Development of Cocrystalline Structures in Polymer Blends
Josef Baldrian, Milos Steinhart, Antonin Sikora, Ginka Todorova
Institute of Macromolecular Chemistry
Czech Republic
Keywords: blends, cocrystals, structure
The aim of this study was to assess the real-time development of poly(ethylene oxide) (PEO) cocrystalline structures in two different binary blends.
Blends of PEO 2000, 3000 4000 and 6000 were studied during isothermal crystallization and during cooling and heating. A single cocrystal system or this system with a small amount of another lamellar systems are formed in the blends during both treatments. The thickness of the cocrystal lamellae increase with increasing concentration of higher molecular-weight PEO in blends. This thickening is caused by a growing number of higher-molecular-weight chains incorporated in cocrystal lamellae. In blends P2/P4 and P2/P6 are thicknesses of lamellae close to the size of extended chains of P2, which is associated with the fact that such short chains are not able to fold. During heating, upon approaching the melting points of the respective components, all blend structures recrystallize in the bulk volume giving a new, single and more stable cocrystal structure.
Binary mixtures of P3 or P4 with triblock copolymer PEO-PPO-PEO were studied. In the neat copolymer and in blends with the predominat copolymer, two different lamellar systems LP1 (with thicker lamellae) and LP2 are simultaneously formed during isothermal crystallization. In blends with a majority of neat PEO, a single lamellar system is developed. The cocrystal systems are formed in all types of blends during crystallization. The LP1 lamellae in blends with P3 consist of extended chains of P3 and of extended PEO tails of copolymer. The LP1 cocrystal structures developed in blends with P4 are probably formed by NIF chains of P4 and NIF and EC of PEO tails of the copolymer. In both kinds of blends, the LP2 lamellar systems are cocrystals consisting of 1F and NIF chains of both components