Phase Separation of Aqueous Poly(2-dimethylaminoethyl methacrylate-block-N-vinylcaprolactams)

Details of the phase separation of the poly(N-vinylcaprolactam) (PVCL) homopolymers and block copolymers of PVCL and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) were studied in aqueous buffer solutions. Phase separation occurred at either one or two temperatures depending on pH. The lower critical solution temperature of PVCL can be fine-tuned by varying the molecular weight of the block, whereas the phase separation temperature of the PDMAEMA block is strongly dependent on pH. The enthalpies of the collapse of the PVCL homopolymer and PVCL-b-PDMAEMA block copolymers were measured and show that the blocks phase separate independently upon heating. PVCL is known to bind amphiphilic cations, and correspondingly, according to light scattering, the block copolymers dissolve as single molecules but also form aggregates at room temperature. At temperatures above the cloud points of both blocks, only homogeneous large aggregates were observed. Zeta potential measurements confirmed that, upon heating, PDMAEMA blocks turn out from the collapsed PVCL globule toward the aqueous phase.