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 explored the mechanochemical degradation of bottlebrush and dendronized polymers in solution (with ultrasonication, US) and solid states (with ball-mill grinding, BMG). Over 50 polymers were prepared with varying backbone length and arm architecture,composition, and size.With US,w ef ound that bottlebrush and dendronized polymers exhibited consistent backbone scission behavior,w hichw as related to their elongated conformations in solution. Considerably different behavior was observed with BMG,a sa rm architecture and composition had as ignificant impact on backbone scission rates.A rm scission was also observed for bottlebrush polymers in both solution and solid states,but only in the solid state for dendronized polymers.Motivated by these results,m ulti-mechanophore polymers with bottlebrush and dendronized polymer architectures were prepared and their reactivity was compared. Although dendronized polymers showed slower arm-scission, the selectivity for mechanophore activation was muchh igher.O verall, these results have important implications to the development of new mechanoresponsive materials.

Step-growth polymerization via C–H activation is an attractive technique due to its advantages such as atom- and step-economy, derived from the reduced the number of synthetic steps required for the overall process and elimination of organometallic byproducts. To expand the utility of C–H activation polymerization beyond C–C bond coupling, we recently developed a highly efficient direct C–H amidation polymerization (DCAP) involving C–N bond formation, as a green polymerization process for synthesizing polysulfonamides. Here, we present a full account of the use of DCAP in the preparation of a library of polysulfonamides and polyamide from various diamides and diazides. From extensive model studies, several directing groups were screened, and it was found that subtle design of the directing groups by altering the steric hindrance and chelating bond angle greatly affected the efficiency of C–H amidation. Five directing groups were selected and seven AA-type monomers and seven BB-type monomers of azides were designed. After optimizing the polymerization process, 25 examples of well-defined high-molecular-weight (up to 171.4 kDa) polysulfonamides and polyamide were prepared. Notably, even diamide monomers containing four reactive ortho-C–H bonds produced defect-free polysulfonamides without cross-linking, supported by 1H NMR spectroscopy and size exclusion chromatography (SEC) traces. Furthermore, many of these polysulfonamides emitted light via an excited-state intramolecular proton transfer (ESIPT) process as a result of tautomerization upon photoexcitation.

The influence of grafting density on polymer conformations and ultrasonic degradation of polynorbornene-g-polystyrene (PS) or poly­(methyl acrylate) (PMA) graft copolymers was explored. Multi-angle light scattering analysis, atomic force microscopy imaging, and molecular dynamics simulations supported that graft copolymers exhibited increased backbone and arm extension and increased arm–arm interactions at higher grafting density. In regard to backbone scission, faster scission rates were observed at higher grafting density, which was further supported by the generation of master curves that account for the rate enhancement due to the polymer being in an extended conformation. The grafting density also influenced arm scission rates, with PS and PMA arms exhibiting opposite trends. Specifically, arm scission was faster for PS at higher grafting density and faster for PMA at lower grafting density, which was attributed to differences in arm extension and arm–arm interactions between the two arm types.

Cyclic polymers are topologically interesting and envisioned as a lubricant material.However, scalable synthesis of pure cyclic polymers remains elusive. The most straightforward way is to recycle a used catalyst for the synthesis of cyclic polymers. Unfortunately, it is demanding because of the catalyst's vulnerability and inseparability from polymers, which depreciates the practicality of the process. Here, we develop a continuous process streamlined in a circular way that polymerization, polymer separation, and catalyst recovery happen in situ, to dispense a pure cyclic polymer after bulk ring-expansion metathesis polymerization of cyclopentene. It is enabled by introducing silica-supported ruthenium catalysts and a newlydesigned glassware. Also, different depolymerization kinetics of the cyclic polymer from its linear analogue is discussed. This process minimizes manual labor, maximizes security of vulnerable catalysts, and guarantees purity of cyclic polymers, thereby showcasing a prototype of a scalable access to cyclic polymers with increased reusability of precious catalysts (≥415,000 turnovers).The economy of lubrication is encumbered by a high replacement cost of lubricants in many applications 1,2 . One of its countermeasures is to increase the lifespan of lubricants, thereby decreasing the replacement frequency. The most common synthetic lubricant by far is polyalphaolefin 3-5 , which gradually loses its viscosity due to permanent chain scissions over time 6 . Cyclic hydrocarbon polymers similar to polyalphaolefins or mineral oils (e.g. polyethylene, polypropylene, polybutadiene, etc.) 7,8 are tribologically interesting because the initial chain scission of cyclic topology increases its viscosity by producing an opened linear topology with a higher chain volume [9][10][11] . This feature of cyclic polymers is envisioned as a viscosity modifier to prolong the lubricant lifetime. Since our discovery of the ring expansion route to cyclic polymers in 2002 11 , we [12][13][14][15][16] and other groups [17][18][19][20][21][22][23][24][25][26] have done exciting research on more functionalized and purer cyclic polymers.One of the most important needs is the development of a practical synthetic process to produce pure cyclic polymers on a larger scale for testing in many applications. To date, all the reported synthetic protocols were operated on a milligram scale in solution by homogeneous catalysis, which was accompanied by rigorous ex situ processes for polymer purification without actual catalyst recovery (Fig. 1a) [24][25][26][27] . Nonetheless, the residual metal catalysts remained at a few hundred ppm level 12 ; in this conventional process, it is difficult not only to obtain an uncontaminated white polymer but also to recycle the precious metal catalysts.