Solid-state structure of polystyrene-block-poly(gamma-benzyl L-glutamate): Helix folding vs stretching
Solid-state structure of polystyrene-block-poly(gamma-benzyl L-glutamate): Helix folding vs stretching
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DOI：
10.1021/ma0606197
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发表时间：
2006-06
期刊：
影响因子：
5.5
通讯作者：
H. Schlaad;B. Smarsly;Ines Below
中科院分区：
文献类型：
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作者：
H. Schlaad;B. Smarsly;Ines Below
研究最深入的体系是基于聚（γ-苄基L-谷氨酸酯）（PBLGlu）的均聚物和嵌段共聚物。已经报道了R-螺旋PBLGlu膜的许多固态改性，最重要的是所谓的形式B和C。7-9形式B具有3D单斜晶胞的明确的晶体结构，并且通过在升高的温度下从极性溶剂如N，N-二甲基甲酰胺（DMF）或苯甲醇浇铸获得。在形式C中，其通过从非极性溶剂如氯仿或1，2-二氯乙烷的膜流延获得，R-螺旋堆积在相当不规则的假六方晶格上。然而，这两种形式的堆积特征不被热退火改变。已知基于例如聚苯乙烯（PS）和PBLGlu的线圈棒嵌段共聚物形成层状超结构，而不管组分的体积分数。在多肽片层内，PBLGlu螺旋垂直于PS-PBLGlu界面取向，并且通常不拉伸而是折叠。螺旋的折叠尚未报道PBLGlu均聚物。然而，取决于所使用的浇铸溶剂，螺旋以2D六边形阵列（1，4-二氧六环）10或更复杂的、尚未明确识别的图案（DMF）排列。此外，溶剂的极性越高，有序度似乎越低。[12]在这一点上，出现了一个有趣的问题，即PBLGlu螺旋的堆积和折叠是否都受浇铸溶剂的控制。溶剂极性似乎不是关键参数（1，4-二氧六环，介电常数ε）2.2; DMF，ε）36.7），9但它可能是氢键能力：1，4-二氧六环和DMF都被归类为中等氢键溶剂。因此，从三种不同的非极性溶剂，即1，4-二氧六环（f膜B）、苯甲醚（TCE，TCE）4.3）（f膜C）和1，1，2，2-四氯乙烷（TCE，TCE）7.1）（f膜D），流延PS52-b-PBLGlu 93的膜（PBLGlu的体积分数：φPBLGlu）0.76）。DMF在早期研究中用于流延PS52-b-PBLGlu 104的膜（f膜A）。11与二氧六环和DMF一样，苯甲醚属于中等氢键溶剂，而TCE是弱氢键溶剂。这两种溶剂的Hildebrandt溶度参数基本相同，δ分别为19.4- 20.5MPa-0.5和24.8MPa-0.5（DMF），13，沸点均在100 ℃以上。
The most thoroughly investigated systems are the homopolymers and block copolymers based on poly (γ-benzyl L-glutamate)(PBLGlu). A number of solid-state modifications have been reported for films of R-helical PBLGlu, the most important ones being the so-called forms B and C. 7-9 Form B has a well-defined crystalline structure with a 3D monoclinic unit cell and is obtained by casting from polar solvents like N, N-dimethylformamide (DMF) or benzyl alcohol at elevated temperature. In form C, which is obtained by film casting from nonpolar solvents like chloroform or 1, 2-dichloroethane, the R-helices are packed on a rather irregular pseudohexagonal lattice. The packing feature of these two forms is, however, not altered by thermal annealing.Coil-rod block copolymers based on, for instance, polystyrene (PS) and PBLGlu are known to form a lamellar superstructure, regardless the volume fractions of components. 10 Within the polypeptide sheets, the PBLGlu helices are oriented orthogonal to the PS-PBLGlu interface and are usually not stretched but folded. A folding of helices has not been reported for PBLGlu homopolymers. However, depending on the casting solvent used, helices are either arranged in a 2D hexagonal array (1, 4-dioxane) 10 or a more complex, not yet clearly identified pattern (DMF). 11 Also, the degree of order seems to be lower the higher the polarity of the solvent. 12 At this point the interesting question arises if not only the packing but also the folding of PBLGlu helices is governed by the casting solvent. Solvent polarity seems not to be the key parameter (1, 4-dioxane, dielectric constant ϵ) 2.2; DMF, ϵ) 36.7), 9 but it could be the hydrogen-bonding ability: 1, 4-dioxane and DMF are both classified as moderate hydrogen-bonding solvents. 13 Therefore, films of a PS52-b-PBLGlu93 (volume fraction of PBLGlu: φPBLGlu) 0.76) were cast from three different nonpolar solvents, namely 1, 4-dioxane (f film B), anisole (ϵ) 4.3)(f film C), and 1, 1, 2, 2-tetrachloroethane (TCE, ϵ) 7.1)(f film D). DMF was used in an earlier study for the casting of a film of a PS52-b-PBLGlu104 (f film A). 11 Like dioxane and DMF, anisole belongs to the class of moderate hydrogen-bonding solvents, whereas TCE is a poor hydrogenbonding solvent. The Hildebrandt solubility parameters of the solvents are about the same, ie, δ) 19.4-20.5 MPa-0.5 and 24.8 MPa-0.5 (DMF), 13 and boiling points are beyond 100 C.