Polymer chemistry addition polymerization reaction

This volume contains 18 papers on the kinetics and technology of addition and condensation polymerization processes. These papers were presented at the sixth symposium on this subject held by the Division of Industrial and Engineering Chemistry and the Division of Polymer Chemistry during the A.C.S. Meeting, Boston April 9-14, 1972. They are concerned with known commercial products. New polymers and novel polymerization reactions presented at the same symposium are collected in the companion volume, Advances in Chemistry Series No. 129. 

A typical cationic uv adhesive formulation contains an epoxy resin, a cure-accelerating resin, a diluent (which may or may not be reactive), and a photoinitiator. The initiation step results in the formation of a positively charged center through which an addition polymerization reaction occurs. There is no inherent termination, which may allow a significant postcure. Once the reaction is started, it continues until all the epoxy chemistry is consumed and complete cure of the resin has been achieved. Thus, these systems have been termed living polymers. 

Acrylic adhesives cure by addition polymerization reactions. These chain reactions are initiated by the formation of free radicals that result in the adhesive curing by way of a very rapid polymer chain growth. This cure chemistry is significantly more rapid than a typical cure curve (i.e., condensation type) found in epoxy and urethane adhesives. A comparison of the cure profile of condensation (epoxy and urethane) versus addition... 

In this paper we have presented evidence to show that it is quite feasible to determine the detailed course of reaction between a polymer and an additive. Further, the understanding of this reaction pathway provides insight into new additives and schemes for the identification of efficacious flame retardant additives. Finally, we have elucidated schemes for the cross-linking of PMMA and have shown that the schemes do provide a route for flame retardation. It is imperative to realize that the purpose of this work is not to directly develop new flame retardants, rather the purpose is to expose the chemistry that occurs when a polymer and an additive react. This exposition of chemistry continually provides a new starting point for further investigations. The more that pathways for polymeric reactions are determined the more information is available to design suitable additives to prevent degradation of polymers. 

Photopolymer technology, which encompasses the action of light to form polymers and light initiated reactions in polymeric materials, is an immense topic. Previous papers in this symposium have described some of basic chemistry utilized in photopolymer technology. The primary objectives of this paper are a) to develop the connections between basic photopolymer chemistry and practical uses of the technology and b) to provide an overview of the wide variety of photopolymer applications that have been developed since the 1950 s. Every attempt has been made to make this review as inclusive as possible, but because of the extensive nature of this topic, there are many applications of photopolymer chemistry that have not been included. In addition, only limited representative references are provided since the patent and open literature for this technology are quite vast (7). 

This section introduces simple polymer reaction chemistry used to produce many commodity polymers. Understanding this simplified approach to the chemistry of polymer production Is Important In troubleshooting many extrusion processes, especially those that are producing unwanted degradation products that contaminate the discharge resin. There are two general types of polymer production processes 1) step or condensation reactions, and 2) addition or vinyl polymerization reactions. An overview of the reaction mechanisms wifi be presented in the next sections. 

Nearly all synthetic polymers are synthesized by the polymerization or copolymerization of different "monomers." The chain growth process may involve the addition chain reactions of unsaturated small molecules, condensation reactions, or ringopening chain-coupling processes. In conventional polymer chemistry, the synthesis of a new polymer requires the use of a new monomer. This approach is often unsatisfactory for Inorganic systems, where relatively few monomers or cyclic oligomers can be Induced to polymerize, at least under conditions that have been studied to date. The main exception to this rule is the condensation-type growth that occurs with inorganic dl-hydroxy acids. 

With regard to the chemistry of polymerization processes, we will only introduce the topic superficially. A polymerization reaction is controlled by several conditions such as temperature, pressure, monomer concentration, as well as by structure-controlling additives such as catalysts, activators, accelerators, and inhibitors. There are various ways a polymerization process can take place such as schematically depicted in Fig. 1.1. There are numerous other types of reactions that are not mentioned here. When synthesizing some polymers there may be multiple ways of arriving at the finished product. For example, polyformaldehyde (POM) can be synthesized using all the reaction types presented in Table 1.1. On the other hand, polyamide 6 (PA6) is synthesized through various steps that are present in different types of reactions, such as polymerization and polycondenzation. 

