Structural mobility of molecular bottle-brushes investigated by NMR relaxation dynamics

The structural mobility of monomeric units of molecular bottle-brushes was studied by a systematic evaluation of NMR relaxation dynamics. The spin-spin relaxation time (T2) was determined by Carr-Purcell-Meiboom-Gill (CPMG) NMR spectroscopic measurements. T2 for protons that reside on the exterior and interior of the bottle-brush macromolecules varied with the grafting density and side chain length in bottle-brush copolymers. Poly((2-(2-bromopropionyloxy)ethyl methacrylate-stat-methyl methacrylate)-graft-butyl acrylate) (poly((BPEM-stat-MMA)-graft-PBA) was studied as a model brush copolymer. The T2 values for protons of MMA units in the brush backbone significantly decreased with increasing side chain length and grafting density of PBA. The mobility and relaxation times T2 for the side chain PBA protons decreased with grafting density. However, after initial increase, the relaxation times eventually decreased with PBA side chain length.