Terminated nitrile

Flexibilized epoxy resins are important structural adhesives [69]. Liquid functionally terminated nitrile rubbers are excellent flexibilizing agents for epoxy resins. This liquid nitrile rubber can be reacted into the epoxy matrix if it contains carboxylated terminated functionalities or by adding an amine terminated rubber. The main effects produced by addition of liquid nitrile rubber in epoxy formulations is the increase in T-peel strength and in low-temperature lap shear strength, without reducing the elevated temperature lap shear. 

Coran and Patel [74] investigated the reactive com-patibilization of PP-NBR and HDPE-NBR blends using phenolic modified polyolefin, maleic anhydride modified polyolefin, and amine terminated nitrile rubber as reactive components. Dynamic vulcanization was also inves-... 

ATBN - amine terminated nitrile rubber X - Flory Huggins interaction parameter CPE - carboxylated polyethylene d - width at half height of the copolymer profile given by Kuhn statistical segment length DMAE - dimethyl amino ethanol r - interfacial tension reduction d - particle size reduction DSC - differential scanning calorimetry EMA - ethylene methyl acrylate copolymer ENR - epoxidized natural rubber EOR - ethylene olefin rubber EPDM - ethylene propylene diene monomer EPM - ethylene propylene monomer rubber EPR - ethylene propylene rubber EPR-g-SA - succinic anhydride grafted ethylene propylene rubber... 

Composite Particles, Inc. reported the use of surface-modified rubber particles in formulations of thermoset systems, such as polyurethanes, polysulfides, and epoxies [95], The surface of the mbber was oxidized by a proprietary gas atmosphere, which leads to the formation of polar functional groups like —COOH and —OH, which in turn enhanced the dispersibility and bonding characteristics of mbber particles to other polar polymers. A composite containing 15% treated mbber particles per 85% polyurethane has physical properties similar to those of the pure polyurethane. Inclusion of surface-modified waste mbber in polyurethane matrix increases the coefficient of friction. This finds application in polyurethane tires and shoe soles. The treated mbber particles enhance the flexibility and impact resistance of polyester-based constmction materials [95]. Inclusion of treated waste mbber along with carboxyl terminated nitrile mbber (CTBN) in epoxy formulations increases the fracture toughness of the epoxy resins [96]. 

Hydrocyanation of aliphatic conjugated dienes in the presence of Ni(0) complexes gives diene rearrangement products and /i.y-unsaUiratcd nitriles in 10-90% yields10. Dienes other than 1,3-butadiene do not produce terminal nitriles, implying that the more highly substituted jr-allyl nickel complex is favored. Thus, reaction of 1-phenylbuta-l,3-diene (1) affords ( )-2-methyl-4-phenylbut-3-enenitrile (2) as the sole product (equation 5). The... 

Much lower yields are achieved when terminal alkynes react with HCN. Terminal nitriles formed due to mainly steric factors are the main products. Regio- and stereoselectivities similar to those in hydrocyanation of alkenes indicate a very similar mechanism. 

Figure 2. Duodenal ulcerogenic and adrenocorticolytic activities of terminal nitriles, amino and thiol alkanes. (Reproduced with permission from Ref. 34. Copyright 1980, International Institute of Stress.)...

A number of olefins are converted in the presence of tetrakis(tri-o-tolyl phos-phite)nickel(O) into the corresponding nitriles. These additions yield the terminal nitriles predominantly [15]. Systematic investigations were performed on the hydrocyanation of olefins containing the norbomene skeleton 9 as a basic structure. Table 1 demonstrates the development of catalysts to gain stereocontrol of product formation. 

Liquid diglycidyl ether of bisphenol A Carboxyl-terminated nitrile rubber... 

Thermolysis of 1,2,4-triazines with a side-chain terminal nitrile group leads to the formation of condensed pyrazines <89JOCl245>. This reaction involves cycloaddition of the nitrile dienophile across C-3 and C-6 of the 1,2,4-triazine followed by aromatization of the intermediate cycloadduct by extrusion of the N—N bridge. As a typical example, the 5,6-diphenyl-1,2,4-triazine (167) is fused under nitrogen at 225-235°C to form the condensed pyrazine (168) in 71% yield (Equation (21)). Intermolecular cyclization of oxadiazinones with enamines also yields condensed pyrazines. The bicyclic intermediates lose carbon dioxide to generate 1,4-diazadienes, which aromatize to the... 

Later, in 1974, amine reactive versions of the liquid nitrile polymers (ATBN) were issued, thereby offering another way to introduce rubbery segments into a cured epoxy resin network. References are cited which provide detailed discussions of nitrile rubber, carboxylic nitrile rubber and both carboxyl- and amine-terminated nitrile liquid polymers (1-4). Table I illustrates CTBN and ATBN products structurally. Table II provides properties for typical solid carboxylic nitrile elastomers. 

