A Blob Model To Study Chain Folding by Fluorescence

Monodisperse polystyrenes (M w /M n < 1.15) with molecular weights of 6K, 40K, and 110K and one polydisperse polystyrene (M w /M n = 1.5) with a molecular weight of 110K were synthesized. The chromophore pyrene was randomly and covalently attached onto the polymers. The dynamics of the chains were investigated quantitatively by monitoring the fluorescence of the pyrene monomer. The polymer coil was divided into several blobs among which pyrene is randomly distributed according to a Poisson distribution. The kinetics of the pyrene groups are monitored by only three parameters: k diff , the rate at which one excited pyrene encounters one ground state (GS) pyrene inside a blob; k e [blob], the product characterizing the exchange of GS pyrene between blobs (k e is the rate of exchange and [blob] is the blob concentration inside the polymer coil); and (n), the average number of GS pyrene per blob. We show that the parameters retrieved by this analysis are internally consistent within the theoretical framework of the blob model. A critical polymer chain length is found above which polymer chain dynamics behave in a similar manner, regardless of the size of the polymer. Below the critical polymer chain length, chain dynamics are chain length-dependent.