*3.1. Synthesis of PVC-g-4VP/4VPPS*

Once the 12 and 23% 4VP grafts were obtained using the conditions reported in Duarte-Peña [33], we proceeded to functionalize them to form the PVC-*g*-4VP/4VPPS. One of the ways to obtain zwitterionic polymers is via the formation of the zwitterion after polymerization, that is, cationic or anionic polymers are functionalized with oppositely charged groups. This was the method used in the case of PVC-*g*-4VP/4VPPS materials, where 4VP was initially grafted onto the PVC matrix and later functionalized with PS to form the zwitterionic polymer 4-vinylpyridine propylsulfobetaine (4VPPS), resulting in a graft composed of 4VP/4VPPS. The process for functionalization consisted of a ringopening alkylation reaction (Figure 1) [25].

**Figure 1.** Reaction scheme for PVC-g-4VP/4VPSS.

Three factors were analyzed on the samples with 12 and 23% of 4VP to obtain the best reaction conditions: PS concentration, reaction time, and temperature. For this process, the reaction time was limited by the stability of the polymeric matrix in DMF, so the maximum reaction time used was 75 min. Figure 2A,B shows the behavior of the reaction yield when increasing the concentration of PS for samples with 12 and 23% of 4VP, respectively. In both cases, the reaction yield increased with a higher concentration; samples with 12% of 4VP required 0.35 M PS to reach 80 % of reaction yield, whereas the samples with 23% of 4VP reached these yields at a concentration of 0.8 and 1 M under the conditions used. Figure 2C,D show that the reaction yield increases with increasing reaction time, reaching

yield values of 80 to 95% between 60 and 75 min for samples with 23% of 4VP and close to 100% at 20 min for 12% of 4VP.

**Figure 2.** Effect of the reaction conditions in the yield percentage. (**A**) PS concentration effect for PVC-g-4VP(12%), conditions: 70 ◦C and 10 min, (**B**) PS concentration effect for PVC-g-4VP(23%), conditions: 70 ◦C and 75 min; (**C**) Time reaction effect for PVC-g-4VP(12%), conditions: 70 ◦C and 0.35 M PS; (**D**) Time reaction effect for PVC-g-4VP(23%), conditions: 70 ◦C and 0.8 M PS; and (**E**) Temperature effect, conditions for PVC-g-4VP(12%): 0.35 M PS and 10 min, and conditions for PVC-g-4VP(23%): 0.8 M PS and 75 min. Reported: mean ± standard error of the mean, *n* = 3.

On the other hand, the temperature played an important role during the reaction because this is an endothermic process that requires energy to overcome the activation barrier and shift the equilibrium towards the formation of the product. Three temperatures were tested: 50, 60, and 70 ◦C. Figure 2E shows the yields as a function of temperature for the two samples, the best yield for both was found at 70 ◦C.

Table 1 shows four graft ranges that were obtained from this synthesis. The material with grafts of 13% 4VP and 32% 4VPPS was discarded for characterization because there was a significant deformation of the catheter.

**Table 1.** Materials synthesized.

