Phase Behavior of the Mixtures of 2- and 3-Components for Poly(styrene-co-octafluoropentyl methacrylate) by Dispersion Polymerization under CO₂

The dispersed-phase polymerization of poly(styrene-co-2,2,3,4,4,4-octafluoropentyl methacrylate), also known as p(styrene-co-OFPMA), took place in supercritical carbon dioxide (sc-CO2). The chemical and physical properties of p(styrene-co-OFPMA) were studied by varying the styrene-to-OFPMA ratios (40:1, 30:1, and 20:1) and 2,2′-azobis(isobutyronitrile) (AIBN) initiator amounts (wt %: 1.0, 2.0, 3.0). The cloud-point data were obtained for various systems, including the binary mixtures of p(styrene-co-OFPMA) (30:1 ratio, AIBN wt %: 1.0, 2.0, 3.0) with supercritical solvents such as sc-CO2, sc-CH3OCH3, sc-C3H6, sc-C4H8, and sc-CHClF2. Phase behavior (i.e., mixtures) was studied at temperatures of 324–455 K and pressure below 201 MPa. In the binary system of p(styrene-co-OFPMA) + sc-CH3OCH3, a lower critical solution temperature (LCST)-type curve was observed, characterized by a positive slope. Conversely, the binary systems of p(styrene-co-OFPMA) + (sc-C3H6, sc-C4H8, sc-CHClF2) exhibited an upper critical solution temperature (UCST) behavior with a decreasing slope. The phase equilibrium curves were obtained for p(styrene-co-OFPMA) [30:1; 1.0% (Mw = 42,400), 2.0% (Mw = 33,800), and 4.0% (Mw = 24,100); AIBN: 1.0 wt %] + sc-C3H6, sc-C4H8, and sc-CHClF2 mixtures. These curves exhibited an increasing slope for p(styrene-co-OFPMA) + sc-CH3OCH3 and a negative slope for p(styrene-co-OFPMA) + (sc-C3H6, sc-C4H8, sc-CHClF2) systems, indicating distinct phase behavior. Tetramethyl orthosilicate (TMOS) addition (0.0–68.9 wt %) to P(styrene-co-OFPMA) (30:1; AIBN wt %: 1.0) + solvents altered the phase equilibrium, switching from UCST to LCST, as evidenced by changes in the pressure–temperature slope.