STRUCTURAL RIGIDITY CONTROL IN ARBORESCENT GRAFT POLYMERS

Successive chloromethylation-anionic grafting sequences on polystyrene have led to well-defined hyperbranched macromolecules. Polymers with branching functionalities f > 5000 and molar masses over 10(7) g/mol w ere thus prepared while maintaining a ratio of mass- to number-average molar masses M(w)BAR/M(n)BAR = 1,1-1,3. Three series of styrene polym ers were prepared by varying the density of grafting sites along the c hain, resulting in controllable stiffening of the molecular structure. Characterization of the branched molecules by size-exclusion chromato graphy/low-angle laser light scattering and light scattering confirmed a geometric increase in molar mass for successive generations, and a low ratio of mass- to number-average molar masses. Static and dynamic light scattering experiments showed that the molecules behave like har d spheres in dilute solutions. Measurements in the semidilute range, h owever, showed a progressive structural stiffening effect as the branc hing density increases.