Named pair array from variable

Is this even possible? I'm building a string, properly formatted, to create a named pair or associative array. The string is fine, and when I use it directly to create the array, all is well. When I try to use the var to create the array, I get an empty array (I think). Huh? Here is what I have: $myString = "'username' => 'password' , 'mickey' => 'mouse' , 'donald' => 'duck'"; $myArray = array($myString); print ("array val: $myArray[username]"); // get an empty string here