Sneha Chakrapani - Academia.edu (original) (raw)
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University of Malaya, Malaysia
Université des Sciences et Technologies de Lille (Lille-1)
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Papers by Sneha Chakrapani
This Thesis investigates multicomponent polymer systems in the context of their characterization ... more This Thesis investigates multicomponent polymer systems in the context of their characterization and their synthesis. The composition of the different polymers comprising multicomponent polymer systems is a vital variable in tuning their properties. Herein, low-field 1 H NMR Spectroscopy (60 MHz), a newly commercially available technology, is inspected as a possible low-cost alternative to the significantly more expensive (in terms of capital and maintenance costs) higher-field NMR spectrometers (> 250 MHz) for the compositional analysis of multicomponent polymer systems, namely polymer blends and block copolymers. The results from a low-field spectrometer are corroborated using a high-field spectrometer and are found to be adequately quantitative within the typical confidence for compositional analyses of this nature using traditional high-field NMR spectroscopy. Next, a series of copolymers of styrene and isoprene are synthesized by anionic copolymerization using a co-solvent mixture of cyclohexane and triethylamine, of varied relative compositions to probe the impact on compositional drift (statistical composition along the polymer chain). Copolymerization reactions are monitored online using in-situ Attenuated-Total-Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) to obtain monomer conversions as well as overall conversions in order to completely describe the copolymer compositional profiles. Compositional drift profiles are used to extract reactivity ratios using the Beckingham-Sanoja-Lynd approach to define the copolymer architecture and as a quantitative means of comparison. Conclusively, this system allows for the tuning of copolymer compositional profiles as desired with potential applications in designing polymer architectures with desired properties. vi
The Analyst, 2019
A low-field, 60 MHz, 1H NMR spectrometer yields quantitatively comparable results to 400 MHz spec... more A low-field, 60 MHz, 1H NMR spectrometer yields quantitatively comparable results to 400 MHz spectrometers for the compositional analysis of multicomponent polymer systems.
Macromolecules, 2020
The properties of polymer materials are largely a result of the local and long-range order of pol... more The properties of polymer materials are largely a result of the local and long-range order of polymer chains and systems of polymer chains. The ability to tune polymer chain architecture at the monomer and chain levels through controlled synthesis is therefore a powerful tool for manipulating its properties. Perhaps, the most widely used synthetic means to manipulate polymer properties is copolymerization, where more than one monomer is simultaneously polymerized. For living anionic copolymerization, the statistics of comonomer incorporation have long been known to be dependent on the solvent, temperature, and initiator. Here, we leverage solvent dependence in the anionic copolymerization of styrene and isoprene to tailor the compositional profile along the polymer chain. Copolymerization of styrene and isoprene is conducted with varied quantities of a polar modifier (triethylamine), and the conversion is monitored by in situ attenuated total reflectance Fourier transform infrared spectroscopy. Monomer conversion profiles are used to extract reactivity ratios as a metric for examining the change in the compositional drift as the solvent composition is varied. Increasing triethylamine content leads to a continuous flattening of the compositional profile from the extreme nearly pure diblock structure for synthesis in cyclohexane to an essentially flat compositional profile in 50/50 (vol./vol.) cyclohexane/triethylamine. The ability to continuously tune compositional drift, as shown here, between these two extremes is a powerful synthetic tool for preparing copolymers and block copolymers with tunable properties.
This Thesis investigates multicomponent polymer systems in the context of their characterization ... more This Thesis investigates multicomponent polymer systems in the context of their characterization and their synthesis. The composition of the different polymers comprising multicomponent polymer systems is a vital variable in tuning their properties. Herein, low-field 1 H NMR Spectroscopy (60 MHz), a newly commercially available technology, is inspected as a possible low-cost alternative to the significantly more expensive (in terms of capital and maintenance costs) higher-field NMR spectrometers (> 250 MHz) for the compositional analysis of multicomponent polymer systems, namely polymer blends and block copolymers. The results from a low-field spectrometer are corroborated using a high-field spectrometer and are found to be adequately quantitative within the typical confidence for compositional analyses of this nature using traditional high-field NMR spectroscopy. Next, a series of copolymers of styrene and isoprene are synthesized by anionic copolymerization using a co-solvent mixture of cyclohexane and triethylamine, of varied relative compositions to probe the impact on compositional drift (statistical composition along the polymer chain). Copolymerization reactions are monitored online using in-situ Attenuated-Total-Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) to obtain monomer conversions as well as overall conversions in order to completely describe the copolymer compositional profiles. Compositional drift profiles are used to extract reactivity ratios using the Beckingham-Sanoja-Lynd approach to define the copolymer architecture and as a quantitative means of comparison. Conclusively, this system allows for the tuning of copolymer compositional profiles as desired with potential applications in designing polymer architectures with desired properties. vi
The Analyst, 2019
A low-field, 60 MHz, 1H NMR spectrometer yields quantitatively comparable results to 400 MHz spec... more A low-field, 60 MHz, 1H NMR spectrometer yields quantitatively comparable results to 400 MHz spectrometers for the compositional analysis of multicomponent polymer systems.
Macromolecules, 2020
The properties of polymer materials are largely a result of the local and long-range order of pol... more The properties of polymer materials are largely a result of the local and long-range order of polymer chains and systems of polymer chains. The ability to tune polymer chain architecture at the monomer and chain levels through controlled synthesis is therefore a powerful tool for manipulating its properties. Perhaps, the most widely used synthetic means to manipulate polymer properties is copolymerization, where more than one monomer is simultaneously polymerized. For living anionic copolymerization, the statistics of comonomer incorporation have long been known to be dependent on the solvent, temperature, and initiator. Here, we leverage solvent dependence in the anionic copolymerization of styrene and isoprene to tailor the compositional profile along the polymer chain. Copolymerization of styrene and isoprene is conducted with varied quantities of a polar modifier (triethylamine), and the conversion is monitored by in situ attenuated total reflectance Fourier transform infrared spectroscopy. Monomer conversion profiles are used to extract reactivity ratios as a metric for examining the change in the compositional drift as the solvent composition is varied. Increasing triethylamine content leads to a continuous flattening of the compositional profile from the extreme nearly pure diblock structure for synthesis in cyclohexane to an essentially flat compositional profile in 50/50 (vol./vol.) cyclohexane/triethylamine. The ability to continuously tune compositional drift, as shown here, between these two extremes is a powerful synthetic tool for preparing copolymers and block copolymers with tunable properties.