Polyol prepolymer products

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. 

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. 

A follow-up quantitative GC-MS analysis did not disclose excessive levels of TCPP in the unstained polyurethane foam, as compared with samples taken from other, problem-free enclosures. However, significant variability in the flame retardant amounts at different foam locations was detected. Therefore, based upon a follow-up review of the manufacturing process, it was hypothesized that the flame retardant had separated from the polyol prepolymer (since specific gravity of TCPP is close to 1.3 g/cc). It was not clear whether this separation was due to inadequate stirring, pauses in production of malfunction in the polyol / isocyanate mixhead. However, in the final analysis it was clear that the flame retardant on the ABS surface acted as a stress crack agent, and it was occasionally being delivered with the foam to the ABS surface in excess amounts. Polyurethane delivery equipment troubleshooting was subsequently undertaken by the enclosiu e manufacturer. 

In more recent years, molded flexible foam products are becoming more popular. The bulk of the molded flexible urethane foam is employed in the transportation industry, where it is highly suitable for the manufacture of seat cushions, back cushions, and bucket-seat padding. TDI prepolymers were used in flexible foam mol ding ia conjunction with polyether polyols. The introduction of organotin catalysts and efficient siHcone surfactants faciHtates one-shot foam mol ding, which is the most economical production method. 

Semiflexible molded polyurethane foams are used in other automotive appHcations, such as instmment panels, dashboards, arm rests, head rests, door liners, and vibrational control devices. An important property of semiflexible foam is low resiHency and low elasticity, which results in a slow rate of recovery after deflection. The isocyanate used in the manufacture of semiflexible foams is PMDI, sometimes used in combination with TDI or TDI prepolymers. Both polyester as well as polyether polyols are used in the production of these water-blown foams. Sometimes integral skin molded foams are produced. 

Polyurethane foams may be rigid, semi-rigid or flexible. They may be made from polyesters, polyethers or natural polyols such as castor oil (which contains approximately three hydroxyl groups in each molecule). Three general processes are available known as one-shot, prepolymer or quasi-prepolymer processes. These variations lead to 27 basic types of product or process, all of which have been used commercially. This section deals only with flexible foams (which are made only from polyesters and polyethers). Since prepolymers and... 

Blocked isocyanate, for our purposes, will refer to the reaction product of a diisocyanate or isocyanate-terminated prepolymer in which the isocyanate functionality has been reacted with a blocking agent . Once blocked , the diisocyanate can be added to polyols or certain chain extenders, and these materials will not react at room temperature. The concept is shown in the sixth item of Fig. 1. An adhesive formulated with a blocked isocyanate is basically a two-component adhesive that does not react until heated to the activation temperature. When an adhesive is made with a blocked isocyanate together with hydroxyl-containing curatives, the adhesive has a good long shelf life at room temperature. However, once heated... 

Ultralow-monol polyols, 223 Ultrapek, 327, 328 Ultraviolet (UV) radiation, 209 Ultraviolet spectroscopy, 490 Unimolecular micelle, 58 United States, phenolic production in, 375 Unsaturated maleate/O-phthalate/ 1,2-propanediol polyester prepolymer, 101-102 Unsaturated polyester resins (UPRs), 19, 29-30, 58-59... 

One of the more advanced technical offerings from castor oil is a line of polyester diols, triols, and higher functional polyols derived from 100% castor oil as products for the preparation of polyurethane prepolymers and elastomers [68]. The Polycin line of polyols are prepared by transesterification of ricinoleic acid and derivatives. The producers (Vertellus) offer diol and triol products, as well as a recently developed series of diol and triol glyceryl ricinoleate esters that are stated to be prepared from 100% castor oil, making them fully renewable in content. The products are recommended for coatings, sealants, and adhesive applications. 

In most cases, linear prepolymers are used for the production of elastomers. Gas evolution via dry polyols or diamines is therefore not encouraged. When a foam is required, however, a slight adjustment is made in the construction of the prepolymer. We referred to it earlier when we discussed polyfunctional polyols. By including a trifunctional alcohol in the prepolymer recipe or by using a polyol from a trifunctional initiator (e.g., trimethylol propane), a three-dimensional character is introduced into the prepolymer. 

With hydrophobic polyurethanes, the only option is adhesion. The polyol and isocyanate environments producing hydrophobic polyurethanes by the prepolymer method are thought to be too severe for hving cells. As noted earher, the weaker adhesion of adsorption to a hydrophobic polyurethane can be an advantage. Sanroman compared die adsorption and entrapment techniques and determined that the adsorption technique was superior based on citric acid productivity and operational stability. 

Perhaps the most interesting application of polyurethane foam as a substratum for cell growth was studied by Bailliez et al. While not specifically a remediation study, their work compared hydrophobic and hydrophilic polyurethanes, TDI- and MDI-based prepolymers, and entrapment and adsorption methods, and also investigated the production of hydrocarbons by Botryococcus braunii. An unfortunate feature of biotechnical research in the use of polyurethanes is that the chemistry is rarely explained. While Bailliez includes some detail, much of their work simply designates products without specific references to the polyols. It is, of course, part of the mission of this book to show that polyurethanes are specialty chemicals. It cannot be assumed... 

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. 

PPDI PPG Prepolymer Processability initiating agent. An abbreviation for paraphenylene diisocyanate. Polypropylene glycol. The product from reacting a polyol with an isocyanate. The relative ease with which a raw or compounded polymer can be handled. 

Second-generation solventless polyurethane adhesives Two-component second-generation adhesive systems are the most widely used of the 100% solids products. These two-part adhesives comprise an isocyanate terminated prepolymer based on the reaction product normally of MDI and polyols (polyether or polyester) in the presence of excess isocyanate, and a polyol (polyether or polyester based). 

HDl isocyanate prepolymers (addition products of HDl and a di- or higher functional polyol)... 

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