Micellar-cluster association of ureidopyrimidone functionalized monochelic polybutadiene

Abstract

A series of monochelic polybutadienes with a ureidopyrimidone terminal group (MPBd-UPy) has been synthesized using anionic polymerization and chain-end transformation. Monochelic polybutadiene with two UPy terminal groups, MPBd-(UPy)₂, has also been synthesized to study the effect of chain-end concentration on hydrogen bonding association. The transformation of the precursor ω-hydroxyl terminated polybutadiene into the ureidopyrimidone functionality via the reaction with 1-(6-isocyanatohexyl)-3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl) urea (UPy-NCO) turns free-flowing liquid samples into a semi-solid, viscous material, due to the well-known quadruple hydrogen bonding ability of UPy. The dimerization association of MPBd-UPy has been studied thoroughly using size exclusion chromatography, intrinsic viscosity and dynamic light scattering. Solutions of MPBd-UPy exhibit a high Huggins parameter, 0.40 < K_H > 0.63, depending on the molecular weight and the number of UPy groups at the chain-end. Studies reveal that along with hydrogen bonded dimers, (MPBd-UPy)₂, they also aggregate intermolecularly to form star-like micelles that are in equilibrium with the dimers. The presence of multiple populations with R_h as high as 700 nm, which decreases with increasing temperature in toluene has been identified. The UPy aggregated micellar clusters have distinct endothermic transitions in the solid-state and atomic force microscopy studies show the presence of micellar-clusters forming a well-defined assembly of fibrous like parallel lines on a mica surface.