Prepolymer Production

Prepolymers are normally produced with a mole ratio of approximately two moles of diisocyanate to one mole of polyol. If the ratio is very much larger (e.g., four to one), the resultant product is called a quasiprepolymer. 

There are several reasons to work through the prepolymer route as opposed to the one-shot technique. These include  

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The isocyanurate reaction can be both beneficial and troublesome. It can be the bane of production engineers. Low levels of alkaline impurities present in urethane raw materials such as polyols, tackifiers, etc., can cause problems in prepolymer production, resulting in high viscosity products at levels of 5 ppm or less. At higher levels of alkaline impurities, more serious problems can occur, including poor shelf life, poor caulkability, or poor sag resistance. At levels of 15 ppm or higher, the alkalinity can cause an isocyanurate reaction in a prepolymer that can result in a gelled reactor. 

Several experimental studies have described the respiratory effects of HDI after acute inhalation exposures in laboratory animals. The acute inhalation toxicity of the aerosols of HDI and various prepolymer products were tested on male and female Wistar rats exposed to 105, 143, 259, 341, 383, 443, 575, 589, or 719 mg HDI/m (15.3, 20.7, 37.6, 49.4, 55.5, 64.2, 83.4, 85.4, 104.3 ppm) in inhalation chambers for 4 hours. All HDI-exposed rats exhibited signs of labored breathing at all exposure concentrations. Lung edema and pneumonia were observed upon necropsy (Kimmerle 1976). 

Dow Chemical Company (1990), in their pamphlet on prepolymer production, gives a formula to calculate the total heat given off by the instantaneous reaction of polyol with an isocyanate. Figure 3.6 indicates the instantaneous heat rise generated when polyols of different molecular weights are reacted with TDI and MDI. The slow addition of the polyol will allow heat to be dissipated, and thus the full rise in temperature will not be realized. 

Prepolymer production is a time-dependent operation that reaches an optimum point, after which the properties are reduced. The production control must be such that the critical parameters of temperature and time are closely monitored. 

Both the ratios in the prepolymer production and the curing ratios will affect the final properties of the polyurethane. In the initial prepolymer production, the properties vary according to the molar ratios of the prepolymer. This is illustrated by the graphs compiled in Saunders and Frisch (Saunders, 1962). 

Resin Certain liquid prepolymer products, such as epoxies and unsaturated polyesters, which are subsequently cross-linked to form hardened polymer. 

NSC 406696 Suool B Tetramethylene 1,4-diol Tetramethylene glycol 1,4-Tetramethylene glycol. Curative, chain extender provides reactive H-source in prepolymer production used to provide hard segments in PU. Used as an intermediate and in polyurethane formulation in the hard segment as a curative. Crystals mp = 20.1° bp = 235° = 1.0171 Xm = 291 nm (e = 200, H2SO4) freely... 

Polyurethane prepolymer (product of reaction of 1 mol of polyethylene glycoladipate and 2 mol of TDI) 50... 

Recent research literature shows an alternative greener pathway to achieve the same using hydrogen peroxide as the oxidizing agent and zeolite infused with tin as the catalyst. The reaction products in this case will be the lactone and water. When adapted for commercial production, this pathway could represent a potent pollution prevention strategy for prepolymer production industries. 

Trimethylolpropane triacrylate Benzoylhexanol Urethane acrylate prepolymer Product 65 (shop primer for concrete floors) Methyl methacrylate 91... 

The above-described results laid the foundation for elaboration of catalytic systems based on MSCBs and alkali derivatives useful for the anionic polymerization of different vinyl monomers. As initiators, two-component systems (MSCB -silanolate or alcoholate) and single-component systems ( prepolymers - products of interaction of disilanolates with MSCB) were tested. 

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