Final answer:
The strongest type of interaction between polymer chains of Kevlar is hydrogen bonding. There is additional strength derived from the interaction between the unhybridized p orbitals in the six-membered rings, called aromatic stacking.
Step-by-step explanation:
Hydrogen bonds are the strongest kind of interaction between Kevlar polymer chains. In the polymer structure, hydrogen bonds are formed between the partially positively charged hydrogen atom in the N-H bond of one adjacent monomer and the oxygen atom of the carbonyl group on another monomer. The interaction between the unhybridized p orbitals in the six-membered rings, known as aromatic stacking, contributes an extra strength.