MODELING REACTIVE BLENDING - AN EXPERIMENTAL APPROACH

We present an experimental study of polymer-polymer reaction kinetics at the interfaces between two immiscible polymer phases under flow in a batch mixer of type Haake Rheocord. To that end, we have developed a model chemical system that is composed of a mixture of polystyrene (P S) and poly(methyl methacrylate) (PMMA). A small fraction of PS bear h ydroxyl terminal group (PS-OH) and that of PMMA contain nonclassical i socyanate moieties that are randomly distributed along the PMMA chains (PMMA-r-NCO). This reactive system is particularly pertinent to model ing practical reactive blending processes because the amount and rate of copolymer formation can be determined with great accuracy ton the o rder of ppm). This study shows that the overall reaction rate is contr olled primarily by interfacial generation through convective mixing. M ost reaction and morphological development are accomplished within a v ery short period of time (1-3 min). For a PS/PMMA (60/40) reactive ble nd, the ultimate size of the PMMA particles is as small as 0.2 mu m an d is reached within 2 to 3 min. A surface coverage of about 0.5 of the PMMA particles by a monolayer of the copolymer is enough to prevent d ynamic coalescence, whereas a much higher surface coverage is needed t o eliminate static coalescence. In the nonentangled regime (M-n of the PS-OH = 7800 g/mol, temperature has a significant effect on the react ion rate, while it has little effect in the entangled regime (M-n of t he PS-OH = 53,200 g/mol). (C) 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2153-2163, 1998.