在这项研究中,通过可逆加成-断裂链转移(RAFT)聚合制备的六臂星形聚(N-乙烯基己内酰胺)(PNVCL)聚合物使用己胺进行氨解反应。可以获得化学交联的凝胶或高度末端官能化的星形聚合物,这主要取决于在RAFT官能团的转化过程中使用的溶剂的类型。当在THF中进行氨解时,观察到溶液的粘度增加。相比之下,当反应在二氯甲烷中进行时,可以获得链端硫醇(PNVCL)6星形聚合物。此外,当纯化的(PNVCL-SH)6星形聚合物与THF接触时,凝胶化发生在短短几分钟内,随着粘度的明显增加,形成物理凝胶,在12小时后变成化学交联的凝胶。有趣的是,当纯化(PNVCL-SH)6个星形聚合物在蒸馏水中搅拌时,即使在高水溶液浓度(40mg/mL),粘度或凝胶化没有增加,并且没有观察到明显的凝胶。即使在水中搅拌4天后,通过动态光散射(DLS)分析流体动力学直径(Dh)也没有检测到可量化的变化。另一方面,如UV-Vis光谱分析和GPC所证明的,通过添加CS2然后添加苄基溴,(PNVCL-SH)6星形聚合物中的硫醇基团容易地转化为三硫代碳酸酯基团。修改后,(PNVCL)6星形聚合物在308nm处表现出三硫代碳酸酯基团的典型吸收带的强烈黄色。为了进一步证明高效的新型三硫代碳酸酯末端功能,用N-异丙基丙烯酰胺(NIPAM)成功地扩链PNVCL聚合物,形成六臂星形PNIPAM-b-PNVCL嵌段共聚物。此外,(PNVCL-SH)6星形聚合物中的末端硫醇末端官能度通过二硫键形成与1-半胱氨酸连接以进一步证明其反应性。ζ电位分析显示这些星形聚合物由于1-半胱氨酸末端官能化的pH响应行为。通过这种使用方法和适当选择溶剂,具有不同端基的各种对环境敏感的星形聚合物可以很容易地获得。
In this study, six-arm star-shaped poly(N-vinylcaprolactam) (PNVCL) polymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization were subjected to
aminolysis reaction using hexylamine. Chemically crosslinked gels or highly end-functionalized star polymers can be obtained depending mainly on the type of solvent used during the transformation of the RAFT functional group. An increase in the viscosity of the solution was observed when the
aminolysis was carried out in THF. In contrast, when the reaction was conducted in dichloromethane, chain-end thiol (PNVCL)6 star polymers could be obtained. Moreover, when purified (PNVCL-SH)6 star polymers are in contact with THF, the gelation occurs in just a few minutes, with an obvious increase in viscosity, to form physical gels that become chemically crosslinked gels after 12 h. Interestingly, when purified (PNVCL-SH)6 star polymers were stirred in distilled water, even at high aqueous solution concentration (40 mg/mL), there was no increase in the viscosity or gelation, and no evident gels were observed. The analysis of the hydrodynamic diameter (Dh) by dynamic light scattering (DLS) did not detect quantifiable change even after 4 days of stirring in water. On the other hand, the thiol groups in the (PNVCL-SH)6 star polymers were easily transformed into trithiocarbonate groups by addition of CS2 followed by benzyl bromide as demonstrated by UV-Vis spectroscopical analysis and GPC. After the modification, the (PNVCL)6 star polymers exhibit an intense yellow color typical of the absorption band of trithiocarbonate group at 308 nm. To further demonstrate the highly effective new trithiocarbonate end-functionality, the PNVCL polymers were successfully chain extended with N-isopropylacrylamide (NIPAM) to form six-arm star-shaped PNIPAM-b-PNVCL block copolymers. Moreover, the terminal thiol end-functionality in the (PNVCL-SH)6 star polymers was linked via disulfide bond formation to l-cysteine to further demonstrate its reactivity. Zeta potential analysis shows the pH-responsive behavior of these star polymers due to l-cysteine end-functionalization. By this using methodology and properly selecting the solvent, various environment-sensitive star polymers with different end-groups could be easily accessible.