Plastic is a frequently used material that can vastly harm the environment. Most disposed plastics persist in the environment, breaking down into smaller particles known as microplastics that harm aquatic life and humans. Polymers capable of degradation can alleviate the presence of microplastics in the environment, but degradation rates are often slow (>100 years) and harsh acidic or basic conditions may be required for complete degradation.
Another significant source of the persisting plastic waste in the environment comes from paints and coatings, via breakdown of paint debris after the product serves its intended use. Like plastics, the polymeric particles end up persisting in the environment. Paint and coating formulations can additionally contain organic solvents which release volatile organic compounds (VOCs) that are harmful to the environment and human health. A safer alternative are water-based formulations, but they often lack consumer-desired qualities such as high gloss and a smooth finish.
Research conducted by Ho et al. explores the design of water-based coatings with the formation mechanism of solvent-based coatings using CO2-responsive polymers. In the presence of carbonated water, the polymer is protonated and dissolves in the water, while reverting to the unprotonated form when CO2 is removed. Use of such polymers for coating applications avoid the need for traditional organic solvents and offers desired coating qualities.
This research aims to build on the work from Ho et al. to design a polymer that is both CO2-responsive and degradable. A polymer with both capabilities can reduce the presence of persistent particles in the environment and avoid the use of organic solvents. The CO2-responsiveness can occur as a response to a pH change in the external conditions (bodies of water) after the polymer serves its purpose, encouraging degradation by increasing water uptake.
To design the polymer, both a CO2-responsive portion and a degradable portion are required. The degradable portion contains molecules capable of chemical hydrolysis, such as esters, and the CO2-responsive portion contains a tertiary or bulky secondary amine that allows switching. Once a polymer with both capabilities is synthesized, tests will be performed to investigate the rate of degradation, and the conditions that best facilitate break down of the polymer. CO2-responsiveness testing will additionally be done in water with different pH values, to ensure protonation of the polymer in the necessary conditions to become soluble. Once the degradable and CO2-responsive polymer can be adequately tested, it can be ideally used as an alternative to current coating materials. Exploring degradable and CO2-responsive polymers will address the issues of persistent microplastics associated with current coatings and plastics.