Thermal decomposition kinetics and structure of novel polystyrene clusterswith MTEMPO as a branching agent

Polystyrene clusters were prepared by using a trace amount of 4-methacryloy loxy-2,2,6,6-tetramethylpiperidine-1-oxy (MTEMPO) as a branching agent. Suc h clusters can undergo a thermal decomposition into linear chains at temper atures higher than 100 degreesC. The thermal decomposition was studied by a combination of static and dynamic laser light scattering (LLS). The time d ependence of the weight-average molar mass (M-w), the root-mean-square z-av erage radius of gyration ([R-g(2)](z)(1/2), and the average hydrodynamic ra dius ([R-h]) was used to monitor the decomposition kinetics and cluster str ucture. It has been found that M-w proportional to t(-alpha), and the decom position can be roughly divided into three stages; namely, from large clust ers to smaller ones; from smaller clusters to less-branched ones; and final ly to short linear chains. The scaling of [R-g] proportional to M-w(0.33 +/ - 0.01) in the first stage indicates that these clusters are uniform in den sity, which is rare and much different from conventional polymer clusters w hose density decreases from center to periphery. Moreover, we observed, for the first time, that [R-g]/[R-h] proportional to M-w(-0.20 +/- 0.01), reve aling that even for a uniform cluster swollen in a good solvent, its periph ery is still more hydrodynamically draining.