Ring-Opening Metathesis Polymerization of Functionalized Cyclobutenes Derivatives

Abstract

In the last decade, the development of well-defined carbene catalysts has revolutionized the field of ring-opening metathesis polymerization (ROMP). Nevertheless, little attention has been paid to monomer design for ROMP. In this project, a new family of functionalized polycyclic monomers based on the endo-Tricyclo[4.2.2.0^2,5]deca-3,9-diene structure with a variety of functional groups at the 7,8 positions has been prepared.

Polymerization studies were performed with well-defined Schrock's molybdenum catalysts and a variety of Grubbs' ruthenium carbene catalysts. A living polymerization was obtained with Cl₂Ru(=CHPh)(PCy₃)₂ (Ru-III).

¹⁹F NMR analysis indicated that the ortho and meta fluorinated substituents of the N-phenyl succinimide moiety could be regarded as sensitive reporters vis-à-vis the microstructure of the polymer. "Blocky" copolymers from a mixture of cis-cyclooctene and 7,8-N-2,3,4,5,6-pentafluorophenyl succinimide endo-Tricyclo[4.2.2.0[superscript 2,5]]deca-3,9-diene (M-7) could be prepared with Ru-III. The presence of cis-cyclooctene was shown to have an influence on the kinetics of the polymerization and the polymer microstructure.

Kinetic studies with Ru-III indicated that faster polymerizations were obtained when the N-succinimide moiety was more electron-rich. The influence of steric hindrance on the polymerization was studied by the functionalization of the monomer structure with bulky polyaryl ether dendrons. A controlled polymerization was obtained with the very active Ru(=CHPh)Cl₂(PCy₃)(1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) (Ru-VI). This behavior was explained by the decrease of the propagation rate due to the bulkiness of the dendritic functional groups.

Polymers functionalized with a variety of N-succinimide moieties displayed a remarkable thermal stability with decomposition temperatures above 300°C. No Tg was observed below decomposition temperature, indicating the generation of a very rigid polymer backbone.

Graft copolymers based on a ROMP polymer skeleton and with poly(methylmethacrylate) branches could be prepared in a one-pot procedure using the single catalyst Ru-III and monomers based on the endo-Tricyclo[4.2.2.0[superscript 2,5]]deca-3,9-diene structure functionalized with a tertiary alkyl bromide, present as an ATRP initiator. Both distinct polymerization processes were shown to occur in tandem and in a controlled fashion.