Studies On The Cyclization In Typical Hyperbranched Polymerization Systems

The effect of cyclization on the average properties of polymers formed in two types of hyperbranched polymerization systems are mainly investigated by the method of Monte Carlo simulation,where one is the polycondensation of AB_g type of monomer,and another is the self-condensing vinyl polymerization(SCVP)system.To simulate the cyclization effect,a set of differential kinetic equations to describe the growth of polymers involving the cyclization are explicitly.Furthermore,we present a growth generation model of polymers,and then the simulation is performed by using the intermolecular and intramolecular reaction rates given by the principle of statistical mechanics.Consequently,the number of tree-like and cyclic polymers,the number of loops and its size distribution as well as the number-and weight-average molecular weights are presented.Also,the cyclization effect in the polycondensation of AB_g type of monomer is discussed by the principle of statistical mechanics,which can give its influences on some typically thermodynamic quantities.It is shown that,for the two types of polymerization systems under study,the volume fraction of monomers,solvent quality and functionality play an important role in cyclization.As a result,the cyclization effect depends in essence on the cooperation of the above three factors.There are four chapters in the dissertation,and their abstracts are given as follows,respectively.Chapter 1:The development of hyperbranched polymers and the history of studying intramolecular reaction are summarized.In detail,the properties of hyperbranched polymers generated by the polycondensation of AB_g type of monomer,and SCVP system are outlined.The influences of the intramolecular reaction in various polymerization systems are analyzed from both experimental and theoretical viewpoints,in particular in the typical hyperbranched polymerization systems.Chapter 2:In this chapter,we studied the cyclization phenomenon in AB_g type hyperbranched polymerization system.We derived a set of differential kinetic equations describing the growth of treelike and cyclic polymers,and then proposed a scheme of“generation”to specify the growth of polymers with more details.Furthermore,the rate constants of inter-and intramolecular reactions are deduced to perform the MC simulation.As a result,the number of treelike polymers and cyclic polymers,the size distribution of rings,and the weight-average molecular weight are presented.Based on the simulation results,a significant effect of cyclization on the average properties of polymers is found.Chapter 3:We present the effect of cyclization on the average properties of hyperbranched polymers formed in the SCVP system of pure AB~*inimers by the method of Monte Carlo simulation.A model to specify the generations of all units in a branched polymer is proposed to describe intramolecular reaction,and from which a set of kinetic differential equations was given to describe the growth of various polymers.The simulation is performed by using the intermolecular and intramolecular reaction rates under different solvent conditions.Consequently,the number of treelike and cyclic polymers,the size distribution of rings and the weight-average molecular weights were obtained,by which the effect of cyclization on the average properties of polymers was discussed.Chapter 4:On the basis of the principle of statistical mechanics,the thermodynamic perturbation theory is used to investigate several thermodynamic quantities in the polycondensation of AB_g type of monomer.As a consequence,the number of rings(also,the number of polymers with ring),the number of ring units,and the ring faction are deduced.Starting from these quantities,the chemical potential and pressure induced by the cyclization,solvent quality are presented,which showed how they change with the monomer concentration and functionality.Meanwhile,the phase equilibria of gas-liquid like in the system is carried out,which showed the effect of cyclization on the critical temperature and density.Overall,the dependence of cyclization on the monomer concentration,solvent effect,and functionality is discussed in typical hyperbranched polymerization systems.It is shown that cyclization is determined by the cooperation of monomer concentration,functionality,and solvent quality.In these factors,the monomer concentration plays a leading role,while solvent quality becomes significant only at a high concentration,and more generally,there is a competition between the latter two factors.It is expected that the present study may offer useful clues for designing related materials.