Conformational Characteristics of Poly(trimethylene sulfide) and Structure−Property Relationships of Representative Polysulfides and Polyethers

Abstract

Conformational characteristics of poly(trimethylene sulfide) (PTMS) have been investigated by a rotational isomeric state analysis of ab initio molecular orbital calculations and 1 H and 13 C NMR experiments for a monomeric model compound, 1,3-bis(methylthio)propane, and the characteristic ratio and dipole moment ratio of the unperturbed PTMS chain. Both C-S (the first-order interaction energy, -0.30 kcal mol -1 ) and C-C (-0.58 kcal mol -1 ) bonds prefer the gauche conformation. For comparison, conformational analysis of the corresponding polyether, poly(trimethylene oxide), has also been carried out. The C-O (+0.97 kcal mol -1 ) and C-C (-0.47 kcal mol -1 ) bonds show trans and gauche preferences, respectively. These results are consistent with the conformational stabilities predicted by the natural bond orbital analysis on model compounds of poly-(ethylene sulfide) (PES) and poly(ethylene oxide). Without the strong S‚‚‚S repulsion, therefore, the C-C bond adjacent to the C-S bond exhibits its inherent gauche preference. Without the (C-H)‚‚‚O attraction, the ethereal C-C bond is subject to the attractive gauche effect. For representative polysulfides and polyethers, relationships between conformations in the Θ and crystalline states and thermal properties have been investigated. Even in the Θ and crystalline states, the polymers mostly keep the conformational preferences found for their small model compounds; as an exception, poly(propylene sulfide) and poly(propylene oxide), having a methyl side chain, crystallize to adopt the metastable all-trans conformation. On average, the configurational entropy of the polymers amounts to 80-90% of entropy of fusion, and the configurational energy change between crystalline and molten states accounts for ca. 30% of enthalpy of fusion. Of the polymers investigated here, PES has an exceptionally high melting point; the dipole-dipole interaction in the PES crystal was evaluated to be -1.0 kcal mol -1 (ca. 30% of the enthalpy of fusion), thus being the source of the thermostability.

Structure–Property Relationships of Poly(ethylene carbonate) and Poly(propylene carbonate)

“…At a phase transition such as melting, the S conf value corresponds to the entropy change at constant volume and is related to that ((Δ S ) p ) at constant pressure and that (Δ S v ) due to the volume change (Δ V ) by 40,41 where Δ S v = (α/β)Δ V with α and β being the thermal expansion coefficient and isothermal compressibility, respectively. The S conf /(Δ S ) p ratio has been estimated as, for example, 0.8–0.9 for polyethers and polythioethers 42 and 0.5–0.7 for polyesters, 27 while amorphous elastomers exhibit comparatively small S conf /(Δ S ) p values such as 0.5 (natural rubber) and 0.6 (gutta percha). 41 Therefore, amorphous PEC and PPC would also have somewhat smaller S conf /(Δ S ) p ratios than those of semicrystalline polymers.…”

Ethane-1,2-diyl bis(benzenedithioate)

“…In addition, dipole moments, formed close to the O=C bonds, are either parallel or antiparallel to one another. The dipoledipole interactions are known to stabilize the crystal structure (Sasanuma & Watanabe, 2006). On the other hand, Figure 2 shows that the C=S bonds of BDTBE do not have such clear orientations, because the small difference in electronegativity between C and S little polarizes the C=S bond.…”

“…The S-CH 2 -CH 2 -S part of crystallized poly(ethylene sulfide) (PES, [-CH 2 CH 2 S-] x ) lies in the gauche + -transgauche-(g + tg -) conformation (Takahashi et al, 1968); the two S-C bonds are in opposite gauche states, and dipole moments are formed along bisectors of the C-S-C angles. The dipole-dipole interaction was suggested to be the source of its high melting point (215-220 °C) in comparison with that (66-69 °C) of poly(ethylene oxide), [- (Sasanuma & Watanabe, 2006 CO-] x ). Crystal conformations of polymers are requisite to derive their configurational properties and thermodynamic quantities.…”

Predictive elucidation of conformational characteristics and configurational properties of poly(1-methylphosphirane) and poly(1-phenylphosphirane) as a molecular design

“…1 shows the principal elements included in skeletal bonds of polymers. So far, we have carried out conformational analyses of polymers whose backbones contain oxygen, sulfur, selenium, nitrogen, or silicon; we have elucidated conformational characteristics, configurational properties, crystal structures, electric and optical properties, and crystallization and melting of polyethers (including O), [1][2][3][4][5][6][7][8][9][10] polysulfides (S), 1,2,7,10,11 polyselenoethers (Se), 12 polyimines (N), 13,14 and polysilanes (Si) 15,16 especially in terms of weak intramolecular interactions generated by the heteroatoms. In a series of studies, we have also aimed to relate the structures and properties of the above polymers to the periodic table, i.e., electronic structures of the heteroatoms and, furthermore, to develop a methodology for molecular design of polymers.…”