Graphene Oxide Network Formation and Crosslinking in Polybenzoxazines and Poly[(R)-3-hydroxybutyrate]

The search for improvement of the physical properties of two very dissimilar polymeric materials is the aim of this doctoral thesis. The high performance properties of polybenzoxazines are tackled via the preparation of novel amino-functional benzoxazine monomers, as well as by the addition of graphene oxide (GO) for the preparation of polybenzoxazine nanocomposites. The synthesis of the amino-functional benzoxazine monomers is attempted by employing two different approaches. Both amino-monofunctional and bifunctional benzoxazine monomers (P-a- NH2 and P-ddm-NH2) are successfully prepared via deprotection of amine-protected benzoxazines. Tetrachlorophthalimide and trifluoroacetyl are found to be suitable protecting groups. The reactivity of the aminofunctionalized benzoxazine monomers is confirmed through reaction with acid chlorides. Amide-containing benzoxazine model compounds along with polyamides containing benzoxazine moieties in the main chain are prepared accordingly. Thermal properties of the crosslinked poly(amide-benzoxazine)s demonstrate the potentiality of such materials for high performance applications. GO-base polybenzoxazine nanocomposites are also successfully prepared. The focus of this study is placed rather on the degree of dispersability of GO nanoparticles. Rheological analysis of the nanocomposites prepared using two different benzoxazines as matrices, both prior and after polymerization, reveals the importance of the interfacial interactions between GO surface and the polybenzoxazines in order to favor dispersability and thus to modify the physical properties of the nanocomposites. The biobased and biodegradable linear polyester poly[(R)-3-hydroxybutyrate] (PHB) degrades at temperatures close to its melting temperature (175 oC). The mechanism for the thermal degradation involves the random formation of shorter polymer segments containing crotonyl and carboxyl end groups. Different additives known to react with carboxyl groups and influence the melt stability of well-established polyesters are added to PHB. Their effect on the thermal degradation is analyzed by rheological means and by molar mass measurements. Among the additives employed, multifunctional epoxide and carbodiimide cause minor improvements on the melt rheology. No effect in the rheological behavior is observed when aryl phosphites are employed. Lastly, the use of bifunctional oxazoline and epoxide, and trifunctional aziridine increases the rate of thermal degradation by drastically decreasing the melt stability and thus the molar mass of PHB. GO was also employed as a means to modify the physical properties of PHB. Moderate influence on the thermal properties is observed using DSC and TGA. Although the temperature of decomposition of PHB remains unaltered with the addition of GO, molar mass measurements show an increase of the rate of thermal degradation of PHB in the nanocomposites. The rheological properties, on the other hand, are greatly influenced by the addition of GO nanoparticles. Micromechanical effect and GO network formation are observed to be the cause for such enhancement. In addition, the dynamic properties in the solid state are analyzed according to the modified Halpin-Tsai model for platelet reinforcement. The linear viscoelastic behavior of both GO-based benzoxazine and PHB nanocomposites were analyzed using scaling concepts for fractal networks. In both cases, small percolation volume fractions for the formation of spacefilling network of GO nanoparticles are determined. Finally, the results from the analysis are used to quantify the degree of dispersion and are employed for comparison purposes

Dispersion and interaction of graphene oxide in amorphous and semi-crystalline nano-composites: a PALS study

The influence of dispersion and interaction of Graphene Oxide (GO) in semi-crystalline Polyhydroxy butyrate (PHB) and glassy amorphous Poly(tBP-oda) is explored by Positron Annihilation Lifetime Spectroscopy (PALS). The ortho-Positronium lifetimes which represent the main free volume hole size of both polymers are mainly affected by the large differences in internal stresses built up by the shrinkage of the polymers during their preparation, restricted by the platelet structure of GO. The ortho-Positronium intensities, which represent the ortho-Positronium formation probabilities, suggest a strong dependency of on the dispersion of the nano-particles and their aspect ratio

Network formation of graphene oxide in poly(3-hydroxybutyrate) nanocomposites

Network formation of graphene oxide (GO) nanoplatelets was held accountable for the modification of the rheological properties of nanocomposites based on poly(3-hydroxybutyrate) (PHB). The nanocomposites were prepared by a casting procedure from the green solvent γ-butyrolactone. The nature of the GO network and percolation limits were analyzed by making use of the molar mass reduction of PHB that takes place in the melt, as well as by studying the deformation dependence of the viscoelastic behavior of the nanocomposites. The percolation volume fraction for the formation of GO network was found to be below 0.07%, while a corresponding GO aspect ratio of 400 was determined. The equilibrium shear modulus (|G∗eq|) of the GO network and the critical strain γc of the nanocomposites could be described both by a power-law dependence on the volume fraction of GO nanoparticles. Further assessment of the structure formation of the GO nanoparticles was made in the solid state, wherein the shear modulus of GO was analyzed with the Halpin-Tsai model. The values thus determined suggested the existence of tiled nanoplatelets within the formed network structure in the nanocomposites. The thermal properties of the nanocomposites were examined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The microstructure of the samples was also characterized using X-ray diffraction (XRD) measurements

Quantifying Dispersion in Graphene Oxide/Reactive Benzoxazine Monomer Nanocomposites

