Hydrolytic stabihty

A number of commercial phosphoms-containing polyols have been made by the reaction of propylene oxide and phosphoric or polyphosphoric acid. Some have seen commercial use but tend to have hydrolytic stabiHty limitations and are relatively low in phosphoms content. BASF s Pluracol 684 is a high functionahty polyol containing 4.5% P, sold for Class 11 rigid foam use. 

A comparison of coatings formulations based on various glycols to determine the effects of the various glycol stmctures on the performance properties of the coatings has been made. Properties compared included degree of cure, flexibiHty, hardness, hydrolytic stabiHty, processibiHty, chemical and stain resistance, and viscosity (18,19). 

Sodium cyanoborohydride has become important in biochemical appHcations that require hydrolytic stabiHty of the reducing agent and chemoselectivity, in sensitive molecules. It is also a preferred reagent for oxime reductions. 

A remarkable feature of phosphazene polymers of types (1) and (2) is that appropriate substituents (which are readily attached) can be used as toggle switches to turn several properties, such as hydrolytic stabiHty and electrical conductivity, on and off (1). 

In addition to the mobihty control characteristics of surfactants, critical issues in gas mobihty control processes are surfactant salinity tolerance, hydrolytic stabihty under reservoir conditions, surfactant propagation through the reservoir, and foam stabihty in the presence of cmde oil saturations. 

Alcohol ethoxysulfates have been used in field tests as nitrogen (177) and carbon dioxide (178) foaming agents. Field use of alcohol ethoxysulfates is restricted to low temperature formations owing to its limited hydrolytic stabihty at low pH and elevated temperature (179). It has been reported that some foams can reduce residual oil saturation, not by oil displacement, but by emulsification and imbibition of the oil into the foam (180). 

Historically, these sulfonates have been difficult to produce in good quaUty and to formulate into laundry powders because of thermal and hydrolytic stabihty problems. Used basically as an anionic, oleochemically sourced replacement for LAS, FAE sulfonate benefits include good detergency at low concentration, low environmental load, and good supply of high quaUty material (71). To avoid possible thermal stabihty problems, these sulfonates have found apphcation in Hquid products. They are used in at least one U.S. dishwashing Hquid, and the cocoyl derivative, Alpha-Step MC48, is marketed by Stepan Chemical Company. 

The principal constituents of rosin (qv) are abietic and related acids. Tall oil (qv) is a mixture of unsaturated fatty and aHcycHc acids of the abietic family. Refined tall oil may be high in rosin acids or unsaturated acids, depending on the refining process. Ethoxylates of rosin acids, eg, dehydro abietic acid, are similar to fatty acid ethoxylates in surfactant properties and manufacture, except for thek stabiHty to hydrolysis. No noticeable decomposition is observed when a rosin ester of this type is boiled for 15 min in 10% sulfuric acid or 25% sodium hydroxide (90). Steric hindrance of the carboxylate group associated with the aHcycHc moiety has been suggested as the cause of this unexpectedly great hydrolytic stabiHty. 

In addition, polyester polyols are made by the reaction of caprolactone with diols. Poly(caprolactone diols) are used in the manufacture of thermoplastic polyurethane elastomers with improved hydrolytic stabiHty (22). The hydrolytic stabiHty of the poly(caprolactone diol)-derived TPUs is comparable to TPUs based on the more expensive long-chain diol adipates (23). Polyether/polyester polyol hybrids are synthesized from low molecular weight polyester diols, which are extended with propylene oxide. 

Ionic polymers are also formulated from TDI and MDI (43). Poly(urethane urea) and polyurea ionomers are obtained from divalent metal salts of /)-aminohen2oic acid, MPA, dialkylene glycol, and 2,4-TDI (44). In the case of polyureas, the glycol extender is omitted. If TDI is used in coatings apphcations, it is usually converted to a derivative to lower the vapor pressure. A typical TDI prepolymer is the adduct of TDI with trimethyl olpropane (Desmodur L). Carbodiimide-modified MDI offers advantages in polyester-based systems because of improved hydrolytic stabihty (45). Moisture cure systems based on aromatic isocyanates are also available. 

Polyester and polyether diols are used with MDI in the manufacture of thermoplastic polyurethane elastomers (TPU). The polyester diols are obtained from adipic acid and diols, such as ethylene glycol, 1,4-butanediol, or 1,6-hexanediol. The preferred molecular weights are 1,000 to 2,000, and low acid numbers are essential to ensure optimal hydrolytic stabihty. Also, caprolactone-derived diols and polycarbonate diols are used. Polyether diols are... 

