To distinguish between Pathways 2 (ω depolymerization) and 3 (cyclization of small molecule fragments), samples of pDOT were treated with substoichiometric amounts of ethanethiol/DBU. When 10 mol-% of ethanethiol/DBU (relative to thioester linkages) was used, 80 mol-% conversion to DTO was found with 20 mol-% residual polythioester (Figure ) after 18 h at RT. Increasing the reaction time to 10 days did not increase the amount of formed DTO. SEC analysis showed a shift toward lower molecular weights, indicating partial degradation (Figure ). When the same intact homopolymer was treated with only 2 mol-% of ethanethiol/DBU, formation of 8 mol-% of DTO was observed (Figure ). With a shortage of reactive thiolate, the cleavage of two adjacent thioester units (mechanism iii) becomes less likely, making the backbiting mechanism (Scheme 3 , Pathway 2) more plausible. This self-immolative pathway is also supported by the lower pKa of the benzylic thiol within the polymer chain (pKa of benzyl mercaptan in water = 9.43) compared to ethanethiol (pKa in water = 10.3), making the polymeric thiolate a better leaving group than ethane thiolate. We therefore assume that the degradation of pDOT in the presence of base or anions (at least when a substoichiometric amount of thiolate is employed) starts with the transthioesterification of a random thioester within a chain, followed by selfimmolative depolymerization from the ω end of the polymeric thiol (Scheme 3, Pathway 2). Assuming quantitative unzipping of a thiolate-terminated chain, a single thioester cleavage event should reduce the average molecular weight of the (remaining) polymer to half, since, on average, half of each chain depolymerizes, while the other (ethyl thioester α-terminated) half is presumed to remain intact until it is attacked by another thiolate from its middle. In theory, a chain of, say, 32 (= 2 5 ) repeat units should thus require 5 thiolates (5/32 = 15.6 mol-%) to achieve full degradation to DTO, while a longer chain with a DP of 128 (= 2 7 ) would degrade fully in the presence of 5.5 mol-% (= 7/128) thiolate. Applying this theory to the observed DTO formations gave an initial DP of the intact homopolymer of 23 for the degradation observed with 10 mol-% thiolate and an initial DP of 6 for the degradation observed with 2 mol-% thiolate. This discrepancy indicated that either the thiolate reagent did not react quantitatively under the employed conditions and/or that the backbiting did not depolymerize the entire half of the chain making a larger amount of thiolate necessary. Thermal degradation. Inspired by the strikingly different TGA profiles of BF3•Et2Oand MeOTf-initiated polymers (Figure ), the thermal degradation in the absence of solvent was explored further. The thermal degradation of the MeOTf-initiated sample (Figure , grey curve) was nearly identical to a curve recorded as comparison of the small molecule DTO (Figure , green curve). We therefore hypothesized that, for the MeOTf-initiated sample, upon heating in the absence of solvent or nucleophiles, degradation to DTO took place at or below the onset of observed mass loss and that the observed decrease in mass stemmed mostly from the thermal disintegration of DTO. To investigate, samples of MeOTf-initiated pDOT (Table , entry 8) and BF3•Et2O-initiated pDOT (Table , entry 4) were heated to 140 °C in air in a test-tube without solvent or additives. During heating, the fluffy white polymers gradually changed to a brown/orange colour and became denser with a sand-like appearance supporting the formation of a crystalline product. 1 H NMR analysis of the mixtures confirmed 35 mol-% degradation to DTO for the MeOTf-initiated sample after heating overnight, while a significantly lower DTO content of 6 mol-% was found in the BF3•Et2O-initiated polymer after heating for 1 week to 140 °C (Table , entries 1, 2).