Effect of chain architecture on surface segregation in functional polymers: Synthesis and surface properties of end- and center-functional poly(D,L-lactide)

Poly(D,L-lactide)s with fluorocarbon functional groups located at either the chain end or center are synthesized by the ring-opening solution polymerization of D,L-lactide using monohydroxy or dihydroxy terminated semifluorinated alcohols as co-initiators respectively. The surface composition-depth profiles of the fluorocarbon functional groups are determined by angle dependent X-ray photoelectron spectroscopy (ADXPS) measurements. All polymers exhibit surface segregation of the lower surface tension fluorocarbon functional groups. The extent of surface segregation decreases with molecular weight and, for polymers of equivalent molecular weight, is higher for the end-functional polymers than for center-functional polymers, consistent with the mean field lattice model (MFLM) predictions of O'Rourke-Muisener et al. We find that the MFLM with a single set of bulk and surface interaction parameters provides reasonable predictions of experimental ADXPS concentration depth profiles for all molecular weights and polymer architectures studied. Moreover, these interaction parameter values are in good agreement with those calculated by group contribution methods based upon the chemical structure of the functional groups.