## 6 Impact of Multi-Arm Topology on PCL-Based Polymer Properties for Drug Delivery
This wealth of structure-physical property allows the copolymer arm to become a particular choice in various domains, especially for the formation of nanoaggregates that are performed by the separation of phase and thermal properties, such as the \(\mathrm{T_{g}}\) and \(\mathrm{T_{m}}\) of the copolymer. The advancement in copolymer synthesis has resulted in the creation of alternative architectures known as \"Y-shaped structures\". These special star-shaped polymers have garnered significant attention due to their one-of-a-kind morphology and phase behavior. [PERSON] et al. [PERSON] et al. (2016) were able to synthesize AB\({}_{2}\) type star polymers (A:PBA) by using a combination of (RAFT), (ROP), and \"Click\" chemistry (Figure 5). Their PCL-based polymers have attracted particular interest in the field of controlled drug release. Those  
Figure 4: The potential of multi-arm polymers to form new types of core cross-linked stars and their eventual hydrolysis. architectures have unique sol-gel properties, where they can be injected in the form of a solution and form gels at body temperature. Analysis shows that the melting temperature (T\({}_{\rm m}\)) of PCL blocks increases with the number of CL repetitive units per hydroxyl. The obtained multi-arm polymers are crystalline because the T\({}_{\rm m}\) value of the polymers is higher than room temperature. This has also been observed in several studies such as the A\({}_{2}\)B\({}_{2}\) multi-arm polymers of PCL-b-PS radiating from a pentaerythnitol core, which have shown lower thermal transition temperatures and lower crystallinity compared to their linear architecture [78; 179]. Varying the length of the PCL arm not only influences the thermal properties of the copolymer but also impacts the characteristics of the resulting nanoaggregates. It was found by the group of [PERSON] [180], who presented an elegant methodology for generating multi-arm stars based on (PCL)\({}_{2}\)-PS and (PCL)\({}_{2}\)-PMMA, that changing the length of the PCL arm chain allowed for the modification of the thermal stability of the micelles and also for the modulation of their size during self-assembly, which is of great interest in the field of nanoaggregate formation. Another promising result was also achieved by [PERSON] and colleagues [181]. The AB\({}_{2}\)-type miktoarm copolymer (PEG-PCL\({}_{2}\)) was synthesized using a \"core-first\" strategy, which involves functionalizing the end of the mPEG chain, leading to the formation of two initiation centers on the mPEG macroinitiator for PCL arm growth. Polymerizations were carried out with different equivalents of the CL monomer to give a series of multi-arm copolymers with different PCL lengths. Linear PEG-b-PCL diblock copolymers, with a composition and overall molecular weight similar to that of miktoarm PEG-PCL\({}_{2}\) copolymers, were also prepared to better understand the structure-property relationship between multi-arm copolymers and their linear counterparts (Figure 6). Figure 5: The Evolution of Melting Temperature (Tm) of PCL Blocks with CL Repetitive Units in Y-Shaped Structures. The structures based on multiarms demonstrated a superior capability compared to micelles formed from linear block homologues. Additionally, multi-arm micelles loaded with the DOX molecule exhibited a reduced release rate, increased cellular absorption, and improved cytotoxic effects compared to linear copolymer micelles. This finding indicated that multi-arm structures are more suitable than other morphologies for the efficient administration of drugs. The relationship between topology and its effect on self-assembly properties will be discussed in other sections. Modifying the composition of the copolymer in a multi-branched topology can lead to a more significant effect, namely a variation in the types of nanoaggregates formed depending on the structure. [PERSON] et al.