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

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. Graphical Well-Defined Cross-Linked Grids.