Polyurethanes curing

Polythia six-membered ring systems, 3, 1039-1086 Polythiazides as diuretic, 1, 174 Polythiiranes, 7, 182 Polytopal rearrangements phosphoranes, 1, 529-530 rules, 1, 530 Polyurethanes curing agents... 

The kinetics of polyurethane curing in adiabatic conditions was studied by the thermometric method (see Section 2.2) for a composition based on macro(diisocyanate) and diamine.48 It was proved that in this case, the second-order kinetic equation was inapplicable for the rangep > 0.7. By analyzing the time dependencies of temperature of the reactive medium, it was established that the... 

Figure 3.4. Dependencies of parameters Go (1), AG (2), and0 (3) of a three-constant model on time in polyurethane curing.

Figure 3.8. Experimental curves of heat output during polyurethane curing. 1 - true curve (as a result of filtration) 2 - no filtering (2).

Cast polyurethanes cured with water would need the bulk of the carbon dioxide to be flashed off and the remainder held in place by compression molding. 

This type of polyurethane cures irreversibly by chemical reaction at room temperature. Branched or cross-linked thermoset polymers are made with higher functional monomers. Thermoset polyurethanes have a higher... 

Polyetherimide A wide variety of commercially available adhesives can be used in bonding polyetherimide to itself or to dissimilar materials. Among these are polyurethane [(cure at RT to 302°F (150°C)], RTV silicones, hot melts (polyamide types) curing at 401 C (205°C) and epoxies (non-amine type, two-part) (12). 

First, attention will concentrate on the polyurethane curing reaction itself that is, the polyaddition of isocyanate and hydroxyl groups. Degree of cure and isocyanate conversion rates (as deduced from FTIR) will be discussed for the bulk and compared with thin films on Au, Al, and Cu (Section 6.3.1). Secondly, the morphology of cured films (OM, SFM) will be treated in Section 6.3.2. 

In general, the quantitative results of the polyurethane cure substantiate increased isocyanate conversion rates in the vicinity of any of the three metals, being most pronounced on Cu and to some extent on A1 but also detected even in ultrathin films on Au. Nevertheless, considerable catalysis, by some orders of magnitude, of polyurethane formation is only found for films on Cu. Once more, the effectiveness of copper even in films of some microns thickness is easily explained by the dissolution of Cu ions. 

Investigation of microstructure in polyurethanes cured at 333 1K has shown that two levels of heterogeneity characterize pol5mrethanes based on mixtures of compatible oligomers when smaller globule-like structural elements are grouped into macroglobules. Introduction of... 

The value ofVjA is determined by the concentration of network knots. These knots usually have a functionality of 3 or 4. This functionality depends on the type of curing agent. Crosslinked polyurethanes cured by polyols with three OH-groups are examples of the three-functional network. Rubbers cured through double bond addition are examples of four-functional networks. 

Key words vegetable oil-based polyurethane, preparation of polyurethane, curing of polyurethane, stmcture-property relationships of polyurethane, application of polyurethane. 

How are vegetable oil-based polyurethanes cured with NCO/OH ratios of <1 and >1 ... 

Lomod, Copolyester elastomer, GE Plastics Lonzacure, Polyurethane curing agent. Air Products and Chemicals, Inc. 

The polymer matrix can be specifically tailored to meet the requirements of the application or to enhance the stability of the specific enzyme to be immobilized. For instance, the porosity of poljmrethane foams can be influenced by the amount of surfactant added to the mixture prior to polymerization. Formation of gas as polyurethane cures causes pockets of air to form within the foam. Varying the concentration of surfactants added to promote porosity enables pore size to be varied. This can impact the ability to pass solutions through the polymers as well as their optical density for sensing applications. 

Reaction Injection Moulding.— By contrast with the epoxy resins, polyurethanes cure at much lower temperatures, 40 °C upwards. The reactants are usually polyether or polyester triols and diols (polyols) and isocyanates or isocyanate-tipped polyester piepolymers. The process problems are essentially those of mixing the reactants sufficiently rapidly to achieve composition uniformity and to control the temperature in the mould. Where foams are produced, control of bubble nucleation is an additional complicating factor e.g. Menges and Schwesig ). 

Kinetics and energetics of a fast polyurethane cure. J. Appl. Polym. Sci., 21, 2029-2039. 

Aromatic polyurethanes are made from isocyanates that contain unsaturated carbon rings, for example, toluene diisocyanate. Aromatic polyurethanes cure faster due to inherently higher chemical reactivity of the polyisocyanates [8], have more chemical and solvent resistance, and are less expensive than aliphatics but are more susceptible to UV radiation [1,9,10]. They are mostly used, therefore, as primers or intermediate coats in conjunction with nonaromatic topcoats that provide UV protection. The UV susceptibility of aromatic polyurethane primers means that the time that elapses between applying coats is very important. The manufacturer s recommendations for maximum recoat time should be carefully followed. 

Phosgene reacts with ethylene glycol to form ethylene carbonate, which is used to produce HER for polyurethane curing. 

The convertible binders undergo chemical reaction in the film. The drying and hardening of the film is catalyzed by driers with oxygen absorption. Hence, there is a limit to the thickness of the film, which will dry. The two-pack materials, notably epoxies and polyurethanes, cure by chemical reaction between two components in the film with no oxygen absorption. 

The best-performing composite was prepared with H30 at 8 wt. % montmorillonite. The ratio 1.83 indicated the largest enhancement of modulus relative to the pure polyurethane for the 8 wt.% containing composites. The percent elongation to failure increased from 236 15% for the pure polymer to 374 32% for the 8% loaded polyurethane-montmorillonite composite. These hyperbranched polyols provide a significant enhancement of mechanical properties for the polyurethane cure chemistry evaluated with Cloisite 30B as the dispersed-phase reinforcement. Additional work needs to be done with Cloisite 30B present during the cure to ascertain if further benefits to mechanical properties are derived from the reaction of the isocyanate with the primary hydroxyls on the quat exchanged onto the montmorillonite. 

A. Chambles, "A Study of Polyurethane Cure by Infrared Spectrophotometry", Rep. 1977, Y/DK-183, Union Carbide, Oak Ridge, TN. 

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