Stability hydrolytic

A coalescing agent should have good hydrolytic stability (a high degree of resistance to hydrolysis) so that it can be used successfully in both low and high pH latex systems. 

It is desirable for a coalescing aid to have low water miscibility for the following reasons  

Polyesters do vary in their resistance to hydrolysis and this variability is reflected in the hydrolytic stability of the polyurethanes. Sometimes it is possible to perform hydrolysis tests on the polyols which give good correlation with the stability of final polyurethane. One such method is the hydrolysis of the polyester by sodium hydroxide solution at 100°C. 

Approximately 5g of a polyol are added to 150g of OTm sodium hydroxide at 100°C. Samples of this mixture are withdrawn, weighed and quenched with water, and the remaining alkali titrated with hydrochloric acid using phenolphthalein as indicator. A graph of NaOH content versus hydrolysis time can then be drawn for comparison purposes. 

Silicone surfactants in aqueous solutions show the same general behavior as conventional hydrocarbon surfactants - the surface tension decreases with increasing concentration until a densely packed film is formed at the surface. Above this concentration, the surface tension becomes constant. The concentration at the transition is called the critical micelle concentration (CMC) or critical aggregation concentration (CAC). The surface and interfacial activity of silicone surfactants was reviewed by Hoffmann and Ulbricht [27]. Useful discussions of the dependence of the surface activity of polymeric silicone surfactants on molecular weight and structure are given by Vick [28] and for the trisiloxane surfactants by Gentle and Snow [29]. 

A useful way to compare the surface activity of different surfactants is in terms of their efficiency and effectiveness [30]. Efficiency measures the surfactant concentration required to achieve a certain surface tension, while effectiveness is measured by the maximum reduction of the surface tension that can be obtained for that particular surfactant. In the following discussion these terms will be used in this specific defined sense. 

The efficiency of the nonionic trisiloxane surfactants is comparable to nonionic hydrocarbon surfactants with a linear dodecyl hydrophobe. The surface properties of a homologous series of trisiloxane surfactants M(DE OH)M with n = 4—20 show that the CAC, the surface tension at the CAC and the area per molecule each vary with molecular structure in a way that is consistent with an umbrella model for the shape of the trisiloxane hydrophobe at the air/water interface [29]. The log(CAC) and the surface tension at the CAC both increased linearly with EO chain length. 

In spite of its obvious practical importance, the spreading behavior of mixtures of silicone surfactants and hydrocarbon surfactants has not been systematically studied. Early 

19F NMR studies of BF3 NH2C2Hs/DMSO solutions indicated that little change occurred in the amount of BF3 NH2C2H5, BF, and BF3(OH) species in the presence of added H20 over a period of 4 days at 23 °C. 

However, if a large (ten-fold) excess of HzO was added to the BF3 NH2C2H5/ DMSO solution and the temperatures raised to 85 °C for 1 h, the amount of fluorine presentas BF3 NH2C2H5 decreased by 50 % while thatpresent as BF3(OH) NH3 C2H5 increased from 5 to 40%. The more stable BF4 species were unaffected. 

The BF3NHC5H10 species in DMSO behaved similarly to the corresponding BF3 NH2C2H5 species upon exposure to H20 at 23 and 85 °C. 

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This dicarboxyhc ester is then copolycondensed with the other reactants in PET manufacture to produce a flame-retardant polyester [63745-01-7]. The advantage of this rather unusual phosphinate stmcture is its high thermal and hydrolytic stability. The fabric is probably used mainly for flirnishings in pubhc buildings in Japan. 

Chemical Resistance and Hydrolytic Stability. Modified ethylene—tetrafluoroethylene copolymers are resistant to chemicals and ... 

Sulfonic acids may be hydrolytically cleaved, using high temperatures and pressures, to drive the reaction to completion. As would be expected, each sulfonic acid has its own unique hydrolytic desulfonation temperature. Lower alkane sulfonic acids possess excellent hydrolytic stability, as compared to aromatic sulfonic acids which ate readily hydrolyzed. Flydrolytic desulfonation finds use in the separation of isomers of xylene sulfonic acids and other substituted mono-, di-, and polysulfonic acids. 

