Cyclo‐ and cyclized diene polymers. XIV. Structure and properties of poly(2,3‐dimethylbutadiene‐1,3)

Polymerization of 2,3-dimethylbutadiene-1,3 with the Ziegler-type catalyst Al(i-C4H9)3-TiCl4 yields cis-1,4-polydimethylbutadiene, when the Al component is in excess, and cyclic polydimethylbutadiene with reduced unsaturation and some trans-1,4 units in the chain, when the Al/Ti ratio is 1 or less. Similar cyclic polymer is formed in polymerization initiated with acid catalysts such as AlC2H5Cl2. Polydimethylbutadiene obtained with the complex cobalt catalyst Al(i-C4H9)2ClCoCl2·pyridine is predominantly cis-1,4 with about 20% of 1,2 units. Radical polymerization at elevated temperature gives high 1,4-polydimethylbutadiene with both cis and trans units. The polymer obtained by irradiation of dimethylbutadiene at low temperatures is also cyclic with some trans-1,4 units. Irradiation of dimethylbutadiene in thiourea canal complex leads to relatively high trans-1,4 polymer. Absorption bands in the infrared spectra at 1125, 1201, and 1251 cm.−1 are typical of cis-1,4, and bands at 1156, 1227, and 1263 cm.−1 are typical of trans-1,4, structures.