## 3 Results  
### Nuclear Magnetic Resonance  
Propylene-_co_-styrene monomer copolymers were synthesized via the Friedel-Crafts alkylation reaction between chlorinated polypropylene and substituted benzene using Lewis acid as the catalyst. As shown in Figure 1, the chain structure of chlorinated polypropylene is well characterized [12], but fairly complicated, consisting of chain units with isolated chlorine atoms (83.4%) including those at the tertiary (65.9%) and secondary (17.5%) carbon, neighboring chlorine atoms (6.4%), and small amounts of chlorine methane (10.1%). During the Friedel-Crafts alkylation reaction, the chlorine at different carbons causes the formation of different carbocation and gives rise to different chain units incorporated in the PP chain of the resulting copolymer when further reacted with substituted benzene [13; 14]. Since the Friedel-Crafts alkylation reaction undergoes a carbocation mechanism, the carbocation intermediate also causes alternative C-C bond cleavage besides reacting with the substituted benzene, resulting in a decrease in the molecular weight of the copolymer. As the first priority given its structural similarity to the styrene unit in PS, benzene used as an alkylation reagent in the Friedel-Crafts reaction in our first trial proved unsuccessful due to its too low molecular weight, which was less than 10,000 g/mol of the resulting copolymer (P0), caused by severe cationic chain scission. Henceforth, substituted benzene with an electron donating group, i.e., methyl, ethyl, and methoxyl groups, was used instead of benzene in the Friedel-Crafts alkylation reaction, and the results showed that the electron-donating substitute could effectively suppress carbocation chain scission as the molecular weight of the copolymer increased with increasing electron-donating potentiality in the order of methoxyl > methyl > ethyl (Table 1). By using the Friedel-Crafts alkylation reaction, poly(propylene-_co_-methyl-styrene), poly(propylene-_co_-ethyl styrene), and poly(propylene-_co_-methoxyl styrene) were synthesized accompanied by molecular weight decline due to the carbocation chain scission side reaction. As shown in Figure 2, the reaction occurred predominately on the para-position of substituted benzene, most likely due to more steric hindrance on that of the ortho-position, and this was the reason that there was no multi-alkylation on the same benzene ring observed in Figure 2, which could cause cross-linking of the polymer chain. The content of the remnant chlorine atom on the polymer chain is too low to be visible in the NMR spectra, and the trace could only be detected by ICP analysis (Table 1), suggesting that the chlorine atoms were almost consumed by the Friedel-Crafts alkylation and chain scission reactions (as shown in Scheme 1) [15]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Styrenic Unit** & **Aromatic Ring/100 C\({}^{\text{a}}\)** & \(M_{\text{w}}\)\({}^{\text{b}}\) (10\({}^{\text{d}}\))** & **Cl Content\({}^{\text{c}}\) (mg/g)** & \(T_{\text{m}}\)\({}^{\text{d}}\) (\({}^{\text{c}}\)**C)** \\ \hline CPP & - & - & 9.75 & 101 & 141.5 \\ P0 & benzene & 0.7 & 0.89 & 2.6 & 140.3 \\ P1 & methylbenzene & 3.5 & 4.50 & 1.6 & 144.4 \\ P2 & ethylbenzene & 3.6 & 3.89 & 2.2 & 144.7 \\ P3 & methoxyl-benzene & 4.0 & 7.31 & 1.3 & 151.7 \\ \hline \hline \end{tabular}  
* Calculated by \({}^{1}\)H-NMR, \({}^{\text{b}}\) determined by GPC with PS as the standard, \({}^{\text{c}}\) determined by ICP, \({}^{\text{d}}\) determined by DSC.  
\end{table} 
Table 1: Synthesis of the propylene-_co_-styrene monomer copolymers. CPP, chlorinated PP. Figure 1: \({}^{1}\)H-NMR spectrum of chlorinated polypropylene. Due to the fair complexity of the chain structure of CPP, carbocation rearrangement, and chain scission, the precise chain structure of the resulting copolymers cannot be fully defined yet.