## 6 Impact of Multi-Arm Topology on PCL-Based Polymer Properties for Drug Delivery  
PCL star polymers synthesized through ring-opening polymerization using multifunctional initiators have been extensively studied due to their potential for various applications such as investigating thermal behaviors, unimolecular micelles, and as the polymer network components. [PERSON]'s paper [156] demonstrated that increasing the number of arms in multi-arm structures of PCL star polymers leads to a decrease in melting temperature, crystallization temperature, and degree of crystallinity. Furthermore, PCL star polymers with more branches have slower crystallization rates despite having higher molar mass, contrary to the behavior of linear chains, where higher molar mass results in increased crystallinity (Figure 3). Other thermal studies on star-shaped PCLs with 8 arms [157], 6 arms [158], and 7 arms [159], as well as on star-shaped PCLs with 8-arms [160] and silsesquioxane (with an average of 30 arms) [161], have shown the same tendency of lowered melting temperatures. In addition, star polymers exhibit significantly improved thermal stability when compared to linear polymers of the same molecular weight. In this regard, recent work revealed that the crystallization rate of PCL (\(X_{\text{c,PCL}}\)) reaches a maximum value of 65.3% for the linear polymer, with a subsequent decrease observed as the number of PCL arms increases. The order of crystallinity was found to be as follows: \(X_{\text{c,LPCL}}>X_{\text{c,3 PPCL}}>X_{\text{c,4 SPCL}}>X_{\text{c,6 PCL}}\)[162]. It was noted that the degree of crystallinity of the host polymer matrix seemed to be an important parameter because higher drug release rates were observed in polyesters with a low degree of crystallinity [163]. Evidently, several studies have shown that the degree of crystallinity of the copolymers directly influenced their apparent enzymatic degradation and, consequently, their efficiency to inhibit the drug target [164]. These fabulous results observed with multiple-armed macromolecular chains have laid the groundwork for the development of more complex architectures that are based on variations in arm structures. One such architecture is the miktoarm, or \"mixed arm\", which will be discussed in detail next. According to the literature findings (summarized in Table 2), these architectures exhibit lower thermal transition temperatures and lower crystallinity than linear analogues. Figure 3: Influence of Arm Number in PCL Star Polymers on Melting Temperature, Crystallization Temperature, and Degree of Crystallinity. The development of multi-arm polymers is a subfield of PCL-based macromolecules that has garnered significant attention. The combination of ring-opening polymerization with other polymerization methods, such as ATRP, NMP, RAFT, and click conjugation, has enabled the creation of intricate structures [173; 174; 175]. As a result of the flexibility of these combined techniques, a diverse array of architectures can be obtained. The work of [PERSON] [176] and [PERSON] and colleagues [177] facilitated the first experiments that demonstrated the potential of multi-arm polymers in forming new types of nanoaggregates that were previously unseen with linear topologies, such as star structures with cross-linked cores (core cross-linked star). One of these works utilized PCL-PMMA, which was produced by linking homopolymers of PCL and PMMA. The variation in the length and arms of PCL led to the creation of a wide range of nanocapsules that can be degraded in a selective manner based on the length of the PCL arm, something that was not achievable with linear architectures. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Polymers** & **Type** & **Arms** & \(\mathbf{T_{C,PCL}}\) & \(\mathbf{T_{m}}\) & \(\mathbf{T_{g}}\) & \(\mathbf{X_{C}\%}\) & **Molten State** & **Morphology** & **Year** & **Ref.