The same team has also described the selective hydrogenation of cis-2-pentenenitrile with surfactant-stabiUzed ammonium perfluorotetradecanoate bimetallic Pd-Ru nanopartides prepared via in situ reduction of their simple salts in reverse micelles in SCCO2 [22]. The optimized ratio Pd Ru nanopartide (1 1) shows the highest activity for the hydrogenation of functionalised alkene under mild conditions. No hydrogenation of the terminal nitrile of the molecule in amine was observed and, finally, this fluorinated micelle-hosted bimetallic catalyst gives relevant activity and selectivity in the supercritical fluid without deactivation for at least three catalytic cycles. 

Thermoplastic rubber block copolymers, with completely new adhesive performance, were developed in 1965 [21]. The first commercial product was Shell Chemical s Kraton 101, of styrene polybutadiene-styrene composition. This development led to the carboxy-terminated nitrile (CTBN) rubber modifiers used to flexibilize epoxy and other brittle resin adhesives in the late 1960s. Today, the thermoplastic rubber block copolymer adhesives are used in hot melt-, solvent- and water-based adhesives, and as hot melt- and solvent-based sealants. Major applications are as pressure-sensitive adhesives, construction adhesives and sealants, and general assembly adhesives. 

Conversely, the brittleness of cured epoxy resins can be ameliorated by copolymeiizing with flexible curing agents. The two most popular types are carboxyl-terminated nitrile rubber and mercaptan-terminated polysnlflde rnbber oligomers (Fig. 3.35). 

HOC(CH2CH=CHCH2)m(CH2(j H)nCOH Carboxyl-Terminated Nitrile Rubber... 

Compatibilizer preparations are needed for use with a polypropylene and NBR/ HNBR blend, the components of which are grossly incompatible [7]. This could be a one-step process if one starts with commercially available maleic anhydride (MA) modified polypropylene and amine-terminated nitrile rubber. Then one can melt mix the above fimctionalized polymers in a batch or a continuous mixer and prepare the compatibilizer, as shown in step 2 below. One can also modify the polypropylene as described below in step 1, and use it to prepare the compatibilizer. 

Maleic anhydride modified polypropylene is then melt-mixed with secondary amine-terminated nitrile rubber (NHR-NBR, known as ATBN) to form a graft copolymer containing nitrile rubber (NBR) segments and polypropylene (PP) segments. 

Nickel-catalyzed hydrocyanation of a-olefins t)q)ically produces the terminal nitrile as the more abundant, but not exclusive isomeric product. In contrast, nickel-catalyzed hydrocyanation of vinylarenes typically generates the branched product. This branched selectivity arises fijom the stability of -phenethyl complexes, as is shown in more detail in Section 16.2.5 on as)unmetric hydrocyanation. The relative rates for hydrocyanation follow the trend ethylene > styrene > propene 1-hexene > disubstituted olefins. Examples of these reactions and selectivities for formation of the linear and branched products are shown in Scheme 16.1. ... 

Reactions of mtemal olefins are more complex than reactions of terminal olefins (Scheme 16.3). As mentioned previously, terminal nitriles are often formed from reactions of internal olefins. The formation of terminal nitriles results from insertion of the internal olefin to form a branched alkylmetal intermediate (A in Scheme 16.3) that undergoes isomerization to the terminal alkyl intermediate B prior to reductive elimination of the final linear nitrile faster than it undergoes reductive elimination to form the branched nitrile. Internal olefins react more slowly than terminal olefins, and this relative rate can be traced to the slower insertion of internal olefins into metal hydrides. Lewis acids, such as ZnClj and AlClj, promote these reactions of isolated alkenes. 

The enantioselective hydrocyanation of alkenes has the potential to serve as an efficient method to generate optically active nitriles, as well as amides, esters, and amines after functional group interconversions of the nitrile group. As in asymmetric hydroformylation, asymmetric hydrocyanation requires control of both regiochemistry and stereochemistry because simple olefins tend to generate achiral terminal nitrile products. The hydrocyanation of norbomene will give a single constitutional isomer and was studied initially. However, modest enantioselectivities were obtained, and the synthetic value is limited. ... 

Although less studied, the hydrocyanation of alkynes in the presence of soluble transition metal complexes has also been reported. - The reactions conducted with nickel(O) catalysts occur with cis stereochemistry, high regioselectivity, and moderate-to-high yields. Again, both steric and electronic effects control the regioselectivity. These points are illustrated by the data in Equation 16.11. Terminal, straight-chain alkynes such as l-hex)me react to form predominantly the branched nitrile, whereas tert-butyl acetylene reacts to form mostly the terminal nitrile. Reactions conducted with DCN have shown that the addition occurs in a syn fashion. ... 

Apart from carboxyl and amine-terminated nitrile rubbers, the rubbers having other end groups like amine [12-14], mercaptan [15, 16] hydroxyl [17] and epoxy [18,... 

Tripeptides with a C-terminal nitrile moiety, which are employed in the inhibition of proteinases, have also been synthesized by the phosphoryl chloride method [1090]. 

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