Synthesis and applications of materials and polymers containing graphenic and/or triptycene moities

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, February 2013."November 2012." Cataloged from PDF version of thesis.Includes bibliographical references.In this thesis, molecular design is used to synthesize novel materials with specific properties. The materials presented herein are based on two motifs. In part I, new methods of functionalizing graphenic materials and the applications of those materials are presented. In part II, new triptycene-based polymers are synthesized and their performance is explored. Part I: Graphenic Materials Chapter 1: Three different types of epoxy-functionalized multiwalled carbon nanotubes (EpCNTs) were prepared via multiple covalent functionalizaton methods. The effect of the different chemistries on the adhesive properties of a nanocomposite prepared from commercial epoxy at 0.5, 1, 2, 3, 5, and 10 weight % CNT was studied. It was found that a covalently functionalized EpCNT (EpCNT2) at 1 weight % increased the lap shear strength, by 36 % over the unfilled epoxy formulation and by 27 % over a 1 weight % unmodified MWNT control sample. SEM images revealed a fracture surface morphology change with the incorporation of EpCNT and a deflection of the crack fronts at the site of embedded CNTs, as the mechanism accounting for increased adhesive strength. Chapter 2: In this chapter, the hydroxyl functionalities in graphene oxide (GO, a highly oxidized analogue of graphite), the vast majority that must be allylic alcohols, are subjected to Johnson-Claisen rearrangement conditions. In these conditions, a [3, 3] sigmatropic rearrangement after reaction with triethyl orthoacetate gives rise to an ester functional group, attached to the graphitic framework via a robust C-C bond. The resultant functional groups were found to withstand reductive treatments for the deoxygenation of graphene sheets and a resumption of electronic conductivity is observed. The chemical versatility of the ester groups allows for a variety of functional graphenes to be synthesized, and several of these have been used to successfully build layer-by-layer (LBL) constructs. Chapter 3: The effects of quantity of graphene and carbon nanotube-based fillers and their pendant functional groups on the shear properties of a thermoset epoxy were investigated. Two novel functionalized graphenes, one with epoxy functionality and the other with an amine, are synthesized for this purpose. The properties of the epoxy nanocomposites containing epoxy- and amine-functionalized graphene are compared with those containing GO, Claisen-functionalized graphene, MWNT, the EpCNTs, and the unfilled epoxy. One of the EpCNT (EpCNT3) was found to increase the plateau shear storage modulus by 136 % (1.67 MPa to 3.94 MPa) and the corresponding loss modulus by almost 400 % at a concentration of 10 weight %. A hybrid system of EpCNT3 and graphite was also studied, which improved the storage modulus by up to 51 %. Part II: Triptycene-Based Polymers Chapter 4: A series of soluble, thermally stable aromatic polyimides were synthesized using commercially available five and six membered ring anhydrides and 2, 6- diaminotriptycene derivatives. All of these triptycene polyimides (TPIs) were soluble in common organic solvents despite their completely aromatic structure, due to the threedimensional triptycene structure that prevents strong interchain interactions. Nanoporosity in the solid state gives rise to high surface areas (up to 430 m2/g) and low refractive indices (1.19- 1.79 at 633 nm), which suggest very low dielectric constants at optical frequencies. The decomposition temperature (Td) for all of the polymers is above 500 'C, indicating excellent prospects for high temperature applications. Chapter 5: Several new triptycene-containing polyetherolefins were synthesized via acyclic diene metathesis (ADMET) polymerization. Two types of triptycene-based monomer with varying connectivities were used in the synthesis of homopolymers, block copolymers, and random copolymers. In this way, the influence of the triptycene architecture and concentration in the polymer backbone on the thermal behavior of the polymers was studied. Inclusion of increasing amounts of triptycene were found to increase the glass transition temperature, from -44 °C in polyoctenamer to 59 °C in one of the hydrogenated triptycene homopolymers (H-PT2). Varying the amounts and orientations of triptycene was found to increase the stiffness (H-PT1), toughness (PT1₁- b-PO₁) and ductility (PT1₁-ran-PO₃) of the polymer at room temperature. Chapter 6: A novel all-hard block polyurea containing triptycene units was synthesized from N,N-carbonyldiimidizole and 2,6-diaminotriptycene. The incorporation of triptycene along the backbone prohibits the polymer from hydrogen-bonding with itself and leave the sites of the urea open for the capture of H-bond accepting analytes. Targeted analytes include cyclohexanone, a signature of the powerful explosive RDX (1 ,3,5-trinitro- 1,3,5- triazacyclohexane) and organophosphate nerve agents. This triptycene-polyurea (TPU) was found to be fluorescent in solution in the presence of H-bonding solvents. TPU was cast into thin films and a 12% increase in the fluorescent emission at 443 nm was observed in the presence of saturated cyclohexanone vapor. The sensitivity and selectivity of this response is enhanced by creating a hybrid system with squaraine (Hbond acceptor) and a HFIP-dypyrrin based dye (H-bond donor).by Stefanie A. Sydlik.Ph.D

