In recent years, the research on organic-inorganic nanocomposites has attracted much attention. On the one hand, the nanocomposite combines the performance advantages of different raw materials to form a synergistic effect, so that the comprehensive performance of the obtained nanocomposite is superior to that of the raw materials^[1]; On the other hand, the new composite materials can be endowed with new properties in mechanics, optics, thermology, electricity and so on, and are praised as the most promising materials in the 21st century^[2]. Polymer matrix composites are widely used as a dominant composite material. The polymer has the advantages of simple synthesis method, light weight and good ductility, and the addition of particles for compounding, such as TiO₂, SiO₂, Al₂O₃ and the like, can endow the polymer-based composite material with excellent mechanical strength and thermal stability^[3]. Among them, nano SiO₂ particles, commonly known as silica, is a structure material based on amorphous oxides, which is a white powdery solid macroscopically, with irregular Si-O crystals inside and a large number of hydroxyl groups on the surface, which can be modified by covalent conjugation or physical adsorption. Its excellent colloidal stability and processability make it ideal for use in model systems. It is widely used in the preparation of polymer matrix composites because of its high specific surface area, high stability, durability and good biocompatibility. In addition, the addition of SiO₂ can not only improve the mechanical strength, but also reduce the shrinkage stress, reduce the coefficient of thermal expansion and enhance the optical and electrical properties of composites, which are widely used in thin films, coatings, cosmetics, polymer electrolytes, photovoltaic solar cells and other fields^[4][5].

Polymerization-induced self-assembly (PISA) is a new self-assembly method developed in the field of polymer chemistry and physics in recent years. At first, insoluble monomers are polymerized by soluble macromolecular segments. With the growth of insoluble segments, the block copolymers can be driven to self-assemble in situ. Compare with that traditional self-assembly method, the method has the advantages that the post-polymerization process such as solvent selection and the like involved in the method are avoided, the steps are simpl, high-solid-content preparation can be realized, and the morphology of the assembly is easy to control. It has been used to prepare polymer assembly nanoparticles with various morphologies, among which the most common polymer assembly morphologies are spherical, worm and vesicle, and of course there are also some special polymer nanomorphologies, such as jellyfish, yolk/shell, oligomembrane vesicles and so on^[6]. On the basis of polymer-based assemblies, a variety of methods for preparing organic-inorganic hybrid nanoparticles based on PISA have been gradually formed. Although this has become a hot research direction of nano-hybrid materials, there are few reports on the preparation of SiO₂/ polymer hybrid particles based on PISA. Therefore, we started from the preparation methods of this kind of hybrid materials.After sorting out the relevant literature, we innovatively classified them according to the interaction mechanism between SiO₂ and polymers and the different composite methods, and logically discussed them according to the four methods of physical encapsulation, chemical grafting, supramolecular interaction and in-situ growth. This paper focuses on the principles and steps of the above four synthesis methods, as well as the related properties and applications of the SiO₂/ polymer composites prepared in the literature. At the same time, the advantages and disadvantages of the four synthesis methods and the potential application fields of each method are analyzed and summarized in this paper, hoping to provide a reference for researchers in related fields to select the appropriate composite method according to the performance requirements of composites.It also provides some enlightenment for the future work on improving the synthesis method of SiO₂/ polymer composites and developing new SiO₂/ polymer composites.

In the early stage of research, the most simple and direct way of blending is physical blending, that is, in the absence of external forces, polymer matrix and nano-SiO₂ particles are compounded to obtain SiO₂/ polymer composites. For example, the addition of SiO₂ to epoxy coatings by mechanical mixing and ultrasonic dispersion can significantly improve the thermal stability and resistance to cracking of epoxy coatings^[7]. The conductivity and high thermal stability of the novel gel nanocomposite polymer electrolyte synthesized based on SiO₂ nanoparticles are improved. The addition of SiO₂ adds mechanical stability to the polymer electrolyte and reduces the risk of leakage at high temperatures, thereby improving battery stability^[8]. The composite coating prepared by incorporating SiO₂ into rubber-modified polybenzoxazine (PBZ) can form a nanostructured surface with super-hydrophobic and super-lipophilic properties, which shows effective anti-corrosion and anti-icing properties in practical applications^[9]. The successful preparation of the above SiO₂/ polymer composites lays a good foundation for the preparation of SiO₂/ polymer nanocomposites based on PISA.

In 2019, Zhang et al. proposed a method to prepare SiO₂/ polymer composite electrolyte by PISA one-pot method^[10]. The composite polymer electrolyte (SPE) was synthesized in a one-pot manner by directly adding polyethylene glycol (PEG), polystyrene (PS), lithium bistrifluoromethylsulfonyl imide (LiTFSI), gas-phase SiO₂ nanoparticles, etc. Into the carbonate-terminated polyethylene glycol (CH₃O-PEG-IC), as shown in Fig. 1. In the synthesized SPE, CH₃O-PEG-IC not only acts as a polymerization solvent, but also plays a major conductive role in the SPE. Due to the good compatibility between the PEG shell of PEG-b-PS and the CH₃O-PEG-IC matrix, the PEG-b-PS assembly particles are well dispersed, thus ensuring a continuous lithium ion transport network in the polymer electrolyte. The gas-phase nano SiO₂ particles are used for improving the electrochemical stability and reducing the interface resistance. The electrochemical stability of PISA-SPEs was studied by linear sweep voltammetry (LSV) and cyclic voltammetry (CV) techniques, and the excellent anodic stability of 5. 5 V was demonstrated. Furthermore, LiFePO₄|PISA-SPEs|Li solid state batteries were prepared using polymer electrolytes, which exhibited a stable and reversible specific discharge capacity of 109 mAh/G after 300 cycles at room temperature. The high performance battery prepared in this paper is expected to replace the traditional solid-state lithium battery.

