Which part of an atom is directly involved in chemical changes

The answer is The valence Electrons

Explanation:

The number of electrons in the outer layer of a particular atom determines its reactivity or tendency to form chemical bonds with other atoms. This outer layer is known as the valence layer and the electrons that are inside it are called valence electrons, which are the electrons that are in the highest energy layer of the atom, these being responsible for the interaction between atoms of different elements or between atoms of the same element, also being used in the formation of compounds due they are easy to form links.

the dissolution of polymer can be thermodynamically described in 2 steps.