Polymers $(15$ P$)$

Today, polylactic acid $($PLA$)$ is one of the most widely used biodegradable polymers.

a$)$ PLA belongs to the group of thermoplastics. What are the main differences

between thermoplastics and thermosets $?(4$ P$)$

b$)$ PLA can be made by polycondensation of monomer lactic acid:

Lactic acid

Draw the chemical structure of the repeating unit of PLA. $(3$ P$)$

c$)$ Which of the following designations are correct for PLA $?$ Briefly explain

your choice. Caution: Wrong ticks compensate correct ticks. $(3$ P$)$

Homopolymer

Copolymer

Polyester

Polyamide

Polyolefin