In
polymer chemistry,
branching occurs by the replacement of a
substituent, e.g., a
hydrogen atom, on a
monomer subunit, by another
covalently bonded chain of that
polymer; or, in the case of a
graft copolymer, by a chain of another type. In
crosslinking rubber by
vulcanization, short
sulfur branches link
polyisoprene chains (or a
synthetic variant) into a multiply branched
thermosetting elastomer. Rubber can also be so completely vulcanized that it becomes a rigid
solid, so hard it can be used as the bit in a
smoking pipe.
Polycarbonate chains can be crosslinked to form the hardest, most impact-resistant thermosetting
plastic, used in safety
glasses.