Ionic polymerization cationic

Problem 30.7 Which method of ionic polymerization—cationic or anionic—is preferred for each monomer Explain your choices. 

In configuration (A) one pair of electrons in each monomer unit is impaired (in the ir-orbital), which enables a single electron to react with an external single electron and end up as a free radical. This is the key to the most conventional mode of polymerization, via free radicals. Configuration (B) leads to an excess of electrons on one side (anion) and a shortage on the other side (cation). This leads to ionic polymerization (cationic or anionic). Hence there are choices of various mechanisms for polymerization, where the chemical nature of the monomer (characteristics of the substituent groups) dictates the preferred mechanism. This is shown in Table 2-3. 

Ionic polymerization (cationic polymerization, anionic polymerization) n. A polymerization conducted in the presence of electrically charged ions that become attached to carboxyhc groups on carbon... 

The active centers that characterize addition polymerization are of two types free radicals and ions. Throughout most of this chapter we shall focus attention on the free-radical species, since these lend themselves most readily to generalization. Ionic polymerizations not only proceed through different kinds of intermediates but, as a consequence, yield quite different polymers. Depending on the charge of the intermediate, ionic polymerizations are classified as anionic or cationic. These two types of polymerization are discussed in Secs. 6.10 and 6.11, respectively. 

Ionic polymerizations, whether anionic or cationic, should not be judged to be unimportant merely because our treatment of them is limited to two sections in this text. Although there are certain parallels between polymerizations which occur via free-radical and ionic intermediates, there are also numerous differences. An important difference lies in the more specific chemistry of the ionic mechanism. While the free-radical mechanism is readily discussed in general terms, this is much more difficult in the ionic case. This is one of the reasons why only relatively short sections have been allotted to anionic and cationic polymerizations. The body of available information regarding these topics is extensive enough to warrant a far more elaborate treatment, but space limitations and the more specific character of the material are the reasons for the curtailed treatment. 

Both modes of ionic polymerization are described by the same vocabulary as the corresponding steps in the free-radical mechanism for chain-growth polymerization. However, initiation, propagation, transfer, and termination are quite different than in the free-radical case and, in fact, different in many ways between anionic and cationic mechanisms. Our comments on the ionic mechanisms will touch many of the same points as the free-radical discussion, although in a far more abbreviated form. 

The aim of the present work was optimization of synthesis of SG -polymeric cation exchanger composite films by sol-gel technology in the presence of non-ionic surfactants and their application for detenuination of Zn (II) as phenanthrolinate (Phen) complex. 

The ability to ionically polymerize apparently correlates in many cases with the capacity of the substituents to act as electron acceptors (anionic polymerizability) or as electron donors (cationic polymerizability) on the rt-bond of the vinyl group. These relationships should be visible in carefully chosen quantum chemical parameters. 

Even parameters which are suited to characterizing cationic polymerizability (AE(1)+ x(HOMO)mononicr x(LUMO)c J can be used here. This is not surprising due to the diametral-analogous nature of the ionic polymerizations (see part 4.1.2). 

Ionic Polymerization. Ionic polymerizations, especially cationic polymerizations, are not as well understood as radical polymerizations because of experimental difficulties involved in their study. The nature of the reaction media is not always clear since heterogeneous initiators are often involved. Further, it is much more difficult to obtain reproducible data because ionic polymerizations proceed at very fast rates and are highly sensitive to small concentrations of impurities and adventitious materials. Butyl rubber, a polymer of isobutene and isoprene, is produced commercially by cationic polymerization. Anionic polymerization is used for various polymerizations of 1,3-butadiene and isoprene. 

Ionic polymerizations are generally much faster than radical polymerizations. Both cationic and anionic polymerizations typically proceed with much higher concentrations of propagating centers (10r -10 2 molar) than in radical polymerizations (lpropagating centers do not annihilate each other as do radicals. 

Chain-reaction mechanisms differ according to the nature of the reactive intermediate in the propagation steps, such as free radicals, ions, or coordination compounds. These give rise to radical-addition polymerization, ionic-addition (cationic or anionic) polymerization, etc. In Example 7-4 below, we use a simple model for radical-addition polymerization. 

