Reassessing the Regioregularity of N-(1-Naphthyl)-N′-(n-octadecyl)polycarbodiimide Using Solution Infrared Spectroscopy

Kennemur, Justin G.; DeSousa, Joseph D.; Martin, James D.; Novak, Bruce M.

doi:10.1021/ma2005052

Cited by 5 publications

(27 citation statements)

References 18 publications

(43 reference statements)

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“…These two peaks were first attributed to regioirregular placement of the pendant groups along the polymer backbone but was later disproven by VT-FTIR. 53 It is noteworthy to point out that two peaks corresponding to the imine nitrogen are lower in wavenumber than the values reported by Kennemur et al (ca. 21 and 16 cm −1 , respectively).…”

Section: ■ Introductionmentioning

confidence: 56%

Evidence of Entropy-Driven Bistability through ¹⁵N NMR Analysis of a Temperature- and Solvent-Induced, Chiroptical Switching Polycarbodiimide

Reuther

Novak

2013

J. Am. Chem. Soc.

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The thermo- and solvo-driven chiroptical switching process observed in specific polycarbodiimides occurs in a concerted fashion with large deviations in specific optical rotation (OR) and CD Cotton effect as a consequence of varying populations of two distinct polymer conformations. These two conformations are clearly visible in the (15)N NMR and IR spectra of the (15)N-labeled poly((15)N-(1-naphthyl)-N'-octadecylcarbodiimide) (Poly-3) and poly((15)N-(1-naphthyl)-(15)N'-octadecylcarbodiimide) (Poly-5). Using van't Hoff analysis, the enthalpies and entropies of switching (ΔHswitching; ΔSswitching) were calculated for both Poly-3 and Poly-5 using the relative integrations of both peaks in the (15)N NMR spectra at different temperatures to measure the populations of each state. The chiroptical switching (i.e., transitioning from state A to state B) was found to be an endothermic process (positive ΔHswitching) for both Poly-3 and Poly-5 in all solvents studied, meaning the conformation correlating with the downfield chemical shift (ca. 148 ppm, state B) is the higher enthalpy state. The compensating factor behind this phenomenon has been determined to be the large increase in entropy in CHCl3 as a result of the switching. Herein, we propose that the increased entropy in the system is a direct consequence of increased disorder in the solvent as the switching occurs. Specifically, the chloroform solvent molecules are very ordered around the polymer chains due to favorable solvent-polymer interactions, but as the switching occurs, these interactions become less favorable and disorder results. The same level of solvent disorder is not achieved in toluene, causing the chiroptical switching process to occur at higher temperatures.

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Section: ■ Introductionmentioning

confidence: 56%

Evidence of Entropy-Driven Bistability through ¹⁵N NMR Analysis of a Temperature- and Solvent-Induced, Chiroptical Switching Polycarbodiimide

Reuther

Novak

2013

J. Am. Chem. Soc.

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confidence: 99%

“…The appearance of one predominate imine stretch indicated a regioregular structure, and two or more stretches indicated two structural irregularities. However, recent studies have shown the behavior of the imine stretch region of the IR is more complex as it pertains to symmetry, coupled chromphores, and polycarbodiimides possessing certain pendant groups, and this remains a focus of ongoing investigations . Hence, extracting the preferred regioisomer from the imine stretch remains elusive.…”

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confidence: 99%

“…Much of the research from our group in recent years has involved the study of polycarbodiimides synthesized from nonsymmetric, mainly alkyl/aryl substituted carbodiimide monomers. 6 Within this body of work, a common and illusive thread has been determining the connectivity or regioregularity of polycarbodiimide microstructures prepared from nonsymmetric monomers. The synthesis of polycarbodiimides involves the polymerization of carbodiimide monomers using typically a titanium(IV) alkoxide catalyst; however, other early and late transition metals have been explored (Cu, Zr, Ni) and found to be successful.…”

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confidence: 99%

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Resolving the Regioregularity of Poly(N-n-hexyl-N′-phenylcarbodiimide) via Nitrogen-15 Labeling

DeSousa

Novak

2012

ACS Macro Lett.

