ABSTRACT
Polymers are high molecular weight materials that came to have a wide variety of uses during the twentieth century. Polymers can be made both by modification of natural materials and by synthesis. Modifications of cellulose provide fibers and films such as rayon and cellophane. Synthetic polymers began with phenol-formaldehyde resin and urea-formaldehyde resin. Polymers based on hydrocarbons include polyethylene, polypropylene and polystyrene. Other types of polymers include polyamides, polyesters, polyurethanes and vinyl polymers. The properties of polymers can be controlled by the method of preparation and subsequent treatment. They can assume many shapes and forms including films, sheets, fibers, foams and coatings. Solid objects can be made by molding.
