Vinyl aryl ether structures

Employing an HIPE technique, poly(aryl ether sulfone) monoliths were obtained by the copolymerization of maleimide-terminated aryl ether sulfone macromonomer with styrene, DVB, or bis-vinyl ether in a solution in which petroleum ether (80% by volume) was dispersed [373]. The resulting product possessed an open-cell structure with porous cell walls and enlarged thermostability compared with poly(styrene-co-DVB) mono-hths. Unfortunately the utilization of the material as a possible medium for chromatographic separation has not been reported. 

In the other type, termed isodimorphism, the system consists of two different crystalline structures. The formation of one or the other depends on the sequence distribution (composition) of the crystalline phase. Examples of these types of replacements are found in virtually all types of copolymer, including copolyamides [97-103], synthetic and natural copolyesters [89, 90, 104-107], vinyl copolymers [29,94, 108, 109], diene polymers [110], poly(olefins) [111-114], poly(aryl ether ether ketones) [115], andpoly(phenyls) [116]. A detailed summary of other copolymers in which co-crystallization occurs can be found in [117]. There appear to be two underlying principles that govern isomorphic replacement [117]. These are that the two repeating units should have the same shape and volume and that the new ordered chain conformation be compatible with both types. In many of these examples the melting temperatures are essentially a linear function of the composition, whereas in others there is a smooth monotonic change. 

The classical reaction with chlorosulfonyl isocyanate has been extended to it-vinyl sulfide 449 to give a 2.5 1 diastereomeric mixture of 4-(phenylthio)azetidin-2-ones 343 and 450 (Equation 180) <2000MI935>. The facial selectivity in the cycloaddition has been explained by the conformational preference of the allylic groups in the transition structure. A similar reaction with styrene resulted into synthesis of the racemic 4-aryl-azetidin-2-one (Equation 181) <2000TA2351>. The divinyl ether 451 reacted with acid-free chlorosulfonylisocyanate to form 4-vinyloxyazetidin-2-one 452 (Equation 182) <1996SL895, 1997TA2553, 1998TL8349>. Most of the results in the reactions of isocyanate with vinyl ethers could be rationalized by a -conformational preference of the ether in... 

Carbenium ions are sp2 hybridized with the empty orbital perpendicular to the plane containing the three substituents. Calculations confirm both the flat structure of carbenium ions and the shorter linkage with aryl substituents due to the partial double-bond character. As discussed previously, the positive charge is not localized just on the sp2-hybridized carbon of the carbenium ion, but is dispersed onto neighboring substituents. Table 1 presents the charge distribution in model carbenium ions formed by protonation of propene, isobutene, styrene, a-methylstyrene, methyl vinyl ether, and methyl propenyl ether. 

The C(0)-0 bond length in esters is significantly shorter than the C(sp )-0 bond of aryl or vinyl ethers. In a study of the geometry of thioesters in crystal structures by Zacharias et al. [27] it was found that the bond length does not differ from that of the corresponding bond in aryl and vinyl monosulfides (O 1.336 [21] vs. 1.367 A S 1.767 vs. 1.763 A [27]). This suggests that there is more electron delocal-... 

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