**2.1 Polymers with temperature sensitivity**

These are polymeric frameworks that are susceptible to thermal fluctuations. These polymers exhibit a gel-to-gel shift as temperature dependent, and can be used to deliver medicinal compounds in vivo. This sort of system seems to have a crucial temperature of the solution (usually in aqua) where the polymer and solution phases shift according to respective content. The solubility of several polymers varies dramatically as a result of ambient temperature. This characteristic was used to create aqueous solutions of these polymeric materials that go through a sol-gel changeover when the temperature varies. A maximum crucial solution temperature (MaxCST) exists for thermally sensitive polymer blends that display one component above a specific temperature with phase separation underneath it (MaxCST). Polymeric solutions that seem to be monophasic under a certain temperature but biphasic beyond that temperature are said to have a minimum crucial solution temperature (MinCST) [33, 34]. The MinCST seems to be the temperature where a polymer solution divides into two portions (anisotropic and isotropic states), abundant and deficient in the polymer. Such solution also is monophasic under a certain temperature but biphasic beyond that degree. The enthalpy parameter, which is connected to hydrogen bonding here between polymer and the water molecules, is accountable for polymer breakdown underneath the MinCST. When temperatures are raised just above MinCST, the entropy component (lipophilic contacts) takes precedence, resulting in polymer deposition. Among the most biocompatible polymers with MinCST characteristics includes poly (ethylene oxide). Nevertheless, based on the molecular mass, the MinCST transition of poly (ethylene oxide) aqueous solutions happens at ambient temperature, spanning between 100° C to 150° C. At minimum temperatures than just the poly (ethylene oxide) MinCST, a polymer with ethylene oxide components and hydrophilic sections (e.g. ethanol) would show phase changes. When a linear polymer with small sufficient Ethylene oxide sections is utilized to avoid micelle production, the precipitating from the aqueous phase can be thought about as a rapid MinCST changeover. Furthermore, in the lack of intermolecular and intramolecular hydrogen bonding, a continuous alternation of ethylene oxide-ethylene monomer copolymer pattern throughout the polymer would result in a MinCST defined either by lipophilic/hydrophilic equilibrium.
