Helical conformation and molecular vibrations of polyethylene glycol

Abstract

In our previous paper,' helical parameters of infinite polymer chains were expressed as functions of bond lengths, bond angles, and internal rotation angles.1 In making use of these equations, likely structure models were deduced for polyethylene glycol. The most probable model belongs to the dihedral group, and the internal rotation configurations are trans and gauche for the CH2-0 bond and for the CH2-CHz bond respectively (TGT model).2 This model contains seven chemical units and two turns of the helix per fiber period of 19.25 A. In the present study the infrared active vibrations belonging to the Az and E (e) species have been treated. The AZ vibrations give rise to parallel bands and the E(s) vibrations give rise to perpendicular ones. The normal frequencies and normal modes were calculated by the general method for treating the molecular vibrations of helical polymers belonging to the dihedral group.3 The C-H stretching modes were separated from the low-frequency modes. The modified UreyBradley force field4 was used as the potential function and the potential constants were transferred from p~lyethylene,~ dimethyl ether,5 and propyl alcohol.6 The calculated frequencies and the vibrational assignments are shown in Table I along with the observed infrared freq~encies.~,7 The average deviation between the calculated and observed frequencies is 3% although no adjustments were made for a better fit.For the Az species, the hybridization of the CH2 wagging and twisting modes may be remarked. This hybridization arises from the gauche configuration about the CHZ-CH2 bond and is considered to be responsible for the two strong parallel bands observed at 1344 and 1244 em.-' (On the other hand, for the trans configuration, the hybridization of the CH2 twisting and wagging modes will not occur and the infrared bands due to the pure twisting mode should be very weak.)The parallel band a t 960 em.-' and the perpendicular bands a t 948 and 844 ern.-' were assigned to the CHI rocking modes and used in deducing the configuration about the CHz-CH2 b~n d .~, T ? Davison assigned the bands a t 960 and 948 em.-' to the symmetric CHz rocking mode of the gauche form, and the band at 844 em.-' to the antisymmetric rocking mode of the gauche form.7 On the other hand, Miyake assigned the bands at 060 and 948 em.-' to the symmetric and antisymmetric rocking modes, respectively, of the gauche form, and the band a t 844 cm.-l to the CH2 rocking mode of the trans form, and concluded that the polirethylene glycol chain in the crystalline state contains CH2-CHz groups in the trans form as well as in the gauche form The present normal coordinate treatment has clearly indicated that, for both the A2 and E(s) species, the hybridization of the CH2 rocking mode and the C-0 stretching mode is appreciable, and that not only the bands a t 960,948, and 844 em.-' but also the parallel band at I I02 and the perpendicular bands a t 1150 and 1061 em.-' are due to these hybridized modes. The difficulties encountered in the empirical vibrational assignm...

Glassy dynamics of two poly(ethylene glycol) derivatives in the bulk and in nanometric confinement as reflected in its inter- and intra-molecular interactions

“…1). The IR spectra of PEGEA show absorption bands specific to gaucheconformations around CH 2 − −CH 2 bonds: (i) the simultaneous appearance of CH 2 wagging τ(CH 2 ) at 1350 cm −1 and twisting mode τ(CH 2 ) at 1244 cm −1 , 45 and (ii) a coupled mode of CH 2 wagging and CH 2 twisting at 1415 cm −1 . 46 The double absorption band with the maxima at 1136 cm −1 and 1106 cm −1 corresponds to the stretching vibration of COC units in gaucheconfiguration and trans-configuration, respectively.…”

Infrared spectroscopy and polymer structure

“…Since the energy as a function of torsion angle about a carbon-carbon bond is locally a minimum near the staggered positions (120° apart), the chain in the above example would be expected to twist away from the planar zig-zag form by any appropriate -420° rotation which would relieve the steric repulsion. The introduction of such new rotationally isomeric structures would in general be expected to alter the 14CH2 rock (41) -CC stretch (37) CC stretch (68) -CCH(Cl) bend (17) CH2 twist (11) CC stretch (49) -CCC bend (18) -CCC(Cl) bend 18CCstretch(51) + HCC!bend(19) + CH2rock 17CC stretch (48) + CH2 wag (43) CH2 twist 66 CC stretch (36) -CH,wag (33) + CCH(Cl) bend (27) OH, bend (77) -CCH bend (20) 1455 A1 1426vsa CH,bend(76) -CCHberid (22) vibrational spectrum from that of the regular chain. Through the understanding of such differences we hope to learn something about the kinds of non-crystalline structures which are present45.…”

Measuring the orientation of chains in polypropylene welds by infrared microscopy: A tool to understand the impact of thermo-mechanical treatment and processing

“…[35]. The intensity of the absorptions at 841, 974 and 998 cm À1 significantly depends on the direction of polarization.…”