Molar mass distributions of end‐linked polystyrene star macromolecules

Polystyrene three-arm star molecules with OH tips were prepared by living anionic polymerization using an acetal-protected lithium initiator followed by coupling with 1,3,5-triallyl-oxy-2,4,6-triazine and ensuing cleavage of the acetol groups. The functionalized star molecules were end-crosslinked by toluene-2,4-diisocyanate. Randomly branched samples with various extents of crosslinking were prepared under conditions of full conversion of the isocyanate groups. The samples were fractionated analytically by SEC in on-line combination with LALLS and a viscosity detector. The mass fraction molar mass distributions could be well fitted by the Flory-Stockmayer distribution if the degree of crosslinking was X 200. Power-law behaviour was already obtained at X 70, but the exponent τ exp = 2.36 was found to lie between τ Fs = 2.5 for the mean field approximation and τ perc = 2.2 for the percolation prediction.