The results of electron spin resonance (ESR), static magnetic susceptibility, and electronic transport measurements of heat-treated polyparaphenylene (PPP) at various temperatures ${T}_{\mathrm{HT}}$ are presented as a function of measurement temperature T and magnetic field strength H. A crossover from a disordered polymer $(\mathrm{H}/\mathrm{C}\ensuremath{\approx}0.6)$ to a disordered carbon $(\mathrm{H}/\mathrm{C}l0.2)$ is caused by heat-treatment above $700\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ which gives rise to vast differences in spin environment. ESR measurements of PPP heat-treated to $700\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ show the presence of two spin centers, resulting in two distinct peak-to-peak linewidths of roughly 0.5 and 5 G, corresponding to spins localized within carbonized and noncarbonized regions, respectively. In polymeric regions, slowly diffusing spins $({\ensuremath{\omega}}_{j}\ensuremath{\approx}{10}^{8} {\mathrm{sec}}^{\ensuremath{-}1})$ experience a motionally narrowed hyperfine interaction, which is unresolved due to disorder. Carbonized regions, which control bulk conduction mechanisms, show evidence for a Korringa $1/T$ relaxation mechanism, typical of disordered metals. This is consistent with the transport behavior of PPP heat treated at or above $700\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ which indicates a variable range hopping mechanism for carriers localized within weakly conducting carbonized regions. On the other hand, spins in hydrogen-rich polymeric regions are highly localized and are associated with defects along PPP chains in the form of trapped polarons.