In general, the alkah and alkaline-earth metal salts of the B q- and B22-halogenated derivatives have excellent thermal, oxidative, and hydrolytic stabihties. 

Properties. Polyurethane elastomers generally exhibit good resiHence and low temperature properties, excellent abrasion resistance, moderate solvent resistance, and poor hydrolytic stabiHty and poor high temperature resistance. As castable mbber, polyurethanes enjoy a variety of uses, eg, footwear, toys, soHd tires, and foam mbber. 

Among the polyurethane, polyester, and polyamide thermoplastic elastomers, those with polyether-based elastomer segments have better hydrolytic stabihty and low temperature flexibiUty, whereas polyester-based analogues are tougher and have the best oil resistance (43). Polycaprolactones and aUphatic polycarbonates, two special types of polyesters, are used to produce premium-grade polyurethanes (12). 

UF Membranes Design of UF membranes prizes high retention, hydrolytic stabihty, and good process flux. Since fouling is the principal impediment to flux, and membranes which are hydrophilic gener ly foul less rapidly, there is competition between the truly stable hydrophobic membranes and the less-fouhng-prone hydrophilic ones. 

Polymeric Membranes Economically important applications required membranes that could operate at higher pH than could CA, for which the optimum is around pH = 5. Many polymeric membranes are now available, most of which have excellent hydrolytic stabihty. Particularly prominent are polysulfone, polyvinyhdene fluoride, poly-ethersulfone, polyvinyl alcohol-polyethylene copolymers, and aciylic copolymers. 

Studies of hydrolytic stabihty of polymeric plasticizers, such as poly(propylene adipate) and poly(butylene adipate) were conducted in simulated body fluids such as saliva, gastric and intestinal fluids. It was found that no hydrolysis occurred under saliva and gastric conditions but plasticizers were hydrolyzed to a large extent in simulated intestinal fluid. Enzymes selectively catalyzed the primary alcohol ester linkage. It is expected that other polymeric ester plasticizers will behave in a similar manner. ... 

Poly(arylene ether sulfone)s (PAES)s have been known since the 1970s. They are tough linear polymers and possess a number of attractive features, such as excellent high-temperature resistance, good electrical properties, and good hydrolytic stabihty. The topic has been reviewed previously in the literature [1,2]. 

From this Figure, it is dear that the intrinsic viscosity of unmodified PBT (- -) decreased significantly more rapidly than that of the end-capped PBT samples and that the hydrolytic stabihty increased with decreasing end-group concentrations. Clearly, modifying the carboxyhc add end groups in supercritical fluids has a positive effect on the hydrolytic stabihty. 

The hydrolysis experiments showed that the modification of the carboxyhc add end groups of PBT in supercritical fluids resulted in an increased hydrolytic stabihty compared to the unmodified PBT. The sensitivity of the intrinsic viscosity towards hydrolysis conditions is a measure of the hydrolytic stabihty. Hydrolysis of the ester functionahties in the polymer chain is also reflected in the molecu-... 

In an attempt to gain an element of control over the mechanical, physical and degradation properties of PLA, large-scale efforts are currently underway to chemically and physically modify PLA throng copolymerization and physical blending with prudently chosen secondary constituents. Without immediate consideration for the issue of financial accessibility of PLA-based products, a logical, con lementary conqx)nent to PLA is poly(8-caprolactone)[PCL]. PCL is a flexible, semi-crystalline(Tg -60°C, Tm 60°C) aliphatic polyester with unique biodegradation characteristics and superior thermal and hydrolytic stabihty. ... 

The excellent hydrolytic stability of polysulfones makes them an ideal choice for use in a variety of medical and dental devices. The hydrolytic stabihty allows use in durable medical devices and components that have to be sterilized in a steam autoclave, sometimes hundreds of times over the hfe of the component. Such components include sterdization trays and cases, as well as parts of the surgical instruments themselves, such as the instrument handles. Traditionally, metals such as stainless steel have been used for this purpose. But metals are being replaced by thermoplastic materials. The use of plastics offers the ability to customize designs and colors as well as to mass-produce in a more economical fashion. For large parts, such as surgical instrument sterihzation trays, the weight... 

---