Polyglycolic acid is a thermoplastic polymer and an aliphatic polyester. Plant resin is a viscoelastic solid polymer. Nylon was the first commercially successful synthetic thermoplastic polymer. Acrylic paint is fast drying paint containing pigment suspension in acrylic polymer emulsion. One common substrate is glass fibre coated with polybrene, a cationic polymer. The terms polymer and resin are often synonymous with plastic. It is a thermoplastic (semi-)crystalline polymer, and a type of polyester. Acrylic paint is a fast-drying paint made of pigment suspended in acrylic polymer emulsion. Infrared spectroscopy is also useful in measuring the degree of polymerization in polymer manufacture. Chemical crosslinks consist of covalent bonds between polymer strands. The monomer adds to the pyrophosphate end of the growing polymer. This motif represents crosslinking of the linear polymer. Cellulose is the most abundant organic polymer on Earth. Many viscoelastic materials exhibit rubber like behavior explained by the thermodynamic theory of polymer elasticity. Polyesters are also susceptible to similar polymer degradation reactions.