Abstract
As an example of molecular design of new polymers, structures and properties of poly(ethylene thionoterephthalate) (PET[S2]) and the related polymers have been predicted from calculations of ab initio molecular orbital (MO) theory, rotational isomeric state (RIS) scheme, and periodic density functional theory (DFT). The MO calculations were confirmed by NMR experiments and introduced to the RIS scheme for PET[S2] to yield its configurational properties, which are compared herein with those of analogous polyester, polythioester, and polydithioester. Configurational properties of randomly thiono-substituted poly(ethylene terephthalate) (PET), PET[SzO1–z], were also evaluated as a function of sulfidity (z). On the assumption that the crystal of PET[S2] can be expressed as an isomorphic replacement of the PET crystal, the crystal structure was optimized by a periodic DFT simulation and its Young’s moduli in the a-, b-, and c-axis directions were, respectively, evaluated to be Ea = 0.94(7.20) GPa, Eb = 19.58(22.26) GPa, and Ec = 142.1(182.4) GPa, where the parenthetic values are those of the PET crystal. There is a possibility that properties of PET[SzO1–z] will be controlled between those of PET and PET[S2] by adjusting the sulfidity. The potential practical applications of the polythionoesters are also discussed herein. By purely theoretical computations, the structures and properties of the not-yet synthesized polymers were predicted quantitatively; that is, the theoretical molecular design of new polymers has been achieved.
Highlights
When the primary structure of a new polymer is suggested, if one could predict its higher-order structures and physical properties, it would be considered to be a molecular design.[1]
We investigated conformational characteristics and structure−property relationships of aromatic polyester and polythioesters expressed by chemical formulae given in Figure 1: X = Y = O, poly(ethylene terephthalate) (PET);[2] X = O and Y = S, poly(ethylene dithioterephthalate) (PETS2);[3−5] X = Y = S, poly(ethylene tetrathioterephthalate) (PETS4).[3−5] In Table 1, their conformational characteristics and configurational properties are summarized
For ethylene glycol dibenzoate (EGDB), most and no stable g±g∓ pairs appear in bonds 5 and tg±t and tg±g± conformers have similar ΔGk values
Summary
When the primary structure (constituent atoms and chemical bonds) of a new polymer is suggested, if one could predict its higher-order structures and physical properties, it would be considered to be a molecular design.[1]. We investigated conformational characteristics and structure−property relationships of aromatic polyester and polythioesters expressed by chemical formulae given in Figure 1: X = Y = O, poly(ethylene terephthalate) (PET);[2] X = O and Y = S, poly(ethylene dithioterephthalate) (PETS2);[3−5] X = Y = S, poly(ethylene tetrathioterephthalate) (PETS4).[3−5] In Table 1, their conformational characteristics and configurational properties are summarized. PET[S2]b PETb PETS2c PETS4c the most stable conformation in free state tg±t tg±t g±tg∓ g±tg∓ (∼tg±g±). BFrom free energies at the MP2/6-311++G(3df,3pd)// B3LYP/6-311+G(2d,p) level. CFrom free energies at the MP2/6311+G(2d,p)//B3LYP/6-311+G(2d,p) level.[3−5] dcis and trans.[3−5] etrans−trans, (trans−cis)±, (cis−trans)±, and cis−cis.[5].
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