Three types of conjugated polymers, poly(PZ-Pi), poly(PZ-BPI) and poly(PZ-NPI) were synthesized by Schiff-base reaction. These new conjugated polymers exhibited improved solubility in common organic solvents due to the presence of alkyl side chains as well as azomethine groups, Double layer LEDs made with the synthesized polymers as emitting layer and $Alq_3$, as electron transporting layer exhibited enhanced EL emission and efficiency compared to those of single layer LEDs. Double layer LEDs exhibited gradual shift in the emission peak th the single layer LED, made of only $Alq_3$ as the emitting layer as the thickness of $Alq_3$ layer increased.