Effect of Tacticity on the Phase Behavior and Demixing of PαMSAN/dPMMA Blends Investigated by SANS,Macromolecules

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Effect of Tacticity on the Phase Behavior and Demixing of PαMSAN/dPMMA Blends Investigated by SANS
Macromolecules ( IF 5.1 ) Pub Date : 2020-01-03 , DOI: 10.1021/acs.macromol.9b02115
Yutaka Aoki ₁ , William Sharratt ₁ , Haoyu Wang ₁ , Roisin O’Connell ₁ , Luca Pellegrino ₁ , Sarah Rogers ₂ , Robert M. Dalgliesh ₂ , Julia S. Higgins ₁ , João T. Cabral ₁

Affiliation

We investigate the effect of polymer tacticity on the phase behavior and phase separation of polymer mixtures by small-angle neutron scattering (SANS). Poly(α-methyl styrene-co-acrylonitrile) (PαMSAN) and deuterated poly(methyl methacrylate) (dPMMA) with two degrees of syndiotacticity were selected as a model partially miscible blend, as one of the most highly interacting systems known (defined by the temperature dependence of the blend’s interaction parameter). One-phase (equilibrium) and time-resolved, spinodal demixing experiments were analyzed by de Gennes’ random phase approximation (RPA) and Cahn–Hilliard–Cook (CHC) theory, respectively. The second derivative of the Gibbs free energy of mixing with respect to composition (G″ ≡ ∂²ΔG_m/∂ϕ²) and corresponding χ parameter were obtained from both RPA and CHC analysis and found to correlate well across the phase boundary. We find that blends with higher PMMA syndiotacticity exhibit greater miscibility and a steeper G″ temperature dependence by ∼40%. The segment length of dPMMA with higher syndiotacticity was found to be a = 7.4 Å, slightly larger than 6.9 Å reported for lower syndiotacticity dPMMA. Consideration of thermal fluctuations is required for the self-consistent analysis of the nontrivial evolution of the spinodal peak position q* over time, corroborated by CHC model calculations. The temperature dependence of the mobility parameter, M, can be described by a “fast-mode” average of the diffusion coefficients of the blend constituents, except for quenches originating near the glass transition. A minimum demixing length scale of Λ ≈ 40 nm is obtained, in agreement with the theory for deeper quenches, but deviates at shallower quenches, whose origin we discuss. CHC correctly describes demixing length and time scales, except for quenches into the vicinity of the spinodal boundary. Our data demonstrate the significant effect of relatively minor polymer microstructure variations on polymer blend behavior across both sides of the phase boundary.

中文翻译：

策略对SANS研究的PαMSAN/ dPMMA共混物的相行为和分解的影响

我们通过小角度中子散射（SANS）研究了聚合物立构规整度对聚合物混合物的相行为和相分离的影响。聚（α甲基苯乙烯-共-丙烯腈）（PαMSAN）和氘化的聚（甲基丙烯酸甲酯）（dPMMA）带有两个间规度的选择作为模型部分混溶共混物，如已知的最高度交互系统中的一个（由下式定义混合物的相互作用参数的温度依赖性）。一阶（平衡）和时间分辨的旋节线混合实验分别通过de Gennes的随机相位近似（RPA）和Cahn-Hilliard-Cook（CHC）理论进行了分析。相对于混合组合物的吉布斯自由能（的二阶导数ģ “≡∂ ² Δ ģ从RPA和CHC分析中均获得了_m / R ²）和相应的χ参数，发现它们在整个相界之间具有很好的相关性。我们发现，具有较高PMMA间同立构规整度的共混物表现出更大的可混溶性，并且对G ”的温度依赖性更强，约40％。发现间同立构规整度较高的dPMMA的链段长度为a = 7.4Å ，略大于同上同立构规整度较低的dPMMA的6.9Å。对于旋节峰峰值位置q *随时间推移的非平凡演变的自洽分析，需要考虑热波动，这已通过CHC模型计算得到证实。迁移率参数的温度依赖性M可以用掺混物成分的扩散系数的“快速模式”平均值来描述，除了在玻璃化转变附近产生的淬灭外。与更深的淬火理论相一致，获得了最小混合长度尺度≈40 nm，但在较浅的淬火中却发生了偏离，我们将讨论其起源。CHC正确地描述了混合长度和时间尺度，除了在旋节线边界附近的淬灭。我们的数据证明了相对较小的聚合物微观结构变化对整个相边界两侧聚合物共混行为的重大影响。

更新日期：2020-01-04

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