A more specific form of encapsulation is the use of PISA to obtain an advanced assembly morphology, thereby encapsulating nano SiO₂ particles within the cavities of the advanced assembly. There is no interaction force between nano SiO₂ particles and polymer assemblies. Tan Jianbo's team reported in 2015 that photoinitiated PISA successfully prepared vesicles encapsulating SiO₂ nanoparticles^[11]. Macromolecular chain transfer agent mPEG₁₁₃-CEPA was synthesized by esterification of monomethoxypolyethylene glycol (mPEG₁₁₃) and 4-cyano-4- (ethylthiocarbonthio) pentanoic acid (CEPA), and then the commercial SiO₂ nanoparticles were added into the polymerization solution to polymerize hydroxypropyl methacrylate (HPMA) by photoinitiation at 25 ℃. Fig. 2 is a schematic illustration of the preparation of a polymer assembly. It was found that when the concentration of HPMA was high (usually higher than 15%), advanced morphologies of the vesicles could be prepared. According to the transmission electron microscope (TEM) images, the complete conversion of the monomer was completed within 30 min after irradiation. The SiO₂ nanoparticles were also successfully encapsulated within the vesicle assembly, and the presence of the SiO₂ nanoparticles did not adversely affect the morphology of the polymer assembly. Subsequently, in 2019, the team reported the preparation of composite vesicles by enzyme-assisted photoinitiated PISA^[12]. In this paper, CO₂ responsive vesicles loaded with SiO₂ nanoparticles were prepared by photoinitiation under mild conditions. Combining enzyme assistance with PISA ensures an oxygen-free environment during polymerization, and the tertiary amine group on the polymer chain of 2- (dimethylamino) ethyl methacrylate (DMAEMA) enables vesicles to be CO₂ responsive. Nearly quantitative monomer conversion was achieved within 1. 5 H of 405 nm visible light irradiation. Under the alternate treatment of CO₂ and N₂, the obtained vesicles showed reversible expansion and contraction phenomena, and the loading of vesicles SiO₂ nanoparticles would increase after CO₂ treatment.

In 2015, the Armes team synthesized copolymer vesicles loaded with SiO₂ nanoparticles^[13]. The macromolecular RAFT reagent PGMA-CPDB was synthesized by reversible addition/fragmentation chain transfer (RAFT) polymerization of glycidyl methacrylate (GMA) with isobutyronitrile dithiobenzoate (CPDB) as chain transfer agent. The RAFT aqueous dispersion polymerization of HPMA was designed in the presence of SiO₂ nanoparticles with the content of 5% ~ 35% in the polymerization solution. 1H NMR (¹H NMR) studies showed that HPMA conversion rates higher than 99% were achieved within 2 H at 70 ° C regardless of the presence or absence of SiO₂ nanoparticles. PGMA-PHPMA copolymer vesicles were successfully prepared by RAFT-mediated PISA, and the low-temperature TEM image (Figure 3 (1)) confirmed that the SiO₂ nanoparticles were indeed located in the vesicle lumen. The amount of encapsulated SiO₂ nanoparticles within the vesicles can be quantified using disk centrifugal photometry (DCP), thermogravimetric analysis (TGA), small-angle X-ray diffraction (SAXS). Subsequently, the release of SiO₂ nanoparticles was induced by the transformation of vesicle morphology (Fig. 3 (2a-d)), and the release degree and rate of the encapsulated SiO₂ nanoparticles were fine-tuned by changing the release temperature and aging time. The team also reported in 2017 that vesicle morphology transformation driven by dynamic covalent chemistry promotes the release of vesicle-encapsulated nanoparticles^[14]. RAFT aqueous dispersion polymerization was also utilized to prepare PGMA-b-PHPMA diblock copolymer vesicles loaded with SiO₂ nanoparticles. The addition of 3-aminophenylboronic acid (APBA) to this vesicle in turn causes the reagent to bind specifically to some of the side-chain cis-diol groups on the hydrophilic PGMA chain, thereby forming a phenylboronic acid ester bond in weakly basic aqueous solution (pH ≈ 10), which results in a decrease in the packing parameter and thus causes a morphological transition of the vesicle to a worm (or vesicle to a sphere). The release rate can be fine-tuned by changing the pH of the solution and/or the APBA concentration. It is suggested that for many commercial applications, thermal triggering at temperatures below room temperature is unlikely to be desirable; Moreover, vesicles with thick walls do not undergo thermally induced morphological transitions at all, while dynamic covalent chemistry can drive vesicles to undergo morphological transitions at ambient temperature and in the presence of salt, which in turn induces the release of encapsulated nanoparticles. This molecular recognition block copolymer vesicle also expands the scope of targeted delivery and controlled release applications. The SiO₂/ polymer vesicle nanocomposites mentioned in the above articles focus on the stimuli-responsive vesicles obtained, hoping to use this vesicle model to encapsulate proteins, drugs, enzymes and so on for biomedical applications.

