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Modeling of Poly(3-hexylthiophene) and Its Oligomer's Structure and Thermal Behavior with Different Force Fields: Insights into the Phase Transitions of Semiconducting Polymers
Full text linkThe polymorphism of poly(3-hexylthiophene) (P3HT), one of the reference systems in fundamental studies of polymer semiconductors, is explored by molecular dynamics modeling of selected 3-hexylthiophene (3HT) oligomers, comparing structural and thermal behavior simulation results with rare monodisperse oligomer experimental data. The relative stability of the two crystalline polymorphs and the mechanism of interconversion between them, as the degree of polymerization grows in (3HT)n oligomers (n = 10, 16, 20) to the polymer, can be investigated in infinite periodic oligomer crystals without implicitly imposing infinite molecular weights, as inevitable for polymers. To evaluate the impact of different descriptions of molecular interactions, simulations were performed by using three different force fields specifically adapted to poly(3-alkylthiophenes) (P3ATs). Our results show that MD may adequately describe the key features and relative stability of the different crystal phases and suggest plausible interconversion mechanisms for very rapid solid-solid or melting transitions, albeit with complementary differences among different force fields, which become substantial modeling highly disordered crystal structures or mesophases
The Polymorphic Behavior of Poly(2,2'-dimethyltrimethylencarbonate) and of its Cyclic Monomer. Evidences for a High Entropy Conformationally Disordered Modification
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Definitions and notations relating to tactic polymers (IUPAC Recommendations 2020)
Full text linkThis document summarizes and extends definitions and notations for the description of tactic polymers and the diad structures of which they are composed. It formally recognizes and resolves apparent inconsistencies between terminology used in the polymer field to describe tactic polymers and terminology in more common use in organic chemistry. Specifically, the terms m and r diads are recommended to replace the terms meso and racemo diads. The definitions are also updated from those in the existing Stereochemistry Document to use the term 'stereogenic centre', rather than 'chiral or prochiral atoms'. Further, the terms relating to tacticity have been defined for the constituent macromolecules, rather than for the polymers composed of those macromolecules. Therefore, this document also forms an addendum and corrigendum to the 1981 document, 'Stereochemical definitions and notations relating to polymers'
Atomistic modeling of solid-state phase transitions in poly(3-alkylthiophenes): from form II to form I polymorphs.
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Crystal Structure of Form I of Syndiotactic 1,2-poly(4-methyl-1,3-pentadiene).
No full textThe crystal structure of the form I of syndiotactic 1,2-poly(4-methyl-1,3-pentadiene) has been determined studying the X-ray fiber diffraction pattern recorded onto a Fuji image plate. The chain conformation (T6G2T2G2), previously proposed by Meille et al. on the basis of the identity period, has been confirmed, but with deviations of chain torsion angles from the 60 and 180° values. The crystal system is triclinic, a = 17.513(8) Å, b = 9.117(6) Å, c = 11.251(14) Å, α = 95.20(4)°, β = 98.01(3)°, γ = 92.74(5)°, and V = 1768(3) Å3. The space group is P1̄, with two chains per cell, each formed by six nonequivalent CH2CH[CH=C(CH3)2] chemical units. The crystal structure was determined and refined by the least-squares method, keeping bond lengths fixed and assuming that chemically equivalent bond angles are equal to each other. The refined model shows unrealistic values for some side group bond angles, in particular for the angle between methyl groups. Quite satisfactory results are obtained fixing this angle to the value of 122.7°, as suggested by searching the Cambridge Structural Database. Final disagreement indices are R1 = 14.3% and R2 = 15.0%
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