Design of Well‐Defined Cross‐Linked Grids via Alternating Copolymerization of Phenol End‐Functionalized Polysulfone Oligomers With Methyl Substituted Benzoxazine Monomers

ABSTRACT The cross‐linked polysulfone‐benzoxazine alternating copolymers (PSU‐mBZs) were synthesized by the copolymerization of phenol end‐functionalized polysulfone oligomers (PSU‐OHs) varying molecular weights from 2000 to 5800 g/mol with non‐homopolymerizable methyl substituted benzoxazine (mBZ), respectively. The structures and molecular weights were characterized by FT‐IR, 1 H NMR, 13 C NMR, and SEC. The results showed that the well‐defined model network was designed and synthesized successfully. Therefore, the precise controls in cross‐linking density, glass transition temperature ( T g ), and mechanical properties of PSU‐mBZs were achieved. The cross‐linking density and T g of PSU‐mBZs decreased linearly from 376.03 to 129.87 mol/m 3 and 325°C to 228°C with increasing molecular weight of PSU‐OH, described by the equations y = −0.062 x + 472.82 and y = −0.020 x + 331.96, respectively. Meanwhile, the tensile strength and breaking elongation of PSU‐mBZs increased linearly from 26 to 76 MPa and from 4.8% to 15.9% with increasing molecular weight of PSU‐OH, described by y = 0.013 x + 1.40 and y = 0.0030 x − 1.94, respectively. This work establishes a well‐defined model network for studying microstructure‐macroscopic property relationships. The materials exhibit excellent high‐temperature resistance, tunable mechanical properties, good chemical stability, and potential flame retardancy, making them promising for coatings, resin matrix composites, advanced electronic packaging, and other fields.