Polyurethanes reactions

The unsaturation present at the end of the polyether chain acts as a chain terminator ia the polyurethane reaction and reduces some of the desired physical properties. Much work has been done ia iadustry to reduce unsaturation while continuing to use the same reactors and hoi ding down the cost. In a study (102) usiag 18-crown-6 ether with potassium hydroxide to polymerise PO, a rate enhancement of approximately 10 was found at 110°C and slightly higher at lower temperature. The activation energy for this process was found to be 65 kj/mol (mol ratio, r = 1.5 crown ether/KOH) compared to 78 kj/mol for the KOH-catalysed polymerisation of PO. It was also feasible to prepare a PPO with 10, 000 having narrow distribution at 40°C with added crown ether (r = 1.5) (103). The polymerisation rate under these conditions is about the same as that without crown ether at 80°C. 

The monomeric form of the urethane reaction is shown in the first item of Fig. 1. The urethane or polyurethane reaction for an adhesive would be based... 

Siloxane containing polyester, poly(alkylene oxide) and polystyrene type copolymers have been used to improve the heat resistance, lubricity and flow properties of epoxy resin powder coatings 43). Thermally stable polyester-polysiloxane segmented copolymers have been shown to improve the flow, antifriction properties and scratch resistance of acrylic based auto repair lacquers 408). Organohydroxy-terminated siloxanes are also effective internal mold release agents in polyurethane reaction injection molding processes 409). 

Due to the exothermic nature of the reaction and the phase separation which occurs, temperature and conversion (and MWD and sequence distribution) can only be assigned local, not global, values in polyurethane reaction molding. 

Isocyanate-capped Polypropylene Glycol FIGURE 2.6 Polyurethane reaction for producing prepolymer. 

RIM Abbreviation for reaction injection molding. The RIM process involves the rapid metering and mixing of polyurethane reaction ingredients, followed by their injection into a mold. It allows the rapid production of molded polyurethane components. 

Schoener, T. E. and Housenick, J. B., Polyurethane Reaction System Having a Blocked Catalyst Combination, U.S. Patent No. 6,348,121,2002. 

The uncatalysed reaction of diisocyanates with polyols does not have any significance in the formation of polyurethanes. Reactions are catalysed by acids and organic bases. Among the good catalysts are tertiary amines and organometallic compounds, mainly tin derivatives. 

Prepolymer A polyurethane reaction intermediate made by reacting isocyanate with a polyester or polyether, in which one component is in considerable excess of the other. 

This occurrence significantly affects the stoichiometry, not only from consumption of the isocyanate functionality in the process, but also by production of an amine product with two active hydrogens, which adds reactive functional groups to the glycol component of the polyurethane reaction. For these reasons care has to be taken to exclude moisture for the polyurethane applications described so far. However, for the production of flexible and rigid polyurethane foams the reaction of isocyanate with water is exploited to produce bubbles. 

Reaction with difunctional amines (see the next paragraph) allows the formation of poly (urethane-co-urea) and further extends the versatility of the segment architecture. For further control of the structure, a prepolymer is formed. The reaction, such as the polyurethane reaction shown above, is carried out with excess di-isocyanate so that an isocyanate-terminated prepolymer is obtained. The isocyanates used are typically aromatic, such as toluene di-isocyanate. This prepolymer is then reacted with a short-chain diol or diamine (for a polyurea) to form the final polymer. 

Lee, L.J. Polyurethane reaction injection molding Process, materials, and properties. Rubber Chem. Technol. 1980, 53, 542. 

Typical adiabatic temperature rise of epoxy and polyurethane reactions. 

Kaushik, A. and Singh, P. (2012) Castor oU/trimethylol propane-based polyurethane reactions modeling in a batch reactor. Journal of Applied Polymer Science, 125, E51-E60. 

The kinetics of polyurethane reactions are usually characterized by second order kinetics (17-20), as follows ... 

Infrared spectroscopy has been successfully applied to the study of polyurethane reactions. Attenuated total reflectance (ATR) spectroscopy is particularly useful for monitoring the infrared spectra of a reaction mixture over short time intervals and for characterizing the reaction progress [2]. For instance, the rate of consumption of free isocyanate groups and the competitive formation of urethane. 

A wide range of thermoplastics can be converted into foams. Some of the most common materials include polyurethanes, polystyrene, and polyethylene. Polyurethanes are a popular and versatile material for the production of foams and may be foamed by either physical or chemical methods. In the physical reaction, an inert low-boiling chemical is added to the mixture, which volatilizes as a result of the heat produced from the exothermic chemical reaction to produce the polyurethane (reaction of isocyanate and diol). Chemical foaming can be done through the reaction of the isocyanate groups with water to produce carbamic acid, which decomposes to an amine and carbon dioxide gas. ... 

Bayer Bayflex elastomeric polyurethane reaction injection molding (RIM) is a two-component diphenylmethane diisocyanate- (MDI)-based liquid system produced in unreinforced, glass-reinforced, and mineral-Zmicrosphere-reinforced grades. They possess a wide stiff-... 

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