We have developed a DSC cell embedded into a vapor deposition polymerization reactor, as well as electronics and software controlling the calorimeter. The temperature and heat flow calibrations of this calorimeter were performed in a wide temperature interval. The time constants of the calorimeter were determined and deconvolution procedure of DSC traces was implemented. Polymerization of chlorine substituted p-xylylene (PX-Cl) was investigated using highvacuum in situ DSC. Condensate of the monomer on the substrate was formed using Gorham’s method. Figure 1 shows DSC scans of PX-Cl polymerization and (for comparison) the one of unsubstituted p-xylylene (PX) [1]. The heating rate in both cases was 2.7 oC /min. Щту сфт see that polymerization of PX-Cl begins at considerably lower temperature than that of PX (the temperature range of polymerization is from -135 oC to -75 oC for PX-Cl and from -105oC to -80 oC for unsubstituted PX at heating rate 2.7 oC /min). Moreover, the DSC peak of polymerization of PX-Cl has bimodal shape (there is a shoulder on the left side of the peak), which probably indicates complex mechanism of PX-Cl polymerization. Figure 1. DSC scans of polymerization of PX and PX-Cl condensates without baseline subtraction and smoothing. Heating rate is 2.7 oC /min.