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Nitrogen-15 nuclear magnetic resonance (NMR) spectroscopy and infrared spectroscopy (IR) were performed on an isotopeenriched poly(N-n-hexyl-N′-phenylcarbodiimide) to determine directly the connectivity and regioregularity of a polymer. Up to this point, the imine, CN, IR stretch at 1660−1620 cm −1 was thought to be a sufficient handle to elucidate the presence or absence of a regioregular microstructure; however, recent findings cast some uncertainties when expanded to all polycarbodiimides. Therefore, an enriched 15 N NMR study was undertaken to unambiguously resolve that a N-n-hexyl-N′-phenylcarbodiimide, when polymerized with a 2,2,2-trifluoroethoxide trichlorotitanium(IV) catalyst in chloroform, will produce a completely regioregular polymer. The only regioisomer present is the one in which the phenyl pendant group is positioned on the imino-nitrogen. The study was expanded to a chiral, (R)-BINOL-Ti(IV)-diisopropoxide catalyst which revealed no change in the regioisomer or the degree of regioregularity. In addition to 15 N NMR spectra, the IR imine stretch exhibited isotope shifts for poly(N-n-hexyl-N′-phenylcarbodiimide) when labeled on both imino-and amino-nitrogen or solely the imino-nitrogen of ∼11 cm −1 ; however, no shift was manifested when labeling was restricted to the amino-nitrogen.

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“…The ReactIR TM system was used to calibrate standard solutions and utilized to record the change of concentration of the solution during SMPT processes. The ReactIR TM probe (ReactIR TM 15, Mettler Toledo) was used with 15-s sampling intervals [24]. All transformation experiments were performed in a 100-mL Easy-Max vessel (Mettler Toledo, Greifensee, Switzerland) in conjunction with iControl Easy-max software [25].…”

Section: Methodsmentioning

confidence: 99%

Solvent-Mediated Polymorphic Transformation of Famoxadone from Form II to Form I in Several Mixed Solvent Systems

Ren

et al. 2019

Crystals

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This paper discloses six polymorphs of famoxadone obtained from polymorph screening, which were characterized by XRPD, DSC, and SEM. A study of solvent-mediated polymorphic transformation (SMPT) of famoxadone from the metastable Form II to the stable Form I in several mixed solvent systems at the temperature of 30 °C was also conducted. The transformation process was monitored by Process Analytical Technologies. It was confirmed that the Form II to Form I polymorphic transformation is controlled by the Form I growth process. The transformation rate constants depended linearly on the solubility difference value between Form I and Form II. Furthermore, the hydrogen-bond-donation/acceptance ability and dipolar polarizability also had an effect on the rate of solvent-mediated polymorphic transformation.

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Reassessing the Regioregularity of N-(1-Naphthyl)-N′-(n-octadecyl)polycarbodiimide Using Solution Infrared Spectroscopy

Cited by 5 publications

References 18 publications

Evidence of Entropy-Driven Bistability through ¹⁵N NMR Analysis of a Temperature- and Solvent-Induced, Chiroptical Switching Polycarbodiimide

Evidence of Entropy-Driven Bistability through ¹⁵N NMR Analysis of a Temperature- and Solvent-Induced, Chiroptical Switching Polycarbodiimide

Resolving the Regioregularity of Poly(N-n-hexyl-N′-phenylcarbodiimide) via Nitrogen-15 Labeling

Solvent-Mediated Polymorphic Transformation of Famoxadone from Form II to Form I in Several Mixed Solvent Systems

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Reassessing the Regioregularity of N-(1-Naphthyl)-N′-(n-octadecyl)polycarbodiimide Using Solution Infrared Spectroscopy

Cited by 5 publications

References 18 publications

Evidence of Entropy-Driven Bistability through 15N NMR Analysis of a Temperature- and Solvent-Induced, Chiroptical Switching Polycarbodiimide

Evidence of Entropy-Driven Bistability through 15N NMR Analysis of a Temperature- and Solvent-Induced, Chiroptical Switching Polycarbodiimide

Resolving the Regioregularity of Poly(N-n-hexyl-N′-phenylcarbodiimide) via Nitrogen-15 Labeling

Solvent-Mediated Polymorphic Transformation of Famoxadone from Form II to Form I in Several Mixed Solvent Systems

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Evidence of Entropy-Driven Bistability through ¹⁵N NMR Analysis of a Temperature- and Solvent-Induced, Chiroptical Switching Polycarbodiimide

Evidence of Entropy-Driven Bistability through ¹⁵N NMR Analysis of a Temperature- and Solvent-Induced, Chiroptical Switching Polycarbodiimide