Polyisocyanate polyaddition

The utilisation of the high MW aminic polyether polyols in the synthesis of polymer polyols [graft polyether polyols and polyisocyanate polyaddition (PIPA) polyols] is presented in Chapter 6 [148, 151]. 

The synthesis of polyisocyanate polyaddition (PIPA) polymer polyols is very similar to the synthesis of PHD polyols, with the difference that, instead of polyurea, a PU finely... 

This plastic includes a large group of polyaddition polymers which are formed through the reaction of bifunctional or trifunctional alcohols with di- or polyisocyanates. By varying the starting materials, linear as well as crosslinked macromolecules with correspondingly different properties are formed. Alcohols with three functional groups and/or triisocyanate are used to make crosslinked polyurethane elastomers (PUR). 

Polyisocyanates are very reactive compounds and produce various polymers such as fibers, resins, elastomers, foams, coatings and adhesives by the reaction of polyaddition, polycondensation or stepwise polymerization. 

As mentioned previously, the synthesis of polyurethanes, by the reaction of a diisocyanate (or polyisocyanate) with oligo-diols (or oligo-polyols), is a polyaddition reaction (or step-addition polymerisation), a particular type of polycondensation reaction. There is a great difference between the polycondensation and the polyaddition reactions and the classical radical polymerisation or ionic (living) polymerisation reactions. In radical polymerisations (typical chain reactions), the high MW polymer is formed at the beginning of polymerisation. The reaction system is constituted from monomer and high... 

Diisocyanates are an important class of chemicals of commercial interest, which are frequently used in the manufacture of indoor materials. such as adhesives, coatings, foams and rubbers (Ulrich, 1989). In some types of particle board, the diisocyanates have replaced formaldehyde. Isocyanates are characterized by the electrophilic -N=C=0 group, which can easily react with molecules containing hydroxy groups, such as water or alcohols. On hydrolysis with water, primary amines are formed, while a reaction with alcohols leads to carbamates (urethanes). Polyurethane (PUR) products are then obtained from a polyaddition of diisocyanate and diol components. Compounds commonly used in industrial surface technology are 4,4 -diphenylmethane diisocyanate (MDI) and hexamethylene diisocyanate (HDI). The diisocyanate monomers are known as respiratory sensitizers and cause irritation of eyes, skin and mucous membrane. Therefore, polyisocyanates such as HDI-biuret and HDI-isocyanurate with a monomer content <0.5 % are used for industrial applications, and isocyanate monomers will not achieve high concentrations in ambient air. Nevertheless, it is desirable to measure even trace emissions from materials in private dwellings. 

In drying by polyaddition, low molecular mass reactive polymers such as alkyd resins, saturated polyesters, or polyacrylates react with polyisocyanates or epoxy resins to form cross-linked macromolecules. Because this reaction can take place at room temperature, the binder components must be mixed shortly before application. The period of time during which a coating of this type remains usable after mixing of the components is known as the pot life. These are known as two-pack coatings, differing from the one-pack systems, which can be stored for months or even years. 

Chemically blocking one of the polyaddition binder components (e.g., the polyisocyanate) gives a coating system stable at room temperature. Heat is required to deblock the component and enable cross-linking to occur. Stoving paints of this type are used in industry and in powder coatings. 

The most important combinations of epoxy resins and curing agents are summarized in Table 2.6. Depending on their molecular mass, bisphenol A epoxy resins can be cured by polyaddition via their epoxy or hydroxyl groups. Polyamines, poly thiols, and polyisocyanates are suitable for room temperature cure. Polyanhydrides, polyphenols, acids, and carboxy-functional polyesters are suitable for hot cure. 

Refractive index (nj,) and Abbe s number (Vp) of DMMD are 1.646 and 35.2, respectively 1. Both of these values are so large compared with those of common organic compounds that S-alkylcarbtunate comprising polyurethane with high no and Vd can be obtained from the reaction of DMMD with polyisocyanate. For instance, polyaddition with IMB or l,3-bis(isocyanatomethyl)cyclohexane (IMC) resulted in polyurethane with nu/Vo of 1.661/32.3 or 1.620/38.5, respectively . 

In interfacial polymerization, the monomers A and B are polylunctional monomers capable of causing polycondensation or polyaddition reaction at the interlace [126, 127]. Examples of oil soluble monomers are polybasic acid chloride, bishalo-formate and polyisocyantates, whereas water soluble monomers can be polyamine or polyols. Thus, a capsule wall of polyamide, polyurethane or polyurea may be formed. Some trifunctional monomers are present to allow crosslinking reactions. If water is the second reactant with polyisocyanates in the organic phase, polyurea walls are formed. The latter modification has been termed in situ interfacial polymerization [128]. 

A newly developed third class of vinyl ester resins is represented by the even higher quality VE urethanes based on bisphenol A epoxy. Here, the secondary OH groups of the VE react in polyaddition with polyisocyanates to produce urethane bridges, see Eigure 1.3. Vinyl ester urethane resins (VEU resin, vinyl ester urethane-hybrid resins) combine the good mechanical properties (stiffness) of VE resins with excellent high-temperature resistance (T approx. 220 °C and HDT approx. 210 °C) and excellent chemical resistance (the long-term durability of VEUH resin exceeds that of normal VE). 

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