SYNTHESIS OF MACROCYCLIC POLYSTYRENE-POLYDIMETHYLSILOXANE BLOCK-COPOLYMERS

A series of macrocyclic polystyrene (PS)-polydimethylsiloxane (PDMS) b lock copolymers and similar block copolymers was synthesized by sequen tial polymerization of styrene and hexamethyl cyclotrisiloxane (D3) in itiated by a difunctional anionic initiator in THF at -78-degrees foll owed by coupling with Cl2SiMe2 in very dilute (10(5) - 10(-6) M) solut ions. Total molecular weights ranged from about 2-85 x 10(3). The form ation of monodisperse macrocyclic block copolymers was indicated by th e lower (15-30%) hydrodynamic volume of the rings compared to that of the linear block copolymers. Carbon-13 and Si-29 NMR likewise supporte d the absence of linear polymer in the macrocyclic block copolymer. Th e behavior of second virial coefficient A2 of the rings and the linear s versus temperature was examined by static light scattering in cycloh exane. Below 20-degrees the A2 for the linear polymer goes negative wh ile that for the cycle remains positive. Dynamic light scattering (DLS ) as a function of temperature also reflects that the cyclic polymers remain well solvated even down to 12-degrees-C. The DLS autocorrelatio n functions for the linear triblock however demonstrate the onset of a ggregation and phase separation as the temperature is reduced below 20 -degrees-C.