Stereospecific polymerization and chiral initiation, chiral crystallization and chiral nucleation

A macrovoid structure was found in polysulfone membranes formed by the wet-inversion method using N-methylpyrrolidinone (NMP) and water as the solvent/nonsolvent pair. The addition of Span series surfactants in the casting solution was found to inhibit the macrovoid formation. Sorbitan monooleate (Span-80) was more effective in inhibiting macrovoids than was sorbitan monolaurate (Span-20). The phenomenon of macrovoid suppression became more prominent at higher temperature. The cloud-point shift might account for the temperature effect. But there was no simple explanation for the effect caused by Span-80. The cloud-point position, the demixing rate, and the viscosity of the casting solution were measured. None of them could explain the effect of macrovoid inhibition by the addition of Span-80. However, the penetration test indicated that the penetration of a nonsolvent into a surfactant-free casting solution was caused by a convective flow, but that into Span-80 was through diffusion. It was found that the retardation of nonsolvent penetration was the major cause of macrovoid inhibition.

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“…Polymerization and crystallization hold several principles in common as salt crystals are three‐dimensional ionic polymers 110, 111…”

Section: Miscellaneous Programsmentioning

confidence: 99%

Effect of temperature and span series surfactant on the structure of polysulfone membranes

Tsai

Ruaan

Wang

et al. 2002

J of Applied Polymer Sci

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“…For the former, the stability of helices is predominantly derived from the rigid polymer backbone and the helical sense is kinetically controlled. This type of helical polymers is typified by polyaldehydes,5 polyisocyanides,6 and polymethacrylates bearing bulky pendent groups 7. Additionally, the handedness of these helices is determined during the polymerization.…”

Section: Introductionmentioning

confidence: 99%

The Formation of a Stable, Helical Conformation in Poly(N‐propargylamides) through Synergic Effects among their Pendent Groups

Deng¹,

Zhao²,

Wang³

et al. 2007

Macro Chemistry & Physics

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Copolymerization reactions of two N‐propargylamides [1: HCCCH2NHCO(CH2)5CH3, 2: (HCCCH2NHCOC(CH3)3] were carried out with different monomer feed ratios. Compared with the two corresponding homopolymers, the series of resulting copolymers poly(1‐co‐2) had a higher helix content. They also performed very differently in conformational transitions, either from random coil to helix or from helix to random coil, mainly depending on the composition of the copolymers. Synergic effects among the pendent groups played a significant role in the copolymer main chains adopting stable helices.magnified image

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“…We have demonstrated that crystallization induced by chiral nuclei gave pure chiral sodium chlorate. As we said before, it should be possible to use chiral nuclei to induce crystallization of isotactic polymers (especially with a bulky side group) to crystallize as single helices 28. The most attractive example would be polypropylene, which crystallizes in a 3/1 helical structure.…”

Section: Chiral Crystallization and Chiral Polymerizationmentioning

confidence: 99%

Chiral crystallization and the origin of chiral life on earth

Vogl

2011

J. Polym. Sci. A Polym. Chem.

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The creation of chirality on Earth and the development of chiral life have been discussed in this highlight. Convincing evidence for the introduction of chirality on Earth is still fragmentary. We believe that by a combination of chiral crystallization and formation of helical polymers with preferred chiral conformational structure is the key to this question. This concept of macromolecular asymmetry has inspired ideas and resulted in possible rules for how chiral life as we know it, could have been introduced. These investigations needed the understanding of the requirements for chiral crystallization, for the stereochemistry of the initial formation of helical polymers, the measurements of optical activity of solids and their coordination with the fundamentals of chirality. Spacial modeling of the “oligo‐crystallization” of sodium chlorate led to the conception of “isotactic” linear crystallization, which involves helical propagation. It seems to require unequal sizes of the cations and anions, which, by branching propagation leads to three‐dimensional chiral crystal formation. Linear “isotactic” propagation of crystallization seems to be equivalent to stereo and conformational specific polymerization. One and a half turns of the helix seems to be required for stereo‐ and conformational specificity, that is, between the pentamer and hexamer in chloral polymerization (11/3 or nearly 4/1 helix) and between trimer and tetramer for the sodium chlorate crystal (2/1 helix). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

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Stereospecific polymerization and chiral initiation, chiral crystallization and chiral nucleation

Cited by 24 publications

References 26 publications

Effect of temperature and span series surfactant on the structure of polysulfone membranes

Effect of temperature and span series surfactant on the structure of polysulfone membranes

The Formation of a Stable, Helical Conformation in Poly(N‐propargylamides) through Synergic Effects among their Pendent Groups

Chiral crystallization and the origin of chiral life on earth

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