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Crystal Structure of Atactic and Isotactic Poly(3-hydroxy-2,2-dimethylbutyrate): A Chemically Recyclable Poly(hydroxyalkanoate) with Tacticity-Independent Crystallinity
Macromolecules ( IF 5.1 ) Pub Date : 2024-04-19 , DOI: 10.1021/acs.macromol.4c00165 Miriam Scoti 1 , Li Zhou 2 , Eugene Y.-X. Chen 2 , Claudio De Rosa 1
Macromolecules ( IF 5.1 ) Pub Date : 2024-04-19 , DOI: 10.1021/acs.macromol.4c00165 Miriam Scoti 1 , Li Zhou 2 , Eugene Y.-X. Chen 2 , Claudio De Rosa 1
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The crystal structures of isotactic and atactic poly(3-hydroxy-2,2-dimethylbutyrate) (P3H(Me)2B) are presented. Samples of atactic P3H(Me)2B (at-(R/S)-P3H(Me)2B) and of the R and S enantiomers of isotactic P3H(Me)2B (it-(R)-P3H(Me)2B and it-(S)-P3H(Me)2B, respectively) have been synthesized by ring opening polymerization of racemic and chiral dimethyl-butyrolactones employing a superbase catalyst. A 1:1 racemic mixture of the two R and S enantiomers (it-(R,S)-P3H(Me)2B) has been also prepared. Both the atactic and the pure enantiomer isotactic polymers crystallize showing identical diffraction patterns, indicating crystallization in the same crystalline form and identical crystal structure. The racemic mixture it-(R,S)-P3H(Me)2B also crystallizes giving identical diffraction pattern. This is one of the few examples of crystallization of an atactic polymer despite the configurational disorder and probably it is the first structurally confirmed example of crystallization of atactic and isotactic polymers in the identical crystal structure. This fascinating tacticity-independent crystallinity explains the remarkable thermal and mechanical behaviors of P3H(Me)2B, which is thermally stable and melt-processable and chemically recyclable to the monomer. The crystal structure has been resolved by analysis of X-ray powder diffraction and X-ray fiber diffraction of oriented fibers, combined with conformational analysis based on methods of density functional theory. The ordered crystal structure of the isotactic pure enantiomer it-(R)-P3H(Me)2B (or it-(S)-P3H(Me)2B) is described by chains in a nearly trans-planar conformation with chain axis of 4.7 Å packed in an orthorhombic unit cell with axes a = 13.30 Å, b = 9.99 Å, and c = 4.75 Å according to the chiral space groups P21212 or P212121. The atactic polymer at-(R/S)-P3H(Me)2B crystallizes in the same orthorhombic unit cell having only slightly larger a axis, a = 13.94 Å, b = 10.03 Å, and c = 4.75 Å, with chains characterized by a disordered succession of R and S monomers and a distorted trans-planar conformation that keeps a straight chain axis and the same periodicity of 4.7 Å of the ordered pure enantiomer. This proposed model of the conformation of at-(R/S)-P3H(Me)2B explains the crystallization of the atactic polymer. The crystal structure of at-(R/S)-P3H(Me)2B is, therefore, characterized by the packing of disordered chains in nearly trans-planar conformation according to both the chiral space groups P21212 or P212121 and the achiral space groups Pna21 or Pnn2.
