Polyurethane stabilization

One can also make combined acrylic/urethane (hybrid) aqueous dispersions (33). Acrylic monomers are emulsion polymerized in the presence of an aqueous dispersion of a hydroxy-terminated polyurethane. The polyurethane stabilizes the aqueous dispersion, minimizing need for surfactant. Coalescence requires balance of the Tg of both the urethane and acrylic parts of the system. Compositions based on an IPDl/polypropylene glycol/DMPA urethane with styrene/methyl methacry-late/butyl acrylate are reported to form films at low temperatures. 

HydroxyethyUiydrazine (11) is a plant growth regulator. It is also used to make a coccidiostat, furazoHdone, and has been proposed, as has (14), as a stabilizer in the polymerization of acrylonitrile (72,73). With excess epoxide, polysubstitution occurs and polyol chains can form to give poly(hydroxyaLkyl) hydrazines which have been patented for the preparation of cellular polyurethanes (74) and as corrosion inhibitors for hydrauHc fluids (qv) (75). DialkyUiydrazines, R2NNH2, and alkylene oxides form the very reactive amineimines (15) which react further with esters to yield aminimides (16) ... 

L. B. Barry and M. C. Richardson, "A Less Volatile Performance Equivalent to BHT for Polyether Polyol Stabilization," Polyurethane World Congress 1993, Vancouver, B.C., Canada, Oct. 10—13, 1993. 

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). 

This includes inorganic materials such as glass fibre and mica impregnated or glued together with epoxy, polyesterimide, polyurethane or other resins having superior thermal stability. 

This tri-isocyanate is reported to impart good light stability and weather resistanee in polyurethane eoatings and is probably the most widely used aliphatic isocyanate. A number of other aliphatic polyisocyanates have been introduced recently in attempts to produce polyurethanes with improved light stability. Amine derivatives of diphenylmethane are made by reacting aniline of toluidines with formaldehyde. These can lead to a mixture of di-isoeyanates, the diphenylmethane di-isocyanates (MDIs) of commerce. Triphenylmethane-pp p"-tny tri-isocyanate is produced from leucorosaniline. 

The properties of the polyurethane moulding compositions are also very similar to nylon 66. The greatest difference in properties is in water absorption, the 6,4-polyurethane absorbing only about of that of nylon 66 under comparable conditions. This results in better dimensional stability and a good retention of electrical insulation properties in conditions of high humidity. Resistance to sulphuric acid is somewhat bettter than with nylon 66 but both types of polymer are dissolved by phenols and formic acid. 

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. 

Block copolymers can contain crystalline or amorphous hard blocks. Examples of crystalline block copolymers are polyurethanes (e.g. B.F. Goodrich s Estane line), polyether esters (e.g. Dupont s Hytrel polymers), polyether amides (e.g. Atofina s Pebax grades). Polyurethanes have enjoyed limited utility due to their relatively low thermal stability use temperatures must be kept below 275°F, due to the reversibility of the urethane linkage. Recently, polyurethanes with stability at 350°F for nearly 100 h have been claimed [2]. Polyether esters and polyether amides have been explored for PSA applications where their heat and plasticizer resistance is a benefit [3]. However, the high price of these materials and their multiblock architecture have limited their use. All of these crystalline block copolymers consist of multiblocks with relatively short, amorphous, polyether or polyester mid-blocks. Consequently they can not be diluted as extensively with tackifiers and diluents as styrenic triblock copolymers. Thereby it is more difficult to obtain strong, yet soft adhesives — the primary goals of adding rubber to hot melts. 

A study was done measuring the thermal oxidative stability of polyurethanes made from PPG polyols, varying the isocyanate curative. Oxygen absorption was... 

In the organic chemicals industry, H2O2 is used in the production of epoxides, propylene oxide, and caprolactones for PVC stabilizers and polyurethanes, in the manufacture of organic peroxy compounds for use as polymerization initiators and curing agents, and in the synthesis of fine chemicals such as hydroquinone, pharmaceuticals (e.g. cephalosporin) and food products (e.g. tartaric acid). 

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. 

Polyurethane networks based on triisocyante and diisocyanate connected by segments consisting of polyisobutylene are rubbery and exhibit high temperature properties, hydrolyic stability, and barrier characteristics. ... 

Polyester polyols account for only ca. 10% of the total polyol market, which is dominated by polyether polyols such as hydroxy-terminated polyoxyethylene or polyoxypropylene. Polyester polyols are preferred for applications where better mechanical properties, wear resistance, and UV stability are required. The largest application of polyester polyols is flexible specialty polyurethane foam in the furniture, packaging, and automotive industries. Polyester polyols are also used for nonfoam applications such as coatings, paints, sealants, and adhesives 47... 

---