The miniaturisation and the simultaneous optimisation of small, thin wall and micro injection parts, with masses smaller than a gram and wall thickness smaller than half a millimetre is an aim of present time. For the reason that in conventional injection moulding the melt flow front freezes, special attention is now directed on the expansion injection moulding technology, in which the compression of the melt is separated from the injection phase. The main objective of this thesis was the analysis of the expansion injection moulding process, which on the one hand means attempts at model and series production parts and on the other hand contains material data measurements with pvT-apparatus and following analysis of the degradation behaviour by means of differential scanning calorimetry (DSC) and size exclusion chromatography (SEC). After input of the measured data of the pvT-measurements into a calculation program (Xmeltsoft V.1.0), model and series production parts were manufactured with the help of the expansion injection moulding technology. The model part (check card) was completely filled using polystyrene, but not completely filled with the other investigated thermoplastics materials (PC/ABS, PC) due to the limited specific injection pressure of the used injection moulding machine. The most significant process parameters were investigated by design of experiments which allowed improving the production of the moulded parts. The model part allowed analysing the material degradation at different layers of the moulded part and the practice part (battery case) permitted to analyse the influence of melt residence time on the respective material degradation. Depending on the chosen process parameters, the process induced material decomposition could be established. More reliable results were obtained by using the SEC analysis method, compared to the DSC method.