Thermo-responsive and emulsifying properties of poly(N-vinylcaprolactam) based graft copolymers

Thermo-responsive graft copolymers have been synthesized based on a poly(N-vinylcaprolactam) (PVCL) backbone and either hydrophilic poly(ethylene oxide) (PEO) or hydrophobic poly(tetrahydrofuran) (PTHF) side chains. The phase separation behavior of the graft polymers in water was studied by transmittance measurements and compared to that of the corresponding swollen segmented polymer networks and aqueous solutions of both polymers. The influence of the concentration and length of the grafts on the cloud point temperature (T-CP) has been demonstrated. PVCL-g-PTHF copolymers have been synthesized by using the macromonomer technique, i.e. the radical copolymerization of VCL with a PTHF macromonomer. A special feature of these amphiphilic graft copolymers is their ability to stabilize aqueous emulsions below the T-CP and to suddenly break them above the T-CP. PVCL-g-PEO copolymers were prepared by a grafting onto method. First, succinimide groups were introduced in the backbone, to which amino terminated PEO chains were grafted in the second step. This leads to dihydrophilic copolymers that become amphiphilic after heating their aqueous solutions above the T-CP.