IPDI-based prepolymer

Now that we have a background of prepolymers, let us deal with two specific examples which are used in the construction industry IPDI-based prepolymer and MDI-based prepolymer. 

IPDI-based prepolymer. This is an aliphatic prepolymer formed by the reaction of IPDI with polyether polyol (3000 molecular weight PPO-based triol) (PPG = polypropylene oxide). The NCO group content of such systems is about 3.4%, and the viscosity about 15 000 CP at 20°C. Solid content is typically 98%-100%. The general reaction is given in Figure 2.22. This prepolymer may typically be used in two-part elastomer systems. 

Isophorone diisocyanate (IPDI) based isocyanate curing agents confer very high durabihty to 2 component polyurethane systems, but this is offset by poor flexibility and low reaetivity. Hence IPDI adducts are usually combined with flexible hydroxy prepolymers in low bake applications. They are also used as partial replacements for the aromatic or aliphatic polyisocyanates. Compared to other diisocyanates, IPDI has the advantage that it has relatively low volatility, whilst still being a liquid. 

The ketimine of isophorone diamine is formed by reacting it with methyl isobutylketone, splitting off water in the process. When said ketimine is added to an isocyanate-terminated prepolymer based on IPDI, a semi-stable system is established with a pot life of several hours. The ketimine is a Schiff base and thus can react even in the absence of water. The complexities and advantages of this system are reviewed by Bock and Halpaap [75] ... 

Figure 221 Synthetic route for prepolymers based on isophorone diisocyanate (IPDI).

The prepolymer used in later syntheses was based on monomers with x=2. The number average molecular weight by gel permeation chromatography (GPC) using polystyrene reference was 20,000 and by NMR was 18,000. ( 9) TTiis prepolymer is designated 7-Fox20K. MDI (Kodak) was distilled under reduced pressure and stored in refrigerator before use. IPDI, BDM, tetrahydrofuran (THF), N,N-dimethyl-acetamide (DMAc) and methanol were purchased from Aldrich and used as received. 

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