Open loop PWM with SG3525
I need a open loop system where I can Vary the PWM duty cycle within
the range using a potentiometer without taking a sample from output.
Is it possible with this chip?

Clues are in the data sheet such as this lab test fixture: -

Look bottom left and you'll see a switch that can be set to position 1 - this applies a 10 kohm feedback resistor to the error amplifier and then allows you to set the PWM output with the potentiometer shown top left.