"Side chain engineering" research has yielded many promising and beneficial results, with applications in various fields. However, this research did not receive sufficient focus when nature-sourced polymers are concerned. In this study, we have performed side chain engineering on chitosan, a nature-sourced polysaccharide, by coupling it with a number of aliphatic aldehydes of varying chain lengths. The side chains' length and the pursuing effect on the modified products' properties were studied in great detail. In terms of coupling yields, it was found that some substituents have displayed more favorable results than others by a factor of over 35 times. When studying the modified polymers' physical and mechanical properties, some of them were found to exhibit more rigid mechanical properties by a factor of 3.5 times than others. The effect was also expressed through self-assembly concentrations and encapsulation capabilities of the modified polymers. Remarkably, the combined experimental and calculated kinetic studies showed the results do not necessarily follow a linear progression relating to substituent chain length, but rather a parabolic pattern with a specific extremum point. This study has assisted in shedding light on the inspected phenomenon, explaining that not only steric and electronic factors but also interfacial solubility related factors govern the coupling reaction and the resulting modified polymers' properties. As chemical protocols in various academic, clinical, and industrial studies around the world slowly shift their norms toward finding safer ways for the production of novel materials and technologies, nature-sourced polymers hold great promise as virtually inexhaustible raw materials. The perfection of their chemical modification is therefore relevant now more than ever, with far-reaching and diverse applicative prospects.