Polyether chain

The unsaturation present at the end of the polyether chain acts as a chain terminator ia the polyurethane reaction and reduces some of the desired physical properties. Much work has been done ia iadustry to reduce unsaturation while continuing to use the same reactors and hoi ding down the cost. In a study (102) usiag 18-crown-6 ether with potassium hydroxide to polymerise PO, a rate enhancement of approximately 10 was found at 110°C and slightly higher at lower temperature. The activation energy for this process was found to be 65 kj/mol (mol ratio, r = 1.5 crown ether/KOH) compared to 78 kj/mol for the KOH-catalysed polymerisation of PO. It was also feasible to prepare a PPO with 10, 000 having narrow distribution at 40°C with added crown ether (r = 1.5) (103). The polymerisation rate under these conditions is about the same as that without crown ether at 80°C. 

In a subsequent product work-up, the sulfates are hydrolyzed and the acid is removed by water extraction (206,207). In the extraction step, most water-soluble short polyether chains are also removed, and the molecular weight distribution becomes narrower, from close to the theoretical value... 

Commercial thermoplastic polyesters are synthesized in a similar way by the reaction of a relatively high molecular-weight polyether glycol with butanediol and dimethyl terephthalate (14,15). The polyether chain becomes the soft segment in the final product, whereas the terephthaUc acid—butanediol copolymer forms the hard crystalline domains. 

The flexible backbone of an aliphatic polyether chain can lead to polymers with a low glass transition temperature. Providing crystallisation can be inhibited by... 

Desvergne and Bouas-Laurent have shown that photochemical ring closure of a bis-anthracene bridged by a polyether chain is effective only when lithium cation is present . They presume that cyclization is successful because the conformation is cation locked . The reaction is shown in Eq. (2.6). 

In mimicking this type of function, noncyclic artificial carboxylic ionophores having two terminal groups of hydroxyl and carboxylic acid moieties were synthesized and the selective transport of alkali metal cations were examined by Yamazaki et al. 9 10). Noncyclic polyethers take on a pseudo-cyclic structure when coordinating cations and so it is possible to achieve the desired selectivity for specific cations by adjusting the length of the polyether chain 2). However, they were not able to observe any relationship between the selectivity and the structure of the host molecules in an active transport system using ionophores 1-3 10). (Table 1)... 

The template-directed preparation of cycloi is(paraquat-4,4 -biphenylene (a molecular square ) has been achieved the use of a macrocyclic hydroquinone-based polyether template incorporating an ester moiety in one polyether chain afforded a 1 1 mixture of two topologically stereoisomeric [3]catenanes <96CEJ877>. 

Lehn and Sauvage (1975) Lehn and Montavon (1978). No pAa values could be measured under comparable conditions (see discussion below). "One chain of the bimacrocycle is not a polyether chain but a (CH2)g chain. 

Similar formations of bisanthracenes have been studied with a variety of substituents. An interesting example of a cation-assisted intramolecular anthracene dimerization where the bisanthracene formation includes cycli-zation of a polyether chain to a crown ether is illustrated in (4.27). In the absence of Li+ the dimer reverts back to the open chein compound, but in the presence of Li+ the crown ether is stabilized so that the product itself also becomes more stable 430). 

Since surfactants are commercially produced by means of large-scale chemical processes, complex mixtures of homologues and isomeric compounds, e.g. non-ionics of the alkylethoxylate type that may differ in length of alkyl as well as polyether chains, can result. The determination and differentiation of the products in quality control during production and trade is a somewhat easier task. However, more difficulties arise in the analysis of the compounds of these mixtures and formulations in environmental samples. 

In this AES blend, C12 and C14 alkyl chains of alcohols were coupled with polyglycolether chains, which vary in the number of polyether units resulting in homologue [M — H] ions. The ions observed started at m/z 309 (C12-EO1) and 337 (C14-EO1) differing by A m/z 44 (-CH2-CH2—O—) as listed in Table 2.5.1. Here, the ions observable were characterised indicating the number of alkyl and polyether chain links. In parallel, the precursor compounds from synthesis, the alkylsulfates (x = 0), were still present and can be observed with ions at m/z 265 and 293. 

Applying product and parent ion scans in the FIA-MS-MS(+) mode, the unequivocal identification of the AE blend constituents is not possible. The reason for this failure is the simultaneous presence of C12 and Ci4 AE and AES compounds in the mixture that, under positive APCI ionisation conditions, were ionised with the same patterns of [CnH2n+iO(CH2-CH2-0) + NH4]+ ions (A m/z 44) and the same ion masses according to n, the alkyl chain lengths, and x, the polyether chain lengths. The destructive ionisation process of AES in APCI(+) mode therefore imagines a differentiation of the A m/z 44 compounds but results are not reliable. 

Fluorescent molecule (1) (Figure 6.5) acts as a host for Ca2+ ions. On addition of Ca2+ ions, the flexible polyether chain folds, leading to stacking of the anthracene fluorophores, and monomer emission is replaced by excimer emission. 

To demonstrate further the powerful utiHty of the fluorous/organic biphasic approach to catalyst recycling, a dendrimer-encapsulated catalyst (DEC) with covalently attached perfluorinated polyether chains was synthesized [17] and metallic nanoparticles were introduced into the interior. 

Fig. 24. Synthetic scheme for the introduction of metallic nanoparticles into perfluorinated polyether chain derivatized poly (propylene imine) PPI dendrimers. Reprinted with permission from Ref. 100 Copyright 2000 WUey-VCH...

Formation of Cyclic Oligomers. Chain transfer reactions occur by intermolecular attack of oxygen from another polyether chain on the a-methylene carbons of the oxonium ion. In an intramolecular attack a distant oxygen of the growing polymer chain itself attacks the a-methylene position of its oxonium center. 

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