The present disclosure relates to compositions and methods for isolating nucleic acids from a sample comprising nucleic acids, such as physiologically relevant samples or environmental samples. The sample can be incubated with a population of polymers that bind the nucleic acids to form a coacervate in a liquid-liquid phase separated solution. Incubation can be performed at a temperature above a concentration dependent phase separation transition temperature of the polymers. The resulting coacervate can be decanted from the liquid-liquid phase separated solution. The nucleic acids can be separated from the polymers by adding a salt solution, adjusting the pH, or both to disrupt an electrostatic interaction between the nucleic acids and the polymers.