Topotactic polymerizations

Several reviews of early work on topotactic polymerizations and isomeriza-tions are available, and the reader is referred to the summaries of Morawetz [88] and Gougoutas [8] for a more complete account. The earliest study of a topotactic reaction appears to have been the observation, in 1932, of the polymerization of trioxane to poly-oxy-methylene [89]. Similar polymerizations of tetraoxane [90] and of trithiane [91 ] have also been reported to show retention of crystallographic axes from the monomer lattice. Other examples are discussed below. The topo-tacticity of a reaction can be determined solely by x-ray crystallographic analysis at the reactant and product endpoints. Thus a simple classification of a reaction as topotactic tells very little about how the structure of the crystal lattice changed in the course of reaction. 

The polymerization in clathrates, which has been compared to the template polymerization of biological systems, illustrates the exact requirements which need to be fulfilled for topotactic polymerization via a free radical mechanism. The hopes to find a monomer-polymer crystal pair which meets those conditions seem rather dim indeed. 

In summary, crystallization during ionic and coordination polymerization may give rise to a large variety of morphologies. Some crystalline cyclic monomers seem to be capable of topotactic polymerization reactions which must be simultaneous polymerization and crystallization. A direct influence of nucleation and ordered structure on the polymerization rate was observed for helical polymers in solution giving an... 

Free radical polymerization from crystalline monomers is even more difficult. Besides the general conditions for a topotactic polymerization to provide the proper geometry for monomer approach for reaction and... 

The final group of solid state monomers which have been polymerized are ring type monomers. There polymerizations showns two favorable factors. On ring opening and polymerization the number of covalent bonds stays constant and the heat of reaction and the voliune change are smaller. It seems that in this group of reactions the only topotactic polymerization reactions have been discovered. 

Another claim of a thermal and photochemical homogeneous (or topotactic) polymerization of the diacetylene 30 a (Scheme 2.1.9) is questionable. The claim had to be modified several times, it was admitted later that the polymorph required crystal solvent (e.g. 0.5 dioxane) [57], and 30 a was no longer discussed in the review of the same research group [58] that dealt with 30 b and listed 32 further diacetylenes. First order reaction was claimed in order to try to substantiate topochem-ical behavior [58]. However, inspection of the published kinetic curves indicates zero order up to 90 % conversion after an induction period instead of first order for... 

Y-J. Liu and M. G. Kanatzidis, Topotactic polymerization of aniline in layered uranyl phosphate, Inorg. Chem., 32, 2989-2991 (1993). 

The structural arrangement is shown in 108. Dihydroxy-substituted macrocycles with Me= Si(IV), Ge(IV), or Sn(IV) are converted by heating in bulk or in a high-boiling solvent to the p-oxo-bridged polymers. The topotactic polymerization mechanism is... 

Wegner [13 has pointed out that the "topotactic" polymerization of trioxane In which there Is no lattice control would not be expected... 

Linear, Dendritic, and Hyperbranched Polymers 211 H-bonding induced pseudo-topotactic polymerization... 

Scheme 7.8 CuAAC reaction of preassembled organogelators - a case of pseudo-topotactic polymerization.

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