Benzoxazine (Bz) is a series of bicyclic compounds whose chemical structure consists of a benzene ring fused with an adjacent oxazine ring, which can be synthesized via the Mannich reaction involving phenol derivatives, primary amines, and formaldehyde [1]. Depending on the position of the functional groups employed in the reaction within phenols and primary amines, oxazines are able to be intentionally presented in any region of Bz, such as the main-chain [2], side-chain [3], or terminal group [4], which allows for deliberate control over the molecular structure when preparation. Polybenzoxazine (PBz) is a thermosetting polymer produced through cationic ring-opening polymerization of the corresponding Bz monomer under the induction of heat or initiators. In contrast to other conventional phenolic systems, Bz monomers demonstrate near-zero volume shrinkage and the absence of small molecules released during polymerization [5], thus providing prerequisites for maintaining dimensional stability while molding [6]. In addition, as one of the few high-performance and multifunctional polymers that have been successfully commercialized in the past decades [7], PBz exhibits such advantages as ever-improving mechanical properties [8], high glass transition temperature [9] and char yield [10], low dielectric constant and loss factor [11], as well as good chemical and thermal stability [12,13]. The concept of Bz was originally proposed by Holly and Cope [14] in 1944, and the application of cross-linked PBz (as a surface coating) was first achieved by Higginbottom [15] in 1985. Since then, research related to small-molecular Bz and PBz has been carried out extensively. Materials derived from them are currently widely used in many advanced industries such as flame isolation [16], surface anti-fouling and anti-corrosion [[17], [18], [19]], aerospace [20,21], electronics [22,23], and medicine [24,25]. Furthermore, in recent years, porous films, sponges, and foams fabricated using Bz or PBz as precursors along with porous carbon materials obtained after carbonization have drawn plenty of attention in the domains of oil/water separation [26], gas adsorption [27], electrochemical energy storage [28], and catalysis [29], owing to their ability to readily effectuate heteroatom self-doping and exhibit high specific surface area (SSA).

Aerogel is a kind of solid material with an interpenetrating porous structure that is acquired by replacing the liquid dispersed phase in a gel with gas, all while preserving the integrity of the internal structure without collapse [30]. The remaining three-dimensional (3D) porous structure results in outstanding properties such as low density, high porosity and large SSA. Nearly a century has passed since the initial report of aerogels [31], and their precursors are various and complex so far. Of these, silica aerogels with the most mature preparation processes have been successfully commercialized [32]. Ceramic aerogels, known for their ability to withstand thermomechanical stress and maintain efficient thermal insulation even under extreme conditions (> 1000 °C), have attracted considerable interest in recent years [33,34]. Other inorganic aerogels such as those based on metals [35] and clay [36] have been shown to be promising for electrocatalysis [37], solar desalination [38], etc. Conversely, organic aerogels, exemplified by resorcinol–formaldehyde (RF) aerogels [39] and polyimide (PI) aerogels [40], demonstrate favorable mechanical properties (such as toughness [41] and flexibility [42]) compared with inorganic aerogels, despite possessing relatively poorer thermal stability. Additionally, the emergence of multi-component aerogels has further diversified the repertoire of aerogel types, typical examples of which are those silica aerogels reinforced by fibers [43]. Noteworthily, there is still a lack of an accurate definition of the morphology of aerogels. Except for the classical pearl-necklace-like framework, some materials with fiber-staggered [44] or porous lamellar [45] structures are also categorized as aerogels.

RF aerogels, initially developed by Pekala [39] in 1989 through polycondensation of resorcinol and formaldehyde under alkaline conditions, with low cost, non-polluting solvent preparation [46], and multifunctionality after pyrolysis (or carbonization) in inert atmospheres [47], have become another research focus in the field of organic aerogels after cellulose aerogels. However, despite being very similar to the RF system and exhibiting numerous excellent properties, research on the conversion of Bz into aerogels was not conducted until the beginning of the 21st century. In 2009, Lorjai et al. [48] prepared the first PBz aerogels through heat-induced gelation (130 °C, 96 h) and ambient pressure drying (APD). In 2014, the preparation of PBz organogels at room temperature (r.t., 25 °C) was initially achieved by Mahadik-Khanolkar et al. [49] using HCl catalysis (or initiation), which greatly shortened the gelation time (1.5–7 h). Since then, PBz aerogels have garnered increasing attention as novel organic aerogels and experienced rapid development in recent years. Presently, many studies on PBz aerogels are motivated by exploring their potential properties and applications. A timeline including evolution and progression of PBz aerogels is shown in Fig. 1.

Early associated reviews or publications frequently discuss PBz aerogels in conjunction with other porous materials derived from Bz because of the limited amount of available research [[50], [51], [52]]. In contrast, this article provides a comprehensive description of the preparation and application of PBz aerogels and their corresponding hybrid and composite materials. In Section 2, the existing preparation methods and specific processes of PBz aerogels are presented. Section 3 discusses the microstructure and some unique characteristics of PBz aerogels. Section 4 introduces some multi-component materials with high performance based on PBz aerogels, including aerogel composites and hybrid aerogels. Finally, in Section 6 we give an overview of the current research state of PBz-based aerogels and present some setbacks that need to be overcome in the forthcoming studies as well as possible development directions in the future.