Poly isocyanates isocyanate

Typical of these materials are the poly(vinyl thioethers), the poly(vinyl isocyanates), the poly(vinyl ureas) and the poly(alkyl vinyl ketones). Methyl isopropenyl ketone and certain vinylpyridine derivatives have been copolymerised with butadiene to give special purpose rubbers. 

Perhaps the most thoroughly investigated approach is the modification of preformed polymers in particular poly(vinyl isocyanate) and polyacrylonitrile Figure 29.21). 

Examples shown in this chapter are for PMMA. Other polymers can be separated as well. The polymers separated so far (1,2) include polystyrene, poly(a-methylstyrene), polycaprolactone, polycarbonate, poly(hexyl isocyanate), polytetrahydrofuran, poly (vinyl methyl ether), and polyvinylpyrrolidone. 

PMPPIC = poly(methylene) poly(phenyl) isocyanate PVC = poly(vinyl chloride) p = density Tf = fiber radius... 

Another family of polyols is the filled polyols.llb There are several types, but die polymer polyols are die most common. These are standard polyether polyols in which have been polymerized styrene, acrylonitrile, or a copolymer thereof. The resultant colloidal dispersions of micrometer-size particles are phase stable and usually contain 20-50% solids by weight. The primary application for these polyols is in dexible foams where the polymer filler serves to increase foam hardness and load-bearing capacity. Other filled polyol types diat have been developed and used commercially (mainly to compete with die preeminent polymer polyols) include the polyurea-based PEID (polyhamstoff dispersion) polyols and the urethane-based PIPA (poly isocyanate polyaddition) polyols. 

Polyurethanes. The hard portion of polyurethane consists of a chain extender and poly isocyanate. The soft component is composed of polyol segments. 

PMPPIC Poly(methylene) poly(phenylene) isocyanate... 

One of the pioneering works in this field was the covalent conjugation of heparin to poly-/ -styrene isocyanate 81). The procedure involved the following steps ... 

Although the crystalline poly(allyl isocyanate) polymers are reported to be stable, many of these polymers depolymerize upon heating to yield monomers and cyclic trimers. The level of temperature sensitivity is a strong function of the length of the side chain. Room temperature depolymerization occurs in polar solvents in the presence of an initiator. Interestingly, the solution properties of poly(alkyl isocyanates) display an unusual degree of chain stiffness which is attributed to their helical configuration (64). 

A more remarkable and dramatic change in the conformation of helical polymers upon photoirradiation has been observed for the azobenzene-modified poly isocyanates. Polyisocyanates are typical dynamic helical polymers [59,60]. Even the optically inactive poly(n-hexyl isocyanate) (20), which is devoid of stereogenic centers, exists as an equal mixture of right- and left-handed helical conformations. Equilibrium exists in solution between both helices separated by... 

Figure 7 Characteristics of dynamic helical poly isocyanates.

Figure 8 Schematic representation of the shift in the equilibrium between left- and right-handed helices (A) and the transition from left- to right-handed helix of poly isocyanates (B) by a photochemical trans-cis isomerization of the azobenzene unit.

Figure 9 Schematic representation of the shift between right- and left-handed helices of a poly isocyanate with bicycloketone chromophore pendants subjected to irradiation with r- or l-CPL or noncircularly polarized light (non-CPL).

The major poly isocyanates used (2) are toluene diisocyanate (TDI) and the less volatile 4,4/-methylene diphenylene diisocyanate (MDI), which, because it is a crystalline solid in the pure form, has to be used in a relatively crude form. The crude polyisocyanate is a mixture of MDI variants that is conveniently a liquid product with a mean functionality greater than 2. The use of a pure, liquid diisocyanate, however, would enable polyurethanes to be formed having relatively enhanced physical properties (2) and would also greatly simplify processing by removing the need to use elevated temperatures, solvents, or isocyanate prepolymers as with MDI. 

Bayer AG Polyurethane Foams Obtained from Poly isocyanate and Polyester Containing Aminoplast. British Pat. 1,506,341 (1978)... 

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