The method for preparing the SiO₂/ polymer composite material by the physical encapsulation method is simple and easy to implement, does not need to carry out any pretreatment on the SiO₂ nano particles, and has high economic benefit. As a traditional preparation method of composite materials, physical encapsulation is still widely used in industrial production. At present, there is no method that can prepare nanocomposites on such a large scale as physical encapsulation. However, such a large-scale preparation method of composite materials is usually difficult to meet the high requirements on the performance of composite materials, and the amount of SiO₂ nanoparticles should be controlled, too high content is easy to cause the aggregation of SiO₂ nanoparticles, thus causing the decline of the performance of composite materials. Current research is still exploring new methods to improve the above problems, and this is also a direction of future efforts to prepare high-performance composites by physical blending. In addition, the SiO₂/ polymer composite material prepared by the physical encapsulation method based on PISA is different from the composite material prepared by the traditional physical encapsulation method, and the physical encapsulation method combined with PISA is more inclined to the construction of fine nanostructures, so that the composite material can be better applied at the molecular level.

Chemical grafting can be divided into two types: "grafting to" and "grafting from". "Graf to" refers to that use of grafting to "nanoparticle surface group to condense with specific groups of the polymer. "grafting from" is to first functionalize the surface of grafting from "nanoparticles, and then initiate PISA on the surface to obtain covalently linked SiO₂/ polymer composites. SiO₂/ polymer nanocomposites will now be described in terms of the two graft types described above.

The process of "grafting to" has been used for a long time for the preparation of grafting to "polymer composites. SiO₂/ polymer composite materials with different properties can be prepared by grafting specific reaction sites on the polymer onto SiO₂ nanoparticles through covalent bonds. For example, highly transparent optical films with good film forming and planarity can be prepared by condensation of soluble polyimide (PI) with carboxylic acid end groups with colloidal SiO₂^[15]. Nanometer particles of SiO₂ can be fixed on the surface of the polymer through the condensation reaction of methoxyl groups on the trimethoxysilane (TMOS) modified polymer and hydroxyl groups on the surface of the SiO₂, and the super-hydrophilic surface composite coating with high stability, antifogging, easy cleaning and other properties is obtained^[16]; SiO₂ nanoparticles grafted hyperbranched polyesteramide (HBPAE) as an additive was added into polyvinyl alcohol (PVA) matrix together with lithium perchlorate to obtain a composite polymer electrolyte with greatly improved conductivity^[17]. The methoxyl group of the TMOS modified polybutylene (PB) is bonded with the hydroxyl group of the SiO₂, and the TMOS modified PB can also be used for preparing a corrosion protection coating of low carbon steel^[18]; The coupling agent with the low-molecular-weight sulfur-containing siloxane structure and the organic matter with the aliphatic polyether structure are jointly used for preparing the rubber /SiO₂ composite material, so that the dispersion of the SiO₂ nanoparticles in a rubber matrix can be further improved, and a novel passenger car 'green tire' with extremely low rolling resistance, extremely high skid resistance and extremely high wear resistance can be produced^[19].

With the popularization of the "grafting to" method, the research on the preparation of grafting to "polymer composites by this method combined with PISA has been carried out. Singha et al. Prepared superhydrophobic surface based on PISA in 2017^[20]. First, the copolymer of vinyltriethoxysilane (VTES) and 4-vinylpyridine (4VP), P4VP-co-VTES, was prepared as macromolecular chain transfer agent by RAFT dispersion polymerization. Then, the spherical micelle particles were prepared by soap-free emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) with PISA. The SiO₂ nanoparticles were added to the above latex, and the PTFEMA/SiO₂ composite latex was successfully prepared by covalently connecting the ethoxy group of VTES on the shell of the spherical micelle with the hydroxyl group of the SiO₂, as shown in fig. 4A. The attachment of SiO₂ nanoparticles to the fluoropolymer particles can be clearly observed from the TEM image (4 B). Finally, the composite latex was used to prepare the film and its hydrophobicity was detected. AFM analysis found that the existence of SiO₂ nanoparticles made the surface of the film appear nano-roughness, and the corresponding water contact angle also reached an ultra-high 151.4 ° (Fig. 4C), which proved the superhydrophobicity of the nanocomposite film. According to the thermal analysis data of TGA, the Ts (10% weight loss temperature) is 249 ℃, while the Ts of nanocomposites is 323 ℃. Therefore, the PTFEMA/SiO₂ nanocomposite exhibits higher thermal stability compared to the original PTFEMA. Kong et al. Also prepared a super-hydrophobic film by grafting SiO₂ nanoparticles into two-component waterborne polyurethane. The difference between Kong et al and Singha et al is that Kong et al pretreated the SiO₂ nanoparticles, that is, modified the surface of the SiO₂ nanoparticles with triethoxysilane (TMES) to make the surface of the SiO₂ nanoparticles contain hydrophobic methyl groups, which is more conducive to the hydrophobicity of the composite surface^[21].

