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
Rubber toughening and crazing interaction theory, and more recently those including the effects of critical ligament thickness, critical plastic area, voiding and cavitation, damage competition and others. In 1956, the microcrack theory became the first to explain the toughening effect of a dispersed rubber phase in a polymer. Two key observations that went into the initial theory and subsequent expansion were as follows: (1) microcracks form voids over which styrene-butadiene copolymer fibrils form to prevent propagation, and (2) energy stored during elongation of toughened epoxies is released upon breaking of rubber particles. The theory concluded that the combined energy to initiate microcracks