Solid-State NMR for Polymeric Nanoparticles

这项新工作的主要目标是将固体核磁共振应用于三种类型的聚合物纳米结构的表征：(1)超支化聚碳酸酯，(2)树枝状聚(苄基醚)S，(3)具有核壳结构的纳米尺度的交联型两亲分子。用于解决所有这三个问题的主要技术将是旋转回波双共振(REDOR)检测的稳定同位素标记。这一策略涉及两个或多个稳定同位素标记(有时是一个标记和自然丰度的C-13)，它们被结合在感兴趣的区域或附近，该区域可能是纳米颗粒的界面，或者是核心或表面位置。然后，雷多尔探测到了自旋的异核对之间的偶极耦合。这种耦合直接关系到是否没有或抑制了运动的平均效应。第一个研究目标是用C-13/H-2 REDOR比较线性苯酚聚碳酸酯和相同化学组成的超支化聚碳酸酯中链的填充情况。初步结果表明，在线性系统的链填充中有相当程度的局部有序性。Redor将确定此订单在50%分支存在的情况下持续存在的程度。第二个研究目标是使用C-13/F-19 REDOR来确定链端在树枝状大分子内部结构中的堆积，并确定链端在树枝状大分子之间的互穿程度。稳定同位素标记的树枝状大分子将被嵌入到由其他树枝状大分子或聚苯乙烯组成的基质中，后者形成混合界面。第三个研究目标是将C-12、N-15、H-2和F-19以不同的组合用于两亲性核-壳纳米结构的核、界面和壳，以便多频红外线可以识别界面、交联键和表面位置的接近。这些近似性将被用来生成结构模型，帮助解释化学、生化和机械性质，并为合成更有效的材料提供策略建议。%树枝状大分子和超支化聚合物因其低熔体粘度、高溶解性和许多表面活性官能团的可能性而受到重视。它们可用作包覆剂、超薄膜涂层以及聚合物复合材料中的纳米填充颗粒。单个分子形成离散的纳米结构，分子间几乎没有纠缠，并且具有更稳定的机械纳米颗粒的许多其他特性。由嵌段共聚物形成的交联胶束形成的两亲纳米粒子是真正的纳米粒子，其社会重要性的应用范围广泛，从环境清理到生物医学药物输送，再到支持组织生长的功能化表面。这些纳米级聚合物的应用是否真的会成功，将取决于合成化学家在原子水平上控制结构的能力。这种结构在很大程度上取决于聚合物链在纳米颗粒内部和表面的堆积方式。固体核磁共振对链堆积、交联和官能团的空间分布的表征已经足够详细，因此定向合成定制的纳米结构将是可行的。

The primary goal of the proposed new work is the application of solid-state NMR to the characterization of three types of polymeric nanostructures: (1) hyperbranched polycarbonates, (2) dendritic poly(benzyl ether)s, and (3) cross-linked amphiphiles of nanoscale dimensions with a core-shell morphology. The principal technique to be used to solve all three problems will be stable-isotope labeling with rotational-echo double-resonance (REDOR) detection. This strategy involves two or more stable-isotope labels ( or sometimes one label and C-13 at natural abundance) that are incorporated in or near the region of interest, which might be an interface, or a core or surface site of the nanoparticle. REDOR then detects the dipolar coupling between heteronuclear pairs of spins. The coupling is directly related to an inferred if the averaging effects of motion are absent or suppressed. The first research goal is to use C-13/H-2 REDOR to compare the chain packing in linear phenol-polycarbonate with that in hyperbranched polycarbonate of identical chemical composition. Preliminary results indicate a considerable degree of local order in the chain packing of the linear system. REDOR will establish the extent to which this order persists in the presence of 50% branching. The second research goal is to use C-13/F-19 REDOR to establish the packing of chain ends within the internal architecture of a dendrimer, and to determine the extent of interpenetration of chain ends between dendrimers. The stable-isotope labeled dendrimers will be imbedded within a matrix composed either of other dendrimers or of polystyrene, the latter to form a blend interface. The third research goal is to use C-12, N-15, H-2 and F-19 labels in various combinations for the core, interface, and shell of amphiphilic core-shell nanostructures so that multi-frequency REDOR can identify proximities at interfacial, cross-link, and surface sites. These proximities will be used to generate structural models that help interpret chemical, biochemical, and mechanical properties, and to suggest strategies for the synthesis of more effective materials.%%%Dendrimers and hyperbranched polymers are valued for their low melt viscosity, high solubility, and the possibility of many surface-active functional groups. They can be used as encapsulants, ultra-thin film coatings, and as nanoscale filler particles in polymeric composites. Individual molecules form discrete nanostructures with few intermolecular entanglements and many of the other properties of more mechanically stable nanoparticles. Nanostructured amphiphiles mad by cross-linking micelles formed from from block copolymers are true nanoparticles whose proposed applications of societal importance are vast ranging form environmental clean-up, to biomedical drug delivery, to functionalized surfaces to support tissue growth. Whether any of these nanoscale polymer applications will actually succeed will depend on the ability of synthetic chemists to control structure at the atomic level. This structure depends largely on how polymer chains pack within and on the nanoparticle. The characterization of chain packing, cross-linking, and the spatial distribution of functional groups by solid-state NMR is sufficiently detailed that the directed synthesis of tailored nanostructures will be practical.