Synthesis and structure-property relationships of random and block copolymers : a direct comparison for copoly(2-oxazoline)s

The purpose of this study was to synthesize copolymers of different mol. architecture, i.e., monomer distribution over the polymer chain, and to compare their phys. and mech. properties. A series of random copolymers of 2-ethyl-2-oxazoline (EtOx) and 2-nonyl-2-oxazoline (NonOx) were synthesized via a cationic ring-opening polymn. procedure in acetonitrile under microwave irradn. The polymn. kinetics for EtOx and NonOx were studied in refluxing butyronitrile using thermal heating. The resulting kinetic data were applied to synthesize a series of block copolymers with the same chem. compn. as the random copolymers. The random and block copolymers exhibited the desired compn., mol. wt., and narrow mol. wt. distribution. The surface energies of the random copolymers with 65-85 wt % NonOx were higher than the surface energy of their block copolymer counterparts as the random distribution of EtOx units hindered the segregation of the NonOx units to the surface. The variation in polymer architecture also resulted in different phase segregation behavior and different transition temps., as shown by differential scanning calorimetry (DSC). The obsd. elastic moduli, which differed considerably between the random and the block series, were well explained by the phases identified through DSC. [on SciFinder (R)]