The development of transparent, high thermal conductive materials is essential for future advancement of high- performance ultrahigh-brightness light-emitting diodes (LEDs), electronic devices, and power electronics. Polymer resins having high optical transparencies require the use of amorphous polymers. However, the thermal conductivities of bulk amorphous polymers are very poor due to pronounced phonon scattering. Herein, we show that the cast films of beads-on-string-shaped polyureas (3) prepared through polycondensation of p-bis(3-aminopropyl)-hexaisobutyl-substituted T-8 cage (1) with 1,4-phenylene diisocya- nate (2a), methylenediphenyl 4,4'-diisocyanate (2b), hexamethylene diisocyanate (2c), or methylenedicyclohexyl 4,4'-disocyanate (2d) showed high thermal conductivities and good optical transparencies dependent on the diisocyanate structures. Thermal conductivities of all tested polyurea micrometer thick casting films were higher than 0.3 W/(m K). Specifically, the casting film produced by using 3a showed high thermal conductivity, 0.52 W/(m K), and good optical transparency. The polymer films had contact angles against water greater than 100 degrees, indicating hydrophobic character. The hydrophobic T-8 units in the main chains of the polymers promoted extended conformations which interacted through homogeneous disordered hydrogen-bond networks.