Remarkable sol–gel transition of PNIPAm-based nanogels via large steric hindrance of side-chains,Materials Horizons

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Remarkable sol–gel transition of PNIPAm-based nanogels via large steric hindrance of side-chains
Materials Horizons ( IF 12.2 ) Pub Date : 2023-07-18 , DOI: 10.1039/d3mh00892d
Xiaoxiao Li _{1,

2} , Xueting Li _{1,

3,

4} , Tingting Xia ₁ , Wei Chen ₁ , Kenneth J Shea ₅ , Xihua Lu _{1,

3,

4}

Affiliation

While the block/graft/branched structures are widely studied to favor the reversible physical gelation, there are no reports regarding the steric hindrance-induced sol–gel transition of PNIPAm-based nanogels above their phase transition temperature (T_p). Generally, the introduction of hydrophobic components into poly (N-isopropylacrylamide) (PNIPAm)-based nanogels only led to collapse and lower viscosity instead of the sol–gel transition upon heating above the T_p. Herein, the results of temperature-variable ¹HNMR and FTIR confirm that the introduction of hydrophobic N-tert-butylacrylamide (TBA) with the large steric hindrance of side groups of N-tert-butyl to form NIPAm/TBA copolymer nanogels can dramatically slow down the dehydration of all the hydrophobic alkyl groups, thus resulting in the formation of thermally induced sol–gel transition above the T_p. Furthermore, the N-acrylamido-L-phenylalanine (APhe) monomer composed of a strongly water absorbing carboxyl group and a phenyl group with larger steric hindrance is studied to form P(NIPAm/TBA/APhe) terpolymer nanogels which can self-assemble into colorful colloidal crystals. Surprisingly, owing to the synergistic effect between the water absorbing carboxyl group and the steric hindrance group on the same side group, these colloidal crystals can achieve sol–gel transition above T_p, forming a physically crosslinked colorful hydrogel. This work is expected to greatly advance the design, synthesis, and application of the sol–gel transition of PNIPAm-based nanogel systems.

中文翻译：

基于 PNIPAm 的纳米凝胶通过侧链的大空间位阻实现显着的溶胶-凝胶转变

虽然嵌段/接枝/支化结构被广泛研究以有利于可逆物理凝胶化，但尚无关于基于 PNIPAm 的纳米凝胶在相变温度 (T p ) 以上时空间位阻诱导的溶胶-凝胶转变的_报道。一般来说，在聚（ N-异丙基丙烯酰胺）（PNIPAm）基纳米凝胶中引入疏水性组分只会导致塌陷和粘度降低，而不是在加热到T _p以上时导致溶胶-凝胶转变。在此，变温¹ HNMR 和 FTIR 的结果证实，引入具有N-叔丁基侧基的大空间位阻的疏水性N-叔丁基丙烯酰胺（TBA）形成 NIPAm/TBA 共聚物纳米凝胶可以显着减缓降低所有疏水性烷基的脱水，从而导致在T _p以上形成热诱导溶胶-凝胶转变。此外，研究了由强吸水性羧基和空间位阻较大的苯基组成的N-丙烯酰胺-L-苯丙氨酸（APhe）单体形成P（NIPAm/TBA/APhe）三元共聚物纳米凝胶，该纳米凝胶可以自组装成彩色胶体晶体。令人惊讶的是，由于吸水羧基和同一侧基上的空间位阻基团之间的协同作用，这些胶体晶体可以在T _p以上实现溶胶-凝胶转变，形成物理交联的彩色水凝胶。这项工作有望极大地推进基于 PNIPAm 的纳米凝胶系统的溶胶-凝胶转变的设计、合成和应用。

更新日期：2023-07-18

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