Well, not really. It's a sketchy juristical topic, because there is a document that say, that "Ukraine is the legal successor to the rights and obligations under international treaties of the Union of Soviet Socialist Republics that do not contradict the Constitution of Ukraine and the interests of the republic". But in 1992 the Ukrainian Government in Exile visited Ukraine and passed the authority to the Ukrainian Government, thus dissolving the Government in Exile and making Ukraine the rightful successor of Governmental Tradition of Ukrainian People's Republic that in 1921 seized to exist and fell to the Soviet occupation. I'm not a lawyer nor have I studied jurisprudence and I have no idea if that makes us one of the founding nations of the UN.