Precise construction of quantum spin chains is essential for studying their complex physical properties and for their potential applications in quantum devices. Polymers provide an excellent foundation for building spin chain systems due to their stability and flexibility, while a strategy is required for the creation and protection of spins on the chains. Here we report the fabrication and characterization of spin 1/2 polyfluorene-based chains through on-surface synthetic approach. Dehydroxylation is used to create spins on polyfluorene-based chains, and side groups (phenyl rings) are used to protect the spins from further reactions. The coupling strength between spins is identified in transport measurements with chains suspended between the tip and the sample of a scanning tunneling microscope. Furthermore, collective spin excitations emerge in the decoupled chains. Mean-field Hubbard simulations confirm the antiferromagnetic ground states, and Heisenberg spin model calculations capture the complex spin excitation behaviors. Our results demonstrate the use of polymers to construct spin chain systems, paving a way for study and manipulation of quantum properties in polymers chains.