High-density packing of the main chains of amorphous high-refractive-index polyguanamine derivatives and aromatic polyamide block copolymers has been investigated in 2D molecular films. Polymer main chains with multiple and bulky aromatic rings are difficult to pack owing to steric hindrance. However, the intermolecular affinity can be enhanced by chain rearrangement. The polymer chain arrangement in 2D films has been controlled at the air/water interface. Furthermore, rearrangement of the main chains at the water/substrate interface during transfer to the solid substrate is also important. The highly hydrophobic polyguanamine derivatives form single-particle layers at the air/water interface, with their bulky functional groups packed densely in nanospheres owing to π–π interactions. The hydrophobic aromatic polyamide copolymers form an expanded monolayer including unpacked chains at the air/water interface. As these copolymers are rearranged during transfer to the solid substrate, densely packed molecular arrangements with end-on configurations are attained in the films.