Polyisocyanate copolymers

Even stiffer chains than aromatic polyamides were built into networks with flexible crosslinking residues. A specially synthesized polyisocyanate copolymer was prepared by Aharoni [278] containing 25% 1-decenyl- and 75% n-octyl-isocyanate residues. This LCP was then lightly crosslinked by heating in solution in the presence of a free radical initiator (AIBN) to produce a gelled insoluble network. A characteristic structure appears as ... 

It is considered that, if ideal, optically active poly(alkyl(aryl)silane) homopolymer and copolymer systems could be obtained which had stiffer main-chain structures with longer persistence lengths, it should be possible to clarify the relationship between the gabs value and the chiral molar composition. The magnitude of the chirality of the polyisocyanates allowed precise correlations with the cooperativity models.18q In the theory of the cooperative helical order in polyisocyanates, the polymers are characterized by the chiral order parameter M, which is the fraction of the main chain twisting in one helical sense minus the fraction of the main chain twisting in the opposing sense. This order parameter is equal to the optical activity normalized by the value for an entirely one-handed helical polymer. The theory predicts... 

Polyurethane-acrylic coatings with interpenetrating polymer networks (IPNs) were synthesized from a two-component polyurethane (PU) and an unsaturated urethane-modified acrylic copolymer. The two-component PU was prepared from hydroxyethylacrylate-butylmethacrylate copolymer with or without reacting with c-caprolactonc and cured with an aliphatic polyisocyanate. The unsaturated acrylic copolymer was made from the same hydroxy-functional acrylic copolymer modified with isocyanatoethyl methacrylate. IPNs were prepared simultaneously from the two-polymer systems at various ratios. The IPNs were characterized by their mechanical properties and glass transition temperatures. 

Another significant helical amplification in optically active copolymers with preferential screw-sense helicity is known as the majority rule phenomenon [ 17,18]. In this case, the screw sense of a helical main chain bearing nonracemic chiral side groups is controlled by the ee only and a population of preferential screw-sense helicity and optical activity were nonlinearly amplified by ee of chiral side groups. Since Pino et al. first reported this phenomenon in poly-a-olefins made of vinyl co-monomers bearing nonracemic chiral moieties [21], this majority rule has already been established in stiff polyisocyanates bearing a nonracemic chiral side chain [17,18]. 

An urethane-based pressure-sensitive adhesive composed of a liquid hydroxytelechelic polybutadiene and a polyisocyanate does not require a solvent in coatings onto label sheets. This polymer together with the (polystyrene-co-butadiene) copolymer and a polyisocyanate was applied in steel coatings 239 240>. 

Carbamylation and Thiocarbamylation Reactions (Figure 3.16a) These reactions have been widely used for protein immobilization on many polymers, including polyisocyanate and polyisothiocyanate styrene and on other copolymers containing these styrene units and isocyanate or isothiocyanate groups [157,158]. 

In the following discussion, only the most widely used adhesive types are described. These are the urea-formaldehyde (UF) resins, melamine-formaldehyde (MF) resins, phenol-formaldehyde (PF) resins, diisocyanates, polyisocyanates, polymers and copolymers of vinyl acetate, and polyamides. These are all predominantly thermosetting resin systems. 

These compounds can be copolymerized with styrene to form crosslinked copolymers. When polyisocyanates are incorporated in these reaction systems, the resulting polymers are hybrid polymers containing polyurethane linkages. Rigid foams can be obtained by using the above reaction in the presence of a blowing agent. 

In contrast to polypeptides that have many possible conformations, poly(hexyl isocynate) is known to have a stiff rodlike helical conformation in the solid state and in a wide range of solvents, which is responsible for the formation of a nematic liquid crystalline phase.45-47 The inherent chain stiffness of this polymer is primarily determined by chemical structure rather than by intramolecular hydrogen bonding. This results in a greater stability in the stiff rodlike characteristics in the solution as compared to polypeptides. The lyotropic liquid crystalline behavior in a number of different solvents was extensively studied by Aharoni et al.48-50 In contrast to homopolymers, interesting new supramolecular structures can be expected if a flexible block is connected to the rigid polyisocyanate block (rod—coil copolymers) because the molecule imparts both microphase separation characteristics of the blocks and a tendency of rod segments to form anisotropic order. 

Figure 8. Majority rules effect in polyisocyanates (left) CD spectra of homo- and copolymers (right) structure and compostion of the polymers. (Reprinted with permission from ref 60. Copyright 1995 American Association for the Advancement of Science.)...

Polyurethane is a term used to represent the group of polymers that contain the urethane linkage, sometimes called an ester of carbamic acid (Fig. 1). Polyurethanes are block copolymers of the form (AB) that is formed by a polyisocyanate addition reaction. Some PUs are thermoplastics, while others are thermosets. The properties of the PU can be changed substantially by changing the chemical composition of the polymer s constituents, and thus... 

Li.gru.n-VeAd.ved Potyi ocqanaXeA Efforts to increase the incorporation of lignin into polyurethane products have concentrated on transforming polymeric lignins into polyisocyanates useful for reacting with polyols. Two alternative reaction pathways have been explored with the three lignin-like model compounds shown in Figure 3. These models were vanillic acid or a derivative thereof (Model Type A) a derivative of tetralin di-carboxylic anhydride (Model Type B) and a derivative of a styrene-maleic anhydride copolymer (Model Type C). 

In Chapter 3, the chemistry and technology of the most important oligo-polyols used for elastic polyurethanes fabrication, in fact high MW oligomers (2000-12000 daltons) with terminal hydroxyl groups and low functionality (2-4 hydroxyl groups/mol) were discussed. Polyalkylene oxide polyols (homopolymers of PO or copolymers PO - EO, random or block copolymers), polytetrahydrofuran polyols, filled polyols (graft poly ether polyols, poly Harnstoff dispersion - polyurea dispersions (PHD) and polyisocyanate poly addition (PIPA) polyols), polybutadiene polyols and polysiloxane polyols were all discussed. The elastic polyurethanes represent around 72% of the total polyurethanes produced worldwide. 

A variety of urethane coating systems has been introduced based on hydroxyl-containing acrylic and methacrylic ester copolymers that contain hydroxyethyl acrylates or methacrylates and that are generally cured with aliphatic di- or polyisocyanates. Depending upon the type and relative amounts, acrylate or other saturated esters, for example, adipate-isophthalic esters, are also used in combination with aliphatic polyisocyanates. 

This volume continues in the same format as the first edition with updates on the syntheses of various types of polymers, including olefin-sulfur dioxide copolymers, polythioesters, sulfide polymers, polyisocyanates, polyoxyalkyihydroxy compounds, polyvinyl carbazole, polyvinyl acetate, polyallyl esters, polyvinyl fluoride, and miscellaneous polymer preparations. The book should be useful to academic and industrial chemists who desire typical synthetic procedures for preparing the polymers described herein. In addition to reviewing the latest journals, we survey the patent literature and give numerous additional references. 

Binders are macromolecular products with a molecular mass between 500 and ca. 30000. The higher molecular mass products include cellulose nitrate and polyacrylate and vinyl chloride copolymers, which are suitable for physical film formation. The low molecular mass products include alkyd resins, phenolic resins, polyisocyanates, and epoxy resins. To produce acceptable films, these binders must be chemically hardened after application to the substrate to produce high molecular mass cross-linked macromolecules. 

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