In situ-reinforcing composites based on two elastomer matrices very different in melt viscosity, styrene(ethylene butylene)-styrene triblock copolymer (Kraton G1650), and styrene-(ethylene propylene) diblock copolymer (Kraton G1701), and a thermotropic liquid crystalline polymer (TLCP), Rodrun LC3000, were prepared using a twin-screw extruder. The isothermal decomposition behavior and dynamic mechanical properties of the extruded strands were investigated by means of thermogravimetry (TG) and dynamic mechanical analysis (DMA), respectively. No significant change in the shape of TG curves for the neat matrices and their LC3000-containing blends was observed under isothermal heating in nitrogen. In air, G1650 and G1701 showed a single weight-loss stage and rapid decomposition whereas their blends with 30 wt %, LC3000 showed different profiles of weight loss depending on isothermal temperatures. The calculated kinetic parameters indicated that the thermal stability of the polymers is much higher in nitrogen than in air and suggested an enhancement of thermal resistance of the elastomer matrices by addition of TLCP. DMA results showed a great enhancement in dynamic moduli for the blend with 10 wt % LC3000 when compared with the neat matrix. The tan delta peaks corresponding to the elastic and hard phases in both matrices mostly shifted to the lower temperature with LC3000 loading. (c) 2006 Wiley Periodicals, Inc.