471547 Simple Polymerization Reactions for Overcoming Long-Standing Challenges: From Fully Recyclable, Melt-Reprocessable Rubber Tires Containing Dynamic Covalent Bonds to Development of Broad-Temperature-Range Vibration and Acoustic Damping Materials (Invited Talk)
As a second example, I shall consider the challenge of designing polymeric materials via polymerization reactions that can yield excellent vibration and acoustic damping properties over a broad range of temperatures, from a minimum 60 degree C temperature (T) breadth to a maximum exceeding a 100 degree C T breadth. Several successful approaches will be described, all of which rely the production of polymeric materials that undergo nanophase separation with some phase mixing, thereby yielding materials with many compositions, and thus many glass transition temperatures, naturally present at equilibrium. Several cases will be detailed, including gradient copolymers yielding sinusoidal composition profiles at the nanoscale. Such gradient copolymers can be easily achieved by controlled radical polymerization methods, including nitroxide-mediated polymerization. Another case that will described will be polyhydroxyurethane (PHU) synthesized by aminolysis of cyclic carbonates. With PHU, the hydroxyl unit in the hard segment can undergo hydrogen bonding with oxygen atoms in the soft segment, thereby moderating the nanophase separation. Under optimal conditions, with enough but not too much such intersegment hydrogen bonding, excellent damping properties (as determined by tan delta > 0.3) can be tuned over exceedingly broad temperature ranges. The important role of molecular structure impacting nanoscale structure which in turn impact macroscopic properties is evident with PHUs: such properties cannot be achieved with polyurethanes lacking the hydroxyl unit present in PHUs.