Xue-Wei Wei,Guoyong Huang,Jing Wang,Xiaoyu Meng,Qiong Zhou,Hai-Mu Ye
Isodimorphism and isomorphism are becoming mature approaches but separately used to regulate crystallization behavior of random copolymers and thus their performances. Most of the research work is focused on binary copolymers while leaves random copolymers containing more than two kinds of comonomeric units rarely studied in which both isodimorphism and isomorphism may occur together. This experiment is realized in the terpolymers of poly(butylene adipate-ran-butylene succinate-ran-butylene fumarate) (PBASF) wherein butylene adipate (BA) displays isodimorphic behavior with either butylene succinate (BS) or butylene fumarate (BF), and BF builds an isomorphic structure with BS. When the BA content is kept almost unchanged at ∼50 mol %, PBASF can be subtly tailored from a pseudoeutectic state to only isomorphic state by increasing the BF content that suppresses the crystallizability of the PBA-rich phase but hardly affects the PBSF-rich phase. Crystallization behaviors of PBASF from both melt and quenched samples are assayed in detail by using a differential scanning calorimeter, X-ray diffractometer/scatterometer, and Fourier transformation infrared spectrometer, and the mechanism of confined crystallization is clearly unraveled, which is relied on both intersegment hydrogen-bonding interaction and physical restriction. Furthermore, a crystal phase diagram for random terpolymer of PBASF is proposed, which provides an overall guide to tailor its crystallization. This example of the strategy combining isodimorphism and isomorphism raised here sheds light on precise regulation of properties and performances of terpolymer and copolymer with more complicated chain structures.
Meng Liu,Guowen Shen,Zhong Yuan,Sean Parkin,Faquan Yu,Mingtao Zhang,Sihui Long,Tonglei Li
To gain understanding of how the variation in local weak interactions influences intermolecular interactions and subsequent crystal packing, four analogues of 2-(3-chloro-2-methyl-phenylamino)-nicotinic acid [clonixin] were synthesized by replacing the chlorine with fluorine (1), bromine (2), iodine (3), and hydrogen (4). Compounds 1, 2, and 3 were found to be polymorphic as shown by the discovery of two forms for each (1-I, 1-II; 2-I, 2-II; and 3-I, 3-II, respectively), while compound 4 has only a single identified form. Similar to clonixin, the analogue molecules in their crystals are associated either by the acid–acid dimer homosynthon or the acid–pyridine heterosynthon, depending on the dihedral angle between the two aromatic rings. Moreover, forms 2-I, 2-II, 3-I, and 3-II are isostructural to clonixin forms I and IV, compound 4 is isostructural to compound 1 form I, and 2-II is structurally similar to clonixin form II. The phase behaviors of these polymorphic systems were studied by differential scanning calorimetry, and it was found that 2-II converted into 2-I when heated, 3-II transformed into 3-I upon heating, and 1-II underwent transition into 1-I. Quantum mechanical calculations including conformational energy, hydrogen-bonding strength, lattice energy, and molecular contact were performed to provide further insight into the polymorphism. Given that all halogen derivatives are polymorphic, while the hydrogen analogue (4) is not, our study highlights the importance of intermolecular interactions in determining crystal packing.
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