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首页> 外文学位 >Dynamic-covalent star nanostructures prepared from functional block copolymers obtained by reversible addition-fragmentation chain transfer (RAFT) polymerization.
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Dynamic-covalent star nanostructures prepared from functional block copolymers obtained by reversible addition-fragmentation chain transfer (RAFT) polymerization.

机译：由通过可逆加成-断裂链转移（RAFT）聚合获得的功能嵌段共聚物制备的动态共价星形纳米结构。

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摘要

Traditionally, polymeric systems have relied on strong, irreversible, non-labile linkages for maximum strength and durability. However in the past few years, there has been growing interest in polymers containing dynamic linkages that can be cleaved and reassembled under specific environmental conditions. The possibility of inducing a macroscopic response in polymeric materials by reversible cleavage/formation of physical/chemical bonds at the molecular level has triggered significant research effort. This, combined with significant developments in the field of controlled/living polymerizations has led to utilization of both non-covalent and dynamic-covalent linkages for design of block copolymers with cleavable junctions, reversible side-chain functionalization of linear polymers, "self-healing" and shape-memory polymers, and self-assembly of polymeric nanostructures.;Macromolecular star architectures, with several polymer chains connected to a central core, are interesting due to their well-defined and compact structure, a high density of functional groups, and unique properties in solution and in the melt. Incorporation of dynamic linkages into star polymers provides a characteristic of dynamics (e.g., potential for controlled degradability) to these branched macromolecules. While there is precedent to self-assembled macromolecular stars being constructed via supramolecular interactions and dynamic-covalent bonds, the ability of the reversible linkages to afford reversible topological switching between the highly branched star architecture and the individual linear arms has not been thoroughly investigated.;The research discussed here demonstrates the "arm-first" route to star polymers by dynamic-covalent crosslinking of well-defined functional block copolymers synthesized via RAFT polymerization. Three different types of dynamic-covalent chemistries, namely boronic ester formation, Diels-Alder cycloaddition and disulfide chemistry were utilized for synthesis of the core-crosslinked stars. Thus, well-defined block copolymers with a boronic acid, furan, or an anhydride functional reactive block/segment and a non-reactive (inert) block/segment were prepared via RAFT polymerization. Core-crosslinked stars were obtained by reaction of the reactive segments of the block copolymers with multifunctional 1,2-/1,3-diol, bismaleimide, or cystamine dihydrochloride crosslinkers. Various aspects of the star-assembly, such as effect of polymer concentration and polymer:crosslinker stoichiometry on the rate and extent of star formation were investigated The reversibility of the stars induced by specific stimuli (i.e., addition of a competing mono/multifunctional diol in case of the boronic ester linkages, heating/cooling in case of the Diels-Alder linkages and reduction/oxidation in case of disulfide linkages) was further studied over multiple cycles. The ability to switch the macromolecular architecture between stars and linear chains can possibly be further extended to other complex macromolecular architectures. Furthermore, dynamic-covalent chemistry can also be used to induce "macromolecular metamorphosis" or transformation from one complex architecture to another (e.g., star to brush), possibly allowing subtle changes in macroscopic properties in solution or bulk for interesting future applications.
机译：传统上，聚合物系统依靠坚固，不可逆的，非不稳定的连接来获得最大的强度和耐用性。然而，在过去的几年中，人们对包含可以在特定环境条件下裂解并重新组装的动态键的聚合物的兴趣日益增长。通过在分子水平上物理/化学键的可逆裂解/形成在聚合物材料中引起宏观响应的可能性引发了巨大的研究努力。这与受控/活性聚合领域的重大发展相结合，导致利用非共价键和动态共价键来设计具有可裂解键合的嵌段共聚物，线性聚合物的可逆侧链官能化，“自修复” ；具有形状记忆的聚合物，以及聚合物纳米结构的自组装。；具有多个定义明确且紧凑的结构，高密度的官能团以及在溶液和熔体中具有独特的性能。将动态键结合到星形聚合物中为这些支化的大分子提供了动态特性（例如，可控降解性的潜力）。尽管先有通过超分子相互作用和动态共价键构建自组装大分子恒星的先例，但尚未充分研究可逆键在高度分支的恒星结构和单个线性臂之间提供可逆拓扑转换的能力。此处讨论的研究表明，通过RAFT聚合合成的功能明确的功能嵌段共聚物通过动态共价交联，可以“星形优先”的方式获得星形聚合物。三种不同类型的动态共价化学，即硼酸酯形成，狄尔斯-阿尔德环加成和二硫键化学，被用于合成核心交联的恒星。因此，通过RAFT聚合制备具有硼酸，呋喃或酸酐官能反应性嵌段/段和非反应性（惰性）嵌段/段的明确定义的嵌段共聚物。通过使嵌段共聚物的反应性链段与多官能1,2- / 1,3-二醇，双马来酰亚胺或胱胺二盐酸盐交联剂反应，可获得核交联的星形。研究了恒星组装的各个方面，例如聚合物浓度和聚合物：交联剂化学计量对恒星形成速率和程度的影响。通过特殊刺激（例如，在水中加入竞争性单/多功能二醇）诱导恒星的可逆性。在硼酸酯键的情况下，在Diels-Alder键的情况下进行加热/冷却，在二硫键的情况下进行还原/氧化）。在恒星和线性链之间切换大分子结构的能力可能会进一步扩展到其他复杂的大分子结构。此外，动态共价化学也可用于诱导“大分子变态”或从一种复杂结构转变为另一种复杂结构（例如，从星形到刷状），可能允许溶液或大量的宏观性质发生细微变化，以用于有趣的未来应用。

著录项

  • 作者

    Bapat, Abhijeet P.;

  • 作者单位

    Southern Methodist University.;

  • 授予单位 Southern Methodist University.;
  • 学科 Chemistry Polymer.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 186 p.
  • 总页数 186
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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