Effect of compatibilizer concentration and weight fraction on model immiscible blends with interfacial crosslinking

Reactive compatibilization, in which a compatibilizer is formed by an interfacial coupling between two reactive polymers, is commonly used when blending immiscible homopolymers. We consider reactive compatibilization using two multifunctional reactive polymers, which leads to a crosslinked copolymer at the interface. Experiments were conducted on model blends of polydimethylsiloxane (PDMS) and polyisoprene (PI). Compatibilizer was formed by a chemical reaction between amine-functional PDMS and maleic anhydride-functional PI. Droplet-matrix blends with a PI: PDMS ratio of 30: 70 or 70: 30 and reactive compatibilizer loadings from 0.1% to 3% were examined by optical microscopy and rheometry. Experiments reveal that the effects of interfacial crosslinking are highly asymmetric, with PI-continuous blends showing altogether different behaviors from PDMS-continuous blends. The PI-continuous blends show unusual features including drop clusters and nonspherical drops. In contrast, PDMS-continuous blends displayed a typical droplet-matrix morphology with round drops that do not appear to stick together. The rheological properties are also asymmetric: The PI-continuous blend showed gel-like behavior in oscillatory experiments, high viscosity, and viscosity overshoots during startup of shear flow, whereas PDMS-continuous blends showed liquidlike behavior that is qualitatively similar to that of compatibilizer-free blends. We speculate that the observed structural and rheological asymmetry is attributable to the asymmetry of the compatibilizer architecture on the two sides of the interface. (C) 2011 The Society of Rheology. [DOI: 10.1122/1.3571549]