Molecular Weight and Functionality Determination of Polyisobutylenes Containing Tertiary Chlorine Chain Ends by Thermal Dehydrochlorination

A sensitive thermal dehvdrochlorination method has been used to determine quantitatively the HCl arising from -CH2C(CH3)2Cl endgroups in polyisobutylenes synthesized by BCb as the co-initiator. Quantitative endgroup analyses provided number-average molecular weights, M n and functionality, F n. Select M n data obtained by this endgroup analysis is in agreement with those obtained by osmometry, GPC, and NMR techniques; indeed, M n's obtained by this dehydrochlorination technique appears to be more accurate (2-3% error) than conventional methods (∼5-10% error). The rate of HCl loss from -CH2C(CH3)2Cl termini is first order in HCl with an ΔEa of 19.1 kcal/mol in the 170-200°C range. This relatively low activation energy is most likely due to internal strain in the -CH2C(CH3)2CH2C(CH3)2Cl endgroup. These studies quantitatively substantiate earlier conclusions in regard to the mechanism of endgroup formation in BC13 coinitiated isobutylene polymerization.