Polymers containing calix[4]arenes and triptycenes : new syntheses, properties and applications
Author(s)
Yang, Yong, Ph. D. Massachusetts Institute of Technology
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Massachusetts Institute of Technology. Dept. of Chemistry.
Advisor
Timothy M. Swager.
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This thesis details the development of new synthetic methods for making polymers with complex molecular structures. Calix[4]arenes and triptycenes are the two major molecular building blocks for constructing the functional polymers. Unusual properties, with the emphasis on mechanical and sensory properties, are demonstrated. In Chapter 2, early investigations on the synthesis of main-chain calix[4]arene polymers are introduced. High molecular-weight main-chain calixarene homopolymers via linkages on lower rims are synthesized by the polymerization based on acetylenic coupling reaction. The conformation of calixarene monomers dictates the ability to produce the new polymers: the calix[4]arene monomers with a partial cone conformation produce high molecular-weight polymers while the calix[4]arene monomers with a cone conformation only afford oligomers. Other polymerization methods, including Sonogashira coupling and Cu(I)catalyzed Huisgen 1,3-dipolar cycloaddition, are also investigated but found to be inferior to the acetylenic coupling polymerization. In Chapter 3, main-chain calix[4]arene elastomers are achieved by metathesis reactions. Alkene-bridged calix[4]arene monomers are synthesized by ring-closing metathesis (RCM). All the three possible conformers (cone, partial cone, and 1,3-alternate) are used as comonomers with cyclooctene and norbornene in ring-opening metathesis polymerization (ROMP). The resultant polymers are high molecular-weight, transparent and stretchable materials with high calixarene incorporation (up to 25 mol% or 70 wt%) and low glass transition temperatures. The conformational properties of the calixarene moieties play a crucial role in determining the mechanical properties of the polymers. (cont.) In Chapter 4, the single-walled carbon nanotube (SWCNT)/polythiophene (PT)/calixarene polymer (CP) three-component hybrid system is demonstrated to be a simple chemiresistive sensory platform by utilizing the host-guest chemistry between calixarenes and analytes. To improve the sensing performance, a new polythiophene with pedant calixarenes (CalixPT) is then synthesized by a precursor polymer route. The new CalixPT is able to disperse SWCNTs. The stable and homogeneous dispersions can be easily processed to chemiresistive sensors for selective detection of xylene isomers. The sensing performance of the simplified SWCNT/CalixPT two-component system is greatly enhanced. In Chapter 5, high molecular-weight 1,4-linked triptycene polycarbonates (PCs) are synthesized by an optimized melt polymerization process. The triptycene-PCs exhibit improvements in modulus by over 20% and improvements in compressive strengths by nearly 50% at both low and high strain rates without any apparent sacrifice to ductility and transparency, in comparison to commercial bisphenol A PC. This is a further evidence of previously proposed molecular threading and interlocking mechanisms derived from the unique internal free volume (IFV) of the triptycene units. In Chapter 6, a modified ring-opening insertion metathesis polymerization (ROIMP) in ionic liquids (ILs), which employs the use of simple acyclic dienes as the comonomers and takes advantage of ILs' high boiling point to allow the application of high reaction temperature and low pressure, is developed. The new polymerization method is applied to making triptycene elastomers (both 1,4-linked and 2,6-linked) with high molecular weights and triptycene incorporations. (cont.) The 1,4-linked triptycene elastomers are for fundamental studies of the IFV mechanism. The 2,6-linked triptycene elastomers are proposed to exhibit negative Poisson's ratio at the molecular level.
Description
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008. Includes bibliographical references.
Date issued
2008Department
Massachusetts Institute of Technology. Department of ChemistryPublisher
Massachusetts Institute of Technology
Keywords
Chemistry.