The most common polymer is polyethylene , which has only hydrogen atoms are attached to its carbon chain. The more branches a polymer has, the greater the tendency for the polymer to be in the amorphous state. Important branched polymers are polyethylene and polypropylene . Rubbers are generally cross-linked by a process known as vulcanisation in which a sulphur atom forms the bridge between chains. Resins are heavily cross-linked chemically forming mammoth 3D amorphous structures.
Crystals have a geometrical arrangement of atoms, which is repeated indefinately.
The bond type and atom size determine the crystal structure. Some crystal structures are fcc, bcc, hcp and diamond. Amorphous solids do not have long range atomic order because the sub-units are disordered. Polymers have long Carbon chains which are held together by a combination of weak and strong bonds.