INTEGRAL AND NONINTEGRAL CHAIN FOLDING IN POLY (ETHYLENE OXIDE) / POLY (METHYL METHACRYLATE) BLENDS

M. Horký¹, J. Baldrian², A. Sikora², M. Steinhart², P. Vleek², H. Amenitsch³, S. Bernstorff⁴

¹Faculty of Nuclear Science and Physical Engineering, Czech Technical University, V Holešoviekách 2, 180 00 Prague 8, Czech Republic
²Institute of Macromolecular Chemistry, Academy of Sciences of Czech Republic, Heyrovský Sq. 2, 162 06 Prague 6, Czech Republic
³Institute for Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Steyergasse 17, 8010 Graz, Austria
⁴Sincrotrone Trieste, Basovizza, 34012 Trieste, Italy
E-mail: baldrian@imc.cas.cz

Keywords: polymer blends, melt-crystallization, lamellar structure, time-resolved SAXS, WAXS, PEO, PMMA

Chains of low molecular weight fractions of poly (ethylene oxide) (PEO) form crystalline lamellae with an integral number of chain folds (IF). The most stable structure is formed at low supercoolings without any fold - extended chain (EC) lamellae. Recently it has been reported that a nonintegral-folded chain (NIF) lamellae can be formed.

The rate of crystallization in blends with amorphous poly (methyl methacrylate) (PMMA) is reduced by dilution of the crystallizable PEO near the growth surface. Also the molecular weight of components and strength of their interactions affects the kinetics of crystallization. It follows that the formation of EC, IF and NIF lamellar crystals and their development during crystallization in a blend should be different from the case of a neat polymer. The primary objective has been to study the influence of amorphous diluent (PMMA) on the structure development of PEO during melt-crystallization.

DSC and WAXS measurements of PEO/PMMA blends show partial miscibility of components. The X-ray crystallinity decreases with increasing content of the amorphous diluent. From its values it follows that in the blends with PEO concentration higher than 30 wt.%, a two-phase system exists: crystalline PEO and an amorphous mixture of PMMA with small amount of PEO. The blend with 80 wt.% of PMMA is amorphous, the components are completely miscible.

The time-resolved SAXS measurement of the blends crystallization was performed at synchrotron ELETTRA in Trieste. The results demonstrate great influence of PMMA on the structure development of PEO in blends during isothermal melt-crystallization. A dominant structural phenomenon in the early stages of crystallization is the formation of NIF lamellae in blends with 20 and 40 wt.% of PMMA. The lamellae are unstable, they grow very fast and then quickly recrystallize to more stable 1F or EC structures. The formation of NIF crystals of PEO in blends is very sensitive to the amount of PMMA. Growing content of PMMA increases the starting time of the crystalline structure formation and reduces crystallization and recrystalization rates of NIF lamellae. Crystallization in the blend with 60 wt.% of PMMA proceeds so slowly that PEO chains form directly 1F and EC crystals.

Research supported by the Grant Agency of the Czech Republic and the Academy of Sciences of the Czech republic (Grant No. 203/96/1387, K2050602/12)