For pg free minoxidil, why not use propanediol instead of glycerin?

Ive tried pg free minoxidil containing glycerin and it didn't absorb as quickly in my scalp as minoxidil with pg(i'm allergic to pg). I just googled propylene glycol alternative and i found propanediol to be the next best thing to pg. Any reason why noone has tried putting propanediol into minoxidil? I might buy a jug of propanediol and pg free minoxidil to find out.