Such polyurethanes have excellent hydrolytic stability compared to water-reducible polyesters and superior abrasion resistance. In view of the importance of developing low solvent emission coatings, considerable effort is being devoted to new types of water-borne urethane resins (62,63). 

Polyarylates are sensitive to heat. Although mechanical properties are not much affected, colors darken. Properties are given in Table 8. Hydrolytic stability and resistance to organic solvents are fair. 

Rejection Rejection is defined in Background and Definitions. The highest-rejection membranes are those designed for single-pass production of potable water from the sea. The generally accepted criterion is 99.4 percent rejection of NaCl. Some membranes, notably cellulose triacetate fibers are rated even higher. A whole range of membranes is available as rejection requirements ease, and membranes with excellent chlorine resistance and hydrolytic stability can be made with salt rejection over 90 percent. 

This material had poor hydrolytic stability and was no more than a laboratory curiosity. Treatment with sodium trifluoroethoxide and heptafluorobutoxide has recently been found to yield a useful fluorophosphazene polymer ... 

The rubber has a very low of -68°C, excellent hydrolytic stability and excellent resistance to ozone, solvents and acids. In addition the rubber does not bum even in an oxidising atmosphere. Although its properties are virtually unchanged in the range -75 to + 120°C it does not possess the heat resistance of other fluoroelastomers. This polymer was marketed by Firestone in the mid-1970s as PNF rubber, but in 1983 the Ethyl Corporation obtained exclusive rights to the Firestone patents and the polymer is now marketed as Eypel F. 

Excellent hydrolytic stability (a weakness of many polyimides). 

Christopher and Fox have given examples of the way in which polycarbonate resins may be tailor-made to suit specific requirements. Whereas the bis-phenol from o-cresol and acetone (bis-phenol C) yields a polymer of high hydrolytic stability and low transition temperature, the polymer from phenol and cyclohexanone has average hydrolytic stability but a high heat distortion temperature. By using a condensate of o-cresol and cyclohexanone a polymer may be obtained with both hydrolytic stability and a high heat distortion temperature. 

The commercial polymers are of comparatively low molecular weight (M = 25 000-60 000) and whilst being essentially linear may contain a few branches or cross-links arising out of thermal oxidation. Exposure to ultraviolet light causes a rapid increase in gel content, whilst heating in an oven at 125°C causes gelation only after an induction period of about 1000 hours. Eor outdoor applications it is necessary to incorporate carbon black. The polymers, however, exhibit very good hydrolytic stability. 

PPO forms one of a group of rigid, heat-resistant, more-or-less selfextinguishing polymers with a good electrical and chemical resistance, low water absorption and very good dimensional stability. This has led to a number of applications in television such as tuner strips, microwave insulation components and transformer housings. The excellent hydrolytic stability has also led to applications in water distribution and water treatment applications such as in pumps, water meters, sprinkler systems and hot water tanks. It is also used in valves of drink vending machines. 

Excellent hydrolytic stability. (For example, PEK has very good resistance to hot water at 125°C, under which conditions other heat-resisting plastics such as the polyimides are liable to fail.)... 

These materials not only have a good resistance to burning and flame spread but are also able to withstand service temperatures of up to 150°C. At the same time polyisocyanurate foams have the very good hydrolytic stability and low thermal conductivity associated with rigid polyurethane foams. 

Butyl titanate polymers find use in surface coatings but as a class, titanium polymers lack hydrolytic stability. 

The resulting poly(cw-syndiotactic-phenylsilsesquioxanes) are claimed to have equal thermal stability to conventional silicones but with markedly improved hydrolytic stability. 