This type of polymerization was traditionally called addition polymerization, because each monomer has at least one double bond to which are added elements of two other monomers. The monomer and the repeat unit in the polymer have the same empirical formula. A more precise term for this type of reaction is chain-reaction or chain-grotvth polymerization, because this describes the chemistry by which the polymerization takes place. Many of our most familiar polymers are prepared using this chemistry, which will be developed in Chapter 5. 

The book is divided into eight chapters. The Introduction is a primer for both synthetic polymer chemistry in general, and cationic polymerizations in particular. More advanced readers may go directly to the following chapters. The second chapter covers the reactions of carbenium ions with various nucleophiles and focuses on the ionization of covalent species and the addition of carbenium ions to alkenes, arenes, and other ir-nucleo-... 

These possibilities are shown in Figure 1.15 and each will have a major effect on the chemorheological properties of the polymer compared with the linear parent. The detailed chemistry and mechanism of the reactions that lead both to linear polymers and to these different architectures are discussed in this section. The route to achieve these structures may involve stepwise polymerization addition polymerization, or post-polymerization modification. Each of these polymerization reactions, with particular emphasis on the way they may be adapted to reactive processing and the chemorheological consequences, is considered separately. Further detailed architectures such as graft and block copolymers with several different chemical components are then considered. 

The nature of the reactive centre defines the chemistry of the polymerization, the rate and conditions under which high polymer may form, and particular features of the polymer architecture (such as the tacticity see Section 1.1.2). The nature of the reactive centre and the monomer may also control the side reactions (such as branching) and defect groups that may be introduced, which may affect the subsequent performance of the polymer. In the following, we will consider the most common types of addition polymerization since this may define the properties of the polymer that then control the chemorheology. Certain of these reactions are more important than others in reactive processing, and the particular examples of reactions that occur in forming networks as well as modification of polymers will be considered in more detail. 

There are two fundamental polymerization mechanisms. Classically, they have been differentiated as addition polymerization and condensation polymerization. In the addition process, no by-product is evolved, as in the polymerization of vinyl chloride (see below) whereas in the condensation process, just as in various condensation reactions (e.g., esterification, etherification, amidation, etc.) of organic chemistry, a low-molecular-weight by-product (e.g., H2O, HCl, etc.) is evolved. Polymers formed by addition polymerization do so by the successive addition of unsaturated monomer units in a chain reaction promoted by the active center. Therefore, addition polymerization is called chain polymerization. Similarly, condensation polymerization is referred to as step polymerization since the polymers in this case are formed by stepwise, intermolecular condensation of reactive groups. (The terms condensation and step are commonly used synonymously, as we shall do in this book, and so are the terms addition and chain. However, as it will be shown later in this section, these terms cannot always be used synonymously. In fact, the condensation-addition classification is primarily applicable to the composition or structure of polymers, whereas the step-chain classification applies to the mechanism of polymerization reactions.)... 

Risse and S. Breunig, S. Transition metal catalyzed vinyl addition polymerizations of norbor nene derivatives with ester groups, Makromol. Chem. 193, 2915 (1992) C. Mehler and M. Risse, Addition polymerization of norbornene catalyzed by paUadium(2+) compounds. A pol3mierization reaction with rare chain transfer and chain termination, Macromol. 25, 4226 4228 (1992) R.G. Schulz, The chemistry of palladium complexes. III. The polymerization of norbornene systems cat alyzed by palladium chloride (1), Polym. Lett. 4, 541 (1966) C. Tanielian, A. Kiennemann, and T. Osparpucu, Influence de differents catalyseurs a base d elements de transition du groupe VIII sur la polymerisation du norbornene, Can. J. Chem. 57, 2022 (1979) A. Sen and T. W. Lai, Cat alytic polymerization of acetylenes and olefins by tetrakis(acetonitrile)paUadium(II) ditetrafluorobo rate, Organometallics 1, 415 (1982) C. Mehler and W. Risse, Pd(II) catalyzed polymerization of norbornene derivatives, Makromol. Chem. Rapid Commun, 12, 255 (1991). 

M. Apostolo, a. Tredici, M. Morbidelli, and A. Varma, Propagation velocity of the reaction front in addition polymerization systems. Journal of Polymer Science, Part A Polymer Chemistry, 35 (1997), pp. 1047-1059. 

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