In some respects thermosets are the opposites of thermoplastics: When heated they aren’t getting soft or even melting, but decompose, since their melting temperature is above the decomposition temperature.
Furthermore, if forced, they don’t deform, but rather break. Overall they are much harder and more brittle than thermoplastics. If you want to process them, you have to do that machanically – as e.g. with wood by sawing, filing or rasping (in practice, however, PVC items are produced in the desired form right away and don’t need mechanical treatment).
Polyesters are versatile plastics which accompany our everyday life. All sorts of things may be produced of Polyesters. Apart from textile fibres (like Trevira®, Dacron®, Diolen®) there are for example the famous plastic beverage bottles made of PET (polyethylene terephthalate) and other food packaging. Even CDs are made of polyester, namely polycarbonate, which is an ester of carbonic acid.
As a textiel fibre PET has several useful properties: It is hardly strechable and therefore very shape-retaining, crease-resistant, tearproof and only takes little water, so it’s very suitable e. g. for sportswear, which is meant to dry quickly on the body to avoid cooling down.
Copolymerization influences the properties of plastics by combining various plastics with different properties to one single plastic. This means that copolymeres don’t only consist of one sort of plastic, like polyacrylic, but of two or more, like polyacrylic and PVC.
The essential characteristic of elastomeres is that they may be stretched to at least twice their length and return to their original state when released.