cloud-point temperature of these homopolymers were gradually increased and decreased, respectively, with the increase in the x m values of the synthesis solvent mixtures. Moreover, the corresponding linear PNIPAM homopolymers prepared in the absence of Y(OTf) 3 showed an almost constant isotacticity of m = 45% and a cloud-point temperature of 33.0 °C. A SEM study revealed that the resulting hydrogels were highly porous except for the gels prepared at x m = 0 and 0.76. The swelling ratios of these hydrogels in water at different temperatures and in different methanol-water mixtures at 20 °C and the deswelling rate and the reswelling rate of these hydrogels were studied. All of these swelling results were compared with that of the corresponding gels prepared in the absence of a Lewis acid (Biswas, C. S.; Patel, V. K.; Vishwakarma, N. K.; Mishra, A. K.; Bhimireddi, R.; Rai, R.; Ray, B. J. Appl. Polym. Sci.2012, DOI: 10.1002/app.36318) and explained on the basis of the porosity of the gel, the state of aggregation and isotacticity of the PNIPAM chain segment, and the cononsolvency of the methanol-water mixture toward the PNIPAM chain segment. © 2012 American Chemical Society.
Synthesis of alkyne-terminated xanthate RAFT agents and their uses for the controlled radical polymerization of N-vinylpyrrolidone and the synthesis of its block copolymer using click chemistry
(2013) Vijay Kumar Patel; Niraj Kumar Vishwakarma; Avnish Kumar Mishra; Chandra Sekhar Biswas; Pralay Maiti; Biswajit Ray
Two new alkyne-terminated xanthate reversible addition-fragmentation chain-transfer (RAFT) agents: (S)-2-(Propynyl propionate)-(O-ethyl xanthate) (X3) and (S)-2-(Propynyl isobutyrate)-(O-ethyl xanthate) (X 4) were synthesized and characterized and used for the controlled radical polymerization of N-vinylpyrrolidone (NVP). X3 showed better chain transfer ability in the polymerization at 60°C. Molecular weight of the resulted polymer increased linearly with the increase in monomer loading. Kinetics study with X3 showed the pseudo-first order kinetics up to 67% monomer conversion. Molecular weight (Mn) of the resulting polymer increased linearly with the increase in the monomer conversion up to around 67%. With the increase in the monomer conversion, polydispersity of the corresponding poly(NVP)s initially decreased from 1.34 to 1.32 and then increased gradually to 1.58. Chain-end analysis of the resulting polymer by 1H-NMR and FTIR showed clearly that polymerization started with radical forming out of xanthate RAFT agent. Living nature of the polymerization was also confirmed from the successful homo-chain extension experiment and the hetero-chain extension experiment involving synthesis of poly(NVP)-b-polystyrene amphiphilic diblock copolymer. Formed alkyne-terminated poly(NVP) also allowed easy conjugation to azide-terminated polystyrene by click chemistry to prepare well-defined poly(NVP)-b-polystyrene block copolymers. Resulting polymers were characterized by GPC, 1H-NMR, FTIR, and thermal study. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 Copyright © 2012 Wiley Periodicals, Inc.
Synthesis of well-defined amphiphilic poly(d,l-lactide)-b-poly(N- vinylpyrrolidone) block copolymers using ROP and xanthate-mediated RAFT polymerization
(Elsevier Ltd, 2012) K. Ramesh; Avnish Kumar Mishra; Vijay Kumar Patel; Niraj Kumar Vishwakarma; Chandra Sekhar Biswas; Tapas Kumar Paira; Tarun Kumar Mandal; Pralay Maiti; Nira Misra; Biswajit Ray
Well-defined amphiphilic poly(d,l-lactide)-b-poly(N-vinylpyrrolidone) (PDLLA-b-PNVP) block copolymers were successfully prepared using ring-opening polymerization (ROP) and xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization. Synthesized PDLLA-b-PNVP block copolymers were characterized by 1H NMR spectroscopy and GPC. Spherical micelles of ∼30.2 nm diameter were formed from the aqueous solution of amphiphilic diblock copolymer PDLLA42-b-PNVP63 as revealed by TEM and supported by 1H NMR and light scattering. The critical micelle concentration value of the block copolymers, determined by fluorescence spectroscopy using pyrene as probe, increased with the increase in the chain length of PNVP block. The average hydrodynamic radius (Rh) of the micelles remained almost constant above the cmc value over the angles of scattering measurement. Thermal properties of these block copolymers were studied by TGA, DTA and DSC. Crystalline properties of these block copolymers were studied by WXRD. © 2012 Elsevier Ltd. All rights reserved.
