## 3 Results and Discussion  
As the most basic and most abundant sulfur source, elemental sulfur is stable in thermodynamic stability under normal temperature. The elemental sulfur molecule is formed by eight sulfur atoms connected in a cyclo-S\({}_{8}\), as shown in Scheme 1. On heating at 130 \({}^{\circ}\)C, the solid elemental sulfur melts into yellow liquid sulfur, therefore no additional solvent is needed in the inverse vulcanization synthesis process of poly(S-MVT)s. When heated over 159 \({}^{\circ}\)C, sulfur rings start to break, forming chain-like free radical monomers \(\bullet\)S\({}_{8}\bullet\), which inevitably result in a reversible reaction of S\({}_{8}\) ring-opening polymerization (ROP) into linear polysulfides with diradical chain ends, i.e., chain-like free radicals \(\bullet\)(S\({}_{8}\))\({}_{n}\bullet\) with varying n values (\(n>1\)). When the temperature reaches 185 \({}^{\circ}\)C, the sulfur chains are almost highly polymerized [25]. Owing to the existence of quantities of free radicals, the polymerization of vinyl monomers-MVT-can easily be initiated (Figure S1a). The sulfur diradicals can initiate the addition of vinyl double bonds of MVT, and they can also abstract vinyl hydrogen atoms from the MVT molecules to form vinyl radicals and sulfhydryl group. A vinyl radical then reacts with the sulfur diradical to form a C-S bond linked to a thiyl radical. After the rearrangement of radicals and then proton abstraction reaction, it is possible to form branched fragment and methyl group terminal (Figure S1a,b) [21]. These reactions occurred repeatedly to form a random poly(S-MVT) with branched fragments and methyl group terminals. Poly(S-MVT)s with MVT contents of 10%, 15%, 20%, 30%, 40%, 50% (mass percentage) were prepared. The color of the product turns from orange to red as the amount of MVT increases, and the color becomes darker and eventually becomes dark red (Figure S2). All the copolymers are soluble in organic solvents of chloroform, THF (Figure S3). Therefore, FTIR and liquid \({}^{1}\)H NMR were first used to investigate the chemical structure of poly(S-MVT). FTIR spectra of MVT and poly(S-MVT)s (Figure S4) indicated that the stretching vibration of C=C (1670 cm\({}^{-1}\)) and stretching (3086 cm\({}^{-1}\)) and out-of-plane bending vibrations (976 and 901 cm\({}^{-1}\)) of C-H arising from the vinyl group are absent in the spectrum of the Poly(S-MVT). Compared with MVT, poly(S-MVT) present new peaks, as clearly shown in Figure 1a. The peaks at 420 and 1055 cm\({}^{-1}\) can be assigned to S-S bond, and the peaks at 505, 673, and 935 cm\({}^{-1}\) may be assigned to the C\(-\)S bond between the vinyl group and sulfur chains. Moreover, a sharp peak appeared at 3437 cm\({}^{-1}\), which can be attributed to the N-H stretching mode from the protonated nitrogen atoms of thiazole ring [26]. These results provide evidence for the successful polymerization reaction of elemental sulfur and MVT. The \({}^{1}\)H-NMR spectra of all poly(S-MVT)s (Figure S5) clearly indicated the complete conversion of MVT through disappearance of the signals corresponding to vinylic proton signals at 5.2, 5.4, and 6.7 ppm, regardless of the content of MVT in raw materials. As shown in Figure 1b, new signals appeared in the range between 5 and 1.5 ppm and were attributed to protons of methane (Hc, Hc'), methylene (Hd, Hd'), and methyl (Ha') units from the structure that we proposed in Scheme 1. Thermogravimetric analysis (TGA) of poly(S-MVT)s showed first decomposition steps around 200 \({}^{\circ}\)C, which were very close to that of elemental sulfur [27; 28; 29], and can be ascribed to the volatilization of sulfur. The second steps around 350 \({}^{\circ}\)C were related to the weight loss of MVT (Figure S6). The dependence of the second step on the MVT content indicates that the feed ratio of MVT was completely conserved in the copolymers.