Structurally controlled polymers with ultimate precision - Synthesis, characterization and properties

The fusion of polymer synthesis and characterization and their interactive stimulation is inevitable not only for the formation of polymers with highl y controlled structures but also for the development of polymer characteriz ation, thereby bringing about the spiral progress of both fields. As a typi cal example of precise polymer synthesis, the preparation of uniform PMMA w ith 100% isotacticity is described. Stereospecific living polymerization of 1-phenyldibenzosuberyl methacrylate with methyl alpha-lithioisobutyrate in tetrahydrofuran at -78 degrees C gave an isotactic polymer with narrow mol ecular weight distribution. The PMMA derived therefrom was found by 750 MHz H-1 NMR spectroscopy to consist of 89% of the PMMA which is 100% isotactic in the whole chain, and 11% of the PMMA which is 100% isotactic in the cha in with only one raceme diad at the initiating chain end. The PMMA was frac tionated into uniform PMMAs by supercritical fluid chromatography. The isot actic uniform PMMAs, crystallized from methanol solutions, showed the degre e of crystallinity close to 100%. Highly syndiotactic PMMA was derived from poly(tri-methylsilyl methacrylate) prepared with t-C4H9Li/bis(2,6-di-t-but ylphenoxy)methyl-aluminum in toluene at -95 degrees C. Stereocomplex format ion of isotactic and syndiotactic uniform PMMAs were studied by on-line GPC /NMR measurements at 750 MHz and -15 degrees C in acetone/acetone-d(6). Ste reocontrol of ditactic polymers of crotonates (structural isomers of methac rylates) has been achieved far several polymerization systems, Le., threodi isotactic, disyndiotactic, and diheterotactic polymerizations, which demons trates another state-of-the-art structural control at ultimately high level .