The first representatives of main chain unhydrolysable linear polymers made up of levoglucosan units were synthesized in 1985 by anionic polymerization of 2, 3-epoxy derivatives of levoglucosan ( 1, 6; 2, 3-dianhydro-4-O-alkyl-?-D-mannopyranoses ).
22.
Polystyrene standards with PDI of less than 1.2 are typically used to calibrate the GPC . Unfortunately, polystyrene tends to be a very linear polymer and therefore as a standard it is only useful to compare it to other polymers that are known to be linear and of relatively the same size.
23.
Whereas an uncharged linear polymer chain is usually found in a random conformation in solution ( closely approximating a self-avoiding three-dimensional random walk ), the charges on a linear polyelectrolyte chain will repel each other via double layer forces, which causes the chain to adopt a more expanded, rigid-rod-like conformation.
