Superb overview of NASA propfan program circa 1988. Not highly technical but well-presented in historical context, nicely illustrated, and containing several conceptual drawings of potential propfan aircraft. Worth your time.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890003194_1989003194.pdf
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890003194_1989003194.pdf