Figg C Adrian, Simula Alexandre, Gebre Kalkidan A, Tucker Bryan S, Haddleton David M, Sumerlin Brent S
George & Josephine Butler Polymer Research Laboratory , Center for Macromolecular Science & Engineering , Department of Chemistry , University of Florida , PO Box 117200 , Gainesville , FL 32611-7200 , USA . Email:
Department of Chemistry , University of Warwick , Coventry CV4 7AL , UK.
Chem Sci. 2015 Feb 1;6(2):1230-1236. doi: 10.1039/c4sc03334e. Epub 2014 Nov 14.
Polymerization-induced self-assembly (PISA) is a versatile technique to achieve a wide range of polymeric nanoparticle morphologies. Most previous examples of self-assembled soft nanoparticle synthesis by PISA rely on a growing solvophobic polymer block that leads to changes in nanoparticle architecture during polymerization in a selective solvent. However, synthesis of block copolymers with a growing stimuli-responsive block to form various nanoparticle shapes has yet to be reported. This new concept using thermoresponsive polymers is termed polymerization-induced thermal self-assembly (PITSA). A reversible addition-fragmentation chain transfer (RAFT) polymerization of -isopropylacrylamide from a hydrophilic chain transfer agent composed of ,-dimethylacrylamide and acrylic acid was carried out in water above the known lower critical solution temperature (LCST) of poly(-isopropylacrylamide) (PNIPAm). After reaching a certain chain length, the growing PNIPAm self-assembled, as induced by the LCST, into block copolymer aggregates within which dispersion polymerization continued. To characterize the nanoparticles at ambient temperatures without their dissolution, the particles were crosslinked immediately following polymerization at elevated temperatures the reaction of the acid groups with a diamine in the presence of a carbodiimide. Size exclusion chromatography was used to evaluate the unimer molecular weight distributions and reaction kinetics. Dynamic light scattering and transmission electron microscopy provided insight into the size and morphologies of the nanoparticles. The resulting block copolymers formed polymeric nanoparticles with a range of morphologies (, micelles, worms, and vesicles), which were a function of the PNIPAm block length.
聚合诱导自组装（PISA）是一种实现多种聚合物纳米颗粒形态的通用技术。以前通过PISA进行自组装软纳米颗粒合成的大多数实例都依赖于增长的疏溶剂聚合物嵌段，这会导致在选择性溶剂中聚合过程中纳米颗粒结构发生变化。然而，利用增长的刺激响应性嵌段来形成各种纳米颗粒形状的嵌段共聚物的合成尚未见报道。这种使用热响应性聚合物的新概念被称为聚合诱导热自组装（PITSA）。在高于聚（N-异丙基丙烯酰胺）（PNIPAm）已知的低临界溶液温度（LCST）的水中，由N，N-二甲基丙烯酰胺和丙烯酸组成的亲水性链转移剂引发N-异丙基丙烯酰胺的可逆加成-断裂链转移（RAFT）聚合。达到一定链长后，增长的PNIPAm在LCST的诱导下自组装成嵌段共聚物聚集体，在其中继续进行分散聚合。为了在环境温度下表征纳米颗粒而不使其溶解，在高温下聚合后立即将颗粒交联——在碳二亚胺存在下酸基团与二胺的反应。尺寸排阻色谱法用于评估单体分子量分布和反应动力学。动态光散射和透射电子显微镜提供了有关纳米颗粒尺寸和形态的信息。所得嵌段共聚物形成了具有一系列形态（例如，胶束、蠕虫和囊泡）的聚合物纳米颗粒，这些形态是PNIPAm嵌段长度的函数。
