Conformational Analysis, RIS Models and Single-Chain Properties of Structurally Modified Polycarbonates, 1. Effect of Cyclohexyl and Phenyl Ring Substitutions

Sulatha, Muralidharan S.; Natarajan, Upendra; Sivaram, Swaminathan

doi:10.1002/1521-3919(20020801)11:6<655::aid-mats655>3.0.co;2-y

Cited by 6 publications

(15 citation statements)

References 22 publications

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“…The statistical weights for energetically favorable conformers and their corresponding torsional states and bond angles, which were derived earlier using conformational analysis with bonded and interatomic nonbonded potentials described by the PCFF force-field, 20 are used here for the calculation of 〈γ 2 〉. The minimum energy torsions and bond angles for these polycarbonates are given in Table 1.…”

Section: Conformationally Averaged Chain Opticalmentioning

confidence: 99%

“…Calculations of optical anisotropy are also performed here for these polycarbonates by assigning equivalent weights for all the energetically favorable conformational rotational isomeric states which were obtained from previous conformational energy calculations. 20 In the case of BPAPC, the calculation was performed using torsions and bond angles as provided by Erman et al, 14 and also independently by using the values derived from our PCFF-based simulations. It should be noted that in the calculation method of 〈γ 2 〉 of polycarbonate chains outlined here, only the trans-trans conformations of the carbonate groups are considered.…”

Section: Conformationally Averaged Chain Opticalmentioning

confidence: 99%

“…Formulation of the polarizability tensors of repeat units of polycarbonates having cyclohexylidene group at the C R carbon and methyl substituents on the phenylene rings is presented and incorporated fruitfully into a RIS scheme for 〈γ 2 〉 estimation. The conformational characteristics, RIS models, and single chain properties of the structurally different polycarbonates chosen in the present work have been studied in detail in an earlier work, 20 where the statistical weights for the probable rotational states of various bond pairs are given. Results of the calculations of optical anisotropy of bisphenyl fragments, carbonate moieties and repeat units of structurally modified polycarbonates are presented and compared with results for BPAPC.…”

Section: Introductionmentioning

confidence: 99%

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

2003

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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.

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Section: Conformationally Averaged Chain Opticalmentioning

confidence: 99%

Section: Conformationally Averaged Chain Opticalmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

2003

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“…Optical anisotropy of these bisphenyl fragments can be calculated using the VOS as reported earlier40, whereas the polarizability tensors for specific groups of bonded atoms, as derived from scattering experiments, were made use of in conjunction with the relevant torsion and bond angles representing the geometry of the concerned molecule. In that report, the geometric parameters for various bisphenyl compounds were taken from force field‐based conformational energy calculations43. In our present study, for the purpose of a comparison with the VOS scheme (for the polarizability part), optical anisotropies of the fragments were recalculated by using VOS method by using experimentally derived group‐polarizability‐tensors using geometry (torsions and bond angles) derived from the ab initio geometry optimizations (Table II).…”

Section: Resultsmentioning

confidence: 99%

“…Calculations were performed on a silicon graphics octane workstation. The initial structures required for geometry optimizations were derived from a classical PCFF force field‐based molecular mechanics conformational analysis43. The equilibrium potential energy local minima geometry states and conformations of the bisphenyl model compounds were determined separately with 6‐31G and 6‐31G** basis sets.…”

Section: Computational Detailsmentioning

confidence: 99%

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

Sulatha

Natarajan

2011

Int J of Quantum Chemistry

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Ab initio geometry optimization and polarizability calculations of a series of bisphenyls, which are the model compounds of chemically different polycarbonates using HF/6-31G and 6-31G** basis sets are presented. Calculated absolute value of the conformationally averaged optical anisotropy (hc 2 i) of diphenyl propane, a model analog of bisphenol A polycarbonate, is higher than the corresponding experimental value in the dilute solution phase. The calculations have reproduced the relative trend in the optical anisotropy for the different bisphenyl model compounds in a manner similar to those using semiclassical approach, by incorporation of the condensed phase polarizabilities and quantum chemically calculated geometry structure into the valence optical scheme. Individual contributions to the gas phase polarizability and optical anisotropy of the model compounds for various dihedral conformers, because of the presence of different aliphatic chemical groups, are correctly predicted by the calculations here.

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Effect of Chemical Substituents on the Structure of Glassy Diphenyl Polycarbonates

Sulatha

Natarajan

2011

J. Phys. Chem. B

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Polycarbonates offer a wide variety of physical property behavior that is difficult to predict due to complexities at the molecular scale. Here, the physical structure of amorphous glassy polycarbonates having aliphatic and cycloaliphatic chemical groups is explored through atomistic simulations. The influence of chemical structure on solubility parameter, torsion distributions, radial distribution function, scattering structure factor, orientation distributions of phenylene rings and carbonate groups, and free volume distributions, leading to interchain packing effects, are shown. The effect of the cyclohexyl ring at the isopropylidene carbon as compared to the effect of the methyl groups positioned on the phenylene rings results in a larger reduction in the solubility parameter (δ). The interchain distance estimated for polycarbonates in this work is in the range of 5-5.8 Å. The o-methyl groups on the phenylene rings, as compared to a cyclohexyl ring, lead to higher interchain distances. The highest interchain distance is observed with a trimethylcyclohexylidene group at the isopropylidene carbon. Atomistic simulations reveal two different types of packing arrangement of nearest-neighbor chains in the glassy state, one type of which agrees with the NMR experimental data. The fundamental insights provided here can be utilized for design of chemical structures for tailored macroscopic properties.

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Conformational Analysis, RIS Models and Single-Chain Properties of Structurally Modified Polycarbonates, 1. Effect of Cyclohexyl and Phenyl Ring Substitutions

Cited by 6 publications

References 22 publications

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

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

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

Effect of Chemical Substituents on the Structure of Glassy Diphenyl Polycarbonates

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