L M Gonçalves José, J Castanheira Edgar, P C Alves Sérgio, Baleizão Carlos, Farinha José Paulo
Centro de Química Estrutural and Department of Chemical Engineering, Instituto Superior Técnico, University of Lisbon, 1049-001 Lisboa, Portugal.
Polymers (Basel). 2020 Sep 23;12(10):2175. doi: 10.3390/polym12102175.
Stimuli-responsive polymer materials are used in smart nanocarriers to provide the stimuli-actuated mechanical and chemical changes that modulate cargo delivery. To take full advantage of the potential of stimuli-responsive polymers for controlled delivery applications, these have been grafted to the surface of mesoporous silica particles (MSNs), which are mechanically robust, have very large surface areas and available pore volumes, uniform and tunable pore sizes and a large diversity of surface functionalization options. Here, we explore the impact of different RAFT-based grafting strategies on the amount of a pH-responsive polymer incorporated in the shell of MSNs. Using a "grafting to" (gRAFT-) approach we studied the effect of polymer chain size on the amount of polymer in the shell. This was compared with the results obtained with a "grafting from" (gRAFT-) approach, which yield slightly better polymer incorporation values. These two traditional grafting methods yield relatively limited amounts of polymer incorporation, due to steric hindrance between free chains in "grafting to" and to termination reactions between growing chains in "grafting from." To increase the amount of polymer in the nanocarrier shell, we developed two strategies to improve the "grafting from" process. In the first, we added a cross-linking agent (gRAFT-) to limit the mobility of the growing polymer and thus decrease termination reactions at the MSN surface. On the second, we tested a hybrid grafting process (gRAFT-) where we added MSNs functionalized with chain transfer agent to the reaction media containing monomer and growing free polymer chains. Our results show that both modifications yield a significative increase in the amount of grafted polymer.
刺激响应性聚合物材料用于智能纳米载体，以提供刺激驱动的机械和化学变化来调节货物递送。为了充分利用刺激响应性聚合物在可控递送应用中的潜力，已将这些聚合物接枝到介孔二氧化硅颗粒（MSN）的表面，MSN机械强度高、具有非常大的表面积和可用孔体积、孔径均匀且可调，并且有多种表面功能化选择。在此，我们探讨了不同的基于可逆加成-断裂链转移（RAFT）的接枝策略对MSN壳层中掺入的pH响应性聚合物量的影响。使用“接枝到”（gRAFT-）方法，我们研究了聚合物链大小对壳层中聚合物量的影响。将其与“从接枝”（gRAFT-）方法获得的结果进行比较，后者产生的聚合物掺入值略好。由于“接枝到”中自由链之间的空间位阻以及“从接枝”中生长链之间的终止反应，这两种传统接枝方法产生的聚合物掺入量相对有限。为了增加纳米载体壳层中的聚合物量，我们开发了两种策略来改进“从接枝”过程。第一种是添加交联剂（gRAFT-）以限制生长聚合物的流动性，从而减少MSN表面的终止反应。第二种是测试一种混合接枝过程（gRAFT-），其中我们将用链转移剂功能化的MSN添加到含有单体和生长的自由聚合物链的反应介质中。我们的结果表明，这两种改性都使接枝聚合物的量显著增加。