grafting from "polymer composites obtained by" grafting from "method cover various aspects and have a wide range of applications. For example, the polymer electrolyte membrane prepared by surface initiation of SiO₂ has ultra-high proton conductivity^[22]. For another example, the prepared SiO₂/ polymer composite additive has good dispersibility and higher mechanical property, antifouling capability, water permeability and the like of the composite material^[23,24]. There are more and more studies on this method, and there are many reports on the preparation of composites based on PISA. Benicewicz group has developed a simple method to prepare nanocomposite particles by grafting polymers on the surface of SiO₂^[25]. In 2012, the team synthesized SiO₂ composite particles grafted with double polymer brushes on the surface of nanoparticles through multi-step RAFT polymerization. Surface-aminated SiO₂ nanoparticles were first grafted with the RAFT reagent CPDB, followed by surface-initiated polymerization of the first monomer, polymethyl methacrylate (PMMA₁, in tetrahydrofuran (THF) solution. After the first polymer brush is obtained, the RAFT reagent on the first polymer brush is subjected to inactivation treatment, the residual hydroxyl of the SiO₂ nanoparticle is then utilized to graft a second RAFT reagent, and the surface is initiated to obtain a second polymer brush PMMA₂, so that the SiO₂ nanoparticle of which the surface is grafted with the double polymer brushes is prepared. They thus proposed a general method to independently control the molecular weight and grafting density of the linked chains. Based on the successful preparation of the above composite materials, the research group successfully prepared SiO₂/ benzyl methacrylate (PHPMA-b-PBzMA) nanocomposite vesicles using the same method combined with PISA in 2017, and the preparation process is shown in Figure 5^[26]. The first block HPMA was grafted onto the surface of 15 nm SiO₂ nanoparticles by RAFT surface initiation in N, N-dimethylformamide (DMF) solution. Then the second RAFT reagent was attached to the surface of unreacted SiO₂ nanoparticles, and the polymerization of BzMA was initiated on the surface, and the self-assembly occurred with the extension of BzMA chain, that is, the SiO₂/ polymer composite vesicles were prepared. The grafting density of the RAFT reagent can be calculated from the characteristic UV absorption peaks and TGA data. In addition, the morphology of the assemblies can be further controlled by adjusting the chain length and grafting density of the two polymer brushes, and the assemblies with other morphologies such as nanotubes and solid spheres are obtained. From the TEM images, it is obvious that the bimodal grafted nanoparticles are more randomly dispersed than the unimodal brush-grafted nanoparticles, so the composites prepared with bimodal grafted nanoparticles as functional additives can show improved mechanical and thermal properties, which provides more potential for the preparation of functional hybrid materials.

In addition to composite vesicles, nanocomposites with other morphologies can also be synthesized. In 2015, Pan Caiyuan's team synthesized pH-responsive diblock copolymer modified SiO₂ nanotubes based on PISA^[27]. They first used RAFT mediated PISA of poly (2- (dimethylamino) ethyl methacrylate) (PDMAEMA) and polystyrene (PS) to prepare polymer nanowires, and the PDMAEMA shell of polymer nanowires containing tertiary amino groups was used as a nanoreactor for depositing SiO₂ nanoparticles. After the deposition is finished, the polymer nanowire is calcined to obtain a SiO₂ nanotube, then the surface of the SiO₂ nanotube is activated and then is grafted with an RAFT reagent, and finally the SiO₂ nanotube of the grafted block copolymer is prepared by surface initiation step by step. Due to the pH responsiveness of the polymer grafted onto the SiO₂ nanotubes, the controlled release of the loaded drug can be achieved by adjusting the pH value of the culture medium. The results of in vitro cell viability and cell internalization studies also demonstrated that the polymer-coated SiO₂ nanotubes have good biocompatibility and excellent endocytosis. In 2019, a polymerization-induced surface self-assembly method for surface reconstruction was proposed, which can also be used to prepare SiO₂/ polymer nanocomposites^[28]. Macromolecular chain transfer agent PDMAEMA was synthesized by RAFT mediated polymerization, and then grafted onto the surface of SiO₂ nanoparticles after surface thiolation to obtain SiO₂/PDMAEMA composite particles. In this method, two RAFT reagents are used, and two kinds of polymerization are carried out simultaneously in the polymerization solution. One is the polymerization of PS initiated by the surface of SiO₂/PDMAEMA nanoparticles, and the other is the polymerization of PS initiated by the macromolecular chain transfer agent PDMAEMA in solution. With the growth of PS chains, self-assembly occurred in solution and on the surface of SiO₂ nanoparticles, respectively, and surface nanostructures consisting of PDMAEMA-PS brushes and "free" PDMAEMA-PS chains were generated on the surface of SiO₂ particles. With the increase of monomer conversion, the polymer morphology on the surface of SiO₂ nanoparticles will change from isolated micelles (Fig. 6) to aggregates and then to layered surface structure, which provides an effective way to control the surface structure and surface chemistry, and can be used to fabricate solid surfaces with different surface chemistry and surface functions.

The application of SiO₂/ polymer nanocomposites prepared by chemical grafting method involves many aspects, and its advantages are obvious.

