Molecular Weight of the Compatibilizer Precursors

This molecular characteristic feature is of a prime importance, since it has a direct influence on the blend viscosity, and in turn on the phase morphology development and the compatibilization reaction. According to the Fortelny equation (Eq. 4.1), the decrease in the molecular weight and thus in the viscosity of the matrix decreases the dispersive forces at the origin of the particle break-up and the interface (available for reaction) generation, and makes the phase coalescence more favorable. Therefore, the surface area of the interface at which the compatibilization reaction occurs is partly controlled by the molecular weight of reactive polymers. 

Moreover, the melt viscosity (or polymer molecular weight) also acts on the general phase morphology, since the component of lower viscosity has marked tendency to encapsulate the second component in binary blends. As a rule, the composition at which the phase inversion occms is governed by the melt viscosity ratio, as predicted by the Jordhamo s equation [77]. 

The molecular weight of the reactive polymers, thus of the constitutive blocks of the compatibilizer, is also critical for efficient entanglements with the phases to be compa-tibilized. Indeed, good interfacial adhesion is essential for stress transfer from one phase to the other one to be efficient and for cracks initiated at the interface to be prevented from growth until catastrophic failure occurs. Kramer et al. studied the fracture mechanism of the polystyrene/poly(2-vinylpyridine) interface modified by the parent di-block copolymer. They found that the minimum degree of polymerization of PVP for entanglement (Npvp) was 255, below which the PVP block was pulled out in slow crack opening experiment [93, 94]. 

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