INFLUENCING POLYMER PROPERTIES BY REGIOSPECIFIC COMPLEXATION

ABA block-copolymers in which the A segments are capable of forming co mplexes and B is a non-complexing segment, have been used to prepare p olymer materials with properties that can be changed by adding a compl exing agent. The complex forming segments were poly(ethylene oxide) (P EO), linear polyethylenimine (LPEI) and poly(N-tert-butylethylenimine) (PTBEI). Commercially available liquid ABA block-copolymers, in which A is PEO and B is poly(propylene oxide), were investigated with high molar mass poly(acrylic acid) (PAA) as the complexing agent for PEO. I t was found that the mixtures containing 3 to 7 wt.-% of PAA, showed a marked shear-thickening behavior leading eventually to gelation. This was attributed to the transformation of intramolecular polymer comple xes, at low shear rates, to intermolecular complexes, at high shear ra tes, due to the chain stretching of PAA. ABA copolymers in which A is LPEI or PTBEI and B polytetrahydrofuran (PTHF), were prepared. Complex ation of these copolymers with low molecular weight poly-acids or PAA in polar and non-polar solvents as well as in bulk have been investiga ted. ABA copolymers in which A is PEO and B a PTHF segment were prepar ed. These block-copolymers show two melting points : one at appr. 55 d egrees C, due to the PEO segments, and one at appr. 30 degrees C due t o the PTHF. Upon addition of alkali metal salts such as sodium iodide or sodium thiocyanate, complexes with PEO are formed and as a conseque nce, the melting point of the PEO segments shifts to appr. 160 degrees C. The complexed materials behave as thermoplastic elastomers up to t hat temperature.