Particle tracking velocimetry (PTV) was used in conjunction with rheological measurements to investigate slip at polymer-polymer interfaces during and after startup shear using simple shear geometry, i.e., a sliding plate rheometer. Polymer pairs include styrene butadiene rubber (SBR) and polyisoprene (PI) of narrow molecular weight distribution, as well as a PI and polydimethylsiloxane (PDMS), with Flory interaction parameter chi approximate to 0.001 and chi approximate to 0.08 respectively. During startup shear, the SBR-PI pair was able to deform without interfacial failure up to a critical strain gamma = 2, revealing a level of interfacial strength consistent with thermodynamic considerations. This pair also exhibited arrested interfacial slip after shear cessation for high Weissenberg numbers when the step strain exceeds unity. In contrast, the PDMS-PI interface is much weaker, and slip occurs at gamma as low as 0.1. These results shed light on the nature of possible mechanical failure at interphases in multicomponent polymer systems during shear and after shear cessation.