The α-termini of RAFT-derived thermoresponsive polymers were functionalised via thiol exchange with pyridyl disulfide. Addition of hydrophilic end-groups dramatically increased the observed cloud point of the polymers, without changing the composition of the main chain. Selective cleavage of the disulfide-linked end-groups was observed under conditions intended to mimic intracellular glutathione concentration. This allowed the thermoresponsive behaviour to be 'switched on' without the need for a temperature stimulus - an 'isothermal' switch.