Oxyethylene unit effect

The presence of three oxyethylene units in the spacer of PTEB slows down the crystallization from the meso-phase, which is a very rapid process in the analogous polybibenzoate with an all-methylene spacer, P8MB [13]. Other effects of the presence of ether groups in the spacer are the change from a monotropic behavior in P8MB to an enantiotropic one in PTEB, as well as the reduction in the glass transition temperature. This rather interesting behavior led us to perform a detailed study of the dynamic mechanical properties of copolymers of these two poly bibenzoates [41]. 

It has been found that the 1,3-dioxolane ring corresponds to approximately two oxyethylene units with regard to effect on the critical micelle concentration and adsorption characteristics [42]. Thus, surfactant type I in Fig. 14 should resemble ether sulfates of the general formula R-(0CH2CH2)20S03Na. This is interesting since the commercial alkyl ether sulfates contain two to three oxyethylene units. 

Fluorescence is measured in dilute solution of model compounds for polymers of 2,6-naphthalene dicarboxylic acid and eight different glycols. The ratio of excimer to monomer emission depends on the glycol used. Studies as functions of temperature and solvent show that, in contrast with the analogous polyesters in which the naphthalene moiety is replaced with a benzene ring, there can be a substantial dynamic component to the excimer emission. Extrapolation to media of infinite viscosity shows that in the absence of rotational isomerism during the lifetime of the singlet excited state, there is an odd-even effect In the series in which the flexible spacers differ in the number of methylene units, but not in the series in which the flexible spacers differ in the number of oxyethylene units. 

Skin safety of niosomes was tested in a number of studies. As an example, the toxicity of polyoxyethylene alkyl ether vesicles containing Ci2-i8 alkyl chains and 3 and 7 oxyethylene units was assessed by measuring the effect on proliferation of cultured human keratinocytes [47]. It was found that the length of either polyoxyethylene headgroup or alkyl chain had only a minor influence on keratinocyte proliferation. However, the ether surfactants were much more toxic than esters tested in this study. The concentrations of ether surfactants required to inhibit cell proliferation by 50% were 10-fold lower than for ester surfactants. Neither the HLB nor the critical micelle concentration values or cholesterol content affected keratinocyte proliferation. 

In POE nonionics, an increase in the number of oxyethylene units in the hydrophilic group above six units, in contrast to its large effect in decreasing the effectiveness of adsorption, seems to cause only a small decrease in the efficiency of adsorption. This appears to indicate a very small change in the free energy of transfer of the molecule from bulk phase interior to the interface with change in the number of oxyethylene units above six in the hydrophilic head. 

Figure 6a. The effect of anionic surfactants used in latex synthesis on the viscosity of 2% solution of HEUR 270. Key A, ammonium salt of nonylphenol ethoxylate average 20 oxyethylene units) sulfate O, ammonium salt of nonylphenol ethoxylate average 9 oxyethylene units) sulfate.

Furthermore, the hydrolysis of butyl acetate and methyl pivalate in benzene in the presence of KOH at 25 °C as well as the reaction of potassium phenolate with benzyl chloride in boiling acetonitrile are accelerated by addition of polyoxyethylene [183]. The catalytic effect of POE is augmented by an increase in the number of oxyethylene units, i.e. 1 <6< 12. PEO is also an interfacial catalyst of the reaction of phenol and 2,4,6-trimethylphenol with methyl iodide in water-chloroform and dichloromethane. The kinetic study of the reaction between benzyl chloride and potassium acetate in the presence of PEO of variable molecular weight in toluene and butanol has been performed with IR spectroscopy [184]. The dissolution of a reagent of poor solubility is apparently a rate-limiting step of the reaction in a solution of low polarity (toluene). The presence of PEO impurities in toluene has been detected. Moreover, effect of PEO and crown ethers as phase transfer catalysts has been compared. In a low-polarity solvent, oligoethylene oxides are more effective catalysts, while in a polar solvent (butanol) the effectiveness of PEO and crown ethers as phase transfer catalysts is similar. 

The effect of oxyethylene chain length on cmc is rather weak as can be seen in Figure 3.2b. The slope of the linear increase is calculated as 0.054 for BmimPF, 0.074 for BmimBF, and 0.058 for water [27]. This corresponds to the cmc increase per oxyethylene unit by a factor of 1.13 for BmimPF, 1.18 for BmimBF, and 1.14 for water. This suggests no significant differences in the affinity of the oxyethylene units with the three solvents. 

The value of a calculated from the surface tension data with n = 2 increases with the number of oxyethylene units, as expected. The surfactant with X = 1 appears to be the most effective one, with the lowest values of the CMC and "ycMc- The variation of ycMc with the number of oxyethylene units X is often attributed to steric crowding of the nonionic head groups, which naturally increases with x. 

Polyamides with short trimethylene aliphatic flexible sequences were described by Nasr-Isfahani et al. [4]. The poly condensation of the diacid l,3-(4-carboxy phenoxy)propane with various aromatic diamines by direct polycondensation provide PAs with moderate yield. These PAs were found to be soluble in polar aprotic solvents and soluble even in acetone and in THF. Ferreiro et al. [5] described the effect of lateral oxyethylene moieties on the properties of aromatic polyisophthalamides. Several polyisophthalamides containing short sequences of oxyethylene as pendent substituents were synthesized by the reaction of three aromatic diamine monomers and four novel diacid monomers containing pendent oxyethylene units by the phosphorylation method of polycondensation. The polymers were prepared in high yield and high molecular weight. 

There are fewer reports of linear, acyclic, ion-binding polymers. It has been reported that poly(oxyethylene) improves the solubility of alkali metals in ethers such as tetrahydrofuran, dime thoxy ethane, and diglyme, stabilizes fluorenyl alkali metal compounds, accelerates Williamson reactions and accelerates several other nucleophilic reactions.All of these effects were attributed to the ability of poly(oxyethylene) to complex with cations in solution. Yanagida and coworkers studied the alkali metal cation complexation of poly(oxyethylene), using a picrate salt extraction technique similar to the one used by Pedersen and Frensdorff. Polymers with more than 23 oxyethylene units were effective iono-phores for potassium, with degrees of extraction (percent extracted) comparable to crown ethers. The extractability per oxyethylene unit was nearly constant, and the complex stability increased linearly with increasing numbers of repeating oxyethylene units. Seven oxyethylenes were the minimum number of repeat units necessary to bind potassium ion effectively in the aqueous phase. The less efficient extraction of short-chain poly(oxyethylene) is apparently caused by its hydrophilic character. 

Fig. 6.19 Plot of log C versus the effective number of oxyethylene units n (O) or n = p + q ( ). (From Ref. 165. Reproduced by permission of Academic Press, Inc.)...

---