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Khandelwal D.,Indian Institute of Technology Delhi | Hooda S.,Acharya Narendra Dev College | Brar A.S.,Guru Nanak Dev University
Journal of Molecular Structure | Year: 2011

Poly(isobornyl acrylate) (PiBA) was prepared by atom transfer radical polymerization (ATRP). Complete characterization of microstructure of PiBA was carried out using one-dimensional [1H, 13C{1H}] and two-dimensional (HSQC, TOCSY and HMBC) NMR spectra. The methyl, methylene, methine, quaternary and carbonyl carbon resonance signals were found to be sensitive to various configurational sequences. The methine carbon (C 12) was assigned up to triad configurational sequences in 13C{1H} NMR spectrum whereas β-methylene carbon resonances were assigned up to diad configurational sequences. The quaternary carbon in 13C{1H} NMR spectrum were resolved completely with the help of HMBC NMR spectrum. The stereoregularity of PiBA was found to be random with mm = 20%, mr = 53%, and rr = 27%. © 2011 Elsevier B.V. All rights reserved. Source


Khandelwal D.,Indian Institute of Technology Delhi | Hooda S.,Acharya Narendra Dev College | Brar A.S.,Guru Nanak Dev University | Shankar R.,Indian Institute of Technology Delhi
Journal of Molecular Structure | Year: 2011

Isobornyl acrylate - methyl methacrylate (B/M) copolymers of different compositions were synthesized by atom transfer radical polymerization (ATRP) using methyl-2-bromopropionate as an initiator and PMDETA copper complex as catalyst under nitrogen atmosphere at 70 °C. 1H NMR spectrum was used to determine the compositions of copolymer. The copolymer compositions were then used to determine the reactivity ratios of monomers. Reactivity ratios of co-monomers in B/M copolymer, determined from linear Kelen-Tudos method (KT) and non linear Error-in-Variable Method (EVM), are r B = 0.41 ± 0.11, r M = 1.11 ± 0.33 and r B = 0.52, r M = 1.31 respectively. The complete resonance assignments of 1H and 13C{ 1H} NMR spectra were carried out with the help of Distortion less Enhancement by Polarization Transfer (DEPT), two-dimensional Heteronuclear Single Quantum Coherence (HSQC). 2D HSQC assignments were further confirmed by 2D Total Correlation Spectroscopy (TOCSY). The carbonyl carbon of B and M units and methyl carbon of M unit were assigned up to triad compositional and configurational sequences whereas β-methylene carbons were assigned up to tetrad compositional and configurational sequences. Similarly the methine carbon of B unit was assigned up to pentad level. 1,3 and 1,4 bond order couplings of carbonyl carbon and quaternary carbon resonances with methine, methylene and methyl protons were studied in detail using 2D Hetero Nuclear Multiple Bond Correlation (HMBC) spectra. © 2011 Elsevier B.V. All rights reserved. Source


Khandelwal D.,Indian Institute of Technology Delhi | Hooda S.,Acharya Narendra Dev College | Brar A.S.,Guru Nanak Dev University | Shankar R.,Indian Institute of Technology Delhi
Journal of Molecular Structure | Year: 2013

Isobornyl acrylate/styrene (B/S) copolymers of different compositions have been prepared by Atom Transfer Radical Polymerization (ATRP) using methyl-2-bromopropionate as an initiator and PMDETA/ CuBr as catalyst under nitrogen atmosphere at 60 °C. Copolymer compositions calculated from 1H NMR spectra are used to determine the reactivity ratios of monomers. Linear Kelen-Tudos (KT) and non-linear error in variable methods (EVM) have been employed for determination of monomer reactivity ratios in copolymers. The reactivity ratios obtained from KT and EVM are found to be rB = 0.41 ± 0.08, rS = 0.92 ± 0.13 and rB = 0.41 and rS = 0.93 respectively. These copolymers have been analyzed for their stereochemical structure using various 1D ( 1H, 13C{1H}, DEPT) and 2D (HSQC, TOCSY, NOESY, HMBC) NMR techniques. 2D HSQC and TOCSY NMR experiments are employed to resolve the highly overlapped and complex 1H and 13C{ 1H} NMR spectra of the copolymers. Spatial coupling of different types of protons are resolved by 2D NOESY NMR spectra. The configurational and compositional sequences of β-methylene carbons are assigned upto tetrad level whereas methine carbon is assigned as triad level of compositional sequences. The quaternary carbon of styrene and carbonyl carbon of isobornyl acrylate have been assigned as triad level of compositional sequences and are further confirmed by 2D HMBC NMR spectra. © 2013 Elsevier Ltd. All rights reserved. Source


