立體規則嵌段共聚物及其摻混物之有序-有序相轉化研究

Order-Order Transition of Stereoregular Diblock Copolymer and Its Blends with the Corresponding Homopolymer

裴柔媛(Pei, Rou Yuan)

指導教授 ： 陳信龍

國立清華大學/工學院/化學工程學系/碩士(2015年)

摘要

我們使用小角度X光散射來研究具組態規則性的嵌段共聚物聚丙烯-聚苯乙烯 (syndiotactic polypropylene-block-polystyrene, sPP-b-aPS) 的雙連續網狀奈米結構。我們發現此共聚物呈現一非典型的ordered bicontinuous double-diamond (OBDD)結構，且該結構經升溫會轉化成典型的ordered bicontinuous double-gyroid (OBDG)結構，該有序-有序轉化 (order-order transition, OOT) 伴隨著domain spacing變化。根據體積守恆的假設，我們提出一普遍適用的模型來計算OBDD和OBDG結構中domain spacing和晶格常數 (lattice parameter) 的比例。此外，我們也建構出OBDD結構在實空間中的3D穿透式電子顯微影像。我們認為，在較低溫時，sPP分子鏈會形成不同長度的螺旋片段，該構造可使分子鏈的內能降低，補償packing frustration熵的損失，因而穩定OBDD結構。另外，我們也發現摻混sPP均聚物 (homopolymer) 後，sPP-b-aPS會由OBDD結構轉化成HEX結構，此過程不可逆。我們認為加入sPP均聚物會使OBDD結構的雙曲線域 (hyperbolic domain) 產生膨脹效應(swell effect)，不但降低其表面曲度(interfacial curvature)，影響sPP和PS的構形(conformation)，且使得sPP均聚物的分子鏈分布不均，造成熵的損失變大，在高溫時這些熵的損失會降低雙曲線型曲度的穩定性，促使OBDD結構轉化為較穩定的hexagonally-packed cylinder (HEX)結構。在OBDD結構轉化成HEX結構的過程中，其體積守恆且lattice parameter幾乎維持不變，因此我們也根據此關係提出了一種可能的轉化路徑。

關鍵字

組態規則性 ； 雙連續相結構 ； 均聚物

並列摘要

We have investigated the formation of ordered bicontinuous nanostructures in a diblock copolymer composed of a stereoregular block, syndiotactic polypropylene - block-polystyrene (sPP-b-aPS). The temperature-dependent small angle x-ray scattering (SAXS) revealed that the ordered bicontinuous double-diamond (OBDD) structure underwent a thermally reversible order-order transition (OOT) to ordered bicontinuous double gyroid (OBDG) upon heating, and the transition was accompanied with a slight reduction of domain spacing, as demonstrated both experimentally and theoretically. Based on the assumption of volume conservation, the ratio of the lattice parameters of these two bicontinuous structures was derived to be a_G/a_D =1.634, which closely agrees with that prescribed by the assumption of Bonnet transformation for the OOT. The OBDD structure was further confirmed by the reconstruction of 3D image using electron tomography. The thermodynamic stability of the OBDD structure may be attributed to the ability of the configurationally regular sPP block to form helical segments even above its melting point, as the reduction of internal energy associated with the helix formation may effectively compensate the greater packing frustration of sPP blocks in the tetrapod of OBDD relative to that in the tripod of OBDG, making the OBDD the more stable structure at the lower temperature. By blending sPP-b-aPS system with a small amount of sPP homopolymer, a phase transition from the OBDD structure to the hexagonally-packed cylinder (HEX) structure occured on heating. The volume fraction of the homopolymer in the blend affected not only the temperature range of the OOT, but also TOOT. The hyperbolic sPP domain of the OBDD structure is swollen, leading to a reduction of the interfacial curvature and hence a perturbation of sPP and PS conformation. Moreover, the distribution of sPP homopolymer chains in the tetrapod is non-uniform, giving rise to a loss of translational entropy. The loss of these entropies, which becomes important at high temperature destabilizes the OBDD structure and drives transformation into HEX phase. A possible kinetic pathway of the OBDD-to-HEX transition was proposed based on the assumption of volume conservation and constant lattice parameter.

並列關鍵字

syndiotactic PP ； OBDD structure ； OBDG structure ； homopolymer

參考文獻

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