Isocyanate-containing monomers

In order to investigate dendrimers of a different nature [230], Bradley described the synthesis and transfection efficiency of polyamidourea dendrimers synthesised from isocyanate-containing AB3 monomers [231-234]. The use of this kind of tris-branched building block was addressed to enhance dendrimer synthesis by replacement of the 1,4-addition step typical of PAMAM synthesis and to a rapid increase in terminal functionality. The dendritic structures were synthesised using a divergent, microwave-assisted, solid-phase approach with the dendrimers assembled on polystyrene resin via an acid labile linker (see Fig. 26). In particular, a G3.0 polyamidourea bis-dendron with the peripheral amino groups conjugated to L-lysine residues demonstrated remarkable transfection abilities [234],... 

The postintroduction of hydrophobes could offer an effective alternative to the mutual solubility problems (Chapter 20) encountered in chain-growth copolymerizations. The introduction of difunctional monomers that contain both unsaturation and isocyanate units (e.g., isocyanatoethyl methacrylate or m-isopropenyl a,a-dimethylbenzylisocyanate) with lower cost non-iso-cyanate-containing monomers (45) provides two routes for postmodification. One route could be the copolymerization with methyl acrylate, followed by the reaction of the isocyanate function with an ethoxylated surfactant, then hydrolysis of the methyl acrylate units. 

This procedure was designed to provide a measure of the absorptivity of the hydrophobic monomer through the use of a model. The use of a monomeric model compound to represent equivalent chromophores attached to polymer molecules was recently reported for polystyrene 15, 16). UV methods were also used in the determination of copolymer composition and reactivity ratios for isocyanate-containing acrylate polymers (IT). 

The labels on the packaging of preparations containing isocyanates (as monomers, oHgomers, prepolymers, etc., or as mixtures thereof) must bear the following inscription ... 

When isocyanate reacts with hydroxyl containing monomer, it produces a polyurethane shell. 

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

Isocyanates can be added to solvent-borne CR adhesive solutions as a two-part adhesive system. This two-part adhesive system is less effective with rubber substrates containing high styrene resin and for butadiene-styrene block (thermoplastic rubber) copolymers. To improve the specific adhesion to those materials, addition of a poly-alpha-methylstyrene resin to solvent-borne CR adhesives is quite effective [76]. An alternative technique is to graft a methacrylate monomer into the polychloroprene [2]. 

Polyaddition reactions based on isocyanate-terminated poly(ethylene glycol)s and subsequent block copolymerization with styrene monomer were utilized for the impregnation of wood [54]. Hazer [55] prepared block copolymers containing poly(ethylene adipate) and po-ly(peroxy carbamate) by an addition of the respective isocyanate-terminated prepolymers to polyazoesters. By both bulk and solution polymerization and subsequent thermal polymerization in the presence of a vinyl monomer, multiblock copolymers could be formed. 

Such reactive isocyanates always contain about 1% by weight of free diisocyanate monomer which is highly toxic, therefore when in use ventilation... 

Polyurethanes are thermoset polymers formed from di-isocyanates and poly functional compounds containing numerous hydroxy-groups. Typically the starting materials are themselves polymeric, but comprise relatively few monomer units in the molecule. Low relative molar mass species of this kind are known generally as oligomers. Typical oligomers for the preparation of polyurethanes are polyesters and poly ethers. These are usually prepared to include a small proportion of monomeric trifunctional hydroxy compounds, such as trimethylolpropane, in the backbone, so that they contain pendant hydroxyls which act as the sites of crosslinking. A number of different diisocyanates are used commercially typical examples are shown in Table 1.2. 

Prepolymeric HDI-BT paint formnlations, which generally contain 1% monomeric HDI, are now widely used for coatings applications, particularly in the automobile and airplane industries (Alexandersson et al. 1987 Karol 1986 Key-Schwartz 1992 Nielson et al. 1985 Rosenberg and Savolainen 1986 Rosenberg and Tuomi 1984). Consequently, many reported occupational exposures to HDI are actually exposures predominantly to HDI-BT (Karol 1986 Karol and Hauth 1982). Although isocyanate prepolymers are safer to use than the free monomers, primarily because of their lower vapor pressures, they can still pose a health risk to workers when inhaled in the aerosol form (Karol and Hauth 1982 Rosenberg and Tuomi 1984). There... 

Nozawa et al. (5) prepared reactive methacrylate monomers containing isocyanate functions, (IV), which were used in dental compositions. 

Example 12.10. Polyurethane (PUR) foams are widely used in the building industry. The name refers to the fact that its monomer contains urethane ( 0-CO-NH ) as a functional group. The polymer is usually made from diisocyanates. Isocyanates are molecules which have a N=C=0 group attached. Upon addition of water the reaction shown in Fig. 12.16 starts. 

Free isocyanate specimen. A measure of the free, unreacted diisocyanate monomer present in an isocyanate prepolymer. Low free isocyanate prepolymers are desirable, as they contain very low levels of volatile isocyanate, making them inherently safer for the end user. 

Polyisocynanurate Polymer hydrolytic stability, mechanical properties, and cost advantages. A polymer containing multiple isocyanate-to-isocyanate bonds. A material consisting of molecules characterized by the repetition of one or more types of chemical units (poly = many, mer from monomer, mono = one). 

Aluminum isopropoxide has been used for the preparation of block copolyesters [147, 148]. Tri-block poly(e-CL-b-DXO-e-CL) was prepared by the sequential addition of different monomers to a living polymerization system initiated with aluminum isopropoxide in THF or toluene solution [95]. An alternative route for the preparation of the tri-block copolymer was to react the diblock poly(e-CL-b-DXO) containing an -OH functionality at the chain end using a difunctional coupling agent such as isocyanate or acid chloride (Scheme 18). However, the molecular weights were low and full conversion of monomers was not achieved. 

In the above-mentioned patents post-polymerization modification is performed in a single step. An alternative is the performance of two sequential modification steps. In the first step the polymer is reacted with tin or germanium derivatives (triphenyl tin, tributyl tin, diphenyl tin dichloride, dioctyl tin dichloride, phenyl tin trichlorde etc.). In the subsequent modification step heterocumulene compounds (ketenes, thioketenes, isocyanates, thioiso-cyanates and carbodiimides) are applied [437,438]. Specific interaction with silica is obtained by end group functionalization with vinyl monomers which contain hydroxyl or epoxy groups. The effects are observed if the PDI is below 5 [439,440]. 

The fundamental chemistry of the structural adhesives described here can change very little. Vinyl and acrylic monomers polymerize by chain growth polymerization initiated by free radicals or ions. Isocyanate and epoxy compounds react with compounds containing active hydrogen in step growth polymeriza-... 

---