<p>New methods for recovering the energy and value from polyolefin plastic waste must account for all the hydrocarbons formed during a deconstruction reaction. Analysis of the reaction mixture distribution is key to determining a catalyst’s performance (activity and selectivity) and evaluating the economic viability of a conversion process. The molecular species present in the reaction mixtures can range from H₂ and CH₄ to hyper-branched hydrocarbons above 100,000 g/mol and any hydrocarbon in between; therefore, multiple analytical techniques are required to quantify all of the products. Here we describe an optimized and validated workflow that uses integrated analytical gas chromatography for concurrent H₂ and gas-phase hydrocarbon quantification of the headspace; complementary gas chromatography, liquid chromatography and multi-nuclear magnetic resonance spectroscopy to quantify the composition of soluble products, as well as gel permeation chromatography to determine of the molecular weight distribution of the residual insoluble polymeric material. Using polyolefin hydrogenolysis in an autoclave reactor as an example, we describe how to specifically adapt these techniques to polymer deconstruction experiments and fully quantify the entire hydrocarbon population, while resolving and assigning specific species and characterizing structures. The information from this comprehensive analysis is needed to study reaction kinetics and to evaluate the intrinsic activity of a catalyst and reactivity of polymers in upcycling experiments, enabling mechanistic investigations and providing data to link experiment and theoretical models. The comprehensive quantitative analysis in this protocol can be completed within 4 d.</p>