Polyurethane amorphous systems

Aud.nopropyl triethoxysilane, 140 Amorphous systems, polyurethane elastomers, 33 Anionic polymerization, caprolactams, 136-38 initiation, 138 thermal initiation, 137f termination reaction, 136 Annular cone and plate, 100-102 Annular vs. truncated cones, 101f Aromatic diisocyanate(s), RIM elastomers, 81... 

The use of monomers that produce amorphous hard segments produces highly compatible systems with poorly defined rubbery plateau and elastomeric behavior. Because no heterogenous conditions develop during the reaction, molecular weight in amorphous polyurethane systems tends to be less affected by reaction rates or polymerization conditions. 

Polyurethane elastomers derive their elastomeric properties from phase separation of the hard and soft copolymer segments, such that the hard (urethane) segment domains serve as crosslinks between the amorphous soft segment domains, which are usually polyesters or polyethers. We are interested in the systems in which the hard segments are prepared from diphenyl-methane 4,4 -diisocyanate (MDI) with a linear diol as the chain extender ... 

Photopolymerization of Powder Formulations Powder coatings are very attractive [314]. The powder is applied on the substrate and exposed to an IR source to get the coalescence of the solid particules then, the cross-linking reaction is carried out under UV (or visible) light in a very short time and at a temperature about 100-120°C. Largely encountered systems are based on, for example, polyesters (with maleates or fumarates unsaturations) and polyurethane vinyl ethers that copolymerize according to a radical process, amorphous polyesters and functionalized polyesters (with allyl ethers). 

A rigid foam is defined as one in which the polymer matrix exists in the crystalline state or, if amorphous, is below its Tg. Following from this, a flexible cellular polymer is a system in which the matrix polymer is above its Tg. According to this classification, most polyolefins, polystyrene, phenolic, polyycarbonate, polyphenylene oxide, and some polyurethane foams are rigid, whereas rubber foams, elastomeric polyurethanes, certain polyolefins, and plasticized PVC are flexible. Intermediate between these two extremes is a class of polymer foams known as semirigid. Their stress-strain behavior is, however, closer to that of flexible systems than to that exhibited by rigid cellular polymers. 

Chem. Descrip. Amorphous hydrated silica, org. surf, treatment Uses Matting agent in add-ca zed systems, board and industrial coatings, coil arid can coatings (> 0.75 mil) high solids systems (> 0.75 mil), radiation-cured systems (> 0.75 mil), kyd urea systems, water-based coatings, 2-component polyurethane systems Features High porosity... 

Numerous polymers have been proposed as shape-memory polymers (SMPs), and many of them are based on polyurethanes. This is because of the intrinsic versatility of segmented copolyurethane systems. By suitable choice of diisocyanate and macrodiol, a wide variation in properties may be obtained, allowing the possibility of tuning the shape-memory response to suit different applications. Usually they are phase-segregated materials. For example, a dispersed rigid phase (usually based on the diisocyanate) provides physical crosslinks, while the macrodiol provides a soft amorphous phase with low glass transition that provides the trigger temperature for shape recovery [63]. 

Aliphatic Polyurethane. Some researchers (1) have suggested that aliphatic polyurethane systems exhibit ferroelectricity that stems from the amorphous part at temperatures above the glass-transition temperature. This liquid state ... 

The potential of ROFTIR has been exploited in a wide variety of polymer systems. These include the orientation processes during elongation and relaxation of polyethylene [299-301, 312] uniaxial deformation phenomena in polypropylene [302, 303, 309-311], PET [304, 305] and polystyrene [306] hard and soft segmental orientations during stretching of polyurethanes [307, 308] and the stress-induced reversible a-P phase transition in crystalline PBT [312-314] and uniaxial deformation of amorphous PBT [315]. 

Polyesters. Unsaturated polyesters dissolved in styrene or methacrylates are used as reactive adhesives. Hot-melt adhesives can be made from saturated and fusible polyesters based on aliphatic and/or aromatic carboxylic acids, in some cases by using dimerized fatty acids. High molecular mass amorphous polyesters and low molecular mass crystalline polyesters are important raw materials for moisture cross-linking polyurethane adhesives in solution or solvent-free systems. 

Method D appears to be possibly the most important type of isocyanate-based adhesive system. It is similar to Method B in that a preformed, fully reacted, high molecular weight polymer is employed as a vehicle in the adhesive formulation. The strength of the vehicle holds adherend members in exact position after assembly until the full bond has formed. Method D differs from Method B in that its vehicle polymer is a polyurethane. A further difference is that the inherent adhesive character and strength of the polyurethane vehicle frequently enables its use without added di- or poiyisocyanate. This strength may be realized in essentially amorphous compositions such as the thermoplastic polyurethane elastomers or millable gums. Or it may be achieved with crystallizing urethane adhesive polymers. 

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