Gamal Mohamed

Bifunctional polybenzoxazine nanocomposites containing photo-crosslinkable coumarin units and pyrene units capable of dispersing single-walled carbon nanotubes

In this study, we have synthesized a new bifunctional benzoxazine monomer (coumarin–Py BZ) possessing both coumarin and pyrene groups through the reaction of 4-methyl-7-hydroxycoumarin (coumarin–OH), paraformaldehyde, and amino-pyrene (Py–NH2) in 1,4-dioxane. Fourier transform infrared (FTIR) and 1H and 13C nuclear magnetic resonance spectroscopy confirmed the structure of this new coumarin–Py BZ monomer. We used differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and FTIR spectroscopy to monitor the curing behavior of coumarin–Py BZ to form poly(coumarin–Py BZ), both before and after photodimerization of the coumarin moiety. DSC profiles revealed that the glass transition temperature of poly(di-coumarin–Py BZ) was higher than that of its corresponding polymer (poly(coumarin–Py BZ)), and consistent with an increase in crosslinking density after UV irradiation. The pyrene moiety of coumarin–Py BZ enhanced the dispersibility of single-walled carbon nanotubes (SWCNTs) in THF, leading to the formation of highly dispersible coumarin–Py BZ/SWCNT nanocomposites stabilized through π–π stacking between the pyrene and SWCNT units, as detected by fluorescence emission spectroscopy. The combination of photo-crosslinkable coumarin groups and SWCNT nanohybrids enhanced the glass transition temperature, thermal stability, and char yield of the polybenzoxazine matrix, based on DSC and TGA analyses.

Unexpected fluorescence from maleimide-containing polyhedral oligomeric silsesquioxanes: nanoparticle and sequence distribution analyses of polystyrene-based alternating copolymers

In this study, we synthesized unusual fluorescent polyhedral oligomeric silsesquioxane (POSS)-containing polymers lacking any common fluorescent units (e.g., phenyl or heterocyclic rings): a poly(maleimide isobutyl POSS) [poly(MIPOSS)] homopolymer and poly(styrene-alt-maleimide isobutyl POSS) [poly(S-alt-MIPOSS] and poly(4-acetoxystyrene-alt-maleimide isobutyl POSS) [poly(AS-alt-MIPOSS)] alternating copolymers, through free radical polymerization, and a poly(4-hydroxystyrene-alt-maleimide isobutyl POSS) [poly(HS-alt-MIPOSS)] alternating copolymer, through acetoxy hydrazinolysis of poly(AS-alt-MIPOSS). We used 1H, 13C, and 29Si nuclear magnetic resonance spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and MALDI-TOF mass spectrometry to examine the chemical structures and sequence distributions of these POSS-containing polymers. The FTIR spectra revealed the existence of specific intermolecular interactions, namely dipole–dipole interactions between the CO groups in poly(MIPOSS) and poly(AS-alt-MIPOSS) and intermolecular hydrogen bonding between the CO groups of the MIPOSS units and the OH groups of the HS units in poly(HS-alt-MIPOSS). Differential scanning calorimetry and thermogravimetric analyses revealed that the incorporation of MIPOSS units could enhance the thermal stability, but decrease the glass transition temperatures, of these alternating copolymers. The photoluminescence emission of poly(MIPOSS) was greater than those of the POSS-containing alternating copolymers, presumably because of the formers crystallinity and clustering of locked CO groups of POSS units.

Polybenzoxazine/Polyhedral Oligomeric Silsesquioxane (POSS) Nanocomposites

The organic/inorganic hybrid materials from polyhedral oligomeric silsesquioxane (POSS, inorganic nanoparticles) and polybenzoxazine (PBZ) have received much interesting recently due to their excellent thermal and mechanical properties, flame retardance, low dielectric constant, well-defined inorganic framework at nanosized scale level, and higher performance relative to those of non-hybrid PBZs. This review describes the synthesis, dielectric constants, and thermal, rheological, and mechanical properties of covalently bonded mono- and multifunctionalized benzoxazine POSS hybrids, other functionalized benzoxazine POSS derivatives, and non-covalently (hydrogen) bonded benzoxazine POSS composites.

