Toughening agents acrylic rubbers

The homopolymers, which are formed from alkyl cyanoacrylate monomers, are inherently brittle. For applications which require a toughened adhesive, rubbers or elastomers can be added to improve toughness, without a substantial loss of adhesion. The rubbers and elastomers which have been used for toughening, include ethylene/acrylate copolymers, acrylonitrile/butadiene/styrene (ABS) copolymers, and methacrylate/butadiene/styrene (MBS) copolymers. In general, the toughening agents are incorporated into the adhesive at 5-20 wt.% of the monomer. 

Two ASA polymers were studied Luran S 757R and Luran S 776S both were made by BASF. The polymers have similar SAN matrices but respectively contain ca. 30 and 40% of the acrylic rubber-toughening agent. The ABS polymer (ABS 500) was made by the Dow Chemical Co. It contained SAN-filled rubber particles ca. 1.0 /an in diameter, suggesting that it was manufactured by bulk or suspension polymerization. 

Their J-39 adhesives are room-temperature curable, second-generation acrylics (16). Methyl methacrylate is the monomer, and a nitrile rubber and Dow ABS resin are used as toughening agents. This family of adhesives have been used in automotive, machinery and aerospace structures. Their J-50 adhesives (17) are two-component, fast-cure acrylics. In addition, they also developed a special adhesive, J-15 structural adhesive, for hydroplanes. 

In rubber toughening, an elastomeric modifier is incorporated into the epoxy matrix as a second phase (as discussed in Chapter 4), which is why improvement in toughness is achieved without a significant sacrifice of the and mechanical properties. The toughening agents reported so far can be classified as commercial, other rubber-based, acrylate-based and hyperbranched polymer-based modifiers. 

The most common preformed rubber particles used as a toughening agent for epoxy polymers are the so-called structured, core-shell latex particles (Figure 4). These particles typically have a polybutadiene-based core and an acrylate-based shell. Such additives can be purchased as powders from Rohm and Haas or Elf-Atochem and can be purchased as epoxy concentrates from the Dow Chemical Company. The key parameter for these modifiers is the composition of the shell polymer, since the shell chemistry plays a crucial role in the overall blend morphology. It should be noted that it is possible to obtain commercial core-shell latex particles with reactive groups in the shell for improved dispersion of the rubber particles. 

Reactive acrylic adhesives generally consist of a solution of a toughening rubber (chlorosulphonated polyethylene) in a partly polymerized mixture of monomers this is mainly methylmethacrylate but ethane diol dimethacrylate is added as a cross-linking agent. The remaining monomer is polymerized in a free radical chain polymerization redox initiation involves an organic peroxide and a tertiary amine. Acrylic cements consist of a partly polymerized acrylic monomer containing an initiator. Cure is established by the thermal or UV decomposition of the initiator (see Radiation-cured adhesives). 

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