As interconnected, flexible systems they are, polymers manifest interesting cooperative dynamics in certain confined environments, external fields and noises. Its cooperative dynamics is important, no only in understanding how a biological system self-organizes by manipulating its flexible degrees of freedom, but also in a multitude of applications such as gene and drug deliveries, DNA separation, and biopolymer sequencing, etc. I will briefly review two related topics we have studied: 1) polymer translocation through a pore in a membrane, 2) dynamics of polymer surmounting potential barriers. Derived from our theoretical studies, novel methods of separating DNA utilizing its coil-to-stretch transition will be suggested. I will discuss how such methods can be realized in modulating electric fields and micro-fluidic channel .