Generally speaking, SiO₂ nanoparticles are covalently attached to polymers to achieve better stability, which contributes to the stable improvement of composite properties. In addition, the SiO₂ nanoparticles are bonded with the polymer to facilitate the dispersion of the SiO₂ nanoparticles in the polymer matrix, thereby effectively preventing the performance of the composite material from being reduced due to the hydrophilicity and easy aggregation of the SiO₂ nanoparticles, and also facilitating the performance improvement of the composite material. The chemical grafting method based on PISA to prepare SiO₂/ polymer composites is more advantageous, which combines the advantages of PISA, not only enriches the morphology of SiO₂/ polymer composite particles, but also realizes mass production. In addition, when the grafting from "polymer composite particles are prepared by using the method of" grafting from ", the grafting density and the molecular weight of the grafted polymer can be designed to meet different performance requirements of the grafting from" polymer nanocomposites. However, the general chemical grafting method is inevitably affected by the reaction conditions because it involves chemical reactions, and some grafting bonds may involve harsh reaction conditions and unsatisfactory grafting efficiency of polymers. According to the literature, the chemical grafting method is mostly used to prepare composites with special performance requirements, which requires high performance of the prepared composites, so it is doomed that the chemical grafting method is not universal, and it is difficult to achieve large-scale application like the physical encapsulation method.

Supramolecular interaction is a method to obtain composite materials based on non-covalent interaction between molecules, including intermolecular hydrogen bonding, electrostatic interaction, Van der Waals force and so on^{[29⇓⇓~32]}. The SiO₂/ polymer nano composite material is obtained by forming a polymer coating layer on the surface of the SiO₂ nano particle under the action of the supermolecules. In the supramolecular interaction, hydrogen bonding and electrostatic interaction are mostly studied. The following is an introduction to the hydrogen bonding and electrostatic interaction in the supramolecular interaction.

Supramolecular hydrogen bonding refers to the formation of hydrogen bonds between hydroxyl groups on the surface of SiO₂ nanoparticles and specific groups on the polymer chain, which combines SiO₂ nanoparticles with polymers to obtain SiO₂/ polymer composites. Due to the hydrogen bonding interaction between the silanol groups and the amide groups on the surface of the SiO₂ nanoparticles, the prepared SiO₂/CMT-PAM nanocomposite shows the maximum methylene blue (MB) dye adsorption capacity as a high-performance adsorbent^[33]. The polyacrylamide-polyethylene glycol /SiO₂ composite material prepared by utilizing the hydrogen bonding action between the amide groups on the polymer and the SiO₂ nanoparticles is a high-quality drilling fluid formula additive^[34].

As mentioned above, the application potential of SiO₂/ polymer composites synthesized by supramolecular hydrogen bonding is huge, and the research on the preparation of SiO₂/ polymer nanocomposites by combining supramolecular hydrogen bonding with PISA is also carried out. Among them, Bourgeat-Lami's research group has made great achievements. First, they reported the synthesis of multi-legged SiO₂/ polymer composite latex particles in 2015^[35]. A solution of a large alkoxyamine initiator is mix with a commercially available silica sol dispersion, and that large alkoxyamine initiator is physically adsorbed on the surface of the SiO₂ nanoparticle through hydrogen bond interactions. Subsequently, the large alkoxyamine initiator adsorbed on the surface of SiO₂ nanoparticles was used to initiate the emulsion polymerization of n-butyl methacrylate and a small amount of PS under mild conditions (85 ° C), and self-assembly occurred on the surface of SiO₂ nanoparticles to prepare SiO₂/ polymer composites with different morphologies (Figure 7). Kinetic analysis showed that the presence of SiO₂ nanoparticles did not affect the polymerization behavior. With the increase of the macroinitiator concentration, the TEM characterization images showed that the morphology of the SiO₂/ polymer composite particles evolved from daisy-like to pod-like and finally to raspberry-like. With the increase of the particle size of the SiO₂ nanoparticles, a similar morphological evolution also occurs. In this paper, we propose a new factor affecting the morphology of the composite particles: macromolecular initiator, and propose a new surface PISA process for the preparation of SiO₂/ polymer composite particles. Subsequently, in 2016, the team reported the synthesis of SiO₂/ polymer composite latex by RAFT mediated emulsion polymerization, and prepared transparent nanocomposite films by water evaporation^[36]. PEG-based macromolecular RAFT reagents were adsorbed on the surface of SiO₂ nanoparticles through hydrogen bonding, and SiO₂/ poly (methyl methacrylate-butyl acrylate) (PMMA-PBA) composite latex was prepared by surface-initiated PISA. The effects of the properties of macromolecular RAFT reagents, the particle size and concentration of SiO₂, and the surface properties of SiO₂ on the morphology of composite colloidal particles were studied. The preparation method of colloidal nanocomposites in this paper overcomes the use of surfactants in traditional emulsion polymerization, and uses the relatively high hydrophilicity of macromolecular RAFT reagents to provide stability for the assembly in aqueous dispersion. This study not only brings new insights into the morphological parameters affecting RAFT-mediated emulsion polymerization, but also opens up a new way to prepare polymer nanocomposite films with enhanced properties without the harmful effects of the surfactants used.

