# A Review of the Synthesis and Applications of Polymer-Nanoclay Composites
## 2 Synthesis
### In-Situ Polymerization Method
#### 2.3.1 Surface-Initiated Controlled/Living Radical Polymerization (SI-CLRP)  
Traditional in-situ polymerization methods involve the initial swelling of layered silicates within a monomer to enable the formation of the polymer within the monomer-clay sheets; the polymerization process can be initiated by heat or radiation, and simply by the diffusion of a suitable initiator or catalyst [41]. The surface-initiated controlled/living radical polymerization(SI-CLRP) method improved the polymerization process by which exfoliation could be facilitated by polymer chains growing from nanoclay filler surfaces, leading to finely-dispersed polymer composites [115]. SI-CLRP delivers an excellent way to ensure and maintain the random dispersion of the single-clay layers and, simultaneously, provide more control over the polymer properties, such as molecular weight, dispersity, functionality, topology, and architecture [116]. Compared to conventional free radical polymerization, controlled radical polymerization minimizes side reactions and allows the synthesis of unprecedented functional polymers with narrow molecular weight distributions while retaining the tolerance of fiberglass reinforced polymers to various reaction conditions. In the SI-CLRP process, polymerization initiators (silane coupling agents, organic salts) are commonly immobilized between the clay layers by replacing the cations of the clay surface. During this polymerization step, the clay layers are highly exfoliated and dispersed [117]. A variety of novel SI-CLRP methods have been developed to improve the properties of synthesized polymer/nanoclay composites, including nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, ring-opening polymerization (ROP), ring-opening metathesis polymerization (ROMP), living anionic polymerization and living cationic polymerization [118]. SI-CLRP has proven to be the most efficient approach in the preparation of core\(-\)shell polymer/nanoclay composites, enabling precise control over the structural parameters of the tethered polymer chains, thus significant technological improvements have emerged since the introduction of the CLRP method over the past 20 years [119]. [PERSON] et al. [120] provided a comprehensive review of the materials obtained by SI-CLRP and their applications, particularly focusing on ATRP. Their study noted that ATRP has been applied for the synthesis of polymer/nanoclay composites, allowing precise control over the particle brush architectures with various polymers. [PERSON] et al. [121] grafted amphiphilic polymer brushes on the surface of halloysite nanoclay via a RAFT method and studied the Pickering emulsification behavior of the composite in a water/soybean oil diphase mixture. [PERSON] et al. [122] proposed a novel approach to graft PS from polydopamine-coated silica particles by RAFT grafting. The approach indicated a significant high grafting density. [PERSON] et al. [123] pioneered a combined polymerization approach (inverse miniemulsion periphery RAFT) for the synthesis of hollow polymer/nanoclay composites, which was a promising material for water-soluble drug delivery applications. Their approach provided a reaction-free interior for the loading of drugs and allows one to readily tune the shell thickness. [PERSON] et al. [124] prepared poly(methyl methacrylate)/ MMT composite materials by the in-situ radical bulk polymerization method. The obtained composites exhibited enhanced storage modulus and mechanical properties. [PERSON] et al. [125] reviewed the various advantages arising from the use of CLRP in synthesizing molecularly imprinted polymers, in terms of sheer binding properties and their remarkable potential for post-polymerization functionalization.