Multifunctional polybenzoxazine nanocomposites containing photoresponsive azobenzene units, catalytic carboxylic acid groups, and pyrene units capable of dispersing carbon nanotubes

In this study, we synthesized a new multifunctional benzoxazine monomer Azo-COOH-Py BZ—featuring an azobenzene unit, a carboxylic acid group, and a pyrene moiety—through the reaction of 4-(4-hydroxyphenylazo)benzoic acid (Azo-COOH), paraformaldehyde, and aminopyrene (Py-NH2) in 1,4-dioxane. Fourier transform infrared (FTIR) spectroscopy and 1H and 13C nuclear magnetic resonance spectroscopy confirmed the structure of this new monomer. Using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and FTIR spectroscopy, we monitored the curing behavior of Azo-COOH-Py BZ leading to the formation of poly(Azo-COOH-Py BZ); we found that the carboxylic acid and azobenzene units acted as catalysts for the ring opening reaction of the benzoxazine unit. The pyrene moiety of Azo-COOH-Py BZ enhanced the dispersibility of carbon nanotubes (CNTs) in THF, leading to the formation of highly dispersible Azo-COOH-Py BZ/CNT nanocomposites stabilized through π–π stacking of the pyrene and CNT units, as detected through fluorescence emission spectroscopy. We also used DSC and TGA to examine the curing behavior of Azo-COOH-Py BZ/CNTs to form poly(Azopy-COOH-Py BZ)/CNTs nanocomposites. Interestingly, DSC profiles revealed that the maximum exothermic peak representing the ring opening polymerization of the benzoxazine unit of Azo-COOH-Py BZ shifted to much lower temperature upon increasing the content of single-walled CNTs (SWCNTs) or multiwalled CNTs (MWCNTs), suggesting that the CNTs acted as catalysts for the ring opening reaction of the benzoxazine. In addition, the curing temperatures for the SWCNT composites were lower than those for the MWCNT composites, suggesting that the SWCNTs were dispersed better than the MWCNTs in their composites and that the thermal stability of the SWCNT nanocomposites was higher than that of the MWCNT nanocomposites. The combination of photoresponsive azobenzene units, carboxylic acid groups, and CNTs enhanced the thermal stability and char yields of the polybenzoxazine matrixes, as determined through TGA analyses.

Strong emission of 2,4,6-triphenylpyridine-functionalized polytyrosine and hydrogen-bonding interactions with poly(4-vinylpyridine)

In this paper 2,4,6-triphenyl pyridine-functionalized polytyrosine (Pyridine-PTyr) was successfully synthesized by living ring-opening polymerization where 2,6-bis(4-aminophenyl)-4-phenylpyridine (Pyridine-NH2) was the initiator. The photo-physical characteristics of Pyridine-NH2 and Pyridine-PTyr were elucidated via UV-vis absorption and photoluminescence spectra, revealing that unlike Pyridine-PTyr, Pyridine-NH2 shows solvatochromic effects in solvents with different polarities. Additionally, Pyridine-NH2 exhibited aggregation-caused quenching (ACQ) phenomena; however, it became an aggregation-induced emission (AIE) material after attachment to the rigid-rod conformation of polytyrosine. Based on differential scanning calorimetry results, we observed that after blending Pyridine-PTyr with P4VP a single glass transition temperature due to their miscibility through the intermolecular hydrogen bonding of the phenolic OH groups in the PTyr backbone and pyridine ring in P4VP was revealed, as indicated by IR spectroscopy. Obviously, the emission intensity of Pyridine-PTyr decreased after blending with P4VP with a hypsochromic shift from 536 to 489 nm, presumably due to the release of the restricted intramolecular rotation of the triphenyl pyridine unit in the center of the polymer and the polymer chains of Pyridine-PTyr became separated random coils based on WAXD results.

