Polymerisation of isobutylene

[H(OR2)2][Al(ORF)4] - a promising initiator for the polymerisation of isobutylene [Ga(arene)x][Al(ORF)4] - a promising catalyst for the polymerisation of isobutylene Literature on the polymerisation of isobutylene

Polymerisation of isobutylene

The classic approach of polymerising isobutylene goes back to the year 1937.^[1]  Using the strong Lewis acid boron trifluoride BF₃ in combination with a proton donating species a new way of synthesizing high molecular weight polyisobutylene (PIB) was discovered (Scheme 1).^{[1, 2]}

Scheme 1 : Polymerisation of isobutylene.

Over the last 80 years, this approach has been augmented by novel proton-, carbocation- and metal-based systems.^{[3-7], [8-34], [35-52]} These systems have led to a vast product lineup, ranging from low to high molecular weight PIB. Depending on its molecular weight PIB can be divided into three major groups:

• High molecular weight PIB (M_n > 200 000 g mol^-1), a rubber like and physically harmless compound, has gradually substituted natural chicle as the main chewing gum base.^[53]
• Medium molecular weight PIB (M_n = 40 000 - 85 000 g mol^-1), a highly viscous liquid with an excellent barrier against moisture and various gases, is mainly used as an adhesive or in sealants.^{[41] [48]}
• Low molecular weight PIB (M_n = 1 000 - 2 300 g mol^-1), a honey like, colourless liquid, is an essential additive for lube oils and fuels.^[54-88]

Coming back to the synthesis of PIB, both proton- and carbocation-based systems solely function as initiators. Metal-based systems however can either initiate or catalyze the polymerisation of isobutylene (Scheme 2).

Scheme 2 : Different methods of synthesizing PIB.

Up to this day most syntheses of PIB, including the industrial scale ones, show a lack in at least one point. May it be low reaction temperatures down to –100 °C, dichloromethane as a carcinogenic and water-hazardous solvent, or relatively high concentrations of the initiating or catalyzing species – all these factors sum up to a negative economic and environmental balance. Thus, current applied research focuses on improving established production methods.^[89-91] More fundamental research however, addresses this problem by designing novel initiator/catalyst systems that enable a more economical and environmental friendly synthesis of PIB.

[H(OR₂)₂][Al(OR^F)₄] - a promising initiator for the polymerisation of isobutylene

[Ga(arene)_x][Al(OR^F)₄] - a promising catalyst for the polymerisation of isobutylene

Literature on the polymerisation of isobutylene