Research Of Kinetics Of Nonideal Ab₂, A₂ +b₃ And Ab^* (atrp) Type Hyperbranched Polymerization

The quantitative prediction of nonideal hyperbranched polymerization is a difficult point in the research field of nonlinear polymer. The molecular weight, polydispersity and the molecular conformation of hyperbranched polymer are difficult to quantitatively analyze and predict by mean-field theory due to its inability in introducing the space effect. The 3D bond fluctuation model easily introducing the basic spacial elements, such as molecular diffusion, polymer chain relaxation and intramolecular cyclization, has ability to simulate nonideal hyperbranched polymerization. The 3D bond fluctuation model is applied to simulate a specific AB₂ system, namely 3, 5-Bis (trimethylsiloxy) benzoyl chloride polycondensation (Macromolecules 2003, 36, 97-108). Through fitting the experimental data about the A conversion dependence of structural units, the reactivity ratio of groups for different units was obtained. Our study shows that 3D bond fluctuation model not only has the excellent ability in mapping the experimental data, but also provides the important information of hyperbranched polymer, such as the molecular weight, polydispersity index and molecular conformation. This fitting 3D bond fluctuation model simulation method can also be applied in the study and prediction of various hyperbranched polymerizations.In the past, kinetic study and gelation theory involved A₂+B₃ type hyerbranched polycondensation are mainly based on mean-field theory. However, this method ignores intramolecular cyclization and steric hindrance which have an intense affect on polymerization, especially the dilute solution system in later reaction period. There is a gap between the kinetics of polymerization in mean field and real system. To deeply understand the kinetic and gelation process, we applied reactive bond fluctuation lattice model to simulate hyperbranched A₂+B₃ polycondensation. Simulation demonstrated that intramolecular cyclization and steric hindrance play crucial influences on molecular parameters such as molecular weight, polydispersity index. The A₂ + B₃ system has high gelation sensitivity to the concentration and feed ratio of monomers and reactivity of functional groups. Further, a specific polymerization system, polycondensation of aromatic terephthaloyl chloride (TCl, A₂) with 1, 1, 1-tris(4-trimethylsiloxyphenyl)ethane (TMS-THPE, B₃) (Macromolecules 2007, 40, 6846) is simulated to predict the molecular weight, molecular weight distribution and conformation of hyperbanched polymer. For AB* type (ATRP) hyperbranched polymerization, the influences of conventional SCVP and ATRP mechanism on hyperbranched polymerization were compared. It was found that ATRP system has higher PI than SCVP. We analysed the trend of weight-average degree of branching P_w and polydispersity index PI as a function of double bond conversion at various activation, deactivation rate constant and amount of catalyst. The higher deactivation rate constant is, the lower P_w and PI are. The increase of activation rate constant and amount of catalyst leads to the increase of termination by combination, which contributes the rapid growth of P_w and PI.