Azopyridine-functionalized benzoxazine with Zn(ClO4)2 form high-performance polybenzoxazine stabilized through metal–ligand coordination

In this study, we prepared a benzoxazine monomer (Azopy-BZ) that features azobenzene and pyridine units through the reaction of paraformaldehyde, aniline, and 4-(4-hydroxphenylazo)pyridine (Azopy-OH), which is obtained through a diazonium reaction of 4-aminopyridine with phenol in the presence of sodium nitrite and NaOH. The azobenzene and pyridine groups in the benzoxazine monomer play the following two roles: (i) allowing photoisomerization between the planar trans form and the nonplanar cis form of the azobenzene unit (characterized using UV-vis spectroscopy and contact angle analyses) and (ii) serving as a catalyst that accelerated the ring opening polymerization of the benzoxazine units, which was characterized by the exothermic peak shifting to a lower temperature during differential scanning calorimetry (DSC) analyses. The curing temperature of the model benzoxazine 3-phenyl-3,4-dihydro-2H-benzoxazine (Pa-type) was 263 °C; it decreased to 208 °C for Azopy-BZ, presumably because of the basicity of the azobenzene and pyridine groups. Blending with zinc perchlorate [Zn(ClO4)2] not only improved the thermal properties, as determined through dynamic mechanical analysis (DMA), due to physical crosslinking of the pyridine units through zinc cation coordination in a metal–ligand bonding mode, but also further facilitated the ring opening polymerization to occur at a temperature of only 130 °C (DSC). Thus, the presence of Zn(ClO4)2 overcame the problem of high temperature curing (ca. 180–210 °C) required for traditional polybenzoxazines. Introducing the azobenzene and pyridine units and the zinc salt into this polybenzoxazine system provided a multifunctional material that exhibited photoisomerization-based tuning of its surface properties, accelerated ring opening polymerization of its oxazine rings, and increasing physical crosslinking density, through metal–ligand interactions, to enhance its thermal properties.

Supramolecular functionalized polybenzoxazines from azobenzene carboxylic acid/azobenzene pyridine complexes: synthesis, surface properties, and specific interactions

In this study we synthesized Azo-COOH BZ, a new benzoxazine derivative containing both azobenzene and carboxylic acid units, through the reaction of 4-(4-hydroxphenylazo)benzoic acid (Azo-COOH, itself prepared through a diazonium reaction of 4-aminobenzoic acid with phenol in the presence sodium nitrite and NaOH) with paraformaldehyde and aniline in 1,4-dioxane. Fourier transform infrared (FTIR) spectroscopy and 1H and 13C nuclear magnetic resonance spectroscopy confirmed the chemical structure of Azo-COOH BZ. We used differential scanning calorimetry (DSC), thermogravimetric analysis, and FTIR spectroscopy to investigate the curing behavior of this new benzoxazine monomer. DSC revealed that the exothermic peak representing the ring opening polymerization of the benzoxazine unit appeared at low temperature relative to those of typical benzoxazines, indicating the presence of the carboxylic acid and azobenzene units of this monomer catalyzing the benzoxazine ring opening reaction. In addition, blending with various molar ratios of a benzoxazine monomer presenting a pyridyl unit (Azopy BZ) led to strong intermolecular hydrogen bonding between the CO2H group of Azo-COOH BZ and the pyridyl group of Azopy BZ. These supramolecular complex systems also featured significantly lower curing temperatures (down from ca. 200 °C of Azo-COOH BZ to 150 °C of supramolecular complex), with their products retaining the high water contact angles required for low-surface-energy applications.

Synthesis and self-assembly of water-soluble polythiophene-graft-poly(ethylene oxide) copolymers

In this study, we synthesized amphiphilic poly(3-hexylthiophene)-graft-poly(ethylene oxide) (P3HT-g-PEO) rod–coil conjugated random copolymers through oxidative polymerization with FeCl3 and facile click chemistry and characterized them using 1H nuclear magnetic resonance spectroscopy, size exclusion chromatography, differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy, UV-Vis spectroscopy, and fluorescence spectroscopy. We then used atomic force microscopy, transmission electron microscopy, and dynamic light scattering to investigate the self-assembled structures formed from these amphiphilic random copolymers in solution and in the bulk state. In the bulk state, DSC analyses revealed that after PEO had been grafted onto P3HT, the crystallization temperature of PEO decreased from +20 to −26 °C as a result of hard confinement of microphase separation in the copolymer system. In addition, we found that the amphiphilic conjugated random copolymers could form micelle structures in the DMF–water system.

