Anion/base-mediated degradation. Initially, aminolysis was tested as this is a main method for the degradation of radically-made DOT copolymers. Herein, three primary short-chain amines (n-propylamine, isopropylamine, ethylamine) were used in a 1:1 (vol:vol) mixture with THF at RT. For all amines, SEC analysis showed the complete disappearance of the polymer and formation of small molecules, suggesting the expected full degradation (Figure , S11A-B). NMR analysis (Figure ) confirmed the formation of small molecules including predominantly the alkylamidethiol molecule expected from quantitative aminolysis (Scheme S1). To explore thiolysis, a sample of pDOT (Table , entry 4, 8) was first treated with a 4fold excess (relative to the concentration of the thioester repeat units) of ethanethiol and DBU in CDCl3 at RT. While aminolysis typically requires a large excess of amine, the stronger nucleophilicity of thiolate anions meant that this 4-fold excess was sufficient to cause full degradation. SEC analysis (Figure ,C) of the isolated products confirmed the disappearance of the polymers and formation of small molecule products. 1 H NMR analysis confirmed the degradation through the disappearance of the characteristic broad multiplets of the benzylic protons (δ = 3.73 and 3.94 ppm, Figure ) of DOT-DOT diads. Instead, the spectrum of the fully degraded sample showed two narrow doublets at 3.56 and 4.27 ppm, in addition to narrow, shifted aromatic signals (Figure ). These chemical shifts were similar (but not identical) to those of the cyclic thioester DTO reported in the literature. To identify this major product of the degradation, DTO was prepared separately through thermal isomerization of DOT. We found that the chemical shifts of DTO depended strongly on the NMR solvent. Gratifyingly, 1-D and 2-D NMR spectra of the decomposition product recorded in CDCl3 (Figure We considered three base/anion-mediated pathways leading to the formation of DTO as the sole degradation product of pDOT: (i) a self-immolative mechanism starting from the α end-group, in which a deprotonated thiocarboxylate attacks the adjacent benzylic position to give one molecule of DTO and releases another thiocarboxylate (Scheme 3, Pathway 1); (ii) a self-immolative degradation through backbiting of a thiol following a single thioester cleavage event (Scheme 3, Pathway 2); and (iii) a two-step process first forming an ethyl thioester-mercapto-functional biphenyl through thiolysis of two adjacent thioester linkages followed by intramolecular cyclization (Scheme 3, Pathway 3). To distinguish between these mechanisms, a series of experiments was conducted.