A novel solvent extraction method to isolate and recover polyolefin materials from coal-plastics coprocessing product streams is reported. The method was applied to samples obtained from a bench-scale continuous unit, coprocessing coal with polyethylene (PE), polypropylene (PP), and polystyrene (PS) feed. Recovered PE and PP have been characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies, and gel permeation chromatography (GPC); PS is completely converted to distillable product. The results indicate that PP undergoes fairly rapid and essentially quantitative reaction and its conversion is complete before reaching the downstream portion of the process. On the other hand, PE undergoes some degradation in the coal liquefaction reactor, with an average reduction in molecular weight distribution for the "unconverted" material by a factor of 10 to 30. GPC can definitively distinguish between fresh (feed) and recycled PE in the process stream and has established that most of the PE degradation occurs in the first-stage liquefaction reactor. This partially converted, but undistillable material then passes into the atmospheric still bottoms stream. The two solid separation methods examined had very different effects on the incompletely reacted PE. Vacuum distillation sequesters the PE in the unconvertable (ashy) fraction, whereas pressure filtration allows most of it to pass through into the recycle stream. A qualitative mechanism for PE breakdown is proposed in which rapid scission occurs at the branching points of the paraffin backbone, followed by eventual breakdown to distillable products.