Butadiene-acrylonitrile copolymers cross-linking

Dimethacrylates form highly cross-linked and, therefore, brittle polymers. To overcome brittleness, manufacturers often blend dimethacrylates with polyurethanes or other polymers such as low-molecular-weight vinyl-terminated butadiene-acrylonitrile copolymers and chlorosulfonated polyethylene. The modified dimethacrylate systems provide tough adhesives with excellent properties. These can be formulated as two-component adhesives, the catalyst component being added just prior to use or applied separately to the surface to be bonded. One-component systems also have been formulated which can be conveniently cured by ultraviolet radiation. 

Acrylonitrile-butadiene-styrene/acidic monomer, an elastomeric copolymer Cross-linked polyethylene Extra-strength molding compound... 

Decker, C. and Nguyen thi viet, T., Photo-cross-linking of functionalized rubbers X. Butadiene-acrylonitrile copolymers, J. Appl. Polym. ScL, 2001, 82, 2204-2216. 

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

The term ABS was originally used as a general term to describe various blends and copolymers containing acrylonitrile, butadiene and styrene. Prominent among the earliest materials were physical blends of acrylonitrile-styrene copolymers (SAN) (which are glassy) and acrylonitrile-butadiene copolymers (which are rubbery). Such materials are now obsolete but are referred to briefly below, as Type 1 materials, since they do illustrate some basic principles. Today the term ABS usually refers to a product consisting of discrete cross-linked polybutadiene rubber particles that are grafted with SAN and embedded in a SAN matrix. 

Butadiene and isoprene have two double bonds, and they polymerize to polymers with one double bond per monomeric unit. Hence, these polymers have a high degree of unsaturation. Natural rubber is a linear cis-polyisoprene from 1,4-addition. The corresponding trans structure is that of gutta-percha. Synthetic polybutadienes and polyisoprenes and their copolymers usually contain numerous short-chain side branches, resulting from 1,2-additions during the polymerization. Polymers and copolymers of butadiene and isoprene as well as copolymers of butadiene with styrene (GR-S or Buna-S) and copolymers of butadiene with acrylonitrile (GR-N, Buna-N or Perbunan) have been found to cross-link under irradiation. 

Experimental results show that at low grafting temperature (30°C) the solubility of grafted polymers is highly modified by butadiene-acrylonitrile chains. Precipitation curves look like those of polymers prepared using dichloroethane and therefore seem compatible with a less cross-linked BD-AN chain structure. At high grafting temperature (70°C), the precipitation curve resembles that obtained with DVB crosslinked copolymers. 

Styrene serves as the monomer for the well-known polymer—polystyrene. It also serves as the source of many copolymers, that is polymers made from two monomers at varying compositions, such as SAN = styrene-acrylonitrile SBR = styrene-butadiene rubber (the major synthetic rubber) SBS = styrene-butadiene-styrene (a modem family of thermoplastic mbbers which are not cross-linked) and the well-known terpolymer ABS which is based on 3 monomers—acrylonitrile-butadiene-styrene. 

In the first one, the two materials are blended on a rubber mill or in an internal mixer. Blending of the two materials can also be achieved by combining emulsion latexes of the two materials together and then coagulating the mixture. Peroxide must be added to the blends in order to achieve some -cross-linking of the elastomer to attain optimum properties. A wide range of blends are made by this technique with various properties [201]. Most common commercial blends of ABS resins may contain 70 parts of styrene-acrylonitrile copolymer (70/30) and 40 parts of butadiene- litrile rubber (65/35). 

The structures listed in Table 1.5 are divided into three categories short sequences, long sequences, and networks. Within the first category, a sequence of placement of individual CRU is considered, within the second the placement of long sequences of CRU defines the copolymer type, while to the third belong cross-linked networks, cross-linked polymers, and chemical-type interpenetrating polymer networks. The network is a cross-linked system in which macromolecules of polymer A are cross-linked by macromolecules of polymer B (Sperling 1992). The composition can be expressed as, e.g., block-co-poly(butadiene/styrene) (75 25 wt%) or grq/if-co-poly[isoprene/(isoprene acrylonitrile)] (85 15 mol%). 

ABS (acrylonitrile-butadiene-styrene) plastics are actually a type of partially grafted copolymer, similar to HIPS but more oil resistant because of the polar acrylonitrile, and with significantly higher impact resistance. It can be made by several methods, through emulsion polymerization, suspension polymerization, or bulk polymerization, but the most important method utilizes emulsion polymerization. In this case a seed latex of cross-linked polybutadiene is made, which constitutes up the core of the latex. This is followed by the addition of a mix of styrene and acrylonitrile monomers, usually 72/28 or similar in weight, respectively, followed by continued polymerization to form the shell of the latex particle. 

In this chapter the homopolymer, polystyrene, is considered together with styrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene copolymers and styrene-a-methylstyrene copolymers. The important styrene-butadiene copolymers are described with other diene polymers in Chapter 18. The use of styrene in the cross-linking of unsaturated polyesters is described in Chapter 10. 

An alternative method of preparing a blend of the two copolymers is by mixing the solids on a two-roll mill. In this case, a non-cross-linked acrylonitrile-butadiene rubber may be used as starting material. The rubber is firstly cross-linked by milling with a peroxide and then the styrene-acrylonitrile copolymer is added. 

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