All bonds issued by a research park corporation under the University Research Park and Economic Development Act are legal and authorized investments for banks, savings banks, trust companies, savings and loan associations, insurance companies, fiduciaries, trustees and guardians and for the sinking funds of political subdivisions, departments, institutions and agencies of this state. When accompanied by all unmatured coupons appurtenant to them, the bonds are sufficient security for all deposits of state funds and of all funds of any board in control of public money at the par value of the bonds. The bonds and the income from the bonds are free from taxation within this state, except estate taxes. The research park corporation in its discretion and by those means as it deems appropriate may waive the exemption from federal income taxation of interest on the bonds. The bonds subject to federal income taxation issued by the research park corporation shall be payable as to principal and interest with such frequency as may be required by the research park corporation.