Rider and Amott were able to produce notable improvements in bond durability in comparison with simple abrasion pre-treatments. In some cases, the pretreatment improved joint durability to the level observed with the phosphoric acid anodizing process. The development of aluminum platelet structure in the outer film region combined with the hydrolytic stability of adhesive bonds made to the epoxy silane appear to be critical in developing the bond durability observed. XPS was particularly useful in determining the composition of fracture surfaces after failure as a function of boiling-water treatment time. A key feature of the treatment is that the adherend surface prepared in the boiling water be treated by the silane solution directly afterwards. Given the adherend is still wet before immersion in silane solution, the potential for atmospheric contamination is avoided. Rider and Amott have previously shown that such exposure is detrimental to bond durability. 

In order to address these issues, a brief discussion of thermal, oxidative, and hydrolytic stability of urethanes will be offered, so as to aid the adhesion scientist in designing a urethane adhesive with the desired durability. 

There appear to be conflicting reports regarding the degradation of urethanes. For example, some urethanes are reported to have relatively poor hydrolysis resistance and good biodegradability [77], while other urethanes are reported to be so hydrolytically stable that they have been successfully used as an artificial heart [78]. Both reports are correct. It will be shown that the thermal, oxidative, and hydrolytic stability of urethanes can be controlled, to some degree, by the choice of raw materials used to make the urethane. 

As previously mentioned, some urethanes can biodegrade easily by hydrolysis, while others are very resistant to hydrolysis. The purpose of this section is to provide some guidelines to aid the scientist in designing the desired hydrolytic stability of the urethane adhesive. For hydrolysis of a urethane to occur, water must diffuse into the bulk polymer, followed by hydrolysis of the weak link within the urethane adhesive. The two most common sites of attack are the urethane soft segment (polyol) and/or the urethane linkages. Urethanes made from PPG polyols, PTMEG, and poly(butadiene) polyols all have a backbone inherently resistant to hydrolysis. They are usually the first choice for adhesives that will be exposed to moisture. Polyester polyols and polycarbonates may be prone to hydrolytic attack, but this problem can be controlled to some degree by the proper choice of polyol. 

Effect of acid number on the hydrolytic stability of urethanes made from polyftetramethylene adipate)... 

From their structures, it appears that the hydrolytic stability of macrocyclic lactones must necessarily be inferior to macrocyclic polyethers. Ease of synthesis of the cyclic esters is therefore one of the aspects which commend them to interest. It is probably for this reason that such lactones have not been made more often by the interesting approach of Kdgel and Schroder . These workers report the ozonolysis of dibenzo-18-crown-6 in a mixture of methanol and dichloromethane at —20°. Reduction of the ozon-ide at —75° using dimethylsulfide followed by warming and addition of acetone led to formation of 6 in 14% yield. The bis-oxalate had mp 164—165° from acetone, very similar to that of the starting crown. The transformation is illustrated below in Eq. (5.9). 

Improved polyurethane can he produced hy copolymerization. Block copolymers of polyurethanes connected with segments of isobutylenes exhibit high-temperature properties, hydrolytic stability, and barrier characteristics. The hard segments of polyurethane block polymers consist of 4RNHCOO)-n, where R usually contains an aromatic moiety. 

The polyether imides show much better hydrolytic stability with little change in tensile strength after exposure to water at 100°C for 1 year. These materials also show exceptional resistance to mineral acids, and are unharmed by most hydrocarbons including gasoline (petrol) and oils. 

Excellent thermal stability, resists creep, inherent high color Excellent processibility, poor UV resistance, brittle Excellent thermal/hydrolytic stability, poor weatherability/ impact strength... 

Much of the recent literature relates to BfVbridged Co" cobaloximes based on dimethyl (89) or diphenyl glyoxime (104).110 The BfVbridged cobaloximes (e.g. 89) show greater stability to hydrolysis than analogous H-bridged species (e.g. 88). The diphenylglyoxime complexes (104) show enhanced air and hydrolytic stability... 

Because of their high degree of hydrolytic stability and the extended abilities and effectiveness of these novel chemistries, wherever phosphate-cycle or chelant programs are employed, the circumstances generally permit all-polymer/all-organic programs to be used as technically and economically viable alternatives. 

The PCAs tend to exhibit good performance as iron dispersants, phosphate stabilizers, and corrosion inhibitors, with additional good thermal and hydrolytic stability. 

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