Comb-Like Graft Copolymers of Poly(oxa)norbornene: Efficient Synthesis Using a Combination of ROMP and Click Chemistry

The combination of ring‐opening metathesis polymerization (ROMP) and copper‐catalyzed azide–alkyne cycloaddition (CuAAC) is described as an efficient click reaction to synthesize a new range of well‐defined comb‐like polynorbornene/polyoxanorbornene graft copolymers containing poly(ethylene glycol) (PEG) and/or poly(ε‐caprolactone) (PCL) as side chains. The “grafting through” method is applied for the synthesis of polyoxanorbornene‐g‐PEG via ROMP of oxanorbornenyl di‐PEG macromonomer prepared by click coupling of azide‐terminated PEG with di‐alkyne‐functionalized oxanorbornene. The well‐characterized macromonomer is then subjected to ROMP. Polynorbornene‐g‐PCL and polynorbornene‐g‐PEG are prepared by the “grafting onto” route. This is achieved by ROMP of 5‐bromohexyloxymethyl norbornene followed by reaction with NaN3 and then click reaction with alkyne‐terminated PEG and PCL. (Polyoxanorbornene‐g‐PEG)‐ran‐(polynorbornene‐g‐PCL) is prepared by ROMP of a mixture of oxanorbornenyl di‐PEG and 5‐bromohexyloxymethyl norbornene followed by reaction with NaN3 and subsequently click reaction with alkyne‐end‐capped PCL. All intermediates and final products are characterized by IR, NMR, MS, and size exclusion chromatography (SEC). Self‐assembly of these comb‐like polymers in solution into micro/nanostructures is foreseen, leading to a wide range of potential applications. A facile synthetic approach to prepare complex but well‐defined macromolecules with different topologies is demonstrated. A new range of comb‐like polynorbornene/polyoxanorbornene graft copolymers containing poly(ethylene glycol) and/or poly(ε‐caprolactone) as side chains are prepared using a combination of ring‐opening metathesis polymerization and click chemistry. These complex polymers can potentially self‐assemble in solution into micro/nanostructures, leading to a wide range of applications.