“Gradient” Polymer Prepared by Complex-Radical Terpolymerization of Styrene, Maleic Anhydride, and N-Vinyl Pyrrolidone via γ-Ray Irradiation by Use of a RAFT Process: Synthesis, Mechanism, and Characterization

A novel “gradient” polymer, prepared by complex-radical terpolymerization of styrene (St), maleic anhydride (MA), and N -vinylpyrrolidone (NVP), was synthesized by use of a reversible addition−fragmentation chain transfer (RAFT) process. The terpolymerization was performed in tetrahydrofuran (THF) at room temperature under γ-ray irradiation in the presence of dibenzyl trithiocarbonate (DBTTC). The constants of complex-radical terpolymerization, complex formation, and some kinetic parameters for the monomer systems were studied by UV, 1 H NMR, Kelen−Tüdöş methods, respectively. The equilibrium constant ( K 2 ) of 1:1 complex between MA and NVP was determined by UV method as 3.57 × 10 -2 L/mol at 293.2 K in CHCl 3 . Obtained results show that the terpolymerization proceeded mainly through “complex” mechanisms in the state of near-binary copolymerization of St···MA (CTC1) and MA···NVP (CTC2) complexes. And as the big difference in the value of the reactivity ratios between the two complexes ( r 1 = 0.17 ± 0.01 and r 2 = 4.20 ± 0.34), the terpolymer displayed the characteristics of “gradient” distribution with controlled molecular weight and narrow molecular weight distribution.