New polyphenylene-based dendronized polymers (denpols), exhibiting extended and rigid conformations, were prepared using ring-opening metathesis polymerization (ROMP). Their mechanochemical degradation was explored in ultrasound-induced elongational flow fields. Degradation rate constants were obtained for polyphenylene-based denpols, of varying generation, across a degree of polymerization (DP) range of ∼100-600. In general, it was found that larger side chains led to increased degradation rates and that the rate enhancement was proportional to the natural log of persistence length (Ln( l)) or the square root of monomer molecular weight ( M). These relationships led to the generation of "master curves" in which the rate constant trends for each polymer series converged, enabling accurate prediction of degradation rate constants for related polymers bearing long alkyl chains or ester-type dendrons. Furthermore, we observed evidence for, and used computational modeling to support, polymer chains undergoing multiple scissions during a single elongation event, leading to faster degradation of daughter fragments that come from parent polymers with large side chains.

Graft and dendronized polymers have attracted much attention in the polymer community, and there have been significant efforts to develop better synthetic methods. Herein, we report the highly efficient synthesis of graft and dendronized polymers by using Cu-catalyzed multicomponent polymerization (MCP). Based on diversity-oriented synthesis, we prepared a library of various graft and dendronized polymers from combinations of three types of monomers (mono-functionalized alkynes, bis-sulfonyl azides, and diamines/diols) that are bench stable and readily accessible. After reaction optimization, 54 samples of high-molecular-weight graft and dendronized polymers were prepared, the MCP method allowing simultaneous manipulation of the structures of both the main chains and the side chains. Moreover, because of the severe steric hindrance of the side chains, these polymers adopted extended conformations, as shown by the large shape parameter in solution. Also, the extended morphology of the single polymer chains was directly visualized by atomic force microscopy and transmission electron microscopy in the solid state. Most importantly, this diversity-oriented polymerization became possible because of highly step-economical and efficient one-step MCP, paving the way toward the easily tunable synthesis of graft and dendronized polymers.

The ultrasonic degradation of polynorbornene-g-polylactide and polynorbornene-g-polystyrene brush polymers was explored. First-order rate constants for backbone scission were obtained for brush polymers with varying arm lengths (ranging ca. 3–8 kDa) and backbone degrees of polymerization (ranging ca. 78–361). Master curves, in which the rate constant trends for all polymers converge, could be generated by accounting for the rate enhancement from the polymer being in an extended conformation and the contour length being equivalent to the combined length of two arms and the backbone. Slow scission of arms from the backbone was also observed, with first-order rate constants being dependent on the arm length.

We demonstrated tandem ring-opening/ring-closing metathesis (RO/RCM) polymerization of monomers containing two cyclopentene moieties and postmodification via insertion polymerization. In this system, well-defined polymers were efficiently formed by tandem cascade RO/RCM reaction pathway. Furthermore, these polymers could be transformed to new A,B-alternating copolymers via a sequential cross metathesis reaction with a diacrylate. Additionally, we demonstrated the concept of multiple olefin metathesis polymerization in which the dicyclopentene and diacrylate monomers underwent all three olefin metathesis transformations (ring-opening, ring-closing, and cross metathesis) in one shot to produce A,B-alternating copolymer.

We investigate the conformation of well-defined dendronized polymers (denpols) based on poly­(norborene) (PNB) and poly­(endo-tricycle­[4.2.2.0]­deca-3,9-diene) (PTD) backbones employing static and dynamic light scattering. Their synthesis by ring-opening metathesis polymerization (ROMP) led to fully grafted and high molecular weight denpols with narrow polydispersity. In dilute solutions, the persistence lengths were estimated by static (radius of gyration) and dynamic (translational diffusion) chain conformational properties of the denpols and were compared to their homologue precursor PNB. The conformation of denpols with a third generation side dendron conforms to a semiflexible chain with a persistence length of about 6–8 nm, virtually independent of the contour length. In the semidilute regime, the thermodynamics and cooperative diffusion of denpols resemble the behavior of the precursor solutions as described by the scaling theory of flexible polymers above the crossover concentration. The assumption of extremely high chain rigidity for this class of polymers is clearly not supported, at least for the third generation dendron.