In 2017, the team again reported the self-assembly of block copolymers on the surface of SiO₂ nanoparticles^[37]. Imilarly, that macromolecular alkoxyamine initiator is adsorb on the surface of SiO₂ nanoparticles through hydrogen bon, and the obtained macromolecular initiator is used for the emulsion polymerization of n-butyl methacrylate and PS,The formed amphiphilic block copolymer is in-situ assembled on the surface of a SiO₂ to form composite materials with various shapes, such as multi-foot shaped, core-shell shaped, snowman-shaped and the like nano-composite particles. The effects of pH and SiO₂ particle size on the morphology of the assemblies were also studied, and it was found that when pH < 6, multipod-like SiO₂/ polymer composite particles were obtained. When the pH is higher, the morphology of the composite is uncertain. When the diameter of the SiO₂ nanoparticles is about 30 nm, the obtained nanocomposite particles are mostly fibers, vesicles and the like; When the particle size of the SiO₂ nanoparticles is larger, the core-shell nanocomposite particles can be obtained. The mechanism of polymerization-initiated self-assembly of block copolymers in the presence of inorganic SiO₂ nanoparticles is first described in detail.

Supramolecular electrostatic interaction means that cationic polymers, monomers and initiators are adsorbed on the surface of silica particles through electrostatic interaction, thus controlling the polymerization reaction on the surface of silica particles. In addition, the surface electrification of the SiO₂ particles can also be changed so as to prepare the anionic polymer /SiO₂ composite material.

Zheng et al. Reported that the synthesized SiO₂/ polymer composites use unmodified SiO₂ nanoparticles as additives, and there is electrostatic interaction between the positively charged polymer matrix and the negatively charged SiO₂ nanoparticles^[38]. The electrostatic interaction between SiO₂ nanoparticles and polymer matrix was investigated by Zeta potential analysis and Fourier transform infrared spectroscopy (FTIR) characterization. It was found that the electrostatic interaction improves the interfacial adhesion and thus contributes to a better dispersion of the SiO₂ nanoparticles in the rubber matrix. Jang et al. successfully prepared polyaniline/polystyrene sulfonate (PANI/PSS) coated SiO₂ nanoparticles composite microspheres by electrostatic interaction^[39]. Firstly, 3-aminopropyltrimethoxysilane is used for carrying out amination modification on the surface of the SiO₂ nanoparticles so that the SiO₂ nanoparticles are positively charged; and due to the charge interaction between the modified SiO₂ and the PANI/PSS, the PANI/PSS can be easily coated on the surface of the SiO₂ nanoparticles in a uniform shell form. The use of the composite SiO₂ nanocomposite microspheres as dispersing materials for rheological fluids shows enhanced rheological activity, providing possibilities for industrial and practical applications. In 2015, Zhu et al. Studied the self-assembly process of polyetherimide (PEI) and SiO₂ nanoparticles with opposite charges, and proposed a new method to construct ultra-thin layers on the surface of polyethylene (PE) separator^[40]. A simple and environmentally friendly molecular self-assembly process of oppositely charged polymer PEI and SiO₂ nanoparticles can improve the thermal stability, ionic conductivity and electrochemical stability of PE separator, thus endowing lithium ion batteries with excellent capacity retention and cycle performance. In 2015, Ding et al. Synthesized SiO₂/ chlorinated polyacrylamide (PMAC) multilayer core-shell nanoparticles with antibacterial ability by layer-by-layer electrostatic self-assembly method. Fig. 8C is the synthesis schematic diagram of the composite particles^[41]. After a solution in which SiO₂ nanoparticles are dispersed is obtained, cationic polyacrylamide (CPAM) and anionic polyacrylamide (APAM) are sequentially added into the solution, stirring treatment is carried out, SiO₂/ polyacrylamide (PAM) composite particles are obtained after centrifugal purification, and then chlorination treatment is carried out to obtain the core-shell type SiO₂/PAMC nano composite particles. Due to the synergistic effect of the SiO₂ nanoparticles and the polymer, the obtained antibacterial core-shell nanocomposite has stable and high antibacterial activity on Staphylococcus aureus and Escherichia coli. Moreover, the in vitro cytotoxicity of the nanoparticles at different concentrations was studied using mouse fibroblasts, and it was found that the synthesized nanoparticles had no cytotoxicity and had adaptive biocompatibility in cell culture evaluation, so the composite material could be used as an antibacterial tool for bacterial infection. Supramolecular electrostatic interactions have been applied to the synthesis of different composites, attracting attention for their simplicity and controllability. The SiO₂/ polyisobornyl acrylate (PMTAC-PBA-PIBA) composite latex prepared by Singha et al. Based on electrostatic interaction combined with PISA showed excellent versatility^[42]. The block copolymer PMTAC-b-PBA was prepared by miniemulsion polymerization with cationic polymer PMTAC as macromolecular RAFT agent, and then the composite latex was obtained by PISA of isobornyl acrylate (IBA) with PMTAC-b-PBA as macromolecular RAFT agent in the presence of SiO₂ nanoparticles. Wherein the negatively charged SiO₂ nanoparticles are adsorbed on the shell layer of the composite assembly through electrostatic interaction with the positively charged MTAC. High-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), and AFM were used to analyze the morphology of the triblock copolymer /SiO₂ nanocomposite emulsion.The core-shell morphology was obtained in the HRTEM analysis of the triblock copolymer, and the TEM image could also observe that the SiO₂ nanoparticles were attached to the surface of the polymer assembly (Figure 8 a). The obtained nanocomposite latex was dip-coated on a glass slide to prepare a thin film, and the SiO₂ nanoparticles were attached to the triblock copolymer and produced a nano-roughened surface, resulting in its super-hydrophobicity. Due to the super-hydrophobicity of the film, the prepared film also has the properties of self-cleaning, anti-icing, anti-bacterial and the like. The method of synthesizing intelligent water-based emulsion in this paper opens up a new direction for the preparation of multi-functional coatings and the application of coatings.

