Synthesis and characterization of novel polystyrene-block-polyurethane-block-polystyrene tri-block copolymers through atom transfer radical polymerization

BACKGROUND: Radical polymerization is used widely to polymerize more than 70% of vinyl monomers in industry, but the control over molecular weight and end group of the resulting polymers is always a challenging task with this method. To prepare polymers with desired molecular weight and end groups, many controlled radical polymerization (CRP) ideas have been proposed over the last decade. Atom transfer radical polymerization (ATRP) is one of the successful CRP techniques. Using ATRP, there is no report on the synthesis of polystyrene-block-polyurethane-block-polystyrene (PSt-b-PU-b-PSt) tri-block copolymers. Hence this paper describes the method of synthesizing these tri-block copolymers. To accomplish this, first telechelic bromo-terminated polyurethane was synthesized and used further to synthesize PSt-b-PU-b-PSt tri-block copolymers using CuBr as a catalyst and N,N,N,N",N"-pentamethyldiethylenetriamine as a complexing agent. RESULTS: The 'living' nature of the initiating system was confirmed by linear increase of number-average molecular weight and conversion with time. A semi-logarithmic kinetics plot shows that the concentration of propagating radical is steady. The results from nuclear magnetic resonance spectroscopy, gel permeation chromatography and differential scanning calorimetry show that the novel PSt-b-PU-b-PSt tri-block copolymers were formed through the ATRP mechanism. CONCLUSION: For the first time, PSt-b-PU-b-PSt tri-block copolymers were synthesized through ATRP. The advantage of this method is that the controlled incorporation of polystyrene block in polyurethane can be achieved by simply changing the polymerization time. (C) 2007 Society of Chemical Industry.