Chain expansion process from knotted globule

Knotting in a polymer chain was investigated by observing the chain expansion process from a collapsed chain for the solution of poly(methyl methacrylate)(PMMA) with Mw = 1.22 × 107 in the mixed solvent tert-butyl alcohol + water(2.5 vol%). Because of very slow phase separation in the solution the chain collapse after a temperature drop and chain expansion after a jump were determined by static light scattering. PMMA chain was shown to collapse rapidly to an unknotted globule, which subsequently contracted slowly to a knotted globule. The chain expansion process from the knotted globule was dominated by the chain compactness and the degree of knotting of the initial globule. A complete chain expansion from a heavily knotted globule often required a very long time indicating an existence of long-lived knots. The chain expansion from the unknotted globule occurred too fast to be followed by scattering experiment.