Officials of the state government may enter into agreements with officials in other branches for the temporary transfer of employees from one branch to another. Said agreements shall be in writing and shall specify the names of employees to be temporarily transferred, the compensation and benefits which the employee will receive from the transferee office, and the duration of the transfer period, which shall in no case exceed 18 months. No agreement between officials shall be valid as to an employee unless he shall have read and signed the agreement. A copy of each agreement entered into pursuant to this section shall be retained by each signatory thereto, and a copy shall also be sent to the office of the commissioner of administrative services at least 14 days before the beginning of the transfer period.