Nitrile polymers properties

Plasticizers. Monomeric (mol wt 250—450) plasticizers (qv) are predominantiy phthalate, adipate, sebacate, phosphate, or trimeUitate esters. Organic phthalate esters like dioctyl phthalate (DOP) are by far the most common plasticizers in flexible PVC. Phthalates are good general-purpose plasticizers which impart good physical and low temperature properties but lack permanence in hot or extractive service conditions and are therefore sometimes called migratory plasticizers. Polymeric plasticizers (mol wt up to 5000 or more) offer an improvement in nonmigratory permanence at a sacrifice in cost, low temperature properties, and processibiHty examples are ethylene vinyl acetate or nitrile polymers. 

Nitrile rubbers are produced over a wide range of monomer ratios and molecular weights, so thek physical constants and basic polymer properties also cover a range of values. Some of the more widely used properties are Hsted ki Table 1. 

St. Clair et. al. investigated a series of maleimide and nadimide terminated polyimides and developed LARC-13 [8,9]. Changing the terminal group from maleimide to nadimide, the value of the lap shear strength of a titanium lap shear joint increased from 7 to 19 MPa [9]. They also added an elastomeric component to the adhesive formulation. The introduction of 15 wt% of a rubbery component, ATBN (amine terminated butadiene nitrile polymer) and ADMS (aniline terminated polydimethyl siloxane) enhanced the adhesive properties as follows 19 MPa to 25 MPa (ATBN) titanium T-peel strength 0.2 kN/m to 1.4... 

Salame, M., Transport Properties of Nitrile Polymers, Amer. Chem. Soc.,... 

In Region IV, performance again increases. Crystallographic transformations in phosphate conversion coatings at 180 C are known to adversely affect phosphate crystal adhesion (26). However, nitrile cyclization may be important at these higHer temperatures. Cyclization is believed to enhance barrier properties of high nitrile polymers (27,28.29). 

Fe203 and Fe304 in presence of a chloride source act as flame retardants for nitrile-containing plastics and rubbers such as acrylonitrile-butadiene-styrene copolymers.52 The activity appears to be connected with the formation of FeCl3 on combustion, but other properties of FeCl3 itself make it unsuitable for direct use. If an alkyl chloride is present iron(II) citrate may be used, and for halogen-containing nitrile polymers acetates, stearates, sulfates and carbonates are effective. 

ANs are those that contain a majority of nitrile polymers. They provide good gas barrier, chemical resistance, and low taste and odor transfer with good impact properties when modified with rubber. Extruded sheet is used extensively in food packaging and rigid packaging applications. This crystalline TP is most useful in copolymers. Its copolymer with butadiene is nitrile rubber. Acrylonitrile-butadiene copolymers with styrene (SAN) exist that are tougher than PS. It is also used as a synthetic fiber and as a chemical intermediate. 

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. 

This continual search to improve the properties of a polymer which was first produced on a commercial scale in 1937 only serves to highhght how important the basic characteristics of nitrile polymers are to the rubber-using sectors of industry. 

Nitrile polymers have found a varied number of applications in the adhesive area. These applications are based on the excellent elastomeric properties of the polymer coupled with its polarity which gives the material good solvent resistance and compatibility with other polar materials. The various commercially available physical forms of nitrile polymers (slab rubber, crumb rubber, liquid rubber and latex) have also increased the ease of processing of the material and broadened the application base. In an attempt to review this broad area, the applications have been subdivided into three parts. In the first section applications involving solely nitrile rubber as the base polymer as well as miscellaneous nitrile rubber blends are reviewed. Due to the large number of applications involved, nitrile rubber/pheno-lic blends have been separated into the second section. For the same reason, nitrile rubber/ epoxy blends are covered separately in the third section. 

These polymers are produced by hydrogenation of the butadiene units of Nitrile polymers and are available with different amounts of unsaturation. As the number of double bonds is reduced, the elastomer becomes more highly saturated and the polymers have better heat resistance. They require peroxide cures to develop optimum properties. 

