Polyolefin Bottlebrush and Bottlebrush Diblock Copolymers From Chain‐End Functionalized Polyolefins and Their Viscosity Behavior

We developed a robust and systematic approach to synthesize well‐defined polyolefin bottlebrush homopolymers and block copolymers using ring‐opening metathesis polymerization (ROMP) of tailored norbornene‐functionalized highly branched polyolefin (PE) macromonomers (MMs). Pd‐diimine catalyst chelates are chosen to yield active ester chain‐end functionalized PEs from living polymerizations which are converted to norbornene‐functionalized PEs (MMs) with high control over molecular weight (Mw). From a series of MMs with molecular weights of 2.3, 5.1, 10.5, and 15.2 kg/mol, bottlebrush (BB) homopolymers with Mw of 3800, 4800, and 6400 kg/mol, as well as a bottlebrush block copolymer with a Mw of 3700 kg/mol, were synthesized and subsequently investigated. WAXS studies confirm the typical molecular BB microstructure in our BB homopolymers, where the backbone‐to‐backbone distance is a linear function of the MMs size. Linear viscoelastic measurements reveal that the BB homopolymers are ultra soft (with plateau modulus < 1.5 kPa) and have very large entanglement molecular weight (>1 Mg/mol). The presented approach establishes a pathway toward polyolefin BB with tunable properties to serve as robust but ultra‐soft adhesives with potential to be developed into soft elastomers.