Studies on the lamellar thickening of a 4-arm poly(ethylene oxide) with Mn=5000 for each arm are reported. The samples were prepared by quenching from 70 ℃ to 10 ℃. Small-angle X-ray scattering (SAXS) was used to track the variation of lamellar structure during heating process. Then the SAXS data were further analyzed using one-dimensional correlation function. The following parameters

such as long period

linear crystallinity

crystalline layer thickness and amorphous layer thickness

were determined. Their changes with increasing temperature suggest three temperature regions. Region Ⅰ is in 26~45 ℃. There are three broad scattering peaks with low scattering intensity. They correspond to lamellae with different thicknesses. The crystalline layer thickness of the dominated lamella is about 9.3 nm. Importantly

the parameters mentioned above remain unchanged in Region Ⅰ. Region Ⅱ within 45~52 ℃ is a transition one. The main peak of the SAXS curves turns into two. The long period

linear crystallinity

crystalline layer thickness and amorphous layer thickness began to increase. Region Ⅲ (52~60 ℃) is a thickening region within which the crystalline layer thickness clearly increased with increasing temperature. At 60 ℃ its value is 15.8 nm. These observed results found in the three regions were further explained based on the role of metastable states of polymer lamellae. Within region Ⅰ macromolecules were in a frozen state

thus it was impossible to detect any change related to the lamellar structure. Within region Ⅱ

the temperature is higher enough to let some thin crystalline layers melt and then the melted macromolecules would recrystallize around the thicker ones. In region Ⅲ the continuous melting-recrystallization process proceeds until the melting point of the sample. The observed melting-recrystallization process reflects the metastability of polymer lamellae: Thinner lamellae are in a metastable state with a lower stability

thus will melt to recrystallize to form thicker lamellae with a higher stability. Acctually

the continuous melting-recrystallization process is a typical Ostwald ripening of polymer lamellae.