Controlled immobilization of methyltrioxorhenium(VII) based on SI-ATRP of 4-vinyl pyridine from halloysite nanotubes for epoxidation of soybean oil

Poly(4-vinylpyridine) (P-4VP) brushes of different lengths were grafted onto halloysite nanotubes (HNTs) by surface-initiated atom transfer radical polymerization (SI-ATRP) and methyltrioxorhenium(VII) (CH3ReO3, MTO) was immobilized onto HNTs through P-4VP brushes to catalyze epoxidation of soybean oil. 2-Bromoisobutyryl bromine was chosen as the initiator of SI-ATRP and anchored by reacting with hydroxyl groups of HNTs. To reduce the effect of 4-vinylpyridine on the initiator, Me6tren as the ligand was introduced into the polymerization. The length of P-4VP brushes was controlled by the polymerization time. Through coordination between N in pyridine rings and MTO, a novel heterogeneous catalyst with different loadings of MTO for epoxidation of soybean oil was prepared. FTIR, TGA, TEM, GPC, UV–visible absorption spectroscopy and 1H NMR were used to characterize HNTs with P-4VP brushes and the heterogeneous catalysts. The results indicated that the length of P-4VP brushes increased with the polymerization time and MTO loading increased with P-4VP brush length. MTO molecules dispersed uniformly in P-4VP brushes and the heterogeneous MTO combined with H2O2 had good catalytic activity and selectivity to epoxidation of soybean oil. TOF of heterogeneous MTO increased with MTO loading and no ring-opening reaction occurred during epoxidation.

Controlled immobilization of methyltrioxorhenium(VII) based on SI-ATRP of 4-vinylpyridine from halloysite nanotubes.Figure optionsDownload as PowerPoint slideHighlights
• Halloysite nanotubes (HNTs) acted as a support of catalysts.
• P-4VP brushes were grafted onto HNTs via SI-ATRP to provide amount of N in pyridine rings.
• MTO was immobilized onto HNTs by stoichiometric coordination with N in pyridine rings of grafted P-4VP.
• The length of P-4VP brushes and MTO loading were controlled by polymerization time.
• The obtained heterogeneous MTO combined with H2O2 had good catalytic activity and selectivity to epoxidation of soybean oil.