A liquid composition including a monomer, a (meth)acrylic polymer and a wax compound. The liquid composition can be used as a syrup and especially as a syrup for impregnation of fibres or fibrous material. Also, a thermoplastic material obtained after polymerization of the liquid composition. Also, a process for manufacturing such a liquid composition. Also, a process for impregnating a fibrous substrate of long or continuous fibres with such a liquid composition. Also, a fibrous substrate impregnated with such a liquid composition which is useful for manufacturing composite parts. Also, a process for manufacturing mechanical parts or structural elements made of composite material and mechanical parts or structural elements made of composite material obtained via a process using such a liquid composition.