Multiresponsive polymers that can respondt o severale xternals timulia re promising materialsf or am anifold of applications. Herein, af acile method for the synthesis of triple-responsive (pH, temperature, CO 2 ) poly(N,N-diethylaminoethyl methacrylamide) by ap ostpolymerizationa midation of poly(methyl methacrylate) (PMMA)i sp resented. Combined with trivalent counterions ([Fe(CN) 6 ] 3À )b oth an upper and lower criticals olution temperature (UCST/LCST)-type phase behaviorc an be realized at pH 8a nd 9. PMMA and PMMA-based blockc opolymers are readily accessible by living anionic and controlled radicalp olymerization techniques, whicho pens access to various responsive polymer architectures based on the developed functionalization method. This method can also be applied on melt-processed bulk PMMA samples to introduce functional, responsive moieties at the PMMA surface.Stimuli-responsiveo r" smart" polymers, which can change their physicochemical properties (e.g.,s olubility) upon applyinga n externals timulus (pH, temperature, light, magnetic fields, CO 2 , etc.), are highly attractivea nd intensively studied materialsd ue to the wide range of applications, such as responsive micelles and micro/nano-gels for biomedical applications, switchable membranes and coatings, smarta ctuators, or CO 2 sensing. [1][2][3] The most prominent examples of multi-responsive polymers are basedo nm ethacrylate or acrylamide-type monomers with pendant N,N-dialkylaminog roups (alkyl = methyl, ethyl, iso-[a] C.Figure 3. Ta iloring the thermo-responsive solution behaviorofP DEAE-MAm 1030 (c = 1gL À1 )int he presence of trivalent [Fe(CN) 6 ] 3À counterions. A) UCST-and LCST-typephase transitions in dependence of pH for two different K 3 [Fe(CN) 6 ]c oncentrations( c = 0.5 mm (squares), c = 0.75 mm (circles)) and B) in dependence of K 3 [Fe(CN) 6 ]c oncentration in pH 8b uffer solutions.