Particle Coagulation Mechanism And Kinetics In Macroemulsion Polymerization And The Preparation Of Monodisperse Polymer Particles

Particle size distribution is the most important issue in emulsion polymerization because of it plays a critical role in determining the properties of ultimate latex such as rheology,film-forming ability and the application fields.At last decades,many methods,for example,seed swollen polymerization,particle aggregation technology were proposed for controlling particle size distribution in emulsion polymerization.However,some disadvantages were presented in these methods: a long polymerization reaction time,multistep process,and high energy requirement etc.This article presents a novel method for controlling particle size distribution in macroemulsion polymerization based on particle coagulation,in which the thermodynamics and kinetics in the polymerization process were used to adjust the particle coagulation extent,further,to control the particle number and size.This article can be divided into six sections as follows:In the first section,some theories about emulsion polymerization and methods controlling particle size distribution were introduced.In addition,the development process of particle coagulative growth in soap-free emulsion polymerization were introduced in detail.This section not only introduces some issues about coagulative growth,but also proposes a project evolution about how to prepare large sized polymer particles based on the particle coagulation technology.In the second section,we firstly introduce some experimental methods for investigating particle coagulation issue,for example dynamic light scattering(DLS)and transmission electron microscopy(TEM)etc.and proposed some methods to ensuring the occurrence of particle coagulation.By using DLS technology to follow the evolution of the average particle size of latex,we can easily calculate particle number during the polymerization process,further illustrate the particle coagulation extent and time.The decrease in particle number during the polymerization is considered as the feature of the particle coagulation.We also used the decrease in particle number to indirectly ensure particle coagulation.The directly evidence of the particle coagulation can be obtained by observing the structure of the ultimate latex particles,a multicores and single shell presents the particle coagulation occurred in polymerization process.In addition,we investigated the effect of the particle nature and aqueous phase on particle coagulation,and illustrated the role of interfacial behavior in determining particle coagulation in emulsion polymerization.The third section describes the nature of the particle coagulation and the application of the particle coagulation in preparing large sized particles.Particle coagulation is a dynamic behavior induced by thermodynamics,in which the increase in the total area of the particles increases the interfacial energy of the particles,resulting in the particle stability reduced,further,particle coagulation occurred.The particle coagulation reduces the particle number,leading to the average particle size enlarged.During the particle coagulation,the competitive growth of different sized particles and the self-sharpening process of the particles narrowed the particle size distribution of the ultimate latex particles.So,the particle coagulation can be considered as a novel method to produce large sized particles.The fourth section discusses the effect of the particle crosslinking and particle coagulation on particle morphology.Particle coagulation can be divided into two process,that is,the primary particles aggregate into particle cluster and the particle cluster gradually transform into mature particles.When the formation process of the mature particles,the soft the particle cluster can be easily transformed into mature particles.In contrast,the hard particle clusters are difficult to form mature particles.The particle crosslinking can increases the modulus of the particles,and reduces the particle coagulation extent.As a result,the irregular particle morphology can be obtained if the particle crosslinking occurred before the particles.On the other hand,the uniform spherical particles can be obtained if the particle crosslinking occurred after particle coagulation.In this section,the crosslinking reaction was controlled by adjusting the crosslinking agent type,the addition time,and the continuing time etc.The fifth section is the most important section in this section,in which the particle coagulation extent and the time were controlled by varying the electrostatic stability of the particles.The in situ charge neutralization between initiator chain ends and surfactant molecules adsorbed on particle surface were controlled by using cationic initiator and anionic surfactant.The decrease in electrostatic repulsive force promoted particle coagulation extent enlarged,moreover,the time occurred particle coagulation also was advanced to primary nucleation period.As a result,monodisperse,large sized polymer particles were obtained.This investigation not only enriches the theory of the macroemulsion polymerization,but also extends the application fields of the particle coagulation.The sixth section,also is the last section of this article,mainly describes some experimental conclusions about the particle coagulation mechanism and the application of particle coagulation,and also is a summary for this article.