Reactive Compatibilization of SAN/EPR Blends. 1. Dependence of the Phase Morphology Development on the Reaction Kinetics

Abstract

SAN containing 20 wt % of reactive SAN-X has been melt blended with EPDM containing 50 wt % of EP chains grafted by maleic anhydride (EP-g-MA). Two types of reactive groups (X) have been attached to SAN (2 mol % of X), i.e., a primary amine and a precursor of it at the processing temperature, i.e., a carbamate. The SAN/rubber weight composition was kept constant at 75/25. The development of the phase morphology from pellet-sized rubber particles to dispersed submicrometer droplets has been investigated during reactive mixing for the two types of reactive SAN and has been found to depend on the interpolymer reaction rate and thus on the relative reactivity of the amine and the carbamate groups attached to SAN toward the maleic anhydride function of EP.

Particle-in-particle morphology for the dispersed phase formed in reactive compatibilization of SAN/EPDM blends

“…Then, SAN can be trapped within these rubber particles on the occasion of coalescence and be ultimately stabilized by the slowly progressing interfacial reaction. This mechanism is consistent with the increasing formation of sub-inclusions with mixing time, as shown elsewhere [23]. Thus the sub-inclusions should be formed not during melting and softening of the blend components [6][7] but rather in the later stage of mixing (when coalescence predominates).…”

“…The advantage of this reaction was to produce the primary amine in situ, thus during the melt processing. At the usual mixing temperature of 200°C, the rate constant of the carbamate thermolysis was found to be 0.0084 min −1 [23].…”

“…SAN-carb) can be derivatized into primary amines (i.e. SAN-NH 2 ) either in solution prior to blending [13] or in situ during the melt process [14]. In solution, this deprotection was carried out in a dioxane-HCl (12 N) (2:1) mixture at room temperature.…”

“…This discrepancy suggests that the stiffness of the polyblends is not governed exclusively by the rubber dispersion. From the comparison of the rubber particle diameter, the shear storage modulus and the wt% of SAN occluded in the EPR phase (as determined by image analysis, [23]) in Table 3, it appears that E is inversely proportional to the wt% of occluded SAN at constant particle size. Indeed, for particle size of ca.…”

“…2 is a typical illustration of the difference observed in the phase morphology when SAN-carb is used rather than SAN-NH 2 , all the other conditions being the same. Since the solid rubber pellets have been added into the melted SAN major phase in order to avoid phase inversion and thus formation of SAN sub-inclusions in the rubber, the observation must result from the coalescence of poorly stabilized rubber particles [23]. Indeed, when the compatibilization reaction is slow compared to the phase dispersion, the SAN-g-EP copolymer is not formed in sufficient amounts to stabilize the interface and to inhibit the EPR particles coalescence.…”