  We calculate the longitudinal polarizations of hyperons in high $p_\perp$
jets in $pp$ collisions in which one of the protons is longitudinally polarized
at RHIC energies using different models for the spin transfer in fragmentation
process. The results show that the measurements of these polarizations can be
used to study the spin transfer in high energy fragmentation processes in
general and to test the different models in particular. Our results show
especially that the magnitude of the polarization of $\Lambda$ is rather small
whereas that of $\Sigma^+$ is considerably larger in the large rapidity region.
The differences between the results from different pictures for $\Sigma^+$
polarizations is also much larger. Hence, the measurement of $\Sigma^+$
polarization should be more effective to distinguish between different models
especially the SU(6) or the DIS picture for spin transfer in fragmentation
processes.
