NMR quantification of the partition of coronal chain segments of block copolymer vesicles

Abstract In vesicles of an ABC triblock copolymer, the soluble A and C blocks can be grafted onto the outer or the inner surfaces of the wall made of the insoluble B block. Traditionally, the determination of the fractions of A and B chain segments partitioned onto these two surfaces has been difficult. We show that they can be readily determined from NMR paramagnetic relaxation experiments. In such an experiment, a paramagnetic reagent that does not readily permeate the vesicular wall is added into a solution. This greatly shortens the spin-lattice relaxation times T 1 of these chain segments on the outer surface relative to those on the inner surface. Treating such T 1 relaxation data with a double exponential function yields the coefficients for these terms with different T 1 values and thus the relative populations for chain segments on the inner and outer vesicular wall surfaces. This method is simple and straightforward.