I think that a few people are confusing "Lexan" (a polycarbonate) with "Perspex" (an Acrylic).
For details of Lexan see
http://www.gelexan.com/gelexan/
Note the statements about its strength and shatter resistance.
Perspex on the other hand is quite easy to break as are most acrylics.
The EV97 Eurostar that someone mentioned is described on the company website as having an "Organic glass" canopy. Googling on that phrase turns up manufacturers of acrylic not Lexan.
Maybe Gengis can comment on this but I would doubt that any low winged aircraft would get past the relevant authorities (BMAA/BGA/PFA/CAA/EASA/FAA) with an unbreakable canopy.