Polymerization of 2-ethyl-2-oxazoline using di-, tetra-, and hexafunctional ruthenium tris(bipyridine) metalloinitiators

Ruthenium reagents with two, four, and six chloromethyl functionalities, [( bpy)(n)Ru-{bpy(CH2Cl)(2)}(3-n)](PF6)(2) (n = 0-2), were employed as multifu nctional metalloinitiators for the cationic polymerization of 2-ethyl-2-oxa zoline to generate orange, glassy polymers with narrow molecular weight (MW ) distributions. MWs were determined by GPC vs PMMA standards and for selec ted samples by GPC with multiangle laser light scattering (MALLS) detection . In-line diode array UV/vis spectroscopic analysis coupled with GPC MW det ermination confirms the presence of [Ru(bpy)(3)](2+) chromophores in the el uting polymers. Polymers are luminescent, and they exhibit thermal properti es analogous to the metal-free PEOX counterparts (T-g similar to 54 degrees C; onset of thermal decomposition at 365-385 degrees C). Unlike reactions run with a labile hexafunctional Fe initiator, reactions wherein MWs > 100K and degrees of polymerization (dp) > 200 are attainable, Ru-centered polym ers reach an upper MW limit of similar to 25K regardless of the number of f unctionalities on the initiator (difunctional, dp = similar to 125; tetrafu nctional, dp = similar to 63; hexafunctional, dp = similar to 42 per initia tor site). High monomer loadings and concentrations and elevated reaction t emperatures were explored to surmount this barrier, and control experiments using different combinations of components found in typical Ru reaction mi xtures are also described. Though M-n vs percent conversion plots are rough ly linear for the Ru initiators, observed MWs are lower than expected value s based on monomer/initiator loading. This may be due to poor correlation o f polyoxazolines with linear PMMA standards and/or to competing chain trans fer side reactions during the polymerization. Linear first-order kinetics p lots were obtained. Comparison of rate constants obtained from the slopes o f these plots reveals the trend expected for the targeted structures: hexa > tetra > di.