【作者】 吴焘；

【导师】 刘世勇；

【作者基本信息】 中国科学技术大学 ， 高分子化学与物理， 2011， 博士

【摘要】 聚合物/无机杂化纳米粒子兼具聚合物和无机材料两者的性能,在过去的几十年中广受关注。在这一领域,响应性聚合物/无机杂化纳米粒子的制备及其应用引起越来越多的研究兴趣。响应性聚合物/无机杂化纳米粒子因其外部环境响应性可以作为智能材料应用于催化、传感器、药物传输、光电器件等领域。这篇论文利用表面引发原子转移自由基聚合（ATRP）制备了温敏性PNIPAM接枝的SiO₂杂化纳米粒子,并以此为基础研究了PNIPAM刷在纳米粒子表面的相转变行为;制备了具有温度/光响应的多色荧光杂化纳米粒子、温敏性聚合物纳米胶囊及金属纳米粒子复合胶囊;利用温敏性杂化纳米粒子作为模板进行Au纳米粒子的自组装。具体来说,本论文的工作包括以下几个方面:1.利用表面引发ATRP聚合NIPAM,在引发剂功能化的SiO₂纳米粒子表面接枝上温敏性PNIPAM刷。在聚合过程中观测到的线性动力学过程、数均分子量随着单体转化率的线性增长以及最终得到PNIPAM链窄的分子量分布说明表面引发ATRP聚合反应具有很好的可控性。光散射结果表明加热过程中杂化纳米粒子表面的PNIPAM刷有两阶相转变行为,其内层链段开始塌缩的温度低于30 oC。大于30 oC时,外层链段开始塌缩。2.通过连续的表面引发ATRP聚合制备了P（NIPAM-co-NBDAM） -b-P（NIPAM-co-SPMA）接枝的杂化SiO₂荧光纳米粒子。PNIPAM刷的内外层分别标记上荧光共振能量转移（FRET）给体分子NBDAE和FRET受体分子SPMA。紫外照射杂化SiO₂纳米粒子的水分散液后,PNIPAM刷外层中SPMA分子从SP形式转变至MC形式,引起NBDAE和SPMA分子间发生FRET过程。通过调节体系的温度可引起P（NIPAM-co-NBDAM） -b-P（NIPAM-co-SPMA）刷的溶胀/塌缩,改变聚合物刷中给体和受体分子间的相对距离,从而调整FRET效率。利用SPMA与NBDAE的荧光强度比值随温度的变化,杂化纳米粒子可以做为宽温度范围内的荧光温度计。当杂化纳米粒子的分散液再次用可见光照射后,SPMA分子从MC形式恢复到非荧光的SP形式,导致FRET过程的终止。制得的杂化SiO₂纳米粒子的水分散液可以发出多色荧光,其荧光可以通过紫外/可见光/温度这些因素合适的组合进行调控。3.利用表面引发ATRP在SiO₂纳米粒子表面引发聚合NIPAM和3-叠氮丙基丙烯酰胺（AzPAM）单体。然后利用点击化学反应将聚合物层交联,腐蚀掉SiO₂核后制得壳层厚度可控的PNIPAM纳米胶囊。壳交联的杂化SiO₂纳米粒子可以作为基体通过原位还原反应负载Ag纳米粒子,去除SiO₂核后可制备负载Ag纳米粒子的PNIPAM杂化纳米胶囊。得到的PNIPAM纳米胶囊和负载Ag纳米粒子的PNIPAM杂化纳米胶囊可以通过温度的调节实现可逆的溶胀/塌缩。对于负载Ag纳米粒子的PNIPAM杂化纳米胶囊,通过PNIPAM壳层的溶胀/塌缩过程,可以调整Ag纳米粒子在交联PNIPAM壳层中的分布。4.通过表面引发ATRP聚合制备了PNIPAM刷接枝的杂化SiO₂纳米粒子。PNIPAM链端的卤素基团用叠氮基团取代后,通过N-炔丙基硫辛酰胺与叠氮基团的点击化学反应高效制备了端基为二硫杂环戊烷的PNIPAM接枝的SiO₂纳米粒子。用其作为模板,在表面PNIPAM层上进行柠檬酸钠稳定的Au纳米粒子的自组装。组装体的紫外-可见光谱随温度的变化结果表明PNIPAM刷的相转变过程可以用来调控组装体中Au纳米粒子之间的空间距离。更多还原

