<p>Polybenzoxazines (PBzs) are a well-established class of phenolic resins synthesized through the thermal ring-opening of benzoxazine monomers, which feature a six-membered heterocyclic ring containing nitrogen and oxygen atoms that act as Lewis base sites in the polymer network. In this study, two conventional PBz systems, poly(2&#xa0;N-ab) and poly(P-pt), were investigated for their structural and thermal behaviors upon coordination with selected metal ions (Mn²⁺, Th⁴⁺, and Cd²⁺). FTIR and XRD analyses confirmed successful metal coordination and structural rearrangements within the polymer matrix. Thermogravimetric analysis (TGA) demonstrated that coordination with Th⁴⁺ significantly enhanced the thermal stability of the PBz hybrids, as evidenced by notable increases in the temperatures at 5% weight loss (Td₅) and 10% weight loss (Td₁₀). Specifically, poly(2&#xa0;N-ab)/Th⁴⁺ exhibited Td₅ and Td₁₀ values of 294&#xa0;°C and 448&#xa0;°C, respectively, markedly higher than 227&#xa0;°C and 260&#xa0;°C for the unmodified polymer. Similarly, poly(P-pt)/Th⁴⁺ showed improvements from 150 to 192&#xa0;°C to 250 and 355&#xa0;°C. The char yield at 800&#xa0;°C also substantially increased, rising from 5% to 83% for poly(2&#xa0;N-ab)/Th⁴⁺ and from 1% to 76% for poly(P-pt)/Th⁴⁺, indicating enhanced residue formation and thermal robustness. Mn²⁺ and Cd²⁺ complexes similarly improved the thermal degradation resistance and char yield, although to a lesser extent than Th⁴⁺. These findings highlight the strong metal–polymer interactions and crosslinking effects that reinforce the thermal integrity of PBz-metal hybrids, making them promising materials for high-performance applications.</p>