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Thermosets play a key role in the modern plastics and rubber industries, comprising ~18% of polymeric materials with a worldwide annual production of 65 million tons. The high density of crosslinks that give these materials their useful properties comes at the expense of facile degradability and re/upcyclability. Here, using the high-performance industrial thermoset plastic poly-dicyclopentadiene (pDCPD) as a model system, we show that when a small number of cleavable bonds are selectively installed within the strands of thermoset plastics using a low-cost comonomer approach, the resulting materials display the same exceptional properties as the native material yet they can undergo triggered degradation to yield soluble, re/upcyclable products of controlled size and functionality. In contrast, installation of cleavable crosslinks, even at comparably high loadings, does not produce degradable materials. These findings shed new light on the topology of polymer networks, revealing cleavable bond location as a universal design principle for controlled thermoset degradation and re/upcycling.<br>

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0 VA, N auchno-I ssledovalelski!£ I nstitut Sintelicheslcogo Kauchuka im S. V . Lebedeva, Leningrad, U.S.S.R . IFor solving the problem of cis-polyisoprene or cis-polybutadiene synthesis one must take into consideration not only the nature of the catalyst determining the character of the monomer addition during the polymerization but also secondary reactions proceeding in the polymer cha in under the influence of the eatalytic complex components. We have found that titanium halides and organoaluminum compounds cause isomerization of the cis uni ts of natmal rubber into the trans units. 1 The percentage of different configurations of the polymer chain uni ts has been determined by infrared spectmscopy from the absorption at 840 em. -l. In some cases it has been dete rmined qualitatively from t.he absorption bands at 1300 and 1100 em. -1 • The data on the relative proportion of cis and trans units are only qualitative sin ce, simultaneously with the polymerization proce s, a considerable TABLE I Tso mPriza tion of Na tura l Ruhlw r ( in a2 % Benzene Solution during 10 hr. ) % by % of units from total number of Hn Rat11ratNI " ·eigh t units o f T Ptnp. , Vnsatura t ion , Catalyst rubber oc. % Ct S tran s DO 99.2

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