Recently much effort has been devoted to developing drug delivery systems based on macromolecules of three-dimensional structure. In addition to dendrimers which are widely studied, hyperbranched polymers are gaining more and more attention. Among numerous polymeric materials used in drug delivery systems, aliphatic polycarbonates are one of the most interesting ones due to biocompatibility, nontoxic degradation products, and the absence of autocatalytic effect during the degradation process. However, they show poor solubility in supercritical carbon dioxide. This paper describes the synthesis of 5-(4-hydroxybutyl)-1,3-dioxan-2-one and its application for preparation of hyperbranched aliphatic polycarbonates. Linear analogues of the poly(5-(4-hydroxybutyl)-1,3-dioxan-2-one) were prepared, too, and the structures were compared by means of C-13 NMR. Ring-opening polymerization of 5(4-hydroxybutyl)-1,3-dioxan-2-one led to polymers containing solely primary hydroxyl groups which were subsequently reacted with trifluoroacetic anhydride. The phase behavior of fluorinated polymer in supercritical carbon dioxide was explored as a function of concentration and temperature. Modified hyperbranched polycarbonate showed reasonably good solubility in carbon dioxide. It was shown that hyperbranched structure of a polymer facilitate solubility even though the carbonate structural units do not promote solubility in scCO(2).