The principal monomer of nitrile resins is acrylonitrile (see Polyacrylonitrile ), which constitutes about 70% by weight of the polymer and provides the polymer with good gas barrier and chemical resistance properties. The remainder of the polymer is 20 to 30% methylacrylate (or styrene), with 0 to 10% butadiene to serve as an impact-modifying termonomer. 

This tendency is related to the polarization properties of the monomer substituents (42). Monomers that are dissimilar in polarity tend to form alternating monomer sequences in the polymer chain. An example is the monomer pair acrylonitrile—styrene. Styrene, with its pendent phenyl group, has a relatively electronegative double bond whereas acrylonitrile, with its electron-withdrawing nitrile group, tends to be electropositive. 

Carbon Cha.in Backbone Polymers. These polymers may be represented by (4) and considered derivatives of polyethylene, where n is the degree of polymeriza tion and R is (an alkyl group or) a functional group hydrogen (polyethylene), methyl (polypropylene), carboxyl (poly(acryhc acid)), chlorine (poly(vinyl chloride)), phenyl (polystyrene) hydroxyl (poly(vinyl alcohol)), ester (poly(vinyl acetate)), nitrile (polyacrylonitrile), vinyl (polybutadiene), etc. The functional groups and the molecular weight of the polymers, control thek properties which vary in hydrophobicity, solubiUty characteristics, glass-transition temperature, and crystallinity. 

Nitrile Rubber. Nitrile mbbers are made by the emulsion copolymerization of acrylonitrile (9—50%) and butadiene (6) and designated NBR. The ratio of acrylonitrile (ACN) to butadiene has a direct effect on the properties on the nature of the polymers. As the ACN content increases, the oil resistance of the polymer increases (7). As the butadiene content increases, the low temperature properties of the polymer are improved (see Elastomers, SYNTHETIC-NITRILE RUBBER). 

Nittile mbber is much like SBR in its physical properties. It can be compounded for physical strength and abrasion resistance using traditional fillers such as carbon black, siUca, and reinforcing clays. The primary benefit of the polymer is its oil and solvent resistance. At a medium ACN content of 34% the swell in IRM 903 oil at 70°C is typically 25—30%. Nitrile mbber processes on conventional mbber equipment and can be compression, transfer, or injection molded. It can also be extmded easily. 

Copolymers of acrylonitrile [107-13-1] are used in extmsion and molding appHcations. Commercially important comonomers for barrier appHcations include styrene and methyl acrylate. As the comonomer content is increased, the permeabiUties increase as shown in Figure 3. These copolymers are not moisture-sensitive. Table 7 contains descriptions of three high nitrile barrier polymers. Barex and Cycopac resins are mbber-modified to improve the mechanical properties. 

A.C7ylonitnk Content. Standard grades available ia the market contain between 15 to 50% acrylonitrile. The acrylonitrile content of nitrile mbber has a significant effect on two properties chemical resistance and low temperature performance. As the acrylonitrile content of the polymer is iacreased, the chemical resistance is improved whereas the low temperature properties are diminished. 

Third Monomers. In order to achieve certain property improvements, nitrile mbber producers add a third monomer to the emulsion polymerization process. When methacrylic acid is added to the polymer stmcture, a carboxylated nitrile mbber with greatly enhanced abrasion properties is achieved (9). Carboxylated nitrile mbber carries the ASTM designation of XNBR. Cross-linking monomers, eg, divinylbenzene or ethylene glycol dimethacrylate, produce precross-linked mbbers with low nerve and die swell. To avoid extraction losses of antioxidant as a result of contact with fluids duriag service, grades of NBR are available that have utilized a special third monomer that contains an antioxidant moiety (10). FiaaHy, terpolymers prepared from 1,3-butadiene, acrylonitrile, and isoprene are also commercially available. 

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