A stopped-flow kinetic study of the assembly of interpolymer complexes via hydrogen-bonding interactions

The formation of soluble interpolymer complexes from poly(4-vinylphenol-g-styrene) (PVPh-g-PS) and poly(styrene-co-4-vinylpyridine) (STVPy) via hydrogen-bonding interactions in tetrahydrofuran (THF) was investigated with viscometry, laser light scattering (LLS), and stopped-flow light scattering. Upon mixing PVPh-g-PS with STVPy solutions in THF, colloidally stable dispersions are obtained, indicating the formation of core-shell structure with the core consisting of hydrogen-bonded interpolymer complexes between PVPh backbone and STVPy and the shell of PS grafts. Both LLS and viscometry results reveal that the complexation between PVPh-g-PS and STVPy proceeds stoichiometrically. Reduced viscosities of PVPh-g-PS/STVPy-49 and PVPh-g-PS/STVPy-74 mixed solutions exhibit minima at weight fractions of PVPh-g-PS similar to 0.5 and 0.6, respectively. At these compositions the interpolymer complexes micelles have the highest scattering light intensities and average densities, [rho]. PVPh-g-PS/STVPy-25 forms aggregates with quite loose structures and low aggregation numbers, which have the smallest sizes and [rho], as compared to that of PVPh-g-PS/STVPy-49 and PVPh-g-PS/ STVPy-74. For PVPh-g-PS/STVPy-49 and PVPh-g-PS/STVPy-74, the average hydrodynamic radius, [R-h], is almost independent of the weight fractions of PVPh-g-PS. The kinetics of the assembly of micellar complexes are then studied with stopped-flow light scattering upon mixing two component solutions in THF. The complexation between PVPy-g-PS and STVPy-25 is so fast ( complete within 1-2 ms) that no relaxation processes are observed, reflecting the loose structure of the formed micellar complexes. The formation of micellar complexes between PVPh-g-PS and STVPy-49 or STVPy-74 occurs within similar to 1-2 s; light scattering intensities exhibit an initially rapid increase and then reach a plateau. Typical relaxation curves at intermediate mixing ratios can be well-fitted with double-exponential functions. Two sequential steps can then be resolved in the assembly of micellar complexes, which are assigned to the initial formation of nonequilibrium aggregates and subsequent structural rearrangements into the final stable micellar complexes, respectively. The effects of mixing ratios and the densities of hydrogen-bonding interaction groups on the complexation kinetics are also studied.