We consider hadronic matter to be composed of quarks and self-interacting bosons and calculate the effective potential in the one-loop approximation in renormalizable field theory. We also calculate the relevant thermodynamical quantities and show that a) a phase transition of the second kind can arise at temperature T=0.17 GeV, b) the level density of hadronic matter agrees with the one of the statistical bootstrap model below the critical temperature and c) our model may predict good fits to the experimental transverse momentum spectra in particle production if based on a fireball model.