Optical Anisotropy of Structurally Modified Polycarbonates Having Cyclohexylidene and Methyl Substituents Using the Rotational Isomeric State Method

Abstract

An extension of the valence optical scheme-rotational isomeric state method (RIS) applicable to calculation of polarizability tensors and optical anisotropy (γ 2 ) of molecular fragments constituting substituted polycarbonate chains is presented. The theoretical approach utilizes experimentally derived anisotropic polarizability tensors of molecular groups in order to be able to account for induction effects and interdependence of backbone conformational states. The presence of a cyclohexylidene group at the bisphenyl C R carbon significantly lowers γ 2 due to the low intrinsic polarizability of the cycloaliphatic substituent and due to the conformational states of backbone phenylene rings. Optical anisotropy value of the bisphenyl containing methyl substituents on the phenyl rings is lower than the value for the unsubstituted bisphenyl. Among the structures investigated here, the repeat unit containing cyclohexylidene group at C R and methyl groups on phenylene rings, leads to the polycarbonate that shows the lowest optical anisotropy. Quantitatively, cyclohexylidene at CR is more effective in lowering the optical anisotropy than methyl groups on backbone phenylene rings. Calculated 〈γ 2 〉/x of the repeat units follows a linear behavior with respect to experimentally observed stress-optical coefficient of these polycarbonates in the melt (Cm). Calculated 〈γ 2 〉/x of these structurally modified polycarbonate chains are all lower than that of BPAPC, and the relative trend in 〈γ 2 〉/x is similar to that observed for Cm and Cg (glassy state) from experiments in the literature.

Ab initio calculations of the geometry and polarizabilities of bisphenyls having aliphatic substituents

“…As the VOS‐derived 〈γ 2 〉 value of DPP is in excellent comparison with the value derived from experimental scattering measurements, we assume that the VOS‐derived values of substituted bisphenyl fragments40 will be closer to their experimental values. Our earlier VOS calculations on a series of chemically different repeat unit and polycarbonate chains showed that the trend in the calculated 〈γ 2 〉 values were in excellent agreement with the experimental stress‐optical properties of these materials in the melt state41, 42. The ab initio calculations reported here for these bisphenyls follows the same trend as what is seen for the VOS‐derived values, although the absolute values are not in agreement.…”

“…We find that the optical anisotropies calculated from polarizabilities obtained from the TDHF method in gas phase are higher than those determined using VOS. However, it has been shown previously that the VOS scheme using experimentally derived group polarizability tensors give excellent comparison with experimentally determined optical anisotropies for model compounds DPP and for BPAPC40, 41 in dilute solution. For example, optical anisotropy calculated for DPP via the VOS method is 39.1 Å 6 for a conformation (ψ b = ψ a = 50°, 2τ′ = 110.7°) and the experimental value is 40 ± 2 Å 6 39.…”

“…A systematic set of theoretical studies on a series of structurally different polycarbonates by Sulatha et al have provided important insights on the relationship between the repeat unit chemical structure and polarizability, optical anisotropy, and birefringence40–42. Polarizability and optical anisotropy calculations for a series of substituted cyclohexanes and their corresponding cyclohexylidene bisphenyl molecules have been computed40, by the incorporation of experimentally derived polarizability tensors of atomic groups into the valence optical scheme (VOS).…”

“…Polarizability and optical anisotropy calculations for a series of substituted cyclohexanes and their corresponding cyclohexylidene bisphenyl molecules have been computed40, by the incorporation of experimentally derived polarizability tensors of atomic groups into the valence optical scheme (VOS). Also, the VOS scheme has been extended to the formulation of polarizability tensors and calculation of optical anisotropies of polycarbonate chains with different chemical structures (aliphatic substitutions)41. The effect of geometry and conformation on the polarizability and optical anisotropy of different repeat units and single chains of structurally different polycarbonates was investigated in detail in that study.…”

Effect of Chemical Substituents on the Structure of Glassy Diphenyl Polycarbonates

“…Molecular simulation studies of chemically substituted (i.e., structurally modified) PCs are very limited. Conformational analyses of model fragments and chains , and optical properties have shown the influence of chemical structure on single-chain properties. Atomistic simulations of the diffusivity of various penetrant gases in the amorphous phase of tetramethyl (TMPC) and tetrabromo (TBPC) derivatives of BPAPC have shown correlation between simulated free volume distribution and diffusional coefficient, consistent with experiment.…”