text: Common synthetic polymers have main chains composed of carbon, i.e. C-C-C-C....  Examples include polyolefins such as polyethylene ((CHCH)) and many substituted derivative ((CHCH(R))) such as polystyrene (R = CH), polypropylene (R = CH), and acrylates (R = COR').
  Other major classes of organic polymers are polyesters and polyamides.  They have respectively -C(O)-O- and -C(O)-NH- groups in their backbones in addition to chains of carbon.  Major commercial products are polyethyleneterephthalate ("PET"), ((CHCOCHOC(O))) and nylon-6 ((NH(CH)C(O))).