Syntheses and reactions of ferrocene‐containing polymers. Part IV. Cationic polymerization of 1.1′‐divinylferrocene. Influence of the polymerization condition on the polymer structure

Cationic cyclopolymerizations of 1.1′‐divinylferrocene with LEWIS acids and alkylaluminum catalysts were performed under various conditions. The cyclization constant rc (the ratio of rate constants of the intramolecular cyclization and the intermolecular propagation) was determined by applying the equation previously empolyed for cyclopolymerizations of o‐divinylbenzene. The rc value (0°C, CH2Cl2) was approximately 1 mole/l. with BF3OEt2, SnCl4, and TiCl4, but increased to 1.8 to 2.8 mole/l. with aluminum‐containing catalysts. It also increased (from 0.67 to 1.49 mole/l.) with increasing polarity of polymerization solvents. The intramolecular cyclization was shown to possess an activation energy higher than that of the intermolecular propagation by 1.2 to 1.5 kcal/mole (AlEtCl2/C6H5CH2Cl, CH2Cl2). These data were interpreted as follows: the intramolecular cyclization of the growing carbonium ion pair becomes more favorable, as the tightness of the ion pair decreases, because of the increase in reactivity. Thermal behaviors of several polymers were examined by differential scanning calorimetry and thermogravimetric analysis, and it was suggested that extensive crosslinking occurred in the molten polymer at about 200°C.