Partially neutralized liquid polybutadiene treated with succinic anhydride (SA), that is, PBSA(PNa), was prepared by partial neutralization with NaOH of adduct polymer (PBSA) from liquid polybutadiene and SA (PNa means that PBSA was partially neutralized with NaOH). PBSA(PNa) was found to act as an effective W/O∼type emulsifier for vinyl monomers such as styrene, MMA, acrylonitrile, and ethylene glycol dimethacrylate. Inverted emulsions having very low viscosity were prepared from the vinyl monomers with various amounts of PBSA(PNa). By polymerization, the emulsions were transformed to a white solid which were dry to the touch. The water-containing polymers obtained are characterized by the properties of showing a very high rate of water loss. The higher the amounts of PBSA-(PNa) and of water in the polymer, the more rapid the water loss becomes. Most of physical properties increase in value by removing water. Further improvement in physical properties is observed by reinforcing with glass fiber; the flexural and impact strengths especially increase remarkably.