Synthesis of well-defined amphiphilic poly(ε-caprolactone)-b-poly(N- vinylpyrrolidone) block copolymers via the combination of ROP and xanthate-mediated RAFT polymerization
(2011) Avnish Kumar Mishra; Vijay Kumar Patel; Niraj Kumar Vishwakarma; Chandra Sekhar Biswas; Manoj Raula; Arvind Misra; Tarun Kumar Mandal; Biswajit Ray
Well-defined amphiphilic poly(ε-caprolactone)-b-poly(N- vinylpyrrolidone) (PCL-b-PNVP) block copolymers were successfully prepared via the combination of ring-opening polymerization (ROP) and xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization. Well-defined poly(ε-caprolactone) (PCL-OH) was synthesized by ROP in bulk at 110 °C using benzyl alcohol as initiator and stannous octate [Sn(Oct)2] as catalyst. The -OH end group was then converted into its corresponding xanthate (PCL-X) via the conversion to its corresponding bromide (PCL-Br). These are verified by 1H NMR spectroscopy. PCL-b-PNVP block copolymers were synthesized via RAFT polymerization in tetrahydrofuran (THF) at 80 °C using PCL-X as macro-chain transfer agent and characterized by 1H NMR spectroscopy and gel permeation chromatography (GPC). The amphiphilic diblock copolymer PCL63-b-PNVP90 forms spherical micelles of ∼34 nm diameter in water as shown by transmission electron microscopy (TEM), supported by 1H NMR spectroscopy, and light scattering. The critical micellar concentrations were determined by fluorescence spectroscopy using pyrene as probe. The critical micelle concentration (cmc) value of the block copolymers increases with the increase in the chain length of PNVP block. The overall hydrodynamic radius (Rh) of the micelles remains almost constant over the concentration range above the cmc value and over the angles of scattering measurement. © 2011 American Chemical Society.
Synthesis, characterization, and application of novel amphiphilic poly(D-gluconamidoethyl methacrylate)-b-polyurethane-b-poly(D-gluconamidoethyl methacrylate) triblock copolymers
(2013) Niraj Kumar Vishwakarma; Avnish Kumar Mishra; Abhinay Mishra; Tapas Paira; Vijay Kumar Patel; Chandra Sekhar Biswas; Tarun Kumar Mandal; Pralay Maiti; Biswajit Ray
Novel amphiphilic ABA-type poly(D-gluconamidoethyl methacrylate)-b- polyurethane-b-poly(D-gluconamidoethyl methacrylate) (PGAMA-b-PU-b-PGAMA) tri-block copolymers were successfully synthesized via the combination of the step-growth and copper-catalyzed atom transfer radical polymerization (ATRP). Dihydroxy polyurethane (HO-PU-OH) was synthesized by the step-growth polymerization of hexamethylene diisocyanate with poly(tetramethylene glycol). PGAMA-b-PU-b-PGAMA block copolymers were synthesized via copper-catalyzed ATRP of GAMA in N, N-dimethyl formamide at 20°C in the presence of 2, 2′-bipyridyl using Br-PU-Br as macroinitiator and characterized by 1H-NMR spectroscopy and GPC. The resulting block copolymer forms spherical micelles in water as observed in TEM study, and also supported by 1H NMR spectroscopy and light scattering. Miceller size increases with increase in hydrophilic PGAMA chain length as revealed by DLS study. The critical micellar concentration values of the resulting block copolymers increased with the increase of the chain length of the PGAMA block. Thermal properties of these block copolymers were studied by thermo-gravimetric analysis, and differential scanning calorimetric study. Spherical Ag-nanoparticles were successfully synthesized using these block copolymers as stabilizer. The dimension of Ag nanoparticle was tailored by altering the chain length of the hydrophilic block of the copolymer. A mechanism has been proposed for the formation of stable and regulated Ag nanoparticle using various chain length of hydrophilic PGAMA block of the tri-block copolymer. © 2012 Wiley Periodicals, Inc.
