| Abstract | When treated with compressed CO₂, syndiotactic polystyrene (sPS) undergoes a number of solid-solid transitions that do not occur on treatment with liquid solvents. For example, planar mesophase → β, α → β, and γ → β transitions can be brought about under appropriate conditions of temperature and CO2 pressure. In addition, the transitions of glassy sPS to the planar mesomorphic and to the α form, and the γ → α transition occur at temperatures lower than when the same transitions are effected under ambient pressure. The dissolved CO₂ lowers the glass transition and the cold crystallization temperatures of sPS at the rate of -0.92 and -0.58 °C/atm, respectively. Crystallization kinetics from the sPS-CO₂ solution follow the Avrami equation, but the value of the exponent n is lower than when crystallization is conducted under ambient pressure. |
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