Synthesizing Ordered Network Structures Using Linear Polymers: A Study on Optimal Synthetic Conditions

We have successfully synthesized linear bifunctional PNIPA polymers with uniform molecular weight using living radical polymerization. Our objective was to construct a polymer network with a consistent and an ordered structure. To achieve this, we prepared a solution with a concentration higher than the overlap concentration (C*) of the linear PNIPA polymers with uniform molecular weight. Next, we introduced a cross-linking agent to bond the polymer ends together. Under our experimental conditions using this linear PNIPA polymer, we prepared polymer networks at different concentrations: 1.2C*, 1.5C*, and 2.0C*. Notably, the polymer network formed at 1.2C*, which is slightly higher than the overlap concentration, exhibited a significantly more ordered structure compared to those prepared at 1.5C* or 2.0C*. This observation was substantiated by the analysis of the polymer network degradation products through SEC measurements and the SAXS results of the polymer network. In the case of PNIPA star-shaped polymers, it has been found that a uniform network structure can be obtained by preparing the polymer network at a concentration of about 2.0C*, which is much higher than C*. The difference in excluded volume between linear polymers and star polymers appears to play a pivotal role in favoring the formation of a more ordered network structure when the concentration reaches the overlap concentration threshold. In summary, our study showcases the successful synthesis of linear bifunctional PNIPA polymers with uniform molecular weight through living radical polymerization. Moreover, we demonstrate that by carefully controlling the concentration during polymer network synthesis, it is possible to achieve a relatively ordered structure, especially when the concentration slightly exceeds the overlap concentration threshold. The insights gained from our findings contribute to a better understanding of polymer network formation and have implications for the design and fabrication of advanced materials.