Synthesis, characterization, and drug release properties of poly(N-isopropylacrylamide) gels prepared in methanol-water cononsolvent medium
(2012) Chandra Sekhar Biswas; Vijay Kumar Patel; Niraj Kumar Vishwakarma; Avnish Kumar Mishra; Rajasekhar Bhimireddi; Ramanand Rai; Biswajit Ray
Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were simply prepared by free radical polymerization in different methanol-water mixture. A scanning electron microscopy study revealed that the freeze-dried hydrogels were macroporous. The swelling ratios in water at 20°C of the resulting hydrogels followed the order: X 0.43>X 0.21>X 0.76 ≈ X 0.57>X 0.31>X 0.13>X 0.06>X 0, where X m denotes a gel prepared in a methanol-water mixture with m mole fraction of methanol (x m). Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with the increase in the temperature. The complete collapse of the PNIPAM chain of all the gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all the PNIPAM gels in the methanol-water mixtures with different x m values at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X 0.43> X 0.31> X 0.21> X 0.57> X 0.76 â≈ X 0.13> X 0.06> X 0. The reswelling rates of these hydrogels decreased in the following order: X 0> X 0.31> X 0.06 ≈ X 0.13 > X 0.76> X 0.57> X 0.21> X 0.43. The release rates of the Tramadol Hydrochloride drug at 37°C from the drug-loaded hydrogels were almost same for all of the hydrogels. © 2012 Wiley Periodicals, Inc.
Synthesis, characterization, and solution behavior of well-defined double hydrophilic linear amphiphilic poly (N-isopropylacrylamide)-b-poly (ε-caprolactone)-b-poly (N-isopropylacrylamide) triblock copolymers
(Springer Verlag, 2014) Avnish Kumar Mishra; Niraj Kumar Vishwakarma; Vijay Kumar Patel; Chandra Sekhar Biswas; Tapas Kumar Paira; Tarun Kumar Mandal; Pralay Maiti; Biswajit Ray
Well-defined linear dihydrophilic amphiphilic ABA-type triblock copolymers of ε-caprolactone (CL) and N-isopropylacrylamide (NIPAAm) have successfully been synthesized with a high yield by combining the ring opening polymerization (ROP) and xanthate-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization methods. The resulted block copolymer shows the formation of micelles in water as supported by light scattering. The critical micelle concentration (cmc) value of the micelle increases with the increase in the chain length of the poly (N-isopropylacrylamide) (PNIPAAm) block. Cloud point of the block copolymers decreases with the decrease in the PNIPAAm chain length. The TGA analysis shows a one-step degradation and a lower thermal stability of the triblock copolymer than the PNIPAAm. The DSC analysis of the triblock copolymer shows the lowering of glass transition temperature (Tg), and melting temperature (Tm) peaks possibly due to the partial miscibility of the poly (ε-caprolactone) (PCL) block with the amorphous PNIPAAm block through the interaction of ester groups of PCL with the amide groups of PNIPAAm. The XRD pattern of the triblock copolymer shows a broad peak due to the suppression of the crystallization of PCL block owing to the mixing of PNIPAAm block with the PCL block. © 2014 Springer-Verlag.
Targeted delivery of doxorubicin-loaded poly (ε-caprolactone)-b-poly (N-vinylpyrrolidone) micelles enhances antitumor effect in lymphoma
(Public Library of Science, 2014) Sumit Kumar Hira; Avnish Kumar Mishra; Biswajit Ray; Partha Pratim Manna
Background: The present study was motivated by the need to design a safe nano-carrier for the delivery of doxorubicin which could be tolerant to normal cells. PCL63-b-PNVP90 was loaded with doxorubicin (6 mg/ml), and with 49.8% drug loading efficiency; it offers a unique platform providing selective immune responses against lymphoma. Methods: In this study, we have used micelles of amphiphilic PCL63-b-PNVP90 block copolymer as nano-carrier for controlled release of doxorubicin (DOX). DOX is physically entrapped and stabilized in the hydrophobic cores of the micelles and biological roles of these micelles were evaluated in lymphoma. Results: DOX loaded PCL63-b-PNVP90 block copolymer micelles (DOX-PCL63-b-PNVP90) shows enhanced growth inhibition and cytotoxicity against human (K-562, JE6.1 and Raji) and mice lymphoma cells (Dalton's lymphoma, DL). DOX-PCL63-b-PNVP90 demonstrates higher levels of tumoricidal effect against DOX-resistant tumor cells compared to free DOX. DOX-PCL63-b-PNVP90 demonstrated effective drug loading and a pH-responsive drug release character besides exhibiting sustained drug release performance in in-vitro and intracellular drug release experiments. Conclusion: Unlike free DOX, DOX-PCL63-b-PNVP 90 does not show cytotoxicity against normal cells. DOX-PCL 63-b-PNVP90 prolonged the survival of tumor (DL) bearing mice by enhancing the apoptosis of the tumor cells in targeted organs like liver and spleen. © 2014 Hira et al.