The polyheteroarylenes of new type, called polyarylenediphthalides (PADPs), containing two adjacent phthalide groups regularly alternating with aromatic (heteroaromatic) fragments in the main chain have been developed. For obtaining PADPs, two approaches based on the dehalogenation reactions were used. In the first, polycondensation of the pseudo-acids chlorides was carried out that led to the polymers with random stereo configuration of diphthalide groups. In the second, stereospecific PADPs were formed using diastereoisomeric pure halogenated biaryl-3,3′-diphthalides (meso and racemic) as monomers that attach themselves to the growing polymer chain entirely keeping their stereo configuration. The obtained polymers start to soften and decompose at ≈350°C in inert atmosphere. Degradation of PADPs at deep carbonizing stages in the inert atmosphere is followed by formation of foamed coke with increased content of diamond-like carbon that possesses a high hardness (≥8 by Mohs scale).