Epoxy Particles

With mixing, add to the particle suspension a quantity of ligand dissolved in coupling buffer in an amount that represents a 1-10 X excess over the molar quantity of epoxide groups present on the particles. 

React at room temperature (for sensitive ligands) or at 45-60°C (for more stable ligands) for at least 20 hours with mixing. 

Block excess epoxy groups by the addition of cysteine to a final concentration of 50 mM. Other small molecules can be used, provided they will efficiently react with the excess epoxides and not result in a modification that could interfere with the subsequent use of the particles. Continue the reaction with mixing for at least 2 hours. 

Wash the particles thoroughly with coupling buffer and then into a more moderate pH storage buffer containing a preservative. 

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For protocol suggestions on conjugation to epoxy groups, see Chapter 2, Sections 1.7 and 4.1. Also, see Chapter 14, Section 4.11, Coupling to Epoxy Particles, for a method to attach affinity ligands to surfaces that are activated with epoxide groups. 

Hyperbranched polymers (Boogh et al., 1999), and crosslinked microparticles based on acrylates and prepared in organic media (Pascault et al., 2000), give size particles in the range of 20-50 nm. Crosslinked epoxy particles made from a latex can be either small, 30-600 nm (Landfester et al., 2000) or very large 10-100 pm (Jansen et al., 1999). In every case the chemistry of the shell has to be controlled. 

Woo et al. (1994) studied a DGEBA/DDS system with both polysul-fone and CTBN. The thermoplastic/rubber-modified epoxy showed a complex phase-in-phase morphology, with a continuous epoxy phase surrounding a discrete thermoplastic/epoxy phase domain. These discrete domains exhibited a phase-inverted morphology, consisting of a continuous thermoplastic and dispersed epoxy particles. The reactive rubber seemed to enhance the interfacial adhesive bonding between the thermoplastic and thermosetting domains. With 5 phr CTBN in addition to 20 phr polysul-fone, Glc of the ternary system showed a 300% improvement (700 Jm-2 compared with 230 J m 2 for the neat matrix). 

Water is also sometimes used as a solvent for water-soluble resins. In the case of epoxy resins, water is generally used to disperse epoxy particles in an emulsion. These waterborne epoxy adhesives are discussed in Chaps. 4 and 14. 

Silyl-terminated polyether can be blended with epoxy resins to form elastic adhesives at room temperature.9 In this system, small rigid epoxy particles are chemically linked by an elastic poly ether phase. A typical formulation is shown in Table 8.4. Elongation and peel... 

The crystallization peak temperature increased when epoxy resin was added to polypropylene, that is, the uncured and cured epoxy particles acted as effective nucleating agents and accelerated the crystallization of PP in the blends. When cured dynamically, the smaller epoxy particles in the blends resulted in the increase in the number of nucleating agents and hence accelerated the crystallization of polypropylene. Blending polypropylene with epoxy resin resulted in the decrease of crystallinity of polypropylene and increased the melting temperature T of polypropylene than those of pure polypropylene. 

The micrographs of polypropylene/epoxy blends shown in Fig. 21.13 contain epoxy particles of diameter 3-4 pm dispersed in polypropylene matrix (70/30). When the blend was compatibilized with MAH-g-PP, fine epoxy particles with an average diameter of 1 pm were dispersed in the PP matrix, that is, the maleic anhydride group of the MAH-g-PP reacted with epoxy group to form a copolymer and acted as a compatibihzer (48). The reaction between the two groups was evident from torque measurements during mixing. 

The torque at equilibrium of the PP/MAH-g-PP/epoxy (60/10/30) blend was obviously higher than that of the PP/epoxy (70/30) blend due to the reaction between maleic anhydride (MAH) groups of MAH-g-PP and the hydroxyl or epoxy groups of the epoxy resin. Dynamic curing prevented the aggregation of epoxy particles resulting in a finer distribution of domains compared to PP/MAH-g-PP/epoxy blends (Fig. 21.13). 

Jan Jansen, B. J. P., Tamminga, K. Y., Meijer, H. E. H., Lemstra, P. J. Preparation of thermoset rubbery epoxy particles as novel toughening modifiers for glassy epoxy resins. Polymer 40... 

Zako, M. and Takano, N. (1999) InteUigent material systems using epoxy particles to repair microcracks and delamination damage in GFRP. Journal of Intelligent Material Systems and Structures, 10, 836-841. 

These observations are similar to those observed in a rubber-toughened epoxy system. Yamanka and co-workers [114] observed a phase-inverted co-continuous structure by decreasing the cure temperature in their PES-modified epoxy system. They reported that a decrease in the cure temperature slowed down the rate of phase separation (based on spinodal decomposition process) without significantly reducing the rate of the chemical reaction. This arrested the phase separation at an early stage of phase separation and finally resulted in an interconnected globular epoxy particle in a co-continuous modifier-rich matrix. 

Therefore, in the case of higher-molecular-weight PES systems, a quicker structural transition would result in a PES-rich gel with a lower molecular weight of epoxy particles and a smaller cluster size. This, in turn, would lead to a decrease in gel strength and an increase of the relaxation exponent. 

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