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Main-chain chiral poly(2-oxazoline)s: influence of alkyl side-chain on secondary structure formation in the solid state

Meta M Bloksma, Marco MRM Hendrix, Silke Rathgeber, Ulrich S Schubert and Richard Hoogenboom (UGent)
(2015) MACROMOLECULAR SYMPOSIA. 350(1). p.43-54
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Abstract
The influence of the side-chains of main-chain chiral poly(2-oxazoline) s on their thermal properties was investigated using differential scanning calorimetry (DSC) and the nature of the obtained melting endotherms was further investigated by thermal annealing of the polymers. Poly(R-2-ethyl-4-ethyl-2-oxazoline) (p-R-EtEtOx) was found to be amorphous, while polymers with longer side-chains are semi-crystalline. Previously we reported that the chirally ordered crystals of poly(R-2-butyl-4-ethyl-2-oxazoline) (p-R-BuEtOx) have a high melting temperature of more than 200 degrees C. in this work we demonstrate that elongation of the side-chains from butyl to octyl results in a decrease in the crystallization rate and melting temperature suggesting that the chirally ordered crystals of p-R-BuEtOx are based on close packing of the main-chain enhancing diploar interactions between the tertiary amide moieties. Crystallizaiton of chiral polymers with longer side-chains results may then be driven by close packing of the side-chains. This is supported by the observation that further elongation of the side-chain length increases the crystallization rate. Moerover, an additional melting endotherm appears for these polymers at a lower temperature upon annealing ascribed to a dual crystal size population. Circular dichroism (CD) measurements of the semi-crystalline main-chain chiral polymer films revealed the presence of chirally ordered crystals while X-ray diffraction (XRD) patterns revealed a closer packing of the chiral poly(2-alkyl-2-oxazoline) s compared to the non-chiral polymers, suggested to result form the chiral ordering in the crystals. Grazing incidence wide angle x-ray scattering (GIWAXS) patterns indicated that the chiral crystals of p-R-BuEtOx do not form a helical structure, however, the substrate does influence the type of structure formed.
Keywords
BEHAVIOR, chiral polymers, POLYMERS, COPOLYMERS, CRYSTALLIZATION, X-RAY, circular dichroism, grazing incidence wide angle X-ray scattering (GIWAXS), CATIONIC-POLYMERIZATION

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MLA
Bloksma, Meta M., et al. “Main-Chain Chiral Poly(2-Oxazoline)s: Influence of Alkyl Side-Chain on Secondary Structure Formation in the Solid State.” MACROMOLECULAR SYMPOSIA, vol. 350, no. 1, Wiley-VCH, 2015, pp. 43–54, doi:10.1002/masy.201400023.
APA
Bloksma, M. M., Hendrix, M. M., Rathgeber, S., Schubert, U. S., & Hoogenboom, R. (2015). Main-chain chiral poly(2-oxazoline)s: influence of alkyl side-chain on secondary structure formation in the solid state. MACROMOLECULAR SYMPOSIA, 350(1), 43–54. https://doi.org/10.1002/masy.201400023
Chicago author-date
Bloksma, Meta M, Marco MRM Hendrix, Silke Rathgeber, Ulrich S Schubert, and Richard Hoogenboom. 2015. “Main-Chain Chiral Poly(2-Oxazoline)s: Influence of Alkyl Side-Chain on Secondary Structure Formation in the Solid State.” In MACROMOLECULAR SYMPOSIA, 350:43–54. Weinheim, Germany: Wiley-VCH. https://doi.org/10.1002/masy.201400023.
Chicago author-date (all authors)
Bloksma, Meta M, Marco MRM Hendrix, Silke Rathgeber, Ulrich S Schubert, and Richard Hoogenboom. 2015. “Main-Chain Chiral Poly(2-Oxazoline)s: Influence of Alkyl Side-Chain on Secondary Structure Formation in the Solid State.” In MACROMOLECULAR SYMPOSIA, 350:43–54. Weinheim, Germany: Wiley-VCH. doi:10.1002/masy.201400023.
Vancouver
1.
Bloksma MM, Hendrix MM, Rathgeber S, Schubert US, Hoogenboom R. Main-chain chiral poly(2-oxazoline)s: influence of alkyl side-chain on secondary structure formation in the solid state. In: MACROMOLECULAR SYMPOSIA. Weinheim, Germany: Wiley-VCH; 2015. p. 43–54.
IEEE
[1]
M. M. Bloksma, M. M. Hendrix, S. Rathgeber, U. S. Schubert, and R. Hoogenboom, “Main-chain chiral poly(2-oxazoline)s: influence of alkyl side-chain on secondary structure formation in the solid state,” in MACROMOLECULAR SYMPOSIA, Awaji-Island, Japan, 2015, vol. 350, no. 1, pp. 43–54.
@inproceedings{8067729,
  abstract     = {{The influence of the side-chains of main-chain chiral poly(2-oxazoline) s on their thermal properties was investigated using differential scanning calorimetry (DSC) and the nature of the obtained melting endotherms was further investigated by thermal annealing of the polymers. Poly(R-2-ethyl-4-ethyl-2-oxazoline) (p-R-EtEtOx) was found to be amorphous, while polymers with longer side-chains are semi-crystalline. Previously we reported that the chirally ordered crystals of poly(R-2-butyl-4-ethyl-2-oxazoline) (p-R-BuEtOx) have a high melting temperature of more than 200 degrees C. in this work we demonstrate that elongation of the side-chains from butyl to octyl results in a decrease in the crystallization rate and melting temperature suggesting that the chirally ordered crystals of p-R-BuEtOx are based on close packing of the main-chain enhancing diploar interactions between the tertiary amide moieties. Crystallizaiton of chiral polymers with longer side-chains results may then be driven by close packing of the side-chains. This is supported by the observation that further elongation of the side-chain length increases the crystallization rate. Moerover, an additional melting endotherm appears for these polymers at a lower temperature upon annealing ascribed to a dual crystal size population. Circular dichroism (CD) measurements of the semi-crystalline main-chain chiral polymer films revealed the presence of chirally ordered crystals while X-ray diffraction (XRD) patterns revealed a closer packing of the chiral poly(2-alkyl-2-oxazoline) s compared to the non-chiral polymers, suggested to result form the chiral ordering in the crystals. Grazing incidence wide angle x-ray scattering (GIWAXS) patterns indicated that the chiral crystals of p-R-BuEtOx do not form a helical structure, however, the substrate does influence the type of structure formed.}},
  author       = {{Bloksma, Meta M and Hendrix, Marco MRM and Rathgeber, Silke and Schubert, Ulrich S and Hoogenboom, Richard}},
  booktitle    = {{MACROMOLECULAR SYMPOSIA}},
  issn         = {{1022-1360}},
  keywords     = {{BEHAVIOR,chiral polymers,POLYMERS,COPOLYMERS,CRYSTALLIZATION,X-RAY,circular dichroism,grazing incidence wide angle X-ray scattering (GIWAXS),CATIONIC-POLYMERIZATION}},
  language     = {{eng}},
  location     = {{Awaji-Island, Japan}},
  number       = {{1}},
  pages        = {{43--54}},
  publisher    = {{Wiley-VCH}},
  title        = {{Main-chain chiral poly(2-oxazoline)s: influence of alkyl side-chain on secondary structure formation in the solid state}},
  url          = {{http://doi.org/10.1002/masy.201400023}},
  volume       = {{350}},
  year         = {{2015}},
}
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