Heterogeneous polymerization reviews

This review deals with current ideas on the mechanisms operative in acrylonitrile polymerization. The topic is of importance in its own right and also because the study of acrylonitrile has cast light on heterogeneous polymerizations in general. It is an active field of research and the interpretations are still controversial. We shall look first at free-radical polymerization in homogeneous solution, where the monomer behaves in a more or less classical fashion. Next we shall consider the complications that arise where the monomer is at least partially soluble in the reaction medium but where the polymer precipitates. These conditions are encountered in bulk polymerization and in most aqueous or organic diluents. Finally we shall examine the less extensive literature on anionic polymerization and show important differences between the radical and the ionic processes. 

There are many unique polymerization processes which share a conunon heritage with emulsion polymerization, but which often are unrecognized as such. It is the purpose of this review to describe some of these emulsion polymerization-like processes and their products. Some further definition is in order unconventional emulsion polymerizations can be described as those processes whereby the product is a polymer latex that physically resembles latex from emulsion polymerization and cannot be grouped into any other recognized form of heterogeneous polymerization. In many cases the reasons why a process is not recognized as an emulsion polymerization is that the polymerization is not via a free-radical process. This review (hscusses four distinct types of polymerization processes, all of which have examples that produce latex particles and in many ways can be described as unconventional emulsion polymerizations. These are free-radical polymerization, ionic polymerization, transition metal catalyzed polymerization and enzyme-catalyzed polymerization. The precise systems discussed in this review are described in Table 23.1. 

In this chapter, the main features of heterogeneous polymerization in scC02 are analyzed. After a critical review of the main contributions in the literature, a comprehensive mathematical model is proposed. Finally, two case studies, selected as representative of dispersion and precipitation process, respectively, are discussed with the aim of elucidating the main mechanisms of the two heterogeneous processes. 

With respect to the possibilities of carbon dioxide as a reaction medium for polymerization reactions, extensive reviews have been published by Scholsky [55], Shaffer et al. [56], Kendall et al. [57], and Cooper [58]. Typically, a division is made between homogeneous and heterogeneous polymerization in SCCO2. 

The aim of this review is to summarize and discuss the kinetic data of the emulsion polymerization and copolymeiization of vinyl chloride. The current understanding of the kinetics of free-radical polymerization of conventional monomer is briefly described and kinetic data of radical polymerization and copolymerization of vinyl chloride in the presence of hydrophobic and hydrophilic additives are summarized. Efiects of the initiator type and concentration, the reaction conditions and the type of diluent are evaluated. Variation of kinetic and molecular weight parameters in the heterogeneous polymerizations with emulsifier type and concentration are discussed. 

The behavior of kinetic systems with even a few interacting species can become very complex. L. Ber nek treats a few key principles and accompanies them with experimental observations in Kinetics of Coupled Heterogeneous Catalytic Reactions. In One-Component Catalysts for Polymerization of Olefins, Yu. Yermakov and V. Zakharov review results... 

NMP of S in heterogeneous media is discussed in reviews by Qiu et at.,205 Cunningham,206 207 and Schork et a/.208 There have been several theoretical studies dealing with NMP and other living radical procedures in emulsion and miniemulsion."09 213 Butte et nr/.210 214 concluded that NMP (and ATRP) should be subject to marked retardation as a consequence of the persistent radical effect. Charlcux209 predicted enhanced polymerization rates for minicmulsion with small... 

Application to heterogeneous polymer solids, and elastic composites, is presented in the Section 7 (Gusev, Suter), which is followed by a summary and the outlook for the various methods reviewed here. It will be apparent to the reader that this review thus assembles several building blocks for the difficult task to bridge the gaps from the atomistic to the macroscopic scales in space and times for the simulation of polymeric materials. Integrating these building blocks into one coherent framework still is not fully solved and a matter of current research. 

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