In Vivo Compatibility of Graphene Oxide with Differing Oxidation States

Graphene oxide (GO) is suggested to have great potential as a component of biomedical devices. Although this nanomaterial has been demonstrated to be cytocompatible in vitro, its compatibility in vivo in tissue sites relevant for biomedical device application is yet to be fully understood. Here, we evaluate the compatibility of GO with two different oxidation levels following implantation in subcutaneous and intraperitoneal tissue sites, which are of broad relevance for application to medical devices. We demonstrate GO to be moderately compatible in vivo in both tissue sites, with the inflammatory reaction in response to implantation consistent with a typical foreign body reaction. A reduction in the degree of GO oxidation results in faster immune cell infiltration, uptake, and clearance following both subcutaneous and peritoneal implantation. Future work toward surface modification or coating strategies could be useful to reduce the inflammatory response and improve compatibility of GO as a component of medical devices.National Institutes of Health (U.S.). Centers of Cancer and Nanotechnology Excellence (1U54CA151884-01)National Institutes of Health (U.S.). Ruth L. Kirschstein National Research Service Award (F32EB018155)David H. Koch Institute for Integrative Cancer Research at MIT (Mazumdar-Shaw International Oncology Fellowship)National Institutes of Health (U.S.). Ruth L. Kirschstein National Research Service Award (F32DK101335)National Institutes of Health (U.S.) (R01- DE016516-06

Triptycene Polyimides: Soluble Polymers with High Thermal Stability and Low Refractive Indices

A series of soluble, thermally stable aromatic polyimides were synthesized using commercially available five- and six-membered ring anhydrides and 2,6-diaminotriptycene derivatives. All of these triptycene polyimides (TPIs) were soluble in common organic solvents despite their completely aromatic structure due to the three-dimensional triptycene structure that prevents strong interchain interactions. Low solution viscosities (0.07−0.47 dL/g) and versatile solubilities allow for easy solution processing of these polymers. Nanoporosity in the solid state gives rise to high surface areas (up to 430 m[superscript 2]/g) and low refractive indices (1.19−1.79 at 633 nm), which suggest very low dielectric constants at optical frequencies. Polymer films were found to be amorphous. The decomposition temperature (T[subscript d]) for all of the polymers is above 500 °C, and no glass transition temperatures can be found below 450 °C by differential scanning calorimetry (DSC), indicating excellent prospects for high-temperature applications. This combination of properties makes these polymers candidates for spin-on dielectric materials.National Science Foundation (U.S.). Graduate Research Fellowship ProgramMassachusetts Institute of Technology. Institute for Soldier Nanotechnologie

A Perspective on the Clinical Translation of Scaffolds for Tissue Engineering

Scaffolds have been broadly applied within tissue engineering and regenerative medicine to regenerate, replace, or augment diseased or damaged tissue. For a scaffold to perform optimally, several design considerations must be addressed, with an eye toward the eventual form, function, and tissue site. The chemical and mechanical properties of the scaffold must be tuned to optimize the interaction with cells and surrounding tissues. For complex tissue engineering, mass transport limitations, vascularization, and host tissue integration are important considerations. As the tissue architecture to be replaced becomes more complex and hierarchical, scaffold design must also match this complexity to recapitulate a functioning tissue. We outline these design constraints and highlight creative and emerging strategies to overcome limitations and modulate scaffold properties for optimal regeneration. We also highlight some of the most advanced strategies that have seen clinical application and discuss the hurdles that must be overcome for clinical use and commercialization of tissue engineering technologies. Finally, we provide a perspective on the future of scaffolds as a functional contributor to advancing tissue engineering and regenerative medicine.National Institutes of Health (U.S.) (Ruth Kirschstein National Research Service Award (F32DK101335))Juvenile Diabetes Research Foundation International (a Postdoctoral Fellowship (3-2011-310)

Epoxy functionalized multi-walled carbon nanotubes for improved adhesives

Three different types of epoxy-functionalized multi-walled carbon nanotubes (EpCNTs) were prepared by multiple covalent functionalization methods. The EpCNTs were characterized by thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), and Raman spectroscopy to confirm covalent functionalization. The effect of the different chemistries on the adhesive properties was compared to a neat commercial epoxy (Hexion formulation 4007) using functionalized and unfunctionalized multi-walled carbon nanotubes (MWCNT) at 0.5, 1, 2, 3, 5, and 10 wt%. It was found that an EpCNT at 1 wt% increased the lap shear strength, tested using the American Society for Testing and Materials standard test D1002, by 36% over the unfilled epoxy formulation and by 27% over a 1 wt% unmodified MWCNT control sample. SEM images revealed a fracture surface morphology change with the incorporation of EpCNT and a deflection of the crack fronts at the site of embedded CNTs, as the mechanism accounting for increased adhesive strength. Rheological studies showed non-linear viscosity and DSC cure studies showed an alteration of cure kinetics with increased CNT concentration, and these effects were more pronounced for EpCNT.Massachusetts Institute of Technology. Institute for Soldier NanotechnologiesNational Science Foundation (U.S.). Graduate Research Fellowshi