Polymer Journal, Vol. 32, No. I, pp 75-78 (2000) NOTES Crystallization of Poly(s-caprolactone)-block-Polystyrene Copolymers from Glassy Microdomain Structures Shuichi NoJJMA,t Hiroshi KAKIHIRA, Satoshi TANIMOTO, Hisayuki NAKATANI,* and Shintaro SASAKI School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST). Tatsunokuchi, Ishikawa 923-1292, Japan * Center for New Materials, Japan Advanced lnstiture of Science and Technology (JAIST), Tatsunokuchi, Ishikawa 923-1292, Japan (Received May 10, 1999) KEY WORDS Crystalline-Amorphous Diblock Copolymer / Microdomain Structure / Glass Transition / Crystallization / Crystallization of block copolymers is significantly affected by the microdomain structure existing in the melt. 1 When the glass transition temperature Tg of the amorphous block is higher than the melting temperature Tm of the crystallizable block, the microdomain structure freezes substantially when the constituent block crystal- lizes. As a result, the crystallization is restricted to occur within the microdomain structure. 2 - 9 In the morphologi- cal studies of such systems, it is of great importance to get information about the microdomain structure. Small-angle X-ray scattering (SAXS) measurements are generally used to characterize the microdomain structure formed in block copolymers consisting of amorphous chains, 10 but this method is not available when the electron density difference between domains is extremely small. This is the case for some crystalline-amorphous diblock copolymers investigated so far, such as poly(e- caprolactone )-black-polystyrene (PCL-b-PS), 2 • 3 • 8 • 9 poly- (tetrahydrofuran)-black-PS (PTHF-b-PS), 11 and poly- (ethylene oxide)-block-PS (PEO-b-PS). 12 Therefore, there is no study to relate the microdomain structure with the final morphology for the block copolymers with Tg>Tm. We have recently reported the effects of Tg and co- polymer composition on the crystallization of PCL- b-PS copolymers. 8 • 9 When the volume fraction of PCL blocks, ¢PcL, is less than 0.26, the PCL block does not crystallize at all, while the crystallinity increases ab- ruptly between 0.34 :s; ¢PcL :s; 0.60 toward a constant value. 2 • 8 This significant change in the crystallinity should relate intimately with the microdomain structure; we can suppose intuitively that when the PCL block is a matrix it crystallizes easily, whereas when it is an isolated phase surrounded by the amorphous PS matrix the crystallization will be extremely disturbed because of the spatial restriction. In this study we try to characterize the microdomain structure of PCL-b-PS in the melt by SAXS. For this purpose, we add a small amount of poly(vinyl chloride) (PVC) to the PCL block 13 to increase the electron den- sity of the PCL domain. The repeating distance of the microdomain structure, which is straightforwardly obtained from SAXS measurements, is evaluated and compared with that of the morphology after the crystallization of PCL blocks. From these results, we elucidate the effect of existing microdomain structures on the final morphology formed at various temperatures in crystalline-amorphous diblock copolymers with a hi_gh Tg amorphous block. EXPERIMENT AL Materials and Sample Preparation PCL-b-PS copolymers used in this study were synthesized by a successive anionic polymerization un- der vacuum. Details of the synthesis and molecular characterization are described elsewhere. 8 · 9 Two PCL- b-PS copolymers, designated by CL64 and CL 70, are used in which the PCL block is a major component because the PCL block crystallizes sufficiently only at a limited composition range ( ¢PcL 2".: 0.6). 9 The results of molecular characterization are shown in Table I. CL64 has a lamellar microdomain structure in the melt judg- ing from ¢PcL and the TEM micrograph after the crystallization of PCL blocks and CL 70 has a cylindrical microdomain structure (see Figure 3). The crystallization of PCL blocks in CL64 and CL 70 was performed by quenching the sample from the temperature above Tm into various crystallization tem- peratures Tc ranging from 20 to 50°C. The crys- tallization of CL64 was also performed by the solu- tion-casting method to compare the final morphology with that of the quenched sample, where toluene, good for both the blocks, was used for the casting solvent and evaporated gradually at various Tc to prepare a crys- tallized thin film of PCL-b-PS. SAXS Measurements SAXS measurements were performed with a point- focusing optics and a one-dimensional position sensitive proportional counter. Details of the optics, instrumenta- tion, and data processing are described elsewhere. 14 · 15 The Lorentz-corrected SAXS curves were finally ob- tained as a function of wave number s defined by t To whom correspondence should be addressed (Tel: +81-761-51-1601, Fax: +81-761-51-1149, e-mail: nojima(ajaist.ac.jp). 75