Branching (polymer chemistry) Branching (polymer chemistry) 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. Branched polymers have more compact and symmetrical molecular conformations, and exhibit intra-heterogeneous dynamical behavior with respect to the unbranched polymers. 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
Toughening several mechanisms that can be employed to toughen a given material such as limiting the initial amount of inclusions, dispersing small particles that will not initiate fracture, or the addition of plasticizers in the case of polymers. Toughening Toughening refers to improving the fracture resistance of a given material. Crack propagation has an associated irreversible work, which is related to a material's toughness. Designing against this crack propagation leads to toughening the material. For the case of a ductile material such as a metal, this toughness is typically proportional to the fracture stress and strain as well as the gauge