Khandelwal D.,Indian Institute of Technology Delhi | Hooda S.,Acharya Narendra Dev College | Brar A.S.,Guru Nanak Dev University | Shankar R.,Indian Institute of Technology Delhi
Journal of Applied Polymer Science | Year: 2012

Isobornyl acrylate (B)/methacrylonitrile (N) copolymers with different compositions were synthesized by the free-radical bulk polymerization with azobisisobutyronitrile as the initiator under a nitrogen atmosphere at 70°C. The copolymer compositions were calculated from quantitative 13C( 1H)NMR spectra. The reactivity ratios of the comonomers in the B/N copolymers determined from the linear Kelen-Tudos method and nonlinear error-in-variable method were r B = 0.66 ± 0.11 and r N = 1.54 ± 0.22 and r B = 0.74 and r N = 1.65, respectively. The complete spectral assignments of the 1H-NMR and 13C( 1H)-NMR spectra were carried out with the help of distortionless enhancement by polarization transfer, two-dimensional (2D) heteronuclear single quantum coherence, and 2D total correlation spectroscopy. The nitrile carbon of the N unit and the methine and OCH carbons of the B unit were assigned to triad compositional sequences, whereas the β-methylene carbons of the B and N units were assigned to the tetrad compositional and configurational sequences. The α-methyl carbon of the N unit was also assigned to the triad level of configurational and compositional sequences. Similarly, the nitrile and quaternary carbon resonances with the methine, methylene, and methyl protons were studied in detail with 2D heteronuclear multiple-bond correlation spectra. © 2012 Wiley Periodicals, Inc. Source


Khandelwal D.,Indian Institute of Technology Delhi | Hooda S.,Acharya Narendra Dev College | Brar A.S.,Indian Institute of Technology Delhi | Brar A.S.,Guru Nanak Dev University | Shankar R.,Indian Institute of Technology Delhi
Journal of Polymer Research | Year: 2014

An investigation of the microstructure of isobornyl methacrylate - styrene (I/S) copolymers prepared by the atom transfer radical polymerization (ATRP) using methyl-2-bromopropionate as an initiator and PMDETA copper complex as catalyst under nitrogen atmosphere at 70 °C has been done by two-dimensional NMR techniques. 2D-HSQC and TOCSY have been utilized to resolve the complex 1H NMR spectrum and to establish the compositional and configurational sequences of isobornyl methacrylate-styrene (I/S) copolymers. 2D HSQC and TOCSY spectra showed compositional and configurational sensitivity of α-methyl carbon of I unit and methine proton of S unit and are assigned up to the triad level. The methylene carbon (C10) also shows triad level of compositional sensitivity in 2D HSQC spectra. Heteronuclear multiple-bond correlation (HMBC) spectroscopy has been used to study carbonyl/quaternary carbon-proton coupling. The carbonyl and quaternary carbons showed compositional and configurational sensitivity upto the triad level. The values of reactivity ratios were determined by Kelen-Tudos (KT) and nonlinear error in variable method (RREVM) using copolymer composition data that were determined by 1H NMR spectrum. Reactivity ratios of comonomers in I/S copolymer, determined from a linear Kelen-Tudos method (KT) and non-linear Error-in-Variable Method (EVM), are rI=0.39±0.09, r S=0.44±0.08 and rI= 0.42, rS=0.47, respectively. © Springer Science+Business Media Dordrecht 2014. Source

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