Environmental and economic concerns associated with petroleum-based plastics waste are pushing significant efforts to the introduction of cleaner sustainable technologies. The highest priorities are methods avoiding the use of polluting and unsafe volatile solvents/chemicals; and allowing the facile replacement of the petrol-based monomers by monomers issued from annually renewable resources. With this respect, the polycondensation – a step-growth polymerization - is being attracted much attention. Polycondensation is widely used in Nature, being the main synthetic platform for natural polymers such as proteins and cellulose. In our man-made technology, the process plays an important role in the synthesis of commodity and technical polyesters and polyamides - versatile classes of polymers covering large applications going from fibers to high-performance polymers, thermoplastics and elastomers. Hence the communication will highlight the benefits of using combined melt-polycondensation to other synthetic procedures as chain-coupling or “click” reactions in order to tailor the properties of the functional (co)polyesters. The results have shown that such combined/copolycondensation can be used as a green method to design sustainable plastics going from reinforcing agents to dispersants and curable coatings. To extend the range of functional polymers, the solid-state modification (SSM) from batch into a continuous process by reactive extrusion (REx) will be discussed as well. It represents an easy-to-use and solvent-free tool as it only affects the amorphous part of the polymer, thus preserving its initial mechanical properties while enhancing its recyclability extent. This last study encompasses the design of a new process for recycling polymeric materials and offers the possibility of making polymers more sustainable and recyclable.