Subsequently, a series of butenylsulfone monomers bearing different migrating groups were tested for 1,4-group transfer (Fig. ). Beside M1, monomers with benzoxazole, benzofuran, and (triisopropylsilyl)acetylene (M2-M4) also exhibited good polymerization reactivity, achieving conversions above 95% under the standard conditions. The Mn of polymer P3 reached 168 kg/mol, a high level challenging to attain with previous methods such as olefins/SO2 copolymerization. While only moderate conversions were given under the identical conditions (Table ), the conversion of M5 (with 1-methylbenzimidazole) was improved to 77%, and M6 (with furan) and M7 (with tert-butylacetylene) yielded the corresponding polymers (P6 and P7) with complete conversions. The same backbone structure bearing various migrating groups exhibited distinct solubility of polymers (Figure ). Generally, enhanced solubility facilitates sustained chain propagation, correlating with the higher Mn observed for P3 and P6, compared to P4 and P7. Notably, deprotection of P4 with the treatment of tetrabutylammonium fluoride (TBAF) efficiently furnished polymer P4-1 containing terminal alkynyl moiety, reserving avenues for post-functionalization via click reaction. Thermal properties of the aliphatic polysulfones were characterized using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Glass transition temperatures (Tg) of the aliphatic polysulfones varied from 82.9 °C to 120.9 °C, influenced by the polarity and steric hindrance of the pendant groups. The presence of C-S bond and the type of pendant group in the aliphatic polysulfones affected the thermal stability, with decomposition temperatures (Td,5%) ranging from 182.7 °C to 334.2 °C. To further enrich the chain structure of aliphatic polysulfones, a series of pentenylsulfone monomers were subjected to 1,5-group transfer (Fig. ). Under the similar conditions, M8 (with benzoxazole), M9 (with 1-methylbenzimidazole), M10 (with benzothiazole), and M12 (with pyrimidine) were readily converted into the corresponding high-MW polymers with high conversions, through temperature control. Of note, P9 even exhibited a higher Mn of 199 kg/mol The conversion of M11 (with benzofuran), M13 and M14 (with alkyne), which performed well in 1,4-group transfer, yet was not satisfactory in 1,5-group transfer process. The conversion of M11 could only be increased to 64%, while these of M13 and M14 still remained low (Table ). H and C NMR spectra indicate that P13 and P14 also follow the 1,5-group transfer polymerization to obtain chain structures with well-defined sequences as other aliphatic polysulfones. The poor solubility of polymerized products led to lower Mn of P13 and P14. Thermal property characterization of polymers (P8-P14) reveals that after adding one more methylene unit into the backbone, the range of Tg is reduced to 60.0-95.9 °C, probably due to the increased flexibility of the chains. However, extended carbon chain does not significantly change the thermal stability of polymers, which is consistent with the trend of pendant group impact in 1,4-group transfer polymerization. According to relaxed potential energy surface scan results (Fig. ), this elimination is barrierless. However, IM-5 is thermodynamically unfavored over IM-4 by 2.9 kcal/mol. Moreover, IM-5 is a nucleophilic radical, and its addition to the vinyl group of monomer M1 via TS-3b requires a barrier of 26.2 kcal/mol with respect to IM-3 as the stable initial state. Such a substantial barrier related to TS-3b is 10.1 kcal/mol higher than that necessitated by TS-3, meaning the addition of sulfonyl radical IM-3 to M1 is kinetically favored over than that between IM-5 and M1. On the other hand, IM-4 can undergo further rearrangement to form a more stable electrophilic sulfonyl radical IM-6, which is energetically favorable by 22.5 kcal/mol. This rearrangement significantly promotes the continuous chain propagation process. Therefore, the proposed mechanism is feasible under the experimental conditions.