Influence of Reaction Conditions and Water on the Manufacture of C9 Aromatic Hydrocarbon Resins

ABSTRACT

Aromatic hydrocarbons (HRs) find many commercial applications, demanding control of the cationic reaction conditions to achieve specific resin properties. For this reason, in the present work a systematic and original investigation of C9 HR production through AlCl ₃ cationic polymerization is presented, with particular emphasis on the role of water, which was treated not as a passive impurity but as a quantified and optimized co‐catalyst. The effects of temperature, solvent, catalyst loading, and catalyst: co‐catalyst ratio were evaluated and correlated with reaction performance and resin properties. The results showed that all reactions provided minimum conversions of 50% and exhibited exothermic peaks up to 20°C, indicating successful polymerization and leading to products with average molar masses exceeding 1.3 kDa. In particular, water was found to significantly influence reaction exothermicity and polymer yield, confirming its role in the formation of active species, while average molar masses and softening points (Ts) were less sensitive to reaction conditions (between 50°C and 70°C). The experimental design was extended to different solvents and increased solvent contents, particularly toluene, enabling extrapolation beyond the initial design space. These results provide a systematic framework for the optimization of HRs synthesis and establish water as a critical design variable in the investigated systems. Multifactorial analysis revealed key correlations among process variables, including a consistent inverse relationship between resin yield and softening point (Ts), highlighting an intrinsic trade‐off in process optimization that has been overlooked in previous studies performed with model and pure monomer feeds.