Latex interpenetrating polymer networks based on polyacrylates and poly(methyl methacrylate)

The effect of methacrylic acid (MAA) concentration in the polyacrylate seed on the formation of latex interpenetrating polymer networks (LIPNs) with poly(methyl methacrylate) (PMMA) as polymer II in the ratio of 65 : 35 (w/w) has been studied. LIPNs were prepared using three different seeds having the compositions of n-butyl acrylate (BA), methyl methacrylate (MMA), and tetra(ethylene glycol)dimethacrylate (TEGDM) in the ratio of 55 : 45 : 0.7 by weight and varying amounts of MAA (0, 2.5, and 6% by wt) at two different pH values (similar to 3.3 and 8.5). LIPNs prepared from seeds having MAA > 2.5% resulted in the formation of continuous films, whereas LIPNs without MAA in the seed yielded discontinuous films (i.e., films with many cracks). Characterization using differential scanning calorimetry (DSC) showed the presence of multiphase morphology in all the LIPNs, indicating better mixing of the two polymers. Another set of LIPNs using the seed of the composition BA : MMA : MAA : TEGDM in the ratio of 63 : 37 : 6 : 0.7 by wt, possessing a glass transition temperature of 0 degrees C and PMMA as polymer II, was prepared at two different pH values, as mentioned earlier, and with two different initiators-namely, 2,2'-azobisisobutyronitrile (AIBN) and potassium persulfate (PPS)-for the polymerization of monomer II. The tensile strength and hardness of both the LIPNs processed at high pH (8.5) did not show significant differences, whereas the LIPNs prepared at low pH using the AIBN initiator showed an inverted core-shell morphology possessing very low hardness and tensile strength with high elongation. The PPS-initiated polymer showed core-shell morphology yielding film of poor strength. (C) 1996 John Wiley & Sons, Inc.