Average molecular heights, moments, and polydispersity indices were calculated for irreversible linear condensation polymerization in an ideal continuous- flow-stirred-tank reactor with variant reaction rate depending on its chain length. Exact solutions were obtained for the case when only monomer has a different reactivity from iris homologues. A new model for chain length dependence in form of k(1+q² mn) was considered to give limited molecular weights within a finite residence time, and limited polydispersity index. The reason is that there is a limitation of residence time for CSTR to give us the proper analytic solution. For comparison it is worthwhile to remember that a batch reactor gives us infinite molecular weight within a finite time instead.