In situ Compatibilization of Polystyrene and Polyurethane Blends by Using Poly (Styrene-co-Maleic Anhydride) as Reactive Compatibilizer
Cassu SN, Felisberti MI

82 (10): 2514-2524 DEC 5 2001

Blends of polystyrene (PS) and polyurethane (PU) elastomer were obtained by melt mixing, using poly(styrene-co-maleic anhydride) (SMA) containing 7 wt % of maleic anhydride groups as a reactive compatibilizer. Polyurethanes containing polyester flexible segments, PU-et, and polyether flexible segments, PU-et, were used. These polyurethanes were crosslinked with dicumyl peroxide or sulfur to improve their mechanical properties. The anhydride groups of SMA can react with the PU groups and form an in situ graft copolymer at the interface of the blends during their preparation. The rheological behavior was accompanied by torque versus time curves and an increase in the torque during the melt mixing was observed for all the reactive blends, indicating the occurrence of a reaction. Solubility tests, gel permeation chromatography, and scanning electronic microscopy confirmed the formation of a graft copolymer generated in situ during the melt blending. These results also indicate that this graft copolymer contains C-C bond between SMA and PU chains.



Unsaturated Polyester Resin Modified with Poly(Organosiloxanes). I. Preparation, Dynamic Mechanical Properties, and Impact Resistance
Rosa VM, Felisberti MI

81 (13): 3272-3279 SEP 23 2001

Unsaturated polyester resins (UP) display a wide range of applications depending on the proper choice of raw materials and cure conditions. However, some applications are limited to their low-impact resistance, which can be enhanced by the incorporation of modifiers that increase the flexibility of the network. This work aims to incorporate flexible poly(organosiloxane) segments in the UP network as a graft copolymer, as a way of minimizing the low adhesion between the resin and the modifier and enhance its flexibility. Because polyester and poly(organosiloxanes) are immiscible mixtures, the grafting copolymerization during the cure can promote compatibilization between both polymers. Hence, glycidyl methacrylate (GMA) is added to the resin network by radical reaction, as well as 1,3-aminopropyltriethoxysilane (APTS), amino groups of which react with GMA. The addition of a siloxane (1,1,3,3-tetramcthyl-1,3-diethoxydisiloxane) allows the poly(organosiloxane) network to grow and the addition of water guarantees the hydrolysis and polycondensation during the cure. In this way it is possible to increase its flexibility. The grafting copolymerization is evaluated by dynamic mechanical analysis and the impact resistance of pure and modified polyester resins is evaluated by the Izod test. The grafting of a flexible segment in the UP chains enhances the impact resistance of the polyester resin at low-modifier concentration.



Unsaturated Polyester Resin Modified with Poly(Organosiloxanes). II. Acoustic Emission Study on Glass-Fiber-Reinforced Resin
Rosa VM, Karger-Kocsis J, Felisberti MI

81 (13): 3280-3289 SEP 23 2001

This work aims to study the adhesion of an isophthalic acid based unsaturated polyester resin chemically modified by grafting copolymerization of a poly(organosiloxane) to the glass fiber. The failure mode of the single-edge notched tensile specimen, cut from pressed plates containing 50 wt % of nontreated and silane-treated milled glass fiber, was studied by acoustic emission (AE) technique. It was found that the aforementioned resin modification enhanced the adhesion between the fiber and the resin. This was suggested by a shift in the AE amplitude and energy toward higher values. On the other hand, the matrix modification had no significant effect if glass fiber with suitable unsaturated polyester resin (UP) sizing was incorporated.



Miscibility, Crystallinity and Morphological Behavior of Binary Blends of Poly(Ethylene Oxide) and Poly(Methyl Vinyl Ether-Maleic Acid)
Rocco AM, Pereira RP, Felisberti MI

42 (12): 5199-5205 JUN 2001

DSC and optical microscopy were used to determine the miscibility and crystallinity of blends of poly(ethylene oxide) (PEO) with poly(methyl vinyl ether-co-maleic acid) (PMVE-MAc). Single T-g was observed for all blends, indicating miscibility. The dependence of T-g on the weight per cent of PEO presents a negative deviation from linearity at high PEO content, associated to a greater blend free volume, mobility and flexibility than in pure PEG. A progressive decrease in the degree of crystallinity and in the size of the PEO spherullites as the PMVE-MAc is added is observed. FTIR provided evidence of specific interaction between the polymers.