Rotational Isomeric State Analysis of Poly(oxyethylene). Conformational Energies and the Random-Coil Configuration

Abstract

ABSTRACT:Configuration-dependent properties of the poly(oxyethylene) (POE) chain were calculated within the framework of the rotational isomeric state (RIS) approximation. Conformational energies of the chain have been determined by the 1 H and 13 C NMR studies on 1,2-dimethoxyethane (DME) and POE as described in our recent paper as well as in the present work. The unperturbed chain dimension C ( = <r 2 ) 0 lnf2), the dipole moment <11 2 )lnm 2 , and the molar Kerr constant <mK>Ix were calculated as a function of RIS parameters such as bond angles, rotational angles, and conformational energies. The value of C ( = 5.2) determined in organic solutions by Beech and Booth was found to be favorably reproduced by these calculations. The SANS result (C=6.9) recently reported by Kugler et al. on the melt exceeds the limit of a probable range estimated from uncertainties involved in each of the RIS parameters. Within the limit mentioned above, a set of RIS parameters was chosen so as to give an optimum agreement with observed values of the configurational properties of POE. Conformational energies thus estimated are as follows: E.= -0.5-kcal mol-1 for the C-C bond and EP =0.8 kcal mol-1 for the C-0 bond, both representing the energy of the gauche form expressed relative to the trans state. Use of the conformational energies (E.= -1.2 and EP = 1.1 kcal mol-1 ) determined in D 2 0 leads to a value of C= 3.2, suggesting that the end-to-end dimension of the chain for the state unperturbed by longrange interactions may be considerably small in pure water.

Investigation of a poly(oxyethylene) chain by a molecular dynamics simulation in an aqueous solution and by Langevin dynamics simulations

“…In the melt relatively high values for co ~ 6-9 [31] are measured, while there are low values from around 2.8 to 5.6 found for POE in pure water or in an aqueous salt solution [32 to 35]. Abe [36] found, in a thorough theoretical investigation on the basis of the rotational isomeric state formalism [37], that only two quantities effect the value of the characteristic ratio appreciably, namely the mean torsional angle 4)cc around the C-C bond in the gauche position and E~, which is the energy difference of the trans conformation to the gauche conformation for the O-C-C-O sequence. These are exactly the quantities, which change the most under the influence of the water.…”

“…E~ and Ep, the corresponding energy differences for the C-C-O-C sequence, can be calculated from the trans-gauche ratios (table 3) same or opposite sign [37]. E~ was taken to be 0.53 kcal mol -~ [36], but variation of E~ does not lead to very different results for E~ and Ep. Figure 16 shows the results for co as a function of ~bcc and E, calculated in the same way as in reference [36].…”

“…E~ was taken to be 0.53 kcal mol -~ [36], but variation of E~ does not lead to very different results for E~ and Ep. Figure 16 shows the results for co as a function of ~bcc and E, calculated in the same way as in reference [36]. All other parameters were kept constant and taken as the average of the values given in table 3.…”

Preliminary Investigation by Raman Spectroscopy of Some Polymeric Matrix With Pharmaceutical Applications

“…The result is a broadening of the spectrum especially in the D-LAM band. The conformation distribution for poly(ethylene oxide) most likely always contains the conformer sequences ttt, tgt, tgg , ttg 4,12,13. …”

Preparation and Characterization of Pure Oligoethylene Glycols I.

“…7 In our previous study, we described a method for preparing a pure oligoethylene glycol, i.e., octadecaethylene glycol (OEG 18). 8 It is of interest to determine characteristic parameters such as the molecular weight M of OEG 18 by light scattering, because a compound of definite molecular weight can be used as a standard sample for calibrating light scattering instruments.…”