4-Methylisophthalic acid is primarily used as an intermediate in the synthesis of more complex chemical compounds. It plays a significant role in the production of high-performance polymers, particularly polyesters and polyamides, which are valued for their thermal stability and mechanical strength. These polymers are often utilized in the manufacturing of fibers, films, and engineering plastics for automotive and electronic applications. Additionally, it serves as a building block in the development of liquid crystal polymers (LCPs), which are essential in the production of advanced display technologies and high-temperature resistant materials. Its derivatives are also explored in pharmaceutical research for the creation of novel drug molecules.