Canal complexes

White91 used a 1,3-butadiene-urea canal complex to produce all-trans- 1,4-poly butadiene. The complex is formed only at temperatures in the range — 55 °C to 25 °C and needs a small amount of methanol to be formed. 

CONTENTS Preface. George W. Gokel. Cryptophanes Receptors for Tetrahedral Molecules, Andre Collett, Jean-Pierre Dutasta and Benedict Lozach. Inclusion Polymerization in Steroidal Canal Complexes, Kiichi Takemoto, Mikiji Miyata. Functionalized Tetraazamacrocycles Ligands with Many Aspects, Thomas A. Kaden. Calixarenes as the Third Supramolecular Host, Seiji Shinkai, Kyushu University, Japan. Fluorescent Chemosensors for Metal and Non-Metal Ions in Aqueous Solutions Based on the Chief Paradigm, Anthony W. Czamik. Index. 

Shimanouchi, Tsuchiya, and Mizushima (196)J and by irradiation of urea-canal complexes [Krimm, Berens, Folt, and Shipman (106) Shimanouchi, Tsuchiya, and Mizushima (196, 197)), have also been studied. Band positions are given in Table 11, together with polarization data [Krimm and Liang (101) Narita, Ichinohe, and Enomoto (144) Shimanouchi, Tsuchiya, and Mizushima (196)) and data on the... 

A low degree of tacticity is obtained because these monomer-orienting forces are quite weak. Thus, polymer stereoregularity is achieved only with certain suitable monomers and at low temperatures. Increased tacticity can be achieved in some cases by using monomer-orienting forces other than the catalyst or the polymer end groups, but these have rather limited utility (canal complexes, solid state polymerizations, etc.). Simple polymerization systems fall outside the scope of this review and are not discussed further. 

De Sanctis, S. C., Giglio, E., Pavel, V., and Quagliata, C. A study of the crystal packing of the 2 1 and 3 1 canal complexes between deoxycholic acid and p-diiodobenzene and phenanthrene. Acta Cryst. B28, 3656-3661 (1972). 

White, D. M. Stereospecific polymerization in urea canal complexes. J. Am. 

Polymerizations in thiourea canal complexes yield high melting crystalline rra/w-1,4-polybutadiene, 2,3-dimethylbutadiene, 2,3-dichlorobutadiene, and 1,3-cyclohexadiene. Cyclo-hexadiene monoxide, vinyl chloride, and acrylonitrile also form stereoregular polymers. On the other hand, polymerizations of isobutylene and of vinylidine chloride fail to yield stereospecific polymers. 

How can canal complexes be used for steric control in free-radical polymerization Give examples. 

R. Takemoto and M. Miyata, Polymerization of vinyl and diene monomers in canal complexes, J. Macromol. Sci.—Rev. Macromol. Chem. Cl8, 83 (1980). 

This type of structure is an example of an organic multimolecular inclusion complex, dependent on the entire packing arrangement of host molecules providing void spaces which can be occupied by guest molecules. Such materials include th familiar examples of he clathrates formed by Dianin s compound, and by hydroquinone, and the canal complexes formed by urea with n-alkanes. ... 

The irj,elusion polymerization of various diene monatiers in apDcholic acid canals was studied in the same way as the case of deoxycholic acid canal complexes [6,7]. The apocholic acid-monomer canal ccxtplexes were at first prepared in sealed tubes by absorbing the monomer molecules into vacant canals of solvent-free apocholic acid crystals. Then the moncxners present in the canals were post-polymerized by heating after y-ray irradiation. 

The crystals of apocholic acid canal complexes kept their original shapes and appearance during the polymerization just like the case of deoxycholic acid. It was assured that all monomers used polymerize in the canals and not outside of them, because the polymer yield was less than 1.0 mg per 0.50 cm of monomer in the absence of apocholic acid under the condition studied. The methanol-insoluble solid or rubbery polymers after the extraction of apocholic acid with boiling methanol were characterized. 

Most of canal corplexes obtained after polymerization melted at higher temperatures than that of apocholic acid itself (176-8°C). The most remarkable increase of the melting point was observed in the case of 2,3-dimethylbutadiene. This is probably because the polymer chains fit in the canals best among the polymers studied due to its suitable size and symnetric shape. On the other hand, polybutadiene does not seem to stabilize the canal complexes due to its small cross section as compared with that of the canal. 

The structure of PAN obtained by anionic or radical polymerization Is usually nonstereoregular. that is, atactic. It also well known that highly stereoregular (isotactic) PAN can be prepared by radiation in a urea canal complex of acrylonitrile (6). 

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