Zhang, F. J. ; Stühn, B. (2007)
Crystallization and melting behavior of low molar weight PEO-PPO-PEO triblock copolymers.
In: Colloid and Polymer Science, 285 (4)
doi: 10.1007/s00396-006-1571-y
Artikel, Bibliographie

Kurzbeschreibung (Abstract)

The crystallization behavior of a series of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers (Pluronics) was investigated using time-resolved small-angle X-ray scattering (SAXS), thermal analysis, and polarized optical microscopy. For comparison, a PEO homopolymer, PEO3K, was also included. Time-resolved SAXS during the crystallization of PEO3K shows a typical ``two-step'' process, i.e., in the initial stage, a metastable crystal with nonintegral folding (NIF) structure forms first, then, it transforms into integral folding (IF) structures, the IF(0) and the IF(1). In contrast with PEO3K, the PEO-PPO-PEO triblock copolymers show a ``one-step'' crystallization process, i.e., the PEO blocks crystallize directly into the final state and do not change with time. In thermal analysis, only one major solid-melt transition is observed during isothermal crystallization and subsequent melting for triblock copolymers. In the full temperature range, a linear crystal growth is observed. The crystal growth rates monotonously decrease with crystallization temperatures. Notches or breaks due to the NIF-IF transition as clearly seen for PEO3K cannot be recognized for Pluronics. Based on these results, we conclude that the crystallization of PEO-PPO-PEO triblock copolymers follows a ``one-step'' process; no metastable structure serving as an intermediate state is formed during the crystallization process within the time scale of the current experiments (< 120 min).

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