The Mechanism for Stopping Chain and Total-Molecule Growth in Complex Branched Polymers, Exemplified by Glycogen.

glycogen as the blood-sugar(glucose) reservoir in animals, and starch as both the glucosestorage polymer for plants and the largest component of humanfood energy. The functional properties of these polymersdepend on their molecular structure. One structural feature ofsignificance is the molecular weight distribution of individualbranches (or chain-length distribution, CLD, in the parlanceused for starch). This is controlled by two rates: those of chaingrowth (propagation) and of chain stoppage. Chain stoppagemechanisms include transfer, abstraction or radical−radicaltermination for free-radical polymerization, and, for starch andglycogen, by branching enzyme (BE).For unbranched polymers (with only one chain), chainstoppage also stops the growth of the whole molecule.However, the only “chemical” mechanisms stopping thewhole (branched) molecule growing indefinitely are depletionof monomer or of one of the reactants or catalysts for chaingrowth. There can also be physical events stopping growth ofthe whole molecule and of an individual chain. A primeexample of these is steric hindrance (also termed crowding), forexample, in dendrimers

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