A novel thermal-resistant copolymer from polysiloxane-based polybenzoxazine precursor and ferrocene-based benzoxazine monomer

Integrating Benzoxazine-PDMS 3D Networks with Carbon Nanotubes for flexible Pressure Sensors

Shapeable and flexible pressure sensors with superior mechanical and electrical properties are of major interest as they can be employed in a wide range of applications. In this regard, elastomer-based composites incorporating carbon nanomaterials in the insulating matrix embody an appealing solution for designing flexible pressure sensors with specific properties. In this study, PDMS chains of different molecular weight were successfully functionalized with benzoxazine moieties in order to thermally cure them without adding a second component, nor a catalyst or an initiator. These precursors were then blended with 1 weight percent of multi-walled carbon nanotubes (CNTs) using an ultrasound probe, which induced a transition from a liquid-like to a gel-like behavior as CNTs generate an interconnected network within the matrix. After curing, the resulting nanocomposites exhibit mechanical and electrical properties making them highly promising materials for pressure-sensing applications.

Preparation and properties of benzoxazine precursors containing siloxane units and their epoxy copolymers

Four siloxane benzoxazines containing different rigid segments were successfully synthesized and characterized herein, including a benzene ring, a biphenyl, a naphthalene ring, and a diphenyl sulfone group. Different rigid segments had different effects on polymer properties. The introduction of the naphthalene ring and sulfone group considerably reduced the curing temperature of benzoxazine. Although the benzoxazine with the naphthalene ring exhibited low heat resistance, all the four samples showed a high char yield at 800°C under nitrogen atmosphere. In addition, during copolymerization with AG-80 epoxy, the introduction of epoxy promoted the curing of the benzoxazines containing the naphthalene ring and sulfone group. The heat resistance of all copolymers was considerably improved, especially for the copolymer containing the naphthalene ring, whose 5% thermal weight loss temperature ( Td5) increased from 248°C to 321°C under nitrogen atmosphere. The copolymer containing the biphenyl structure had the highest glass transition temperature, reaching 259.1°C. Copolymerization with epoxy also considerably improved the tensile strength and elongation at break of the copolymers, which were much higher than those of traditional bisphenol A-aniline based benzoxazine (BA-a). Compared with the neat benzoxazine prepared using siloxane and bisphenol A, the developed copolymers also had better tensile properties, and the copolymer containing the sulfone group showed the greatest improvement (from 49 to 69 MPa, from 3.1% to 9.12%).

Coumarin-Annulated Ferrocenyl 1,3-Oxazine Derivatives Possessing In Vitro Antimalarial and Antitrypanosomal Potency

A tailored series of coumarin-based ferrocenyl 1,3-oxazine hybrid compounds was synthesized and investigated for potential antiparasitic activity, drawing inspiration from the established biological efficacy of the constituent chemical motifs. The structural identity of the synthesized compounds was confirmed by common spectroscopic techniques: NMR, HRMS and IR. Biological evaluation studies reveal that the compounds exhibit higher in vitro antiparasitic potency against the chemosensitive malarial strain (3D7 P. falciparum) over the investigated trypanosomiasis causal agent (T. b. brucei 427) with mostly single digit micromolar IC50 values. When read in tandem with the biological performance of previously reported structurally similar non-coumarin, phenyl derivatives (i.e., ferrocenyl 1,3-benzoxazines and α-aminocresols), structure-activity relationship analyses suggest that the presence of the coumarin nucleus is tolerated for biological activity though this may lead to reduced efficacy. Preliminary mechanistic studies with the most promising compound (11b) support hemozoin inhibition and DNA interaction as likely mechanistic modalities by which this class of compounds may act to produce plasmocidal and antitrypanosomal effects.

Repurposing a polymer precursor: Synthesis and in vitro medicinal potential of ferrocenyl 1,3-benzoxazine derivatives

