5.5. Synthesis of PIBs with Higher Content of Trisubstituted Olefinic End-Groups

High levels of control molecular weight and vinylidene content in modern HRPIB technologies have the opposite effect. Due to lower photooxidative stability of vinylidene olefins, it became necessary to develop approaches to PIBS with a high content of trisubstituted olefinic end-groups. In the recent BASF patent [130], the results of isomerization of commercial HRPIB Glissopal 1000 in the presence of Al₂O₃ and molecular sieves were presented. The course of the reaction is illustrated through the example presented in Scheme 15 and Table 7. This study is of particular interest in terms of isomerization of HRPIBs in the presence of weak acids. It is obvious that such side reactions can proceed during any cationic polymerization of IB.

Structures of PIBs in starting HRPIB (A is the main component) and in isomerization products [130]. Molecular structures are indicated by the symbols used in Table 7.

Isomerization of HRPIB Glissopal 1000 in n-hexane at 80 °C. [130] ¹.

¹ Reaction conditions: HRPIB (40 g), n-hexane (40 g), Al₂O₃ (33 g), molecular sieves 5Å (33 g). ² See Scheme 15.