Acrylate-Based Toughening Agents

Commercially available liquid rubber (CTBN, ATBN)-toughened epoxy often shows outstanding fracture properties, and the technology is exploited in engineering adhesives [58]. However, because the butadiene component of the elastomer contains unsaturation, it would appear to be a site for premature thermal and/or oxidative instability, and such modified resins are not suitable for application at high temperature. One would imagine that excessive crosslinking could take place with time which would detract from otherwise desirable improvements accomplished with these structures. Second, there is some limitation in its use due to a possibility of the 

Functionalised acrylic oligomers can be shown to exhibit considerable utility as 

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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. 

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