Multivalent photo-crosslinkable coumarin-containing polybenzoxazines exhibiting enhanced thermal and hydrophobic surface properties

In this study, mono-, bi-, and trivalent coumarin-containing benzoxazine monomers (mono-, di-, and tri-coumarin BZ) were synthesized in high yield and purity by facile Mannich reactions of 4-methyl-7-hydroxycoumarin and paraformaldehyde with aniline, bisphenol A–NH2, and 1,3,5-tri(4-aminobenzene), respectively, in 1,4-dioxane. 1H and 13C nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) and high resolution mass spectroscopy support the chemical structures of these three benzoxazine monomers. Differential scanning calorimetry (DSC) and FTIR spectroscopy were used to investigate the curing polymerization behavior and photodimerization ([2π + 2π] cycloaddition) of the coumarin units of mono-, di-, and tri-coumarin BZ to form poly(mono-coumarin BZ), poly(di-coumarin BZ), and poly(tri-coumarin BZ), respectively. DSC measurement revealed that the thermal polymerization temperature of coumarin-containing benzoxazine monomers was lower than that of the model compound 3-phenyl-3,4-dihydro-2H-benzooxazine (263 °C) which was attributed to the catalytic effect of the coumarin moiety and a strong electron withdrawing electron conjugated CC bond in the coumarin unit. In addition, the glass transition and thermal decomposition temperatures of poly(tri-coumarin BZ) (Tg = 240 °C; Td5 = 370 °C) were higher than poly(di-coumarin BZ) and poly(mono-coumarin BZ), consistent with the formers higher crosslinking density. In addition, the water contact angles of poly(tri-coumarin BZ) polymers prepared with and without photo-dimerization prior to thermal curing (112 and 110°, respectively) were higher than the corresponding poly(mono-coumarin BZ) and poly(di-coumarin BZ), presumably because of greater degrees of intramolecular hydrogen bonding between the CO units of the coumarin moieties and the phenolic OH units of the benzoxazine rings, resulting in lower surface free energies. Thus, the presence of multivalent photo-crosslinkable coumarin units enhanced the thermal and hydrophobic surface properties of these polybenzoxazines.

Unusual Emission of Polystyrene-Based Alternating Copolymers Incorporating Aminobutyl Maleimide Fluorophore-Containing Polyhedral Oligomeric Silsesquioxane Nanoparticles

In this study, we synthesized an unusual 2-aminobutyl maleimide isobutyl polyhedral oligomeric silsesquioxane (MIPOSS-NHBu) monomer lacking conventional fluorescent groups. We then prepared poly(styrene-alt-2-aminobutyl maleimide isobutyl POSS) [poly(S-alt-MIPOSS-NHBu)] and poly(4-acetoxystyrene-alt-2-aminobutyl maleimide isobutyl POSS) [poly(AS-alt-MIPOSS-NHBu)] copolymers through facile free radical copolymerizations using azobisisobutyronitrile as the initiator and tetrahydrofuran as the solvent. A poly(4-hydroxystyrene-alt-2-aminobutyl maleimide isobutyl POSS) [poly(HS-alt-MIPOSS-NHBu)] copolymer was prepared through acetoxyl hydrazinolysis of poly(AS-alt-MIPOSS-NHBu). We employed 1H, 13C, and 29Si nuclear magnetic resonance spectroscopy; Fourier transform infrared spectroscopy; differential scanning calorimetry; and photoluminescence spectroscopy to investigate the structures and the thermal and optical properties of the monomers and novel POSS-containing alternating copolymers. Intramolecular hydrogen bonding between the amino and dihydrofuran-2,5-dione group and clustering of the locked C=O groups from the POSS nanoparticles in the MIPOSS-NHBu units restricted the intramolecular motion of the polymer chain, causing it to exhibit strong light emission. As a result, the MIPOSS-NHBu monomer and the poly(AS-alt-MIPOSS-NHBu) copolymer both have potential applicability in the detection of metal ions with good selectivity.