X-ray Diffraction and Molecular Modeling Studies of Poly(di-n-alkylsilanes):  The Near Planar Type Phases of Poly(di-n-butylsilane) and Poly(di-n-hexylsilane)

Abstract

X-ray diffraction and molecular modeling have been used to investigate the near planar solid-state phases of poly(di-n-hexylsilane) (pdHexSi) and poly(di-n-butylsilane) (pdBuSi). Structure refinement of diffraction data in conjunction with oligomer cluster energy calculations provides a more unified picture of both the main chain and side chain conformations. In both polymers the alkyl side chain construction is closely identified as an asymmetric cisoid-transoid conformational arrangement. Full refinement of the pdHexSi data identifies subtler features in the alkyl chain organization. All major trends and key structural features are paralleled in empirical MM3 based modeling of isolated di-nbutylsilane and di-n-butylsilane oligomers. Zero-temperature gas-phase calculations identify a well-defined topology of energetically accessible main chain and side chain conformations. Increasing the side chain length, from butyl to hexyl, changes both the distribution and make up of the low energy structures. A combination of intrachain and interchain packing energy constraints stabilize the planar form of poly-(di-n-hexylsilane). Intrachain interactions are significantly weaker in poly(di-n-butylsilane).

Chain Conformations and Photoluminescence of Poly(di-n-octylfluorene)

“…For structural modeling we used a combinatorial method approach in which a large number of possible single chain conformers were examined using empirically determined force-field parameters (MM3* [19]) at zero-temperature in the gas-phase. Recent work in polysilanes [20] and a related PF [21] suggest that this approach, though limited in scope, reveals some basic attributes of the local intrachain structure. In this case over 700 distinct starting F8 decamers were constructed.…”

Novel design, facile synthesis and low infrared emissivity properties of single-handed helical polysilanes

“…Around 45 C, PDHS powder displayed the distinctive thermochromic order-disorder transition from crystalline to a hexagonal columnar mesophase. 28 As the Fig. 6 describes, the melt point and intensity of HPS decreased with broader linewidth, which result from comonomer-induced irregularities and crystalline order disturbance compared to PDHS.…”

Multihydroxy-Functional Polysilanes via an Acetal Protecting Group Strategy

“…The corresponding DSC traces of the copolymers with varying fractions of IMS are depicted in Figure , and the corresponding calorimetric data are listed in Table . While pure PDHS shows the typical endothermic phase transition from crystalline to a liquid-crystalline hexagonal columnar mesophase at 45 °C, a gradual decrease of the transition temperature as well as transition enthalpy is observed for the P(DHS- co -IMS) copolymers. This is caused by the comonomer-induced irregularities and consequent disturbance of the crystalline order in comparison to PDHS.…”

“…For instance, poly(di-n-hexylsilane) (PDHS), soluble in nonpolar organic solvents only, approximates a trans-planar conformation of the backbone at room temperature. 22 At 45 °C, a transition to a liquid-crystalline, hexagonal columnar mesophase (hcm) with conformational disorder of the side chains takes place, which can be followed by calorimetric measurements (DSC) or UV spectroscopy as well as many other techniques.…”