“…Poly(2,6-dimethyl-1,4-phenylene) oxide [ 1 , 2 , 3 , 4 ], often abbreviated as PPO, is the only polymer beside syndiotactic polystyrene (s-PS) [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ] that exhibits not only co-crystalline (CC) phases with low-molecular-mass guest molecules but also corresponding nanoporous-crystalline (NC) phases, as derived by guest removal [ 13 , 14 , 15 , 16 , 17 , 18 , 19 ].…”