This thesis introduces a series of novel, non-conjugated polyarylether hosts that are not subject to the triplet-energy limitations of traditional conjugated polymer hosts. As a result of this major breakthrough, the long-standing problem of triplet energy back transfer has now been overcome, making it possible to design high-efficiency electrophosphorescent polymers (PhPs), especially the blue and all-phosphorescent white ones. In addition, the author proposes a spiro-linked hyperbranched architecture for PhPs to inhibit the undesired triplet energy back transfer process in low triplet-energy hosts. The work in this thesis provides vital new insights into the design of PhPs and has led to several publications in high-profile journals.