Crystallite Dissolution in Poly(ethylene oxide) Polymers Caused by Water

Poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) is a semicrystalline block copolymer (BCP) with interesting properties. It is mechanically tough and amphiphilic. The mechanical toughness is due to the crystallinity of PEO and the glassiness of PS, as well as the morphological structure of the BCP. These polymers have high CO₂, water, and salt solubility that derive from the polar PEO component. Potential applications include CO₂ separation, water purification, and lithium air batteries. In all of the aforementioned applications, water transport is an important parameter. The presence of water can also affect thermal and mechanical properties. Water transport and thermal and mechanical properties of a lamellar PS-b-PEO copolymer, as well as PS and PEO homopolymers have been measured as a function of water activity. Water was found to dissolve PEO crystallites and plasticize PS, which in turn affects the transport. Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy was employed to examine crystallite dissolution and water diffusion. A model accounting for both processes captured the experimental observations.