Living polymerization induced macro- and microdomain investigated by focusing ultra-small-angle neutron scattering

リビングラジカル重合に誘起されるマクロ相分離とミクロ相分離の中性子超小角散乱による研究

元川 竜平   ; 飯田 優羽*; Zhao, Y.; 橋本 竹治; 小泉 智

Motokawa, Ryuhei; Iida, You*; Zhao, Y.; Hashimoto, Takeji; Koizumi, Satoshi

制御ラジカル重合法により、ポリメタクリル酸メチルとポリスチレンで構成されるジブロック共重合体を合成した。この重合溶液について中性子超小角・小角散乱法により観察を行ったところ、均一溶液下でのジブロック共重合体の成長、及び重合の生成物に誘起される相分離構造の出現を小角散乱の時間変化として追跡することに成功した。その際、相分離構造のモルフォロジーとサイズの経時変化を反映して青から赤の構造色が連続的に発現することを明らかにした。また、重合溶液中にミクロ相分離構造が出現すると、重合速度に遅延が起こることを実験的に見いだした。

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.