Disclosed are compositions comprising dimeric decarboxylated rosins (DDCRs), methods for making them, and applications thereof. DDCR of purity from 50-100 wt. % is obtained by decarboxylating a dimeric rosin acid or by dimerizing a decarboxylated rosin, in the presence of a catalyst, followed by one or more purification steps separation on differences in boiling point. The isolated DDCR fractions display unexpectedly high Tg/Mn ratios, softening points and viscosities, and low polydispersities. The DDCR product comprises 50 to 100 wt. % of polycyclic hydrocarbon compounds having one or more aliphatic, unsaturated or aromatic groups, and 34-80 carbon atoms, with a molecular weight Mn of 250-900 Da, and an oxygen to carbon ratio of