Incompatibility epoxy-elastomer

The carboxyl terminated polybutadiene (C-3000) is about equally effective to CTBN in heat distortion temperature and impact but considerably less effective in strength. From the haze data (the percent haze of ERL-4221 modified with 10 phr of CTBN and C-3000 were 17 and 85% respectively) it is quite clear that this elastomer (C-3000) is highly incompatible with the epoxy-hardener system in the cured state. A 2000 molecular weight polybutadiene elastomer, containing no carboxyl groups, was completely incompatible with the epoxy system and segregated in the cured state. 

Rubber as the Disperse Phase. In polyblend systems, a rubber is masticated mechanically with a polymer or dissolved in a polymer solution. At the conclusion of blending, a rubber is dispersed in a resin as particles of spherical or irregular shape. We can further subdivide this system into three classes according to the major intermolecular forces governing adhesion (a) by dispersion forces—e.g., the polyblend of two incompatible polymers, (b) by dipole interaction—e.g., the polyblend of polyvinyl chloride and an acrylonitrile rubber (56), and (c) by covalent bond—e.g., an epoxy resin reinforced with an acid-containing elastomer reported by McGarry (43). 

Block copol3nners form a new class of molecular composite materials by the phase separation of incompatible hard and soft segments which form their macro-molecular structure. Thermoplastic elastomers where the soft segments form the continuous phase have been extensively investigated by means of an adsorption-interdiffusion (A-I) model for the interfacial phase which bonds the hard and soft phases. The molecular structure and rheological activity of the interfacial phase in thermoplastic elastomer block copolymers is shown to play a dominant role in nonlinear viscoelastic response, mechanical hysteresis and energy absorption. Creation of elastomeric microphases in epoxy structural adhesives has been recently identified with in situ block copol3nnerization between carboxy terminated nitrile (CTBN) rubber and the diepoxide. 

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