A chemical engineer is tasked with developing a new type of biodegradable plastic. They decide to use a polymerization reaction involving lactic acid as a monomer. Which of the following principles of polymerization are most critical for ensuring the resulting polymer has the desired properties, such as strength and biodegradability?

The most important ideas are that the polymerization must give the right chain length and stereochemistry, because these determine both strength and how fast the material breaks down. In a lactic‑acid polymer, a ring‑opening or condensation reaction must be carefully tuned so that the average molecular weight is high enough for strength but not so high that biodegradation is too slow. The reaction conditions—temperature, catalyst, and monomer purity—control how many chains grow and how they are arranged (isotactic versus heterotactic), which in turn sets the crystallinity that affects both toughness and biodegradability. For example, using a tin‑based catalyst in ring‑opening polymerization of lactide can produce a PLA with a controlled molecular weight and high isotacticity, giving a strong yet biodegradable plastic.