中文翻译：
无规立构和等规聚(3-羟基-2,2-二甲基丁酸酯)的晶体结构：具有立构规整性结晶度的可化学回收的聚(羟基链烷酸酯)
给出了全同立构和无规立构聚(3-羟基-2,2-二甲基丁酸酯)(P3H(Me) 2 B)的晶体结构。无规立构 P3H(Me) 2 B ( at -( R / S )-P3H(Me) 2 B) 和全同立构 P3H(Me) 2 B ( it -( R )-P3H(Me)的R和S对映体的样品) 2 B 和it -( S )-P3H(Me) 2 B 分别通过使用超强碱催化剂的外消旋和手性二甲基丁内酯的开环聚合来合成。还制备了两种R和S对映体的 1:1 外消旋混合物（it -( R , S )-P3H(Me) 2 B）。无规立构和纯对映异构体全同立构聚合物结晶时显示出相同的衍射图，表明以相同的晶型和相同的晶体结构结晶。外消旋混合物it- ( R , S )-P3H(Me) 2 B也结晶，给出相同的衍射图。尽管构型无序，这是无规聚合物结晶的少数例子之一，并且可能是在相同晶体结构中无规和全同立构聚合物结晶的第一个结构确认的例子。这种令人着迷的与立构规整度无关的结晶度解释了 P3H(Me) 2 B 卓越的热和机械行为，它具有热稳定性、可熔融加工且可化学回收为单体。通过X射线粉末衍射和取向纤维的X射线纤维衍射分析，结合基于密度泛函理论方法的构象分析，解析了晶体结构。全同立构纯对映异构体it -( R )-P3H(Me) 2 B （或it -( S )-P3H(Me) 2 B）的有序晶体结构由具有链轴的几乎跨平面构象的链描述4.7 Å 封装在正交晶胞中，根据手性空间群P 2 1 2 1 2 或P 2 1 2 1 2 1，轴a = 13.30 Å、b = 9.99 Å 和c = 4.75 Å。无规聚合物在-(R / S )-P3H(Me) 2 B 在相同的斜方晶胞中结晶，该晶胞仅具有稍大的轴，a = 13.94 Å、b = 10.03 Å 和c = 4.75 Å，其链的特征是R的无序序列和S单体以及扭曲的跨平面构象，保持直链轴和有序纯对映体的 4.7 Å 的相同周期性。提出的at -( R / S )-P3H(Me) 2 B 构象模型解释了无规聚合物的结晶。因此， at -( R / S )-P3H(Me) 2 B的晶体结构的特征是根据手性空间群P 2 1 2 1 2 或P以近跨平面构象排列无序链。2 1 2 1 2 1和非手性空间群Pna 2 1或Pnn 2。
更新日期：2024-04-19
中文翻译：
无规立构和等规聚(3-羟基-2,2-二甲基丁酸酯)的晶体结构：具有立构规整性结晶度的可化学回收的聚(羟基链烷酸酯)
给出了全同立构和无规立构聚(3-羟基-2,2-二甲基丁酸酯)(P3H(Me) 2 B)的晶体结构。无规立构 P3H(Me) 2 B ( at -( R / S )-P3H(Me) 2 B) 和全同立构 P3H(Me) 2 B ( it -( R )-P3H(Me)的R和S对映体的样品) 2 B 和it -( S )-P3H(Me) 2 B 分别通过使用超强碱催化剂的外消旋和手性二甲基丁内酯的开环聚合来合成。还制备了两种R和S对映体的 1:1 外消旋混合物（it -( R , S )-P3H(Me) 2 B）。无规立构和纯对映异构体全同立构聚合物结晶时显示出相同的衍射图，表明以相同的晶型和相同的晶体结构结晶。外消旋混合物it- ( R , S )-P3H(Me) 2 B也结晶，给出相同的衍射图。尽管构型无序，这是无规聚合物结晶的少数例子之一，并且可能是在相同晶体结构中无规和全同立构聚合物结晶的第一个结构确认的例子。这种令人着迷的与立构规整度无关的结晶度解释了 P3H(Me) 2 B 卓越的热和机械行为，它具有热稳定性、可熔融加工且可化学回收为单体。通过X射线粉末衍射和取向纤维的X射线纤维衍射分析，结合基于密度泛函理论方法的构象分析，解析了晶体结构。全同立构纯对映异构体it -( R )-P3H(Me) 2 B （或it -( S )-P3H(Me) 2 B）的有序晶体结构由具有链轴的几乎跨平面构象的链描述4.7 Å 封装在正交晶胞中，根据手性空间群P 2 1 2 1 2 或P 2 1 2 1 2 1，轴a = 13.30 Å、b = 9.99 Å 和c = 4.75 Å。无规聚合物在-(R / S )-P3H(Me) 2 B 在相同的斜方晶胞中结晶，该晶胞仅具有稍大的轴，a = 13.94 Å、b = 10.03 Å 和c = 4.75 Å，其链的特征是R的无序序列和S单体以及扭曲的跨平面构象，保持直链轴和有序纯对映体的 4.7 Å 的相同周期性。提出的at -( R / S )-P3H(Me) 2 B 构象模型解释了无规聚合物的结晶。因此， at -( R / S )-P3H(Me) 2 B的晶体结构的特征是根据手性空间群P 2 1 2 1 2 或P以近跨平面构象排列无序链。2 1 2 1 2 1和非手性空间群Pna 2 1或Pnn 2。
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