Two structurally different bisbenzoxazine monomers (tBP-oda and tBP-jeff(148)) are synthesized and reinforced with graphene oxide (GO) at concentrations ranging from 0.25 to 3 wt %. Successful synthesis of the benzoxazine monomer and conversion from graphite to GO are verified by proton nuclear magnetic resonance spectroscopy (H-1 NMR), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD), respectively. Dispersibility of GO in the benzoxazine monomers prior to polymerization is studied using rheological analysis, and quantified according to the theory of fractal model of colloidal gels. The polymerization behavior of the GO/benzoxazine mixtures is studied by both differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Rheological analysis is also applied to the nanocomposite precursors. Better dispersions are achieved using tBP-oda, the benzoxazine with a high degree of aromaticity in its chemical structure. The addition of GO exhibits a negative effect on the polymerization of the two benzoxazines. The mechanical properties and the glass transition temperature T-g of GO/poly(tBP-oda) nanocomposites increases, whereas for the GO/poly(tBP-jeffi(148)) nanocomposites, the mechanical properties are moderately enhanced and T-g is reduced as a function of the GO concentration. The modifications of the mechanical and thermal properties of the nanocomposites are mainly attributed to the degree of dispersion of the GO nanosheets

Triggering effect caused by elemental sulfur as a mean to reduce the polymerization temperature of benzoxazine monomers

Mixtures of different benzoxazine resins and elemental sulfur (S8) are prepared and then reacted at 120 °C, below the temperature for radical formation of sulfur. The progress of the reaction and the chemical structures of the main products are monitored and characterized by proton nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infrared spectroscopy (FT-IR). Thermal analysis of all reactive systems are also performed and studied by differential scanning calorimetry (DSC). The introduction of S8 into benzoxazines generates a new structure bearing a Schiff base and a phenolic -OH within the reactive system, which then triggers the reduction of the polymerization temperature in about 15% when as low as 5 mol% of S8 is added.Fil: Rodriguez Arza, Carlos. Case Western Reserve University; Estados UnidosFil: Froimowicz, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnología en Polímeros y Nanotecnología. Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnología en Polímeros y Nanotecnología; Argentina. Case Western Reserve University; Estados UnidosFil: Ishida, Hatsuo. Case Western Reserve University; Estados Unido

New biobased non-ionic hyperbranched polymers as environmentally friendly antibacterial additives for biopolymers

The aim of this research was to develop new biobased non-ionic polymeric additives with significant bacterial inhibition and low leaching potential, so that they can be used to produce biopolymer materials for various applications such as biomedical devices, surgical textile, or food packaging. Two new non-ionic hyperbranched polymers (HBPs) were prepared by a facile solvent-free polymerization of an AB2-monomer derived from naturally existing molecular building blocks 2-phenylethanol, isatin, and anisole. The molecular structures and thermal properties of the obtained HBPs were characterized by GPC, NMR, FTIR, HRMS, MALDI-TOF, TGA and DSC analyses. Disk diffusion tests revealed that the two obtained HBPs showed more significant antibacterial activity against 9 different food and human pathogenic bacteria, compared with small molecular antibiotics. The maximal antibacterial effect of HBPs was achieved at 2 μg per disk (or 0.1 mg mL−1), which was significantly lower (∼1/15) compared to the linear antibacterial polymer chitosan. Such enhanced antibacterial properties can be attributed to the unique highly branched structures and effectively amplified functionalities of HBPs. Finally, the prepared HBPs were added into natural polymers cellulose and polyhydroxybutyrate (PHB), and the resulting biopolymer films showed no significant leakage after being merged in water for 5 days. This was in sharp contrast to the biopolymer films containing a small model compound, which leaked out significantly under the same conditions. To our knowledge, this is the first report on non-ionic bio-based dendritic macromolecules with significant bacteria inhibition and low leakage

Primary Amine-Functional Benzoxazine Monomers and Their Use for Amide-Containing Monomeric Benzoxazines

Amino-functional benzoxazine monomers have been successfully prepared. Several routes have been applied to incorporate amino group into benzoxazine structure. These approaches include reduction of the corresponding nitro-functional benzoxazines and deprotection of protected amino-functional benzoxazine monomers. Various approaches that allow primary amine groups to be prepared without damaging the existing benzoxazine groups have been evaluated. Tetrachlorophthalimide and trifluoroacetyl are found to be suitable protecting groups. In addition, a model compound of amide-functional benzoxazines is prepared from primary amine-functional benzoxazine. Fourier transform infrared spectroscopy (FTIR) and H-1 and C-13 nuclear magnetic resonance spectroscopy (NMR) are used to characterize the structure of the monomers. The polymerization behavior of amino-functional monomers and model compound are studied by differential scanning calorimetry (DSC)

Crosslinked Polyamide Based on Main-Chain Type Polybenzoxazines Derived from a Primary Amine-Functionalized Benzoxazine Monomer

Two types of main-chain type polybenzoxazines with amide and benzoxazine groups as repeating units in the main chain, termed as poly(amide-benzoxazine), have been synthesized. They have been prepared by polycondensation reaction of primary amine-bifunctional benzoxazine with adipoyl and isophthaloyl dichloride using dimethylacetamide as solvent. Additionally, a model reaction is designed from the reaction of 3,3'-(4,4'-methylenebis(4,1-phenylene)) bis(3,4-dihydro-2H-benzo[e][1,3]oxazin-6-amine) with benzoyl chloride. The structures of model compound and polyamides are confirmed by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (H-1 NMR) spectroscopies. Differential scanning calorimetry and FTIR are also used to study crosslinking behavior of both the model compound and polymers. Thermal properties of the crosslinked polymers are also studied by thermogravimetric analysis. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4335-4342, 201