Growth and morphology change of polystyrene-block-poly(2-cinnamoylethyl methacrylate) particles in solvent-nonsolvent mixtures before precipitation

Tetrahydrofuran (THF) and acetonitrile (AN) are good and poor solvents for poly(2-cinnamoylethyl methacrylate) (PCEMA) and polystyrene (PS). Their mixtures with AN volume fractions between 80% and 93% are precipitants for PS but slightly solubilize the PCEMA block of a polystyrene-block-poly(2-cinnamoylethyl methacrylate), PS-b-PCEMA, sample with 380 styrene and 210 CEMA units. Immediately after the addition of AN to a THF solution of the diblock, spherical particles with PCEMA shell and PS core are formed due to phase separation. The core-shell particles then grow in size, presumably mainly due to particle coalescence, and transform into the more complex egglike, onionlike, and berrylike particles in THF/AN with 80%-90% AN before precipitation in several weeks. In THF/AN with 93% AN, no structural mutation is seen in 1 week after the formation of the spherical particles despite eventual polymer precipitation. This resistance of the spherical core-shell particles to morphological transitions may be due to the locking in of the PS core in a glassy state.