Tuning the activity of alternative Ru-based initiators for ring-opening metathesis polymerization of norbornene and norbornadiene by the substituent in 4-CH2R-piperidine

• The piperidine substituents were able to modify the behavior of the complexes in solution.
• Inter/intramolecular interactions concerning the piperidine substituents explained the different metal reactivities for ROMP.
• Homopolymers with quantitative yields under mild conditions were obtained.
• Copolymers with high crosslinking degree and high Tg values were isolated.

The novel [RuCl2(PPh3)2(4-CH2R-pip)] complexes, with R = H (complex 1), Ph (2) or OH (3), were synthesized and applied as initiators for ROMP of norbornene (NBE) and norbornadiene (NBD) under different reaction times, temperatures and monomer concentrations. There is a clear difference in the homopolymer yields in the order 1 > 2 > 3 at [monomer]/[Ru] molar ratio of 5000, at 25 °C for 5–60 min. Difference in the yields tends to disappear at 50 °C, with quantitative yields for 15–30 min with any type of initiator. Results from copolymers obtained at RT for 60 min from fixed amounts of NBE with four different amounts of NBD suggest that the type of initiator also affects the reactions, with more insertion of NBD with 1. The occurrence of cross-linking enhanced as the NBD loading increased, evidenced by decrease in the Mc and increase in the Tg values, besides the influence of the type of initiator.

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