Enhanced Site Isolation in Cross-Link-Functionalized Polystyrene Networks: Mobility Studies Using Steady-State Fluorescence and ESR Techniques

Enhanced site isolation and reduced site mobility have been demonstrated in polystyrene networks having trityl functionality at the cross-links through steady-state fluorescence measurements of intraresin excimer formation by 4-(1-pyrenyl)butanol labels and through ESR nitroxide spin-label studies. Suspension copolymerization of α,α-bis(4-vinylphenyl)benzyl alcohol with styrene afforded beads having trityl groups at the cross-links (C·Tr). Pendent-functionalized beads (P·Tr), prepared by copolymerization of α,α-diphenyl-4-vinylbenzyl alcohol with styrene and divinylbenzene served as a reference. Comparison of ( I e / I m ) as a function of polymer loading and solvent demonstrated that cross-link functionalization reduced site interactions, providing 30% higher effective dilution of labels. ESR of polymers labeled with 2,2,6,6-tetramethyl-4-oxopiperidin-1-oxyl oxime demonstrated C·Tr are less mobile than P·Tr. Possible origins of enhanced site-separation and reduced mobility are discussed and explored through various experiments.