Dynamics of macromolecular chains in solution. A model of local motion in a polycarbonate

Abstract

A semimolecular-level model permitting interpretation of local motion in a polycarbonate chain and giving good agreement between experimental results obtained by certain authors and calculated results for spin-lattice NMR relaxation times for and 13C nuclei over a wide range of frequencies has been considered. The model assumes modulation of the dipole-dipole interaction by (i) specific conformational reorientation of single bonds and (ii) isotropic motion, with correlation times 1 ~10"10 s and 0 ~10"9 s, respectively. In addition, phenyl and methyl groups are assumed to execute fast internal rotation with a correlation time 2 ~10"11 s. The characteristic autocorrelation function derived from molecular-level specificity of the polycarbonate chain is compared with Hall and Helfand's general orientational autocorrelation function. In general, the data suggest that conformational transitions in polycarbonate, as revealed by the NMR method, do not occur necessarily as cooperatively as implied by crankshaft theories and can simply be bond rotations between isomeric transition states.

Molecular Mobility in Para-Substituted Polyaryls. 3. Low-Temperature Dynamics

“…These energies are also in better agreement with calculated estimations for the rotation of crankshafts than the β processes. Moreover, we also notice a better agreement with the experimental values revealed by NMR in dilute solutions of PPS , ( E a (γ,PPS) is close to 14 kJ/mol) and in BPA-PC , (13 kJ/mol). This leads us to assign the γ relaxation modes to very local rearrangements of a few rings, such as crankshaft-like motions, with possibly a small influence of neighboring chain portions.…”

Quasi-static modeling of chain dynamics in the amorphous glassy polycarbonate of 4,4'-isopropylidenediphenol

“…The orientation of the ring axis is approximately preserved in this process, while the rings in between the "exchanging" carbonate groups have undergone a 180°f lip; the carbonate termini have also roughly retained their orientation. Similar concepts have been advanced by Tekely,18 who combined a molecular mechanics conformational analysis of various fragments of PC chains with relaxation times of PC in solution to a conformational reorientation model where the carbonate group is held rigid. Sequential transitions between isomeric states of neighboring bonds of the chain were deemed likely to occur in solution and "crankshaft" type motions should be less probable.…”

Molecular Dynamics Simulation of Bisphenol A Polycarbonate

“…The 3-fold rotation of the methyl group16'22,23 has been proposed by various experiments and the rotational energy barrier is deduced as 4-6 kcal/mol.22 '23 This high rotational barrier is reported to be due to the presence of two methyl groups bound to the same carbon atom. 16 The coupling between the methyl group and the phenylene ring may also inhibit the internal rotation of the methyl group. In our simulation, we do not find this 3-fold rotation of the methyl group.…”