Polymeric hardener

Cast molding is an increasingly used manufacturing process for both rigid gas-permeable and hydrogel contact lenses. In this process, two molds, made from a variety of plastics, are used. A female mold forms the lens front surface (convex) and a male mold forms the lens back surface (concave). The plastic molds are made from metal tools or dies that are usually stainless steel, precision lathed, and polished to the specified lens design. A variety of mold materials are used. The polymerized, hardened lens is released from the mated molds and is processed in much the same way as the spin-cast lenses described above. 

Figure 9 depicts the somewhat similar behavior for a room-temperaturesetting, urea-formaldehyde or phenol-resorcinol-formaldehyde resin-based glue. However, no initial heat-related drop in viscosity occurs during clamping, and the final polymerization hardening proceeds at a slower rate because it occurs at room temperature. 

A great many of outstanding adhesive formulations are based on epoxy resins. A broad spectrum of adhesive formulations with a wide range of available properties have resulted from the use of polymeric hardeners such as polyamides and polyamines, phenolics, isocyanates, alkyds, and combinations of amines with polysulfide elastomers, and the alloying of the epoxy with compatible polymeric film-formers, such as poly(vinyl acetate) and certain elastomers. 

Extension Glass transition temperature Polymerization, hardening, curing Postpolymerization cross-linking Decomposition... 

Hardening of gelatin by crosslinking is an important technique in photographic industry. Although polymeric hardeners are potential candidate, little has been so far investigated (1). This class of compounds are reported to be useful also for the affinity chromatography and for enzyme immobilization (2,6,8). 

Polyurethane adhesives are formed by the reaction of various types of isoeyanates with polyols. The polar urethane group enables adhesion to various surfaees. Depending on the raw materials, glue lines with rubber-like elastic to brittle-hard behavior ean be aehieved. The presence of reactive terminal groups provides a ehemieally hardened adhesive. When polymerized to a high enough molecular weight, the adhesive ean be physically rather than chemically hardened, i.e. a hot melt. 

For thermoset-matrix materials, heat is usually added as a catalyst to speed the natural chemical reaction of polymerization. Two-part epoxies, such as found in your local hardware store, consist of a tube of epoxy and a tube of chemical hardener that react when mixed. Heat... 

Among the various suspension systems mentioned, the details of oil-inwater (o/w) suspension polymerizations are fully known. The criteria of droplet formation, droplet stabilization, and droplet hardening, as will be discussed for the o/w suspension system, can apply equally to the preparation of beaded polymer particles in w/o systems. 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

The insolubilization of cations and anions during the setting and hardening process is thus paralleled by that of silica. Under add conditions orthosilicic add condenses first to form polymeric silidc add and then silica gel (Her, 1979 Andersson, Dent Glasser Smith, 1982). These processes are discussed more fully in Section 6.5.4. Gelation of silica, like the formation of salt gels, is enhanced by a reduction in the acidity of solutions. 

Two matrices are formed a metal polyacrylate salt and a polymer. There is a lack of water in the system because some of it has been replaced by HEM A, and lack of water in glass polyalkenoate cements is known to slow down the ionomer add-base reaction (Hornsby, 1977). Thus, the initial set of these materials results from the polymerization of HEMA and not the characteristic acid-base reaction of glass-ionomer cements. The later reaction serves only to harden and strengthen the already formed matrix. 

Organic synthesis Sulfur mustard (HD) 1.18 Pharmaceuticals Sulfur dyes Insecticides Rubber vulcanization Polymerization catalyst Hardening of soft woods Extraction of gold from ores... 

Resin cure is normally conducted at a temperature of 120°C and pH < 5. The reactions that occur during the final cure of the resin are thought to be similar to those that occur during the acid condensation of the methylolureas. These reactions lead to the formation of the crosslinked polymeric network characteristic of the hardened, cured resin. 

It is known that organotin compounds such as n-butyltin acid and di-n-butyltin dilaureate accelerate the hardening process of epoxy resins106) and initiate ethylene oxide polymerization 107). 

Curing processes are essentially surface processes, often of the nature of hardening or polishing. Radiation curing has the advantage that it does not use a solvent or heat. The polymerization rate is high and can be controlled. For such... 

Dispersion devices, ozone, 17 801-802 Dispersion force, 12 4 Dispersion-free solvent extraction, 10 766 Dispersion hardening, 13 501, 502, 527 of refractory metal alloys, 13 528 Dispersion polymerization, 24 156-157 of acrylamide polymers, 1 323 of methacrylic ester polymers, 16 289 Dispersion processing of FEP polymer, 18 314... 

---