Determination oxyethylene groups

Although the liquid crystalline phase of most polybibenzoates usually undergoes a rapid transformation into a three-dimensional crystal, the introduction of oxygen atoms in the spacer of polybibenzoates has been used to prevent or to slow down this transformation. The dynamic mechanical behavior of polybibenzoates with 2, 3, or 4 oxyethylene groups in the spacer (PDEB, PTEB, and PTTB, respectively) is determined by the composition of the spacer [24], as discussed in this section. 

ISO 2270 1989, Non-ionic surface active agents. Polyethoxylated derivatives Iodometric determination of oxyethylene groups. 

Apparatus The apparatus for oxyethylene group determination is shown in Fig. 35. It consists of a boiling flask, A, fitted with a capillary side tube to provide an inlet for carbon dioxide and connected by a condenser with trap B, which contains an aqueous suspension of red phosphorus. The first absorption tube, C, contains a silver nitrate solution to absorb ethyl iodide. Absorption tube D is fitted with a 1.75-mm spiral rod (23 turns, 8.5-mm rise per turn), which is required to provide a longer contact of the evolved ethylene with the bromine solution. A standard-taper adapter and stopcock are connected to tube D to permit the transfer of the bromine solution into a titration flask without loss. A final trap, E, containing a potassium iodide solution, collects any bromine swept out by the flow of carbon dioxide. 

Increased oxyethylene group content in the polyol results in improved stability as reflected in better retention of tensile strength with thermal exposure. In turn, this coincides with better retention of the weight average molecular weight of the polymers as determined by GPC measurements. 

In the case of nonionic polyoxyethylenated surfactants, the CMC value is determined by the number of hydrocarbon groups, n, as well as oxyethylene groups, m, in the mole-... 

The following protocol describes a mass spectrometric method for determining end group structure of poly (oxyethylene) bis-(ephedrine) by ES-MS/MS/MS [9]. 

Figure 6.1 Apparatus for determination of oxyethylene groups. A 50 ml flask B. Gas inlet tube C Reflux condenser D Bubbler, capacity 7-10 ml (reproduced by kind permission of the International Organization for Standardization, Geneva).

ISO 2270 1989 Non-ionic surface active agents— Polyethoxylated derivatives— lodometric determination of oxyethylene groups. International Organization for Standardization, Geneva. 

The International Organization for Standardization for permission to reproduce diagrams of the mechanical two-phase titration apparatus (Figure 3.2) from ISO 2271 1989, the continuous liquid-liquid extractor (Figure 5.2) from ISO 6845 1989 and the apparatus for iodometric determination of oxyethylene groups (Figure 6.1) from ISO 2270 1989. The complete Standards can be obtained from the ISO member bodies or directly from the ISO Central Secretariat, Case Postale 56, 1211 Geneva 20, Switzerland. 

In this way, the content of oxyethylene groups (and therefore the original polyhydric alcohols) can be determined. Stead and Hindley [74] modified this method and obtained good results for the determination of the oxyethylene group contents of ethylene oxide-propylene oxide copolymers. 

Determination of the content of oxyethylene groups in ethylene oxide-propylene oxide can also easily be carried out by NMR spectrometry without chemical splitting of the ether linkage, identifying the base compounds by this method is difficult. Several methods for the cleavage of ethers have been studied, but few applied to the identification of the base compounds of the polyurethane polyethers. 

To determine oxyethylene and oxypropylene groups in the ethylene oxide propylene oxide copolymers, and polyols, the samples were oxypropylated and then oxyethylated, and these were then decomposed as described above for the determination of the polyol base compounds. The FFAP column is operated isothermally at 65 °C and the flow-rate of the carrier gas is regulated at 60 ml/min. 

Simak [98] investigated absorptions of the C-O-C group in polyethylene terephthalate in the infrared at 15.82, 15.62 and 26.3 pm. Oxyethylene groups have also been determined [99]. 

A 100 mg amount of sample and 2 ml of reagent are mixed in a 20 ml round-bottomed flask and the mixture refluxed on an oil-bath at 120 C for 2 hours. The contents of the flask are cooled to room temperature and then neutralised with 50% aqueous sodium carbonate solution, followed by extraction with about 20 ml of diethyl eflier. The ether layer is washed with de-ionised water and concentrated to a small volume on a steam bath the concentrate is then injected into the gas chromatograph. The FFAP column is operated isothermally at the appropriate temperature for the purpose of both identifying the base compounds and determining their oxyethylene groups contents. For the analysis of the polyether based on 1,2-diaminoethane or 2,2 -diaminodiethylamine the SE-30 column is used. 

The area per molecule of polyoxyethylated non-ionic surfactants at the interface is determined by the length of the hydrophilic oxyethylene chain. In general, for a given hydrophobic chain length the area per molecule increases with increase in the number of oxyethylene groups (see Fig. 1.7). 

International Organization for Standardization, Nonionic surface active agents—polyethoxylated derivatives—iodometric determination of oxyethylene groups, ISO 2270 1989. Geneva, Switzerland. 

Obruba, K., E. Kucerovd, M. Jurecek, Determination of the oxyethylene group by cleavage with nascent hydriodic acid (in German), Mikrochim. Ichnoanal. Acta, 1964(1), 44-48. 

In poloxamer, a synthetic block copolymer of ethylene oxide (EO) and propylene oxide (PO) (USP XXIII, NF18), the oxypropylene/oxyethylene ratio is determined using a H NMR spectrum measured in CDCI3. The oxypropylene units are characterized by a narrow signal at about 1.1 ppm due to the CH3 group. The CH2O/CHO units cause a multiplet between 3.2 and 3.8 ppm. The percentage of oxyethylene can be calculated from the equation... 

---