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

The effect of mixing methods on the dispersion of carbon nanotubes during the solvent-free processing of multiwalled carbon nanotube/epoxy composites

The article of record as published may be found at: http://dx.doi.org/10.1002/polb.23225Several solvent-free processing methods to disperse multiwalled carbon nanotubes (MWCNTs) in bisphenol F-based epoxy resin were investigated, including the use of a microfluidizer (MF), planetary shear mixer (PSM), ultrasonication (US) and combinations. The processed mixture was cured with diethyl toluene diamine. Three complimentary techniques were used to characterize the dispersion of the MWCNTs in cured composite samples: optical microscopy, micro Raman spectroscopy, and scanning electron microscopy (SEM). For sample MF þ PSM, optical micrographs and Raman images showed reduced agglomeration and a homogeneous distribution of MWCNTs in the epoxy matrix. SEM analysis of fractured specimen after tensile testing revealed breakage of nanotubes along the fracture surface of the composite. A comparison of the MWCNT dispersion in the epoxy samples processed using different methods showed that a combination of MF and PSM processing yields a more homogeneous sample than the PSM or US þ PSM processed samples. Mechanical testing of the composites showed about 15% improvement in the tensile strength of samples processed by the MF þ PSM method over other methods. Thermogravimetric analysis (TGA) results showed a small decrease in the onset degradation temperature for poorly dispersed samples produced by PSM compared with the well-mixed samples (MF þ PSM). These results strongly suggest that the MF þ PSM processing method yield better-dispersed and stronger MWCNT/epoxy composites

Supercapacitors from Free-Standing Polypyrrole/Graphene Nanocomposites

Interfacial/in situ oxidative polymerization of polypyrrole in the presence of functionalized graphene sheets produces high-quality composites for supercapacitors, as analyzed by electrochemical impedance spectroscopy and cyclic voltammetry analysis. The synergistic interaction induced by the growth of p-type polypyrrole on the surface of negatively charged carboxylate functionalized graphene sheets results in higher storage capacity than graphene-only or polymer-only films. The high conductivity of p-doped polypyrrole and high surface area of graphene promote high charge accumulation in capacitors. We report the optimization of the relative concentrations of carboxylate functionalized graphene in the polypyrrole matrix to maximize the composition’s capacitance to 277.8 F/g

Plastic Composites from Repurposed Poly(ethylene terephthalate) Wasted Functionalized Graphene Oxide through Dynamic Depolymerization

Plastic upcycling, which involves making plastic-derived products with unique or improved properties from discarded plastic materials, is a promising alternative to recycling and disposal to help reduce the overall production of waste. However, recycled and reused materials typically have inferior mechanical, thermal, optical, and barrier properties compared with virgin plastics. Upcycled plastic materials could improve these properties while addressing future waste accumulation. In this study, we use waste poly(ethylene terephthalate) (PET) collected from disposable food packaging to create a repurposed plastic graphene oxide (GO) composite with a goal of upcycling. We developed a one-pot “dynamic depolymerization” to break down PET in the presence of GO and successfully enabled transesterification of the polymer onto GO. Covalent attachment of PET onto GO and tailorable plastic content was confirmed by thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. These covalent composites (PET-GO) were found to be relatively impermeable to water vapor, showing promise for applications in packaging materials. Aqueous degradation experiments on the composite materials demonstrated that, in bulk conditions, PET-GOs remain mechanically robust while in contact with water over appropriate time scales for packaging applications, while beginning to break down in accelerated conditions. The use of depolymerization methods to promote polymer grafting concurrently with polymer deconstruction could provide a more general method for grafting waste polymers onto oxidized carbonaceous substrates with further study

<i>In Vivo</i> 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 <i>in vitro</i>, its compatibility <i>in vivo</i> 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 <i>in vivo</i> 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

Apparent Roughness as Indicator of (Local) Deoxygenation of Graphene Oxide

Detailed characterization of graphene oxide (GO) and its reduced forms continues to be a challenge. We have employed scanning tunneling microscopy (STM) to examine GO samples with varying degrees of deoxygenation via controlled chemical reduction. Analysis of the roughness of the apparent height in STM topography measurements, i.e. the “apparent roughness”, revealed a correlation between increasing deoxygenation and decreasing apparent roughness. This analysis can therefore be a useful supplement to the techniques currently available for the study of GO and related materials. The presence of a high electric field underneath the STM tip can locally induce a reaction on the GO basal plane that leads to local deoxygenation, and the restoration of the sp² hybridization of the carbons promotes increased planarity. These findings are in line with the apparent roughness values found for GO at varying levels of chemical reduction and illustrates the value of having a tool to gain structural/chemical insight on a local scale. This is the first example of employing an STM tip to locally reduce GO to reduced GO (rGO) and partially reduced GO (prGO) without locally destroying the graphene sample. Local manipulation on the nanoscale has utility for graphene nanoelectronics, and analysis employing the apparent roughness is an additional tool for the study of graphene oxide and related basal plane chemistry

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

Supercapacitors from Free-Standing Polypyrrole/Graphene Nanocomposites

Interfacial/in situ oxidative polymerization of polypyrrole in the presence of functionalized graphene sheets produces high-quality composites for supercapacitors, as analyzed by electrochemical impedance spectroscopy and cyclic voltammetry analysis. The synergistic interaction induced by the growth of p-type polypyrrole on the surface of negatively charged carboxylate functionalized graphene sheets results in higher storage capacity than graphene-only or polymer-only films. The high conductivity of p-doped polypyrrole and high surface area of graphene promote high charge accumulation in capacitors. We report the optimization of the relative concentrations of carboxylate functionalized graphene in the polypyrrole matrix to maximize the composition’s capacitance to 277.8 F/g.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologie