Preparing Multifunctional High-Performance Cross-Linked Polybenzoxazole Aerogels from Polybenzoxazine

Abstract

Polybenzoxazole (PBO) aerogels have such valuable properties as excellent thermal and chemical stability, good fire resistance, and electronic transmission. However, the current processes to produce these aerogels tend to be complex and inefficient, and they are difficult to process into complex shapes. In this paper, we report a strategy to prepare cross-linked PBO (cPBO) aerogels by the polybenzoxazine. The polybenzoxazine aerogels were obtained first and then converted into cPBO aerogels through heat treatment. The prepared cPBO aerogels not only had low thermal conductivity (0.030 to 0.039 W m −1 K −1 ) but also possessed excellent mechanical properties (compressive modulus of 84.68 MPa) and low dielectric properties (1.51 at 1 kHz). These are attributable to the intrinsic structure of cPBO and the high porosity of aerogels in general. Because small-molecule ortho-functionalized benzoxazine has good solubility and can be used to prepare homogeneous solutions with various solid contents, this preparation strategy avoids the defect of directly using PBO resin, which has poor solubility and poor processability. Moreover, the pores of the cross-linked polybenzoxazine aerogels can be retained to the greatest extent during heat treatment. The preparation process is simple, efficient, and has a good application prospect.

Nanoporous Polybenzoxazine Aerogels for Thermally Insulating and Self-Extinguishing Materials in Aerospace Applications

“…The binding energies (BEs) located at 284.22, 285.51, and 290.89 eV in the C 1s spectra in Figure S2a corresponded to C–C, C–H, C–N, and C–OH, respectively. Moreover, the peak at 531.38 eV was reasonably attributed to O–H covalent bonds, including those of hydroxyl groups and intermolecular hydrogen bonds, manifesting the formation of three-dimensional networking structures exclusive to the cross-linking structures by ring-opening reactions, and the BE peaks at 398.77 and 401.29 eV in the N 1s spectra in Figure S2b were assigned to C–N···H in PBO aerogels, implying that intramolecular hydrogen bonds formed in the PBO aerogels and signifying the formation of chemical cross-linking processes by chemical ring-opening reactions (for example, the construction of C­(benzene ring)–N–C­(benzene ring) and hydrogen bonding). This evidence was consistent with the structural results of PBO aerogels obtained via FESEM measurements.…”

“…The characteristic peaks at 284. 25 and signifying the formation of chemical cross-linking processes by chemical ring-opening reactions (for example, the construction of C(benzene ring)− N−C(benzene ring) and hydrogen bonding). This evidence was consistent with the structural results of PBO aerogels obtained via FESEM measurements.…”

Multifunctional Lightweight Guanidine Phosphate/Poly(Vinyl Alcohol) Melamine-Based Hybrid Foam for Superior Thermal Insulation and Flame Retardancy

“…In recent years, aerogels have presented a great development trend as thermal insulation material due to the unique 3D porous structure, high porosity, low density, and low thermal conductivity. 15,16 The most widely used silica aerogels possess an ultralow thermal conductivity of about 0.025 W m −1 K −1 , but the poor mechanical performance and complicated production process restrict the application of aerogels. 17,18 As a result, it is imperative to develop multifunctional high-performance thermal insulation materials for the construction field.…”

“…In contrast, the inorganic thermal insulation materials, such as rock wool, expanded vermiculite, and expanded perlite, have the advantages of low cost and flame retardancy, but they have the shortcomings of high thermal conductivity, processing complexity, and unfriendly environment. In recent years, aerogels have presented a great development trend as thermal insulation material due to the unique 3D porous structure, high porosity, low density, and low thermal conductivity. , The most widely used silica aerogels possess an ultralow thermal conductivity of about 0.025 W m –1 K –1 , but the poor mechanical performance and complicated production process restrict the application of aerogels. , As a result, it is imperative to develop multifunctional high-performance thermal insulation materials for the construction field.…”

Oxazine Ring-Substituted 4th Generation Benzoxazine Monomers & Polymers: Stereoelectronic Effect of Phenyl Substituents on Thermal Properties

“…Polybenzoxazine chemistry has evolved with time and altering the chemical structure of monomers showed profound potential in affecting polymer properties. Interestingly, introduction of additional functionalities besides a reactive oxazine ring in the monomers was helpful in achieving unusual properties and expanded their exploration from conventional to the unconventional domain of applications. − Benzoxazine monomers undergo catalyst-free ring-opening polymerization, albeit demands a very high temperature, which is currently an area of research interest to advance their industrial scalability. To circumvent this problem, two approaches are widely followed.…”