The diverse substitutions along the polymer backbones resulte in a broad range of observed glass transition temperatures (Tg), spanning from -34.8 ºC to 73.9 ºC. The experimental data reveal a clear trend: as the alkyl chain length progressively increases from P1 to P3, the Tg notably decreases. This trend indicates a corresponding increase in the overall flexibility of the molecular chains, offering valuable insights into how structural modifications can significantly impact material properties at the molecular level (Fig. ). Overall, most of the polymers display exceptional thermal stabilities with decomposition temperatures (Td,5%) exceeding 280 °C. The polymers are soluble in polar aprotic solvents such as N, N-dimethylformamide (DMF), tetrahydrofuran (THF), dichloromethane (DCM) and dimethyl sulfoxide (DMSO), while not soluble in relatively polar protic solvents such as water and methanol. We also investigated analogous radical polymerization via 1,4 and 1,6-HAT process, but they did not entirely follow the reaction mode of intramolecular hydrogen atom transfer (Fig. ). When using M9 as the monomer, where the tertiary C-H bond is absent, polymer P9 was obtained under the above polymerization conditions. We confirmed that 1,5-cyano migration occurred in the polymerization by H & C nuclear magnetic resonance (NMR) spectroscopy, 1 H-1 H correlation spectroscopy (COSY), 1 H- C heteronuclear single quantum coherence (HSQC), and 1 H- C heteronuclear multiple bond correlation (HMBC) (Fig. ). The aliphatic peak of 2.77 ppm was assigned to Hb next to the cyano group. The HSQC spectra showed that the carbon coupled to hydrogen next to the cyano group. The HMBC spectra showed that the carbon of the cyano group coupled to Ha, Hb and Hc. By analyzing the results of the NMR, we confirmed that the occurrence of 1,5-cyano migration process, and the construction of ABC (acrylonitrile-ethylenemethacrylonitrile) sequence was established. Subsequently, the suitability of various monomers for radical polymerization via 1,5group transfer was evaluated (Fig. ). Polymerization was achieved with a bulky tetrahydropyran substituent (P10), highlighting the robustness of this method. Furthermore, the sequential polymer composed of acrylonitrile, ethylene, and ethyl methacrylate units (P11) was synthesized with a conversion of 48%. Interestingly, the presence of benzothiazole group was also suitable for 1,5-migration process, leading to the corresponding polymer P12, albeit with a low conversion. To characterize the thermal properties of the resultant polymers, which were ABC sequence-defined, TGA and DSC were also applied. The analyses reveal that all polymers exhibited remarkable thermal stability, with a Td, 5% exceeding 250 °C.