INCORPORATION OF C-60 INTO POLY(METHYL METHACRYLATE) AND POLYSTYRENE BY RADICAL-CHAIN POLYMERIZATION PRODUCES BRANCHED STRUCTURES

Polymerizations of styrene and methyl methacrylate (MMA) containing 1 wt % C-60 initiated by 5 or 10 mol of azobis(isobutyronitrile)/mol of C-60 in 1,2-dichlorobenzene solution produce brown polymers in 53 - 97 % yield with all of the C-60 incorporated, linear polymer equivalent m olecular weights of P-n = 19 000 - 31 000, and P-w/P-n < 2. There are short induction periods before polymerization begins. All of the C-60 is incorporated into the polymer after low conversion of the monomer. Multidetector size exclusion chromatography analyses measured polymer mass by differential refractive index, IM,by two-angle laser light sca ttering, intrinsic viscosity by differential viscometry, and mass of o nly C-60 derivatives by UV. Molar chromatograms show that all of the p olymer at the high end of the molecular weight distributions contains C-60, and there are sizeable amounts of a lower molecular weight linea r polymer. The high molecular weight polystyrene contains as many as 1 0 - 100 C-60 units, but the high molecular weight PMMA contains an ave rage of one C-60 unit per macromolecule. All of the polymers have lowe r intrinsic viscosities and higher M-w than linear standards of the sa me retention volume due to branched or star structures. Calculations f rom a random branching model of Zimm and Stockmayer indicate that the PMMAs have an average branch number of five over the entire molecular weight distribution and systematically increasing average branch lengt hs with an increasing degree of conversion.