## 3 Results and Discussion  
### RAFT Polymerization Kinetics  
It is well known that the chain transfer agent CDSPA provides excellent control over the RAFT polymerization of methacrylate monomers [35]. To verify the applicability of the new functional monomers, POSS-MA and TPS-SS, a polymerization kinetics study, was conducted. The Ln ([M]\({}_{0}\)/[M]\({}_{t}\)) versus time (t) plots for PTBM-0, PTBM-4 and PBM are displayed in Figure 1A. It can be seen that Ln ([M]\({}_{0}\)/[M]\({}_{t}\)) exhibited a linear relationship with the polymerization time, and the monomer conversion increased with increasing polymerization time. All plots were in accordance with first-order kinetics. The rate constants (k\({}_{\text{p}}\)) were as follows: k\({}_{\text{PTBM-0}}\) = 0.094 h\({}^{-1}\), k\({}_{\text{PTBM-4}}\) = 0.050 h\({}^{-1}\), and k\({}_{\text{PBM}}\) = 0.068 h\({}^{-1}\). A comparison between PTBM-0 and PTBM-4 revealed that the incorporation of POSS-based monomers led to a reduction in the overall polymerization rate. This is presumably because of the bulky spatial hindrance of the POSS unit's structure, leading to a decreased collision probability among free radicals and a subsequent reduction in the conversion rate between dormant and active chains. A comparison between PTBM-4 and PBM showed that the addition of TPS-SS units also resulted in a decrease in the polymerization rate, possibly due to the suppression of free radical propagation by the ion pairs in TPS-SS units.  
The plots of the \(M_{\rm n}\) and PDI of copolymers PTBM-0, PTBM-4 and PBM with conversions were shown in the Figure 1B,D, respectively. As the polymerization progresses, the \(M_{\rm n}\) of all groups increased linearly with conversions, and the PDI gradually decreased with the increasing conversions, ultimately falling within the range of 1.2-1.3. Meanwhile, the GPC curves (Figure 2A-C) shift to the left in a regular manner while maintaining a uniform distribution of symmetric peaks, indicating that the polymerization process was well controlled. The practical \(M_{\rm n}\) (GPC) value of the copolymers exhibited some negative deviations from the theoretical values, which may be due to chain transfer and termination of polymerization reactions involving active chains with solvents or other molecules [36]. On the other hand, the coupling termination of propagating radicals resulted in the formation of low molecular weight polymers. As shown in Figure 1B,D, it can be observed that PTBM-4 and PBM, which were synthesized from POSS-based monomer and others, possessed \(M_{\rm n}\) (GPC) values closer to the theoretical molecular weight and narrower molecular weight distributions, indicating that the spatial hindrance of the POSS structure can reduce the coupling termination of propagating radicals. The use of polystyrene as a GPC standard calibration sample may also contribute to deviations from theoretical values [37]. Overall, all groups exhibited the characteristics of controlled radical polymerization, demonstrating the feasibility of preparing photolithography resist polymers through controlled polymerization.  
Figure 1: (**A**) Polymerization kinetic curves of PTBM-0, PTBM-4 and PBM. Dependence of the molecular weight and polydispersity (\(M_{\rm w}/M_{\rm n}\)) on the conversion for (**B**) PTBM-0, (**C**) PTBM-4, and (**D**) PBM.