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

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 T1 of these chain segments on the outer surface relative to those on the inner surface. Treating such T1 relaxation data with a double exponential function yields the coefficients for these terms with different T1 values and thus the relative populations for chain segments on the inner and outer vesicular wall surfaces. This method is simple and straightforward.