Synthesis of Poly(norbornene-methylamine), a Biomimetic of Chitosan, by Ring-Opening Metathesis Polymerization (ROMP)

ROMP is an effective method for preparing functional polymers due to its having characteristics of "living" polymerization and rapid development of catalysts. In the present work, poly(norbornene-methylamine), a mimic of chitosan, was synthesized via ROMP reaction. The amino-protected product, 5-norbornene-2-(N-methyl)-phthalimide, was prepared by a reaction of 5-norbornene-2-methylamine with phthalic anhydride, which was then subjected to the ROMP reaction in the presence of Hoveyda-Grubbs 2nd catalyst to afford poly(norbornene( N-methyl)-phthalimide). The target product, poly(norbornene-methylamine), was obtained by deprotection reaction of poly(norbornene-(N-methyl)-phthalimide). The products in each step were characterized by FTIR and H-1-NMR, and their thermal stabilities were determined by TG analysis. The effects of molar ratio between monomer ([M]/[I]) and catalyst on the average relative molecular weight ((Mn) over bar) and molecular weight distribution of the produced polymer products were determined by gel permeation chromatography (GPC). It was found that the (Mn) over bar of poly(norbornene-(N-methyl)-phthalimide) was controllable and exhibited a narrow polydispersity index (PDI) (similar to 1.10). The synthesis condition of 5-norbornene-2-(N-methyl)-phthalimide was optimized by determining the yields at different reaction temperatures and reaction times. The highest yield was obtained at a reaction temperature of 130 degrees C and a reaction time of 20 min. Our work provides a new strategy to synthesize polymers with controllable structures and free-NH2 groups via ROMP.