## 2 Results and Discussion  
### Effect of Various Experimental Parameters on RAFT Polymerization of DMAEMA  
#### 2.1.1 Polymerization of DMAEMA Using Dithio and Trithio Compounds as a Source of CTA  
A series of RAFT polymerizations of DMAEMA were performed under different conditions to investigate the influence of several experimental parameters such as CTA, CTA/initiator molar ratio, monomer/CTA molar ratio, and reaction time on the controlled character of the process. The RAFT polymerizations of DMAEMA with DBTTC, BDATC, MTTCD and CPTCD as RAFT agents and AIBN as initiator, respectively, were carried out. The conditions and results are summarized in Table 1. The GPC curves of the obtained prepolymers corresponding to Run 1, Run 3, Run 7, Run 9 were shown in Figure 1.  
In the RAFT process, one of the key factors for synthesizing well-defined polymers is the design of CTA, as the choice of the Z and R groups depends on the monomer [44]. When DMAEMA was polymerized in the presence of DBTTC, MTTCD and BDATC (Run 1-2, Run 7 and Run 3-6), the resultant PDMAEMA has a polydispersity index (PDI) \(>\)1.50 and 1.37\(\sim\)1.57, respectively. The reason for this phenomenon is probably that the balance of the reversible addition-fragmentation chain transfer is disturbed by an unapt match of monomer and CTA. However, in the presence of CPTCD (run 8-13), the polymerization showed a better control over the relative molecular mass and distribution. The polymer obtained was narrow in polydispersity index (\(<\)1.36) and the theoretical number average molecular weight \(M_{\text{n,th}}\) was in good agreement with \(M_{\text{n,GPC}}\). Run 9 and Run 13 were performed under same conditions except reaction time. When the reaction time of Run 13 was doubled, neither the molecular weight of polymer nor the conversion of DMAEMA were improved. This may be because the \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Run**} & \multirow{2}{*}{**CTA**} & **Time** & **Monomer/RAFT/** & **Conversion \({}^{\text{c}}\)** & \multirow{2}{*}{\(M_{\text{n}}\)\({}^{\text{*}}\) (GPC)} & \multirow{2}{*}{\(M_{\text{n}}\)\({}^{\text{b}}\) (Theoretical)} & \multirow{2}{*}{\(M\)\(\text{w}\)\(/\)\(M_{\text{n}}\) (PDI)} \\  & & **(h)** & **Initiator (M/R/I)** & **(\%)** & & \\ \hline
1 & DBTTC & 6 & 100:1:0.25 & 55.4 & 42,218 & 8998 & 2.20 \\
2 & DBTTC & 6 & 100:1:0.33 & 61.4 & 36,090 & 9903 & 2.41 \\
3 & BDATC & 6 & 100:1:0.25 & 31.3 & 15,894 & 5201 & 1.37 \\
4 & BDATC & 6 & 100:1:0.33 & 43.0 & 12,783 & 7032 & 1.42 \\
5 & BDATC & 6 & 200:1:0.25 & 20.8 & 42,472 & 6880 & 1.54 \\
6 & BDATC & 10 & 100:1:0.25 & 43.0 & 19,001 & 7308 & 1.57 \\
7 & MTTCD & 6 & 100:1:0.25 & 52.1 & 21,415 & 8544 & 1.81 \\
8 & CPTCD & 6 & 60:1:0.25 & 30.6 & 5230 & 3225 & 1.26 \\
9 & CPTCD & 6 & 100:1:0.25 & 45.5 & 8325 & 7484 & 1.27 \\
10 & CPTCD & 6 & 100:1:0.33 & 45.5 & 7879 & 7491 & 1.29 \\
11 & CPTCD & 6 & 200:1:0.25 & 25.17 & 9570 & 8250 & 1.32 \\
12 & CPTCD & 6 & 300:1:0.25 & 35.7 & 18,833 & 17,160 & 1.36 \\
13 & CPTCD & 12 & 100:1:0.25 & 47.1 & 8132 & 7740 & 1.30 \\ \hline \hline \end{tabular}  
* \(M_{\text{n}}\) value obtained by GPC; \({}^{\text{b}}\) computed by equation: \(M_{\text{n}}\)(th) = \(M_{\text{RAFT}}\) + n\(\cdot\)Conv\(\cdot\)\(M_{\text{DMAEMA}}\); \({}^{\text{c}}\) Conversion calculated based on the gravimetric method. Reaction temperature 70 \({}^{\text{c}}\)C, V\({}_{\text{toluene}}\) = 14.0 mL.  
\end{table} 
Table 1: RAFT polymerization results of DMAEMA in the presence of DBTTC, MTTCD, BDATC and CPTCD. living chains had lost activity and become dead chains. The polymerization is controlled at low ratios of DMAEMA:CTA, while at higher ratios, the polymerization is plagued by transferring to solvent. The contribution of transferring to solvent could have been attenuated by polymerizing at higher monomer concentration, but at such concentration, the increase of viscosity will result in a loss of control and broad PDIs [45].