Macrodiisocyanate

The prepolymers described above are one type of telechelic polymer. A telechelic polymer is one containing one or more functional end groups that have the capacity for selective reaction to form bonds with another molecule. The functionality of a telechelic polymer or prepolymer is equal to the number of such end groups. The macrodiol and macrodiisocyanate telechelic prepolymers have functionalities of 2. Many other telechelic prepolymers were discussed in Sec. 2-12. (The term functional polymer has also been used to describe a polymer with one or more functional end groups.)... 

Similarly, Wasserman and coworkers have studied a wide selection of polymeric materials in aqueous solution that are associative of some kind, i.e., that form some sort of self-assembly through non-covalent interactions [96]. Their study mainly deals with hydrogels of hydrophobically modified polymers, aqueous solutions of polymeric micelles created by block copolymers, and hydrogels based on poly (acrylic acid) and macrodiisocyanates. The spin probes of choice were hydrophobic, such as 5- and 16-DSA (see Eig. 2) or even spin labeled polymers. It was, e.g., possible to screen for the effect of chemical stmcture on the gel formation by recording and understanding the local mobility of the hydrophobic, long chain spin probes as a function of temperature. 

Polyurethanes are used in four principal types of products foams, elastomers, fibers, and coatings. The majority of polyurethane is used as rigid or flexible foams. However, about 15% is used for elastomer applications. Production of polyurethane elastomers involves a number of steps. As indicated above, an intermediate hydroxyl-terminated low-molecular-weight polyester or polyether is prepared. This intermediate is reacted with an isocyanate to form a prepolymer (macrodiisocyanate). The prepolymers are coupled or vulcanized by adding a diol or diamine ... 

Let us consider the properties of an adhesive based on the following mixture of oligomers an unsaturated polyester resin and a prepolymer with end isocyanate groups (or macrodiisocyanate) based on polydiethylene glycol adipate of molecular weight 800 and on TDI (a mixture of the 2,4- and 2,6-isomers in ratio of 65 35), with the... 

The Sprut-5M adhesive consists of unsaturated polyester resin 100 parts hy weight, ATG-M 80 parts (a mixture of 50 parts of macrodiisocyanate md 30 parts of ATG), polymerization initiator (MEKP(O)) 2 parts. Usually lwt% of CN is integrated additionally into the adhesive base. Sprut-5M can be produced using various polyester resins, but the most applicable one is the adhesive based on PM-I resin owing to its availability and low cost. For this reason we will consider the properties of the adhesive based mainly on this resin although it has adhesion strength 20—40% lower than that of adhesives based on PN-11, NPS 609-21M, and other resins, especially when cementing in water. 

With time, the free isocyanate groups of the solid adhesive react with the moisture that diffuses through the adhesive, as confirmed by the decrease of the IR absorption of the isocyanate groups at 2260cm. This process results in polymerization of the macrodiisocyanate. 

Figure 5.3 Effect of water on the specific electrical resistance and the adhesion strength (steel 3-steel 3) of the adhesive based on macrophenylmethane diisocyanate (a), and on macrodiisocyanates made of POPG-1000 and diphenylmethadiisocyanate (b), POPG-2000 and TDI (c), and POPG-1000 and TDI (d) containing 0.2% catalyst and 10% filler (b, A c d), and without filler (b, B) (1) adhesive 0.25 mm thick applied to steel foil (2) electrode in the bulk adhesive (3) electrode on the substrate-adhesive boundary (4) pull-off adhesion strength.

To avoid the appearance of terminal blocks of the type -[I-MD]-, the prepolymer technique is usually used in most of the cases. In this type of synthesis, the MD is first reacted with an excess of I so that the whole amount of MD is transformed in a macrodiisocyanate prepolymer ... 

The reaction between macrodiisocyanate and aromatic diamine (di(3-chloro-4-aminophenyl)methane) was also used. Chemical structure of this network depends on the ratio between rigid bulky triisocyanurate crosslinked points and flexible linear fragments linking them. The products have dilTerent properties with respect to the ratio between crosslinked points and flexible chains. 

Fig. 7. Reaction scheme for the prepolymer formation and conversion of the macrodiisocyanate into non-reactive methylurethane.

The principles of the prepolymer formation and of the analysis of the composition of the prepolymer have already been described in the Experimental Part. The prepolymer formation in the melt was investigated with monodisperse polyols of different chain lengths and for molar ratios of MDI/polyol varying between 2 and 35. In order to facilitate the chromatogrhic analysis and to avoid side reactions of the macrodiisocyanate samples during the analytic procedure the isocyanate groups were converted into inactive methylurethanes (Figure 7) prior to the HPCL analysis. 

A typical HPLC trace of the prepolymer resulting from the system POTM-12 and MDI (molar ratio 1 3) is depicted in Figure 8. It is evident that the composition of the prepolymer with regard to the mole fraction of residual MDI (p=1) and of the macrodiisocyanate without (p=2) and with pre-extension (p>3) can be determined with high accuracy from the chromatogram resolved into the individual sequences containing two terminal diisocyanate residues ("ideal macrodiisocyanate", p=2) and the pre-ex-tended oligomers with one (p=3) or more (p>4) internal diisocyanate units. 

The variation of the molar ratio POTM-n/MDI in the prepolymer formation in bulk has shown that the pre-extension detectable within the experimental error becomes neglectable only at more than fifty-fold excess of MDI however, a ten-fold excess of MDI already reduces the extension of POTM-n to such an extent that over 90% of the prepolymer consists of "ideal macrodiisocyanate molecules, i.e., POTM-n endcapped with MDI, and only less than 10% of the prepolymer molecules are pre-extended. This is considered to be an acceptable compromise between the objective to prepare model PU elastomers with a soft segment distribution as narrow as possible and a reasonable experimental effort. 

OUDM was synthesized from macrodiisocyanate (MDI) based on POPG MM 1000, hexamethylene dusocyanate (HMDI), and HEMA in the ratio 1 2 at 40 °C up to fuU exhaustion of isocyanate groups according to the scheme ... 

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