EFFECT OF TERMINAL BLOCK ON THE MICROFLUIDIZATION INDUCED DEGRADATION OF A MODEL A-B-A BLOCK COPOLYMER

The effect of high shear and turbulent processing on the mechanical degradation of a model series of A-B-A block copolymers was studied. Pluronic(R) L64, L63 and L62 were microfluidized (80 lb/inch2 (psi) inlet air pressure) zero to four volume passes through a Microfluidizer(R) M110T equipped with a high-pressure pump and thermostatted to 23-degrees-C. Viscosity average molecular weight was determined for each copolymer after each cycle using intrinsic viscosity as estimated by capillary viscometry. All three polymers were observed to undergo mechanical degradation. The difference in initial average molecular weight of the A terminal blocks (L64 > L63 > L62) was found to have an effect on overall percent decrease in viscosity average molecular weight. Pluronic(R) L64 was observed to be the most sensitive (20% decrease) and Pluronic(R) L62 was found to be the least sensitive (5% decrease) to the high shear and turbulent forces encountered during microfluidization. The apparent first-order mechanical degradation constants for the polymers were calculated from the slopes of plots of reciprocal average molecular weight vs number of cycles. The apparent degradation constants were estimated as 1.48E-5, 1.15E-5 and 5.51E-6 mol g-1 cycle-1 for Pluronic(R) L64, L63 and L62, respectively. Differences in the mechanical degradation constants may be reflective of differences in the average molecular surface area exposed to shearing stresses and turbulence generated during the microfluidization process.