The method for prepare that composite material SiO₂/ polymer composite material by the supramolecular action method generally does not relate to the pretreatment of the SiO₂ nano particle,And that supramolecular action method very ingeniously utilize the characteristics of the active hydroxyl group on the surface of the SiO₂ nano particle and the charge attribute of the SiO₂ nano particle, has mild experiment condition and simple and easy experiment method, and further expands the method for preparing the SiO₂/ polymer nano composite material. In addition, the preparation of SiO₂/ polymer nanocomposites combined with PISA also broadens the factors affecting the morphology of assemblies that are not mentioned in traditional self-assembly methods (such as the concentration of macroinitiators and the particle size of SiO₂ nanoparticles), which provides more controllable factors for the preparation of assemblies with various morphologies. Supramolecular interactions such as hydrogen bonding and electrostatic interactions can also improve the dispersion of SiO₂ nanoparticles to enhance the properties of composites. However, the supramolecular force is weak, and some supramolecular bonds (such as hydrogen bonds) are dynamically reversible, heat and solvents will affect the supramolecular force, which is not suitable for the synthesis of composites with special requirements for strength and hardness. In the future, it is hoped that supramolecular forces with stronger interaction and more specific binding will be applied to SiO₂/ polymer nanocomposites.

The general steps of preparing SiO₂/ polymer composites by in-situ growth method are to prepare polymer assemblies by PISA method, and then use the specific groups on the assembly shell to adsorb and catalyze the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) precursors on the surface of the assembly, so as to generate SiO₂ nanoparticles in-situ on the assembly to obtain SiO₂/ polymer composites.

Nanocomposites prepared by in-situ growth method are also rich and diverse, such as composite coatings, adsorbents, electrolytes, hydrogels and so on. The SiO₂/ pentablock copolymer composite membrane prepared by He et al. Has excellent hydrophobicity, low wettability and high thermal stability^[43]. The PI/SiO₂ nanocomposite films synthesized by Wang et al. Have excellent thermal stability as well as improved optical transparency^[44]. The addition of TEOS to the aqueous medium of the polymer dispersion also prepared an excellent nanocomposite adsorbent material, which can be used to adsorb MB, rare earth ions and the like in aqueous solution with excellent adsorption performance^[45,46]. Lin et al. Synthesized monodisperse SiO₂ nanoparticles by in-situ growth method, and successfully prepared polymer composite electrolytes with high ionic conductivity^[47]. Depa et al. Synthesized SiO₂/ poly (N-isopropylacrylamide) (PNIPAM)/polyaniline (PANI) composite hydrogels with temperature responsiveness and conductivity by in-situ synthesis, which achieved high conductivity and had potential applications in actuators or switches^[48].

The research on the preparation of SiO₂/ polymer composites based on in-situ growth method combined with PISA appeared earlier. In 2016, Thickett et al. Prepared SiO₂/ polymer composite particles with different morphologies through PISA^[49]. In the first step, the macromolecular RAFT reagent containing alkoxysilane functional methacrylate was synthesized, and then the macromolecular RAFT reagent was chain-extended with benzyl methacrylate (BzMA) in ethanol by RAFT dispersion polymerization to obtain rod-like, spherical and vesicular assemblies. Alkoxysilane groups on the polymer assembly are used to catalyze the hydrolysis of TEOS on its surface to grow SiO₂ nanoparticle shells on its surface. The TEM image as shown in fig. 9 can easily observe the growth of a uniform thickness of SiO₂ shell on the vesicle, and the final composite particle morphology obtained depends on the assembly morphology. This method has the potential of one-pot synthesis of SiO₂/ polymer composites. Hong et al. Prepared SiO₂ nanotubes with controllable diameter and length by template-directed method^[50]. Firstly, PDMAEMA-b-PS polymer assemblies were prepared by RAFT dispersion polymerization of PS in methanol under the guidance of macromolecular RAFT reagent PDMAEMA, and the polymer nanowires were obtained by self-assembly of block copolymers, and the nanowires were used as sacrificial templates. The PDMAEMA shell catalyzes the polycondensation of TEOS in a polymer nanowire shell reactor to form hybrid SiO₂/ polymer hybrid nanowires, and finally the SiO₂ nanotubes are prepared by calcining the hybrid polymer nanowires. Pietrasik et al. used the nanospheres prepared by PISA of block copolymer PDMAEMA-b-PS as a template, and successfully generated SiO₂ nanoparticles in situ attached to its surface to obtain SiO₂/ polymer composites^[51]. The basic amino groups on the polymer nanospheres can load the inorganic precursor TEOS onto the nanosphere shell through electrostatic interaction and catalyze its hydrolysis and condensation. When the molar ratio of TEOS to PDMAEMA was 10 ∶ 1, SiO₂ nanoshells were hardly observed on the polymer nanospheres. When TEOS ∶ PDMAEMA = 100 ∶ 1, clear "raspberry-like" composite nanospheres coated with SiO₂ were obtained. The thickness of the SiO₂ nano shell layer is adjusted by adjusting the proportion of the TEOS and the monomer PDMAEMA, thereby greatly simplifying the method of the traditional nano composite material and being applicable to large-scale preparation. In 2018, Rubio et al. Synthesized nanocomposite membranes in a similar way^[52]. The two blocks of poly (N, N-dimethylacrylamide) (PDMA) and PBzMA prepared by RAFT dispersion polymerization were used to form copolymer nanoparticles in ethanol-water binary mixture by PISA, which was used as a template for the deposition of SiO₂ nanoparticles. It was confirmed by TEM that the TEOS precursor was successfully transformed into SiO₂ nanoparticles deposited on the surface of spherical polymer nanoparticles, and the films prepared by spin-coating the above composites showed more robust and durable characteristics.

