Microstructural investigation of the cooperative gelation of syndiotactic polystyrene and high MW polyethylene glycol di-methyl ether in common solution in THF

The gelation of syndiotactic polystyrene (sPS) in THF in the presence of high molecular weight PEGDME was investigated in detail using contrast-matching SANS complemented by in situ FTIR. Using the contrast-matching method, the scattering contribution of each of the two polymers in the common solution in THF at high temperature (110 °C), in the single-coil conformational state and in the gelation state of sPS (below 40 °C and down to 10 °C) was observed, and the structural characterization of the polymer coils and the junction structures of the gel was obtained. The local scale conformation of the two types of polymer molecules in the different regimes was additionally monitored by FTIR. The gelation and melting temperatures were determined by DSC. sPS changes from the amorphous coil to the helical TTGG conformation when the gelation temperature is passed, forming fibrillar morphologies with a local 2D aspect due to cooperative interactions with the solvent molecules. These are the junction structures of the large-scale network morphology of the gel. The high molecular weight PEGDME transitions from the amorphous coil to an elongated amorphous conformation and incorporates into the fibrillar morphology together with the sPS during the gelation process. High MW PEGDME alone in THF forms a "house of cards" gel consisting of stacked lamellar structures on a smaller length scale, as shown by the scattering data. Thus, in the presence of sPS, smaller and softer structures appear as a result of a cooperative gelation process controlled by sPS. Incorporation of high MW PEGDME into these aggregates leads to polymer nanocomposites that can render the sPS hydrophilic, a topic that should be the focus of future structural and morphological studies.