Why is Stereoregular Polyacrylonitrile Obtained by Polymerization in Urea Canals Isotactic?

Yang, Hyungchol; El‐Shafei, Ahmed; Schilling, Frederic C.; Tonelli, Alan E.

doi:10.1002/mats.200700043

Cited by 7 publications

(3 citation statements)

References 37 publications

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“…9,10 The reasons why isotactic PAN rather than syndiotactic PAN is produced in the urea canals have been given. 11 As one of the most widely used polymers for textiles and precursors of carbon fibers, polyacrylonitrile (PAN) is prepared commercially by radical polymerization of acrylonitrile (AN), without specific stereoregularity along the chain direction. 12 Since a highly stereoregular PAN is essential to obtain hightenacity acrylic fibers and carbon fibers, 13−15 considerable efforts have been devoted to producing PAN in higher isotactic level.…”

Section: Introductionmentioning

confidence: 99%

“…The most prominent example for the host system is urea, which mostly forms hexagonal structure and comprises continuous, parallel tunnels . As for the inclusion polymerization in urea canals, which is a solid-state polymerization process commonly initiated by γ- or X-rays, partially stereoregular polymers can be synthesized from many vinyl and diene monomers, such as 1,3-butadiene, vinyl chloride, and acrylonitrile. , The reasons why isotactic PAN rather than syndiotactic PAN is produced in the urea canals have been given …”

Section: Introductionmentioning

confidence: 99%

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Radiation-Induced Inclusion Polymerization of Acrylonitrile in Urea Canals: Toward Synthesis of Completely Isotactic Polyacrylonitrile with Controlled Molecular Weight

et al. 2013

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Completely isotactic polyacrylonitrile (meso/meso triad >99%) has been synthesized successfully by radiation-induced inclusion polymerization of acrylonitrile in urea canals. The long-lived nature of the growing radical species and the linear dependence of molecular weight on conversion were observed. The molecular weight distribution of product polymers was relatively narrow (<1.5). The results indicate that the dual control of the molecular weight and the tacticity for inclusion polymerization of acrylonitrile in urea canals is achieved. In addition, the effect of experimental factors of inclusion polymerization on the isotacticity of product polymers was investigated. It is found that to ensure completely isotactic polyacrylonitrile, the following conditions should be met simultaneously: (1) acrylonitrile monomers are included in urea canals totally before γ-ray irradiation, (2) the temperature at the chain propagation step is lower than −90 °C, and (3) the heat of polymerization is removed effectively.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Radiation-Induced Inclusion Polymerization of Acrylonitrile in Urea Canals: Toward Synthesis of Completely Isotactic Polyacrylonitrile with Controlled Molecular Weight

et al. 2013

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“…Since the middle 1990s, our research group has formed a large number of crystalline CD‐ICs2–70 containing either high molecular weight guest polymers or small‐molecule guests that can serve as polymer additives [Fig. 1(b,c)].…”

Section: Introductionmentioning

confidence: 99%

Organizational stabilities of bulk neat and well‐mixed, blended polymer samples coalesced from their crystalline inclusion compounds formed with cyclodextrins

Tonelli

2009

J Polym Sci B Polym Phys

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Cyclodextrins (CDs) are cyclic starches containing a-1,4-linked glucose units. Commonly available a-, b-, and c-CDs have six, seven, and eight glucose units, respectively. They are well known for forming noncovalent inclusion complexes (ICs) with a variety of guest molecules, including many polymers, by threading and inclusion into their relatively hydrophobic interior cavities, which are roughly cylindrical, with diameters of $0.5-1.0 nm. Warm water washing of crystalline CD-ICs containing polymer guests insoluble in water or treatment with amylase enzymes serve to remove the host CDs and result in the coalescence of the guest polymers into solid bulk samples. When guest polymers are coalesced from their CD-ICs by carefully removing the host CD lattices, they are observed to solidify with structures, morphologies, and even conformations that are distinct from bulk samples made from their solutions and melts. In addition, molecularly mixed, intimate blends can be obtained upon coalescence of two or more normally immiscible polymer guests from their common CD-ICs. Not only are the organizations and behaviors of bulk polymer samples significantly modified on coalescence from their CD-ICs, but both are also maintained for significant periods of time even when heated above their T g s and T m s, where their chains are mobile. Here, we discuss the long-time, high temperature stabilities of the organizations and properties of bulk polymers coalesced from their crystalline CD-ICs. While random-coiling of their initially coalesced, largely extended, separated, and unentangled chains may be relatively rapid, we conclude that the subsequent slow establishment of homogeneous melts or phase-segregated blends results from the extremely sluggish center-of-mass diffusion that must accompany full entanglement of their chains. Apparently, the process of entangling the largely separated and not fully interpenetrating randomly coiled chains initially coalesced from their CD-ICs is particularly slow, much slower in fact than the center-of mass diffusion of polymer chains in their fully entangled melts. V V C 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys

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Reactions in Solid‐State Inclusion Compounds

Harris

Palmer

Edwards-Gau

2012

Supramolecular Chemistry

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This chapter focuses on chemical reactions occurring within solid organic inclusion compounds, encompassing a broad range of inclusion compounds and a wide variety of different reaction types, including reactions of the guest molecules (such as dimerization, polymerization, cyclization, isomerization, and decomposition), reactions involving the host molecules, and guest exchange processes. In many cases, chemical transformations of guest molecules confined within solid host structures proceed with a high degree of selectivity toward a single product, and often with a high degree of stereoselectivity and/or enantioselectivity, as a consequence of the geometrical constraints imposed on the reacting molecules by the host structure. For this reason, the products obtained from such reactions are often significantly different from those obtained from the corresponding reactions in the solution state or in the “pure” crystalline phase of the guest molecules. Through the examples highlighted in this chapter, general issues relating to reactions in solid organic inclusion compounds are rationalized and discussed.

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Why is Stereoregular Polyacrylonitrile Obtained by Polymerization in Urea Canals Isotactic?

Cited by 7 publications

References 37 publications

Radiation-Induced Inclusion Polymerization of Acrylonitrile in Urea Canals: Toward Synthesis of Completely Isotactic Polyacrylonitrile with Controlled Molecular Weight

Radiation-Induced Inclusion Polymerization of Acrylonitrile in Urea Canals: Toward Synthesis of Completely Isotactic Polyacrylonitrile with Controlled Molecular Weight

Organizational stabilities of bulk neat and well‐mixed, blended polymer samples coalesced from their crystalline inclusion compounds formed with cyclodextrins

Reactions in Solid‐State Inclusion Compounds

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