This paper may be regarded as a sequel to my second book on Cationic Polymerisation [1]. I have aimed here at providing a fairly detailed discussion of some theoretical aspects of the subject which is still (or perhaps now more than ever before) in Dainton s words rudis indigestaque moles (a crude and ill-digested, i.e., confused, mass) [2], I also intend to discuss specifically some of the problems raised by Mayo and Morton in their article Ionic Polymerization in the book Unsolved Problems in Polymer Science [3]. 

The ionic conductivity at the end of a polymerisation is due to whatever cations Pn+ are formed or left when the monomer is exhausted and the anions A- of the initiating salt, plus a very minor contribution from the ions formed from impurities, which will be ignored. In order to analyse the relation between the observed iq, c0 and the ionic conductivity A of the electrolyte, it is necessary to clarify the electrochemistry of the solutions. We note first that the polymeric cations, whatever their structure, (i.e., as they were when propagating or subsequently isomerised), are much larger than the anions, SbF6, so that these carry virtually all the current so that A A, (SbF6), and therefore A, can be calculated-see below. Next, we note that all the iq- c0 plots, including that reported earlier [2], are rectilinear. This means ... 

Ionic polymerization may also occur with cationic initiations such as protonic acids like HF and H2SO4 or Lewis acids like BF3, AICI3, and SnC. The polymerization of isobutylene is a common example, shown in Fig. 14.5. Note that the two inductively donating methyl groups stabilize the carbocation intermediate. Chain termination, if it does occur, usually proceeds by loss of a proton to form a terminal double bond. This regenerates the catalyst. 

The ionic chain polymerization of unsaturated linkages is considered in this chapter, primarily the polymerization of the carbon-carbon double bond by cationic and anionic initiators (Secs. 5-2 and 5-3). The last part of the chapter considers the polymerization of other unsaturated linkages. Polymerizations initiated by coordination and metal oxide initiators are usually also ionic in nature. These are called coordination polymerizations and are considered separately in Chap. 8. Ionic polymerizations of cyclic monomers is discussed in Chap. 7. The polymerization of conjugated dienes is considered in Chap. 8. Cyclopolymerization of nonconjugated dienes is discussed in Chap. 6. 

The species present in cationic ring-opening polymerizations are covalent ester (IX), ion pair (X), and free ion (XI) in equilibrium. The relative amounts of the different species depend on the monomer, solvent, temperature, and other reaction conditions, similar to the situation described for ionic polymerization of C=C monomers (Chap. 5). 

Some early polymerizations reported as Ziegler-Natta polymerizations were conventional free-radical, cationic, or anionic polymerizations proceeding with low stereoselectivity. Some Ziegler-Natta initiators contain components that are capable of initiating conventional ionic polymerizations of certain monomers, such as anionic polymerization of methacrylates by alkyllithium and cationic polymerization of vinyl ethers by TiCLt-... 

Depending on the nature of the active center, chain-growth reactions are subdivided into radicalic, ionic (anionic, cationic), or transition-metal mediated (coordinative, insertion) polymerizations. Accordingly, they can be induced by different initiators or catalysts. Whether a monomer polymerizes via any of these chain-growth reactions - radical, ionic, coordinative - depends on its con-... 

In ionic polymerizations, the molecular weight can be regulated by temperature, type of catalyst and nature of solvent. In some cases also regulators can be used which, as in the case of cationic polymerization of trioxane, lead to the incorporation of special endgroups. 

Like radical polymerizations, ionic polymerizations also occur by a chain mechanism. In contrast to radical polymerizations the chain carriers are macroions carbonium ions in the case of cationic polymerizations and carbanions in the case of anionic polymerization of C=C compounds ... 

Hagglage, J. Hemery P. Bolleau, S. Communication at the 5th Symposium on Cationic and Other Ionic Polymerizations. Kyoto, Japan, 1980. 

While almost all monomers bearing carbon-carbon double bonds may undergo radical polymerization, ionic polymerization is highly selective. This arises to some extent due to the stability of the propagating species. Cationic polymerization involves carbenium ions. 

Unlike cationic polymerization initiated by a conventional catalyst, the propagating species in the present system would bear different type of counter-ion or would be much more free. The counter-anion obtained in this entirely organic system would be large and unstable. The problem of the counterion in charge transfer ionic polymerization certainly requires further study. 

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