Cancer and malaria remain relevant pathologies in modern medicinal chemistry endeavours. This is compounded by the threat of development of resistance to existing clinical drugs in use as first-line option for treatment of these diseases. To counter this threat, strategies such as drug repurposing and hybridization are constantly adapted in contemporary drug discovery for the expansion of the drug arsenal and generation of novel chemotypes with potential to avert or delay resistance. In the present study, a polymer precursor scaffold, 1,3-benzoxazine, has been repurposed by incorporation of an organometallic ferrocene unit to produce a novel class of compounds showing in vitro biological activity against breast cancer, malaria and trypanosomiasis. The resultant ferrocenyl 1,3-benzoxazine compounds displayed high potency and selectivity against the investigated diseases, with IC₅₀ values in the low and sub-micromolar range against both chloroquine-sensitive (3D7) and resistant (Dd2) strains of the Plasmodium falciparum parasite. On the other hand, antitrypanosomal (Trypanosoma brucei brucei) potencies were observed between 0.15 and 38.6 μM. The majority of the compounds were not active against breast cancer cells (HCC70), however, for the toxic compounds, IC₅₀ values ranged from 11.0 to 30.5 μM. Preliminary structure-activity relationships revealed the basic oxazine sub-ring and lipophilic benzene substituents to be conducive for biological efficacy of the ferrocenyl 1,3-benzoxazines reported in the study. DNA interaction studies performed on the most promising compound 4c suggested that DNA damage may be one possible mode of action of this class of compounds.

Synthesis and characterization of siloxane-containing benzoxazines with high thermal stability

To understand the influence of phenyl substituents on silicon and to improve the glass transition temperature ( T g) and thermal stability, phenol/bis ( p-aminophenoxyl) dimethylsiloxane-based benzoxazine (P-adms), phenol/bis ( p-aminophenoxyl) methylphenylsiloxane-based benzoxazine (P-amps), and phenol/bis ( p-aminophenoxyl) diphenylsiloxane-based benzoxazine (P-adps) were designed and synthesized. The structure of the siloxane-containing benzoxazines were confirmed by proton and carbon nuclear magnetic resonance imaging and Fourier transform infrared spectra. The curing reaction of the obtained benzoxazines was studied by differential scanning calorimetry (DSC) and in situ infrared spectra. The influence of the aromatic content on the T g and thermal stability were investigated by modulated DSC and thermogravimetric analysis. Compared to aminopropylsiloxane-based benzoxazines, the bis ( p-aminophenoxyl) siloxane-based benzoxazines possessed relatively higher T g about 140°C due to the replacement of flexible propyl chain by phenoxyl chain. With increasing phenyl substituents on silicon, the polybenzoxazines possessed lower T g and higher thermal stability. It is notedthat the phenol/bis ( p-aminophenoxyl) diphenylsiloxane-based benzoxazine (P-adps) still has low viscosity despite high aromatic content due to the flexible ether linkage (Ar–O–Si).

Synthesis and thermal properties of silicon-containing benzoxazine

A novel benzoxazine, containing silicon (Si) in the main chain and bonded to two benzene ring, was synthesized from aniline, bis( p-hydroxyphenyl)dimethylsilane, and paraformaldehyde. The structure was characterized by proton nuclear magnetic resonance and Fourier transform infrared (FTIR) spectra. The curing behavior of the benzoxazine was evaluated by differential scanning calorimeter and in situ FTIR. The thermal stability of the resulting polybenzoxazine was studied by thermogravimetric analysis under nitrogen and air atmospheres. The results indicated that the Si-containing polybenzoxazine possessed significantly higher initial degradation temperature and char yield than conventional bisphenol A/aniline-based polybenzoxazine.

Silicon/nitrogen synergistically reinforced flame-retardant PA6 nanocomposites with simultaneously improved anti-dripping and mechanical properties

A facile route of ‘copolymerization/blending’ was proposed to fabricate silicon/nitrogen synergistically reinforced flame-retardant PA6 nanocomposites with simultaneously improved anti-dripping and mechanical properties. Firstly, a persistently inherent flame-retardant PA6 (FR-PA6), with 1,3-bis(3-aminopropyl)tetramethyl disiloxane (MSDS), was synthesized via controllable amidation and a polycondensation reaction. Melamine cyanurate (MCA) nanoparticles as a ‘gas phase’ synergistic agent were then added into FR-PA6 to further improve its flame retardancy. The primarily obtained FR-PA6 could be extinguished after a few melt droplets dropped as ignited, and passed the V-2 rating with enhanced mechanical properties, while PA6 had no rating (NR). The prepared FR-PA6/MCA nanocomposites could attain a limiting oxygen index (LOI) value of 32.7%, and passed the V-0 level with only 1 melting droplet with similar mechanical properties to PA6. Accordingly, the special ‘condensed-gas phase’ synergistic flame-retardant mechanism of FR-PA6/MCA nanocomposites was proposed through studying the residues and pyrolysis volatiles. This work provided a facile route as a model for developing functional PA6 for diverse engineering applications.

A facile route was provided to prepare silicon/nitrogen synergistically reinforced flame-retardant PA6 nanocomposites with simultaneously improved anti-dripping and mechanical properties.