Graft copolymer synthesis advantages

Polymeric initiators based on azo or triazene modified poly(organosiloxane)s can be used to synthesize graft copolymers with silicone backbone and thermoplastic side chains. The azo functionality has some advantages such as lower thermal stability, known reaction mechanism, no homopolymer formation and cleaner graft products. However, the synthesis of the triazene polymeric initiators requires fewer synthetic steps. The graft products microseparate but form stable films. 

Interest in this area was aroused after 1980. Three recent reviews summarize the research in this field (202-204). They also present the advantages of this synthetic method in comparison with other techniques for the synthesis of graft copolymers. Among radical, anionic, and cationic types of polymerization, cationic polymerization seems to be the most successful for the synthesis of polymerizable oligomers. 

Thermogels that take advantage of the hydrolytic properties of polyacetals have also been explored. Schacht et al. have reported the synthesis of graft copolymers comprised of a polyacetal backbone with pendant PEG chains. Incorporation of FITC-BSA at 1 wt.% into the thermogels resulted in a sustained release over about 100 days at pH 7.4 and 40 days at pH 5.5. Release of FITC-BSA occurred by a process that appears to be erosion-controlled [8]. 

The controlled synthesis of poly(norbomene-g-/i-butyl acrylate) started from the same poly(NB-co-NB-Br) macroinitiator and took advantage of the high efficiency displayed by Ru(Cp )Cl(PPh3)2 (Cp = pentamethylcyclopentadienyl) (5) in the polymerisation of acrylates. The final graft copolymers were produced with narrow molecular weight distributions (MJM were around 1.2-1.3). 

Because such polyether spacer polymers are also of interest in other fields of polymer-supported immobilization, the first reports published on the synthesis of polystyrene graft copolymers date back to almost one decade agp [111,112]. In fact, these graft supports have been applied successfidly in f ds where insoluble polymers with homogeneous phase reacticais are advantageous, e.g., for phase-transfer reactions [113-116]. 

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