Modified thermosets core-shell particles

Core-shell rubber (CSR) particles are prepared by emulsion polymerization, and typically exhibit two or more alternating rubbery and glassy spherical layers (Lovell 1996 Chapter 8). These core-shell particles are widely used in thermoplastics, especially in acrylic materials (Lovell, 1996), and have also been used to modify thermosets, such as epoxies, cyanates, vinyl ester resins, etc. (Becu et al., 1995). 

Use of nanotechnology is also found in thermosets where a new generation of nanoscale silicone and core-shell particles is dramatically modifying the properties of heat resistant thermosets. Even small additions of the particles can significantly increase the fracture toughness and impact strength of reactive resin and other plastics. 

Another procedure for the preparation of modified thermosets consists of introducing preformed particles in the initial formulation. This technique is also well documented for modified thermoplastics (Paul and Bucknall, 2000). In Chapter 7 different macromolecular architectures such block copolymers, crosslinked microparticles, hyperbranched polymers, and den-drimers, were presented (Fig. 7.11). All these compact molecules can be used as thermoset modifiers. Thermoplastic powders and core-shell polymers are the more accessible preformed molecules. Some examples are given below. 

A crosslinked rubber may be synthesized at the surface of the glass beads to produce a core-shell structure (glassy core and rubbery shell). Thermosets modified with these particles showed a strong toughening effect for an optimum thickness of the rubbery shell (Amdouni et al., 1992). 

Although no generalization can be performed, it is of interest to assess that modifiers with end-groups reacting with the thermosetting polymer [107] lead to a salami structure inside dispersed phase particles, whereas non-functional-ized modifiers lead to a core-shell structure, i.e. a rigid core surrounded by an... 

A high degree of toughening may be attained by the use of CSR particles as modifiers of thermosetting polymers. This is because several adjustable parameters - the chemical structure and size of the core the number, chemical structure, and thickness of shells and the possibility of crosslinking... 

---