| Abstract
| - In a series of neutron reflectivity experiments, we studied the fundamental process of diblockformation during reactive blending processes of an immiscible blend comprised of normal polysulfone(hPSU) containing 30% reactive end group-modified deuterated polysulfone (dPSU−R) and polyamide(PA). Diblock formation (dPSU-b-PA) and dPSU−R enrichment at the interface between the incompatiblepolymers were monitored in thin bilayer films using neutron reflectivity. These results are compared toexperimental results obtained with bilayer films of pure nonreactive deuterated PSU (dPSU) and PAand pure reactive dPSU−R and PA, respectively. The interfacial width in the pure reactive system isslightly larger than that in the pure nonreactive system, indicating the formation of a diblock copolymerat the interface of the reactive system. The results for the diluted system (30% dPSU−R + 70% hPSU)show an enrichment of the deuterated species at the interface. The amount of dPSU−R at the interfacerises from 30 vol % initially, up to an equilibrium value of 47 vol % after annealing at 210 °C withinabout 30 min. This is interpreted as the formation of diblock copolymer out of the reactive components,dPSU−R and PA, as an interfacial reaction. Annealing at T = 210 °C for substantially longer timesreveals no further evolution of the interfacial profile, indicating that the diblock, once formed, stayslocalized at the interface. The formation of a diblock monolayer with complete coverage of the interfacialarea is not observed. This is probably due to steric hindrance and strong segregation of the diblock betweendPSU−R and PA. The block copolymer layer once formed at the interface suppresses the approach ofadditional dPSU−R homopolymer toward the interface due to the conformational entropy costs to thehomopolymer and block copolymer already at the interface. For these reasons, it is possible to diminishbut not eliminate the interfacial tension (γ> 0) between the PSU and PA, as it is not possible to buildup a large enough normalized surface excess, z*/Rg< 1, of dPSU-b-PA.
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