Living polymerization induced macro- and microdomain investigated by focusing ultra-small-angle neutron scattering
Motokawa, Ryuhei ; Iida, You*; Zhao, Y.; Hashimoto, Takeji; Koizumi, Satoshi
By utilizing a biconcave refractive neutron lens (MgF), we constructed a focusing ultra-small-angle neutron scattering (USANS) spectrometer (SANS-J-II) at research reactor JRR3, Tokai Japan. SANS-J-II can successfully reach to =0.0003 , where [= 4sin()/] is the magnitude of scattering vector given by wavelength and scattering angle 2, and simultaneously cover conventional SANS region up to = 0.004 by using 5-inch size & high resolution position sensitive area photomultiplier with scintillator (ZnS). Focusing USANS, thus realized, plays an important role to investigate the time-evolution of hierarchically ordered structures in the living radical polymerization solution, preparing poly (methyl methacrylate)- -polystyrene (PMMA--PS). In the reaction process to synthesize PS block chains from the end of PMMA block chain, we found the interplay between macro and microdomain structures as follows. Small-angle scattering at 0.001 determined time-evolving microdomain structures; as the polymerization proceeds, (1) first by order-disorder transition, a lamellar microdomain appears and (2) second by order-order transitions, the morphologies of microdomains change to PS cylinder and successively to PS sphere. Ultra-small-angle scattering at 0.001 , exhibits power law scattering ( ) due to macrophase separation between PMMA--PS and PS homopolymer, appeared as by product. The exponent varies from 4 to 2, reflecting a grain boundary of macrodomain rich-in PMMA--PS; when a lamellar microdomain appears, Porod law gives = 4, whereas when cylinder and sphere appear, = 2, due to inhomogeniety of the microdomain spatial distribution.