Effect of Polystyrene Synthesis Method on Water Sorption and Glass Transition.

Area of Science:

• Polymer Chemistry
• Materials Science

Background:

• Commodity polystyrene (PS) synthesis differs from PS in block copolymers (BCPs).
• Water sorption and glass transition temperature (Tg) are critical polymer properties affected by synthesis and environment.
• Nanostructured polymer membranes performance depends on humidity.

Purpose of the Study:

• Investigate the impact of synthesis method on PS water sorption and Tg.
• Understand how environmental humidity affects PS properties.
• Examine plasticization in pure polystyrene using a poor solvent system.

Main Methods:

• Free radical polymerization for commodity PS; living anionic polymerization for BCP PS.
• Water sorption measurements under varying humidity.
• Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) to determine Tg and modulus.
• Tensile testing at different relative humidity (RH) levels.

Main Results:

• Commercial PS showed 0.5 mg/g water sorption; anionically synthesized syndiotactic PS absorbed up to 1.5 mg/g due to higher free volume.
• Hydrophilic hydroxyl chain ends increased atactic PS water sorption to 2.3 mg/g.
• Increasing humidity decreased PS Tg by 5 °C and tensile storage modulus from 1.58 GPa (0% RH) to 0.53 GPa (40% RH).

Conclusions:

• Synthesis method critically influences PS water sorption and Tg.
• Hydrophilic modifications and synthesis route significantly enhance water uptake.
• Humidity-induced plasticization lowers Tg and modulus, impacting polymer performance in applications like membranes.