TERNARY PHASE-DIAGRAMS OF POLY(STYRENE-CO-METHYL METHACRYLATE), POLY(METHYL METHACRYLATE), AND POLYSTYRENE - MONOMER SEQUENCE DISTRIBUTION EFFECT AND ENCAPSULATION
Ki. Winey et al., TERNARY PHASE-DIAGRAMS OF POLY(STYRENE-CO-METHYL METHACRYLATE), POLY(METHYL METHACRYLATE), AND POLYSTYRENE - MONOMER SEQUENCE DISTRIBUTION EFFECT AND ENCAPSULATION, Macromolecules, 29(8), 1996, pp. 2868-2877
The phase behavior in ternary blends of polystyrene (PS), poly(methyl
methacrylate) (PMMA), and poly(styrene-co-methyl methacrylate) has bee
n determined as a function of sequence distribution at 150 degrees C.
Two copolymers were investigated which have comparable compositions (4
8-50 mol % methyl methacrylate monomer units) but distinct sequence di
stributions, namely strictly alternating and random. The phase behavio
r was determined via transmission electron microscopy, which found the
number of phases, the relative amounts of the phases, and the spatial
arrangement of the phases. Equilibrium blend compositions were calcul
ated from the experimental results using mass balance equations. These
equilibrium compositions were used to construct isothermal ternary ph
ase diagrams which exhibited three pairwise immiscible binary systems
and a three-phase region. From these ternary phase diagrams, we show t
hat the compositionally symmetric copolymers are more miscible in PMMA
than PS and that this asymmetry in miscibility is more pronounced wit
h the alternating sequence. This sequence distribution effect is discu
ssed in terms of specific interactions between the methyl methacrylate
monomer units. With either alternating or random copolymers, the thre
e-phase blends exhibit encapsulation when the copolymer-rich phase is
less than 25 vol % of the blend; otherwise the copolymer-rich phase fo
rms a continuous matrix. The equilibrium compositions of binary blends
containing poly(methyl methacrylate) and a copolymer were also invest
igated as a function of molecular weight.