Oxyethylene unit

The many commercially attractive properties of acetal resins are due in large part to the inherent high crystallinity of the base polymers. Values reported for percentage crystallinity (x ray, density) range from 60 to 77%. The lower values are typical of copolymer. Poly oxymethylene most commonly crystallizes in a hexagonal unit cell (9) with the polymer chains in a 9/5 helix (10,11). An orthorhombic unit cell has also been reported (9). The oxyethylene units in copolymers of trioxane and ethylene oxide can be incorporated in the crystal lattice (12). The nominal value of the melting point of homopolymer is 175°C, that of the copolymer is 165°C. Other thermal properties, which depend substantially on the crystallization or melting of the polymer, are Hsted in Table 1. See also reference 13. 

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]. 

Table 3 Temperature Location (tan5 basis, 3 Hz) and Activation Energies of the /3 and y Relaxations for Different Samples with Varying Content in Oxyethylene Units (frEo)...

The HLB of a relatively pure poly(oxyethylene) adduct can be calculated from theoretical data [37]. For these agents the HLB is an indication of percentage by mass of the hydrophilic portion, divided by five to give a conveniently small number. For example, if the hydrophilic portion of a purely hypothetical nonionic agent accounted for 100% of the molecule (such a product cannot, of course, exist), its HLB is 20. Similarly, a more plausible product in which 85% of the molecule is accounted for by the hydrophilic portion has an HLB of 85/5 = 17. The ICI Americas Inc. method of calculating the theoretical HLB of a sorbitan monolaurate nonionic having 20 oxyethylene units per molecule is given in... 

In addition to the natural waxes, a number of synthetic waxes were analysed with GALDI-MS carboxylic acids (Hoechst wax-L, -S), esters (Hoechst wax-FL, -H, -O), and glycol esters (Hoechst wax-KP, -KPS). In most cases, significant mass spectra were obtained. The mass spectrum of polyethylene glycol (Carbowax 6000) showed a series of signals the spacing of m/z 44 between the signals corresponds to one oxyethylene unit. 

The influence of the surfactant in the modified polymers of Figure 1 on n (aqueous solutions, Table I) is not overpowering. The surfactant s influence is diminished by the amphiphilic oxyethylene units which lie interfacially flat at the aqueous-air interface. The hydrophobes are structurally similar to the surfactants providing stability to commercial latices and should be capable of competing with the classical surfactants at the latex surface, but this ability is not reflected in 7T values. The oxyethylene units have been demonstrated(18) to provide osmotic stabilization to latex particles. 

The preparation and characterization of alternating copolymers of Maleic anhydride (MAn) and poly (ethylene glycol-vinyl ether) as well as their chemical conversions to provide various alkyl hemiesters (Scheme 1) have been described elsewhere [7]. The matrices are quoted as PAMm z, where m represent the number of oxyethylene units in R and n the number of carbon atoms in R. Human serum albumin (HSA) was provided by Isti-tuto Sierovaccinogeno Italiano SpA, Italy. 

Figure 5. Plots of cloud point vs. number of oxyethylene units(m)...

The physical chemical properties of the surfactants that contain an ester bond between the hydrophobic tail and the polar head group are very similar to those of alcohol ethoxylates of the same alkyl chain length and the same number of oxyethylene units. The CMC and the cloud point values of the linear ester surfactant 1 of Fig. 4 are approximately the same as those of the straight chained alcohol ethoxylate tetra(ethylene glycol)monooctyl ether (C8E4), i.e., around 10 mM and 40 °C, respectively. Thus it appears that the... 

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. 

Interactions. From the 3 values for the systems listed here, it appears that Interaction between an alkyl sulfate and a POE increases with increase in the number of oxyethylene units in the nonionic. 

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. 

Table 17.4 lists values of the CMC for C12-surfactants with different headgroups. Within the nonionic alcohol ethoxylate surfactants, the headgroup area increases with an increasing number of oxyethylene units. The CMC simultaneously increases, illustrating that steric repulsion increases the CMC (Figure 17.3). 

Based on their data for sorption onto a lake sediment, Kiewiet et al. (1996) derived an equation predicting sorption coefficients of CnEOms as a functions of alkyl chain length and the number of oxyethylene units. Di Toro et al. (1990) proposed a model for description of sorption of anionic surfactants which includes sorbent properties (organic carbon content, cation exchange capacity, and particle concentration) and the CMC as a function of the solution properties (ionic strength, temperature). The CMC is used as a relative hydrophobicity parameter. Since the model takes the contribution of electrostatic as well as hydrophobic forces explicitly into account, it is an example of an attempt to model surfactant behavior on the basis of the underlying mechanisms. 

Fig. 4.5. The number of water molecules per polyoxyethylene chain as a function of the number of oxyethylene units for micelles of sodium dodecylpolyoxyethylene sulfates. (From Ref.233 )...

Another factor has to be considered. When the macromonomer chain segments can give rise to transfer reactions, the probability of such events is enhanced because the number of chain segments per unsaturation is high. Homopolymerization of such macromonomers should be expected to involve additional branching and possibly crosslinking. A typical example is that of PEO macromonomers because oxyethylene units are known to induce transfer reactions U3). 

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