Many (semi-)crystalline polymers are polymorphic, having more than one crystalline phase. These are usually academic concerns and not industrial. Polypropylene, for instance, has 3 phases that I am aware of, although I am not aware of any products that actually are constructed from anything other than the run-of-the-mill a-phase. The b-phase can be obtained with special nucleating agents and temperature control, but upon heating, will revert to the a-phase. I recall reading about the g-phase, but it always a minor constituent.
Now comes a new report about that odd duck syndiotactic polystyrene (the kind that can crystallize) that not only has an a-, b-, and g-phase, but also an d- and e-phase too. And in this report, they looked at how well the last two phases adsorbed hydrogen.
That is the most phases that I ever seen for one polymer. Quite impressive.