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In addition to differences among the various modifications of TiCl3 there may be certain structural differences even among α‐TiCl3 samples prepared by differences methods. Electron microscopic examination of two samples has revealed widely different free surfaces, in spite of the fact that both the specific surfaces (measured by adsorption) and the polymerization activities were identical. This might be explained by the finding that the surfaces of the free lateral planes and the quantities of the free edges are the same. This explanation is in agreement with the assumption of Rodriguez and his co‐workers that the active centers of polymerization are situated on the lateral planes and edges of the TiCl3 crystals.

In some cases metal dicarboxylates can be considered as polymers. Formation of crystalline or amorphous polymer depends on the type and ratio of the metal ion to the carboxylate ligand and on the preparation conditions. The “polymer salt” synthesized by the reaction of ZnO and maleic acid shows special feature due to the cis configuration of the dicarboxylic acid. The polymer prepared in a water medium has a fibrillar morphology with a helical structure which is changed by heat treatment: a molecular rearrangement takes place which leads finally to amorphous polymer. The reaction of ZnO and fumaric acid (trans configuration) results in monocrystals containing crystal water or, after heat treatment, in powderlike polymer.

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