Reaction conditions have a huge impact on the resulting polymer properties, but capturing this requires understanding the correlation of the underlying kinetics, the polymer architecture, and polymer flow behavior. Long-chain branched polymers created randomly by free-radical polymerization, such as low-density polyethylene (LDPE), show complex rheological behavior and are thus interesting in this context. A study applying a multiscale modeling approach is used to simulate varying reaction conditions and predict the structure of the resulting LDPE polymer and its flow properties. A significant effect on the molecular weight distribution, but also the viscosity and extensional flow behavior can be predicted. Higher conversions, for example, lead to broader molecular weight distributions, increased long-chain branching degrees, and a higher branching complexity. Consequently, also higher viscosities and increased strain hardening are observed in extension. Additionally, miniplant experiments are performed to resemble the simulations and compare the results. The accordance of predictions and analytical results are very good and validate the model over a wide range of reaction conditions.