【Abstract】 Organic/inorganic hybrid nanoparticles have attracted ever increasing attention in the past decade due to their fascinating optical, electronic, magnetic, and catalytic properties. Recent progress in this area involves the preparation of hybrid nanoparticles coated with stimuli-responsive polymer brushes, which are attractive building blocks for the design and fabrication of smart nanostructured devices. In this dissertation, The fabrication of poly(N-isopropylacrylamide) (PNIPAM) grafted hybrid silica nanoparticles via surface initiated living polymerization and the thermal phase transition behavior of PNIPAM brushes at the silica surface were investigated in detail. On basis of the thermoresponsive PNIPAM grafted silica nanoparticles, we prepared thermoresponsive/photo-switchable fluorescent hybrid silica nanoparticles and thermoresponsive nanocapsules. The thermoresponsive PNIPAM grafted silica nanoparticles can also serve as templates for the self-assembly of Au nanoparticles.1. This section reports on the fabrication of hybrid silica nanoparticles densely grafted with thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) brushes and their thermal phase transition behavior. Surface-initiated atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAM) was conducted in 2-propanol at ambient temperature using CuCl/CuCl2/Me6TREN as the catalytic system, starting from the surface of silica nanoparticles derivatized with ATRP initiators. The surface-initiated ATRP can be conducted in a well-controlled manner, as revealed by the linear kinetic plot, linear evolution of number-average molecular weights (Mn) versus monomer conversions, and the relatively narrow molecular weight distributions of the grafted PNIPAM chains. Laser light scattering (LLS) and optical transmittance were then employed to study the thermal phase transitions of PNIPAM brushes at the surface of silica nanoparticles. Both the intensity-average hydrodynamic radius, <Rh>, and average radius of gyration, <Rg>, exhibit a two-stage decrease upon heating over the broad temperature range of 20–37 oC. The first phase transition takes place in the temperature range of 20–30 oC, which can be tentatively ascribed to the n-cluster-induced collapse of the inner region of PNIPAM brushes close to the silica core; the second phase transition occurs above 30 oC, which can be ascribed to the outer region of PNIPAM brushes, possessing much lower chain density compared to that of the inner part.2. This section reports on the fabrication of hybrid silica nanoparticles densely grafted with thermoresponsive PNIPAM brushes with inner and outer layers selectively labeled with fluorescence resonance energy transfer (FRET) donors, 4-(2-acryloyloxyethylamino)-7-nitro-2,1,3-benzoxadiazole (NBDAE), and photo-switchable acceptors, 1’-(2-methacryloxyethyl)-3’,3’-dimethyl-6-nitro- spiro (2H-1-benzopyran-2,2’-indoline) (SPMA), respectively, via surface-initiated sequential ATRP. P(NIPAM-co-NBDAE)-b-P(NIPAM-co- SPMA) brushes at the surface of silica core exhibit collapse in the broad temperature range of 20-37 oC. UV irradiation of the aqueous dispersion of hybrid silica nanoparticles induces the transformation of SPMA moieties in the outer layer of polymer brushes from non-fluorescent spiropyran (SP) form to fluorescent merocyanine (MC) form, leading to occurrence of FRET process between NBDAE and SPMA residues. Most importantly, the FRET efficiency can be facilely tuned via thermo-induced collapse/swelling of P(NIPAM-co-NBDAE)-b-P(NIPAM-co-SPMA) brushes by changing the relative distance between donor and acceptor species located within the inner and outer layer of polymer brushes, respectively. Thus, hybrid silica nanoparticles coated with P(NIPAM-co-NBDAE)-b-P(NIPAM-co-SPMA) brushes can serve as a sensitive ratiometric fluorescent thermometer. On the other hand, when the hybrid nanoparticle dispersion was irradiated with visible light again after UV irradiation, the MC form of SPMA moieties reverts back to the non-fluorescent SP form, leading to the turn-off of FRET process. Overall, aqueous dispersion of this novel type of hybrid silica nanoparticles is capable of emitting multicolor fluorescence, which can be facilely tuned by UV irradiation, visible light, and temperatures, or a proper combination of them.3. This section report on the fabrication of thermoresponsive cross-linked hollow PNIPAM nanocapsules and silver nanoparticle-embedded hybrid PNIPAM nanocapsules with controlled shell thickness via the combination of surface-initiated ATRP and“click”cross-linking. Starting from initiator- functionalized silica nanoparticles, the surface-initiated ATRP of N-isopropylacrylamide (NIPAM) and 3-azidopropylacrylamide (AzPAM) afforded hybrid silica nanoparticles surface coated with P(NIPAM-co-AzPAM) brushes. Hybrid PNIPAM nanocapsules were then fabricated by the“click” cross-linking of PNIPAM shell layer with a trifunctional molecule, 1,1,1-tris(4-(2-propynyloxy)phenyl)ethane, followed by the subsequent removal of silica cores via HF etching. Shell cross-linked hybrid silica nanoparticles can further serve as templates for the in-situ preparation of silver nanoparticles within the cross-linked PNIPAM layer. After HF etching, silver nanoparticle-embedded hybrid PNIPAM nanocapsules were obtained. Due to the thermoresponsiveness of PNIPAM, cross-linked PNIPAM nanocapsules and silver nanoparticle-embedded hybrid PNIPAM nanocapsules exhibit thermo-induced collapse/swelling transitions. In the latter case, the spatial distribution of Ag nanoparticles within the hybrid PNIPAM nanocapsules can be facilely modulated by temperature variations, as revealed by the thermo-induced red shift of surface plasmon absorption band. Dynamic laser light scattering (LLS) measurements revealed that PNIPAM nanocapsules and Ag nanoparticle-embedded hybrid PNIPAM nanocapsules exhibit more prominent thermo-induced dimensional changes, as compared to shell cross-linked hybrid silica/PNIPAM nanoparticles loaded with or without Ag nanoparticles, respectively.4. This section reports on the fabrication of thermoresponsive hybrid silica nanospheres anchored with gold nanoparticles of tunable spatial distribution. Starting from initiator-functionalized silica nanoparticles, surface-initiated ATRP of NIPAM afforded hybrid silica nanoparticles coated with PNIPAM brushes. The halogen end groups of grafted PNIPAM chains were substituted by azido groups and hybrid silica nanoparticles coated with 1,2-dithiolane end-capped PNIPAM brushes were then obtained via“click”reaction of azido groups with 1,2-dithiolane-3-pentanoic acid-N-propargylamide. The obtained 1,2-dithiolane functionalized hybrid silica nanoparticles were employed as templates for the self-assembly of citrate-capped gold nanopartilces. Laser light scattering (LLS) measurements revealed that PNIPAM brushes at the surface of silica exhibit reversibly thermo-induced collapse/swelling transitions and this phase transition behavior was not affected after the attachment of gold nanoparticles. Due to the thermoresponsiveness of PNIPAM brushes, the spatial distances between gold nanoparticles attached at the surface of PNIAPM brushes could be facilely modulated by temperature variations, as revealed by the thermo-induced red shift of surface plasmon absorption band.更多还原