The research on the preparation of SiO₂/ polymer composites by in-situ growth method has a long history, and the early use of this method is also based on the fact that in-situ growth method is easier to obtain monodisperse SiO₂ nanoparticles, which can achieve better dispersion in the polymer matrix to meet the performance requirements of composites. Combined with the related research of PISA, with the help of the diversity of the assembly morphology, the prepared SiO₂/ polymer nanocomposite particles can also control the morphology of the composite particles by controlling the assembly morphology. But also is different from a composite material prepare by a traditional in-situ growth method, that composite material prepared on the basi of PISA combined with polymerization-induced self-assembly utilizes specific groups on an assembly body to adsorb and catalyze the hydrolysis and condensation of a precursor, so that SiO₂ nanoparticle can be directionally prepared, and the method is significant for preparing the composite material with a specific structure and performance. In addition, the morphology of the composite particles can also be controlled by adjusting the concentration ratio of the TEOS precursor to the polymer monomer, and the performance requirements of the prepared nanocomposites are also guaranteed. The method for prepare that composite material by the in-situ growth method has simple steps, can be use for preparing the composite material which has low performance requirement but needs to be prepared on a large scale, and can also be use for preparing the nano composite material with high performance requirement. The in-situ growth method, which combines the two advantages, can be conveniently applied to nanocomposites with different performance requirements.

To sum up, PISA-based nanocomposites provide more diverse possibilities for the preparation of SiO₂/ polymer nanocomposites. According to the interaction mode between SiO₂ nanoparticles and polymer matrix, the related properties and applications of composites under different compounding methods were systematically expounded in this paper. It is worth pointing out that any synthesis method is not perfect, so it can be selected according to the performance requirements of the actual composite materials. As a traditional composite method, physical encapsulation is always the first choice for preparing SiO₂/ polymer composites on a large scale. Because of its simple preparation method, it is difficult to achieve precise control of its performance, and in order to control the aggregation of untreated SiO₂ nanoparticles, it can only rely on the control of their dosage. Balancing the amount of SiO₂ nanoparticles with the required strength of the composite is also an issue for physical encapsulation. If the properties of the composite materials are required to be high, or the strength of the composite materials is required to reach the high filling of SiO₂ nanoparticles, the chemical grafting method or the in-situ growth method can be used. Both of them can achieve the good combination of polymer matrix and SiO₂ nanoparticles and the good dispersion of SiO₂ nanoparticles, which ensures the excellent performance of nanocomposites. In contrast, chemical grafting may involve complex and harsh reaction conditions, unstable polymer grafting efficiency and low grafting efficiency, so it is not suitable for large-scale preparation of composites. Moreover, the conditions and modes of grafting SiO₂ nanoparticles with different polymers are difficult to be unified, which adds more uncertain factors to the preparation of SiO₂/ polymer nanocomposites by chemical grafting.How to optimize and simplify the experimental conditions of the preparation of SiO₂/ polymer nanocomposites by chemical grafting method and ensure that it is in a stable state is a direction for the improvement of chemical grafting method in the future, only in this way can it be possible to prepare SiO₂/ polymer nanocomposites by this method for large-scale application. In-situ growth method, as a dominant composite method, is the least limited one at present, but in the in-situ growth method, the combination mode of SiO₂ nanoparticles and polymers is changeable (both chemical bonds and supramolecular interactions are involved).Therefore, its limitations are also reflected in the different ways of combination, chemical bonding may have the limitations of chemical grafting, and supramolecular interaction may have the limitations of supramolecular interaction. As a novel method, the successful preparation of supramolecular interaction has brought people a bright feeling, which brings infinite possibilities for the preparation of organic/inorganic nanocomposites, but the supramolecular interaction is weak, which is not suitable for the synthesis of nanocomposites with special requirements for strength and hardness. In addition, the advantages and disadvantages of the above four methods are summarized in Table 1. The way of preparing SiO₂/ polymer nanocomposites based on PISA combined with the above methods is more innovative, and it is certain that with the deepening of the research methods of SiO₂/ polymer nanocomposites, it will inevitably bring deeper excavation of SiO₂/ polymer nanocomposite, so as to better play its advantages.