Ionic polymerization categories

The grafting methods can in principle be divided into three categories, namely, radical polymerization, ionic polymerization, and condensation or addition polymerization. Only the first case is discussed in the following since the most common grafting methods belong to this category. 

The vast majority of ionic polymerizations studied fall into category B. However, there is now a substantial and growing literature about category A, for which the term macrozwitterion has been coined. 

Closely related to the ionic polymerization of heterocyclic monomers is, what we can call, pseudoionic polymerization (or sometimes, perhaps, cryptoionic). We use the preffix pseudo- in the same meaning as it was first used in the vinyl cationic polymerization. It means that propagation actually proceeds on the covalent species that could have been in equilibrium with their ionic counterparts. Several systems falling to this category have recently been described for both anionic and cationic polymerization of heterocyclics. In the anionic processes derivatives of Zn or A1 alkyls or alcoholates are believed to function this way. However, for none of these systems the absence of ionic contribution was shown. Two catalytic systems are of particular interest, namely the -Zn-O-AK systems (20) and>Al-alkyl modified by bulky porphyrin derivatives (21). Both are discussed in this volume and both have been clearly shown to produce living systems. The former with e-caprolactone and the latter... 

We have cited several examples which illustrate characteristic ionic polymerization reactions of unsaturated compounds, which may be contrasted with the behavior of alkanes, for which the initial ion-molecule reactions usually lead to stable ion products which do not react further. It was therefore of interest to investigate ionic reactions in cyclobutane, the saturated hydrocarbon isomeric with the unsaturated butenes, to establish whether cyclanes could properly be classified in either of these categories. Additional impetus for such a study was provided by radiolysis data on cyclobutane which suggested that the cyclobutane parent ion rearranges prior to reaction. ... 

Polymers are macromolecules which are composed of smaller molecules linked by covalent bonds. In terms of the reaction kinetics, polymerizations are traditionally classified into several categories stepwise polymerization, free-radical polymerization, ionic polymerization, ring-open polymerization, and coordination polymerization or polyinsertion. Each polymerization method has a combination of requirements for reaction conditions, and they exhibit certain types of product and process features (Caneba, 1992a, 1992b Odian, 1991). Even though in principle, the FRRPP process can be implemented with a wide variety of polymerization mechanisms, its discovery and immediate implementation has occurred in conjunction with free-radical kinetics. 

Star polymers consist of several linear polymer chains connected at one point. Prior to the development of CRP, star molecules prepared by anionic polymerization had heen examined. However, due to the scope of ionic polymerization, the composition and functionality of the materials were limited. The compact structure and globular shape of stars provide them with low solution viscosity and the core-shell architecture facilitates entry into several applications spanning a range from thermoplastic elastomers (TPEs) to dmg carriers. Based on the chemical compositions of the arm species, star polymers can be classified into two categories homoarm star polymers and miktoarm (or heteroarm) star copolymers... 

The above descriptions of polymerization are based on radical initiators. Actually, photopolymerization reactions are basically classified into two categories radical polymerization and ionic polymerization. Among these two types of photopolymerization, reactions that are typically used for laser fabrication are [1-5] ... 

The mechanism of these reactions places addition polymerizations in the kinetic category of chain reactions, with either free radicals or ionic groups responsible for propagating the chain reaction. 

AB cements are not only formulated from relatively small ions with well defined hydration numbers. They may also be prepared from macromolecules which dissolve in water to give multiply charged species known as polyelectrolytes. Cements which fall into this category are the zinc polycarboxylates and the glass-ionomers, the polyelectrolytes being poly(acrylic acid) or acrylic add copolymers. The interaction of such polymers is a complicated topic, and one which is of wide importance to a number of scientific disciplines. Molyneux (1975) has highlighted the fact that these substances form the focal point of three complex and contentious territories of sdence , namely aqueous systems, ionic systems and polymeric systems. 

For styrene-based random copolymers, functional groups can be introduced into the polymer chains via copolymerization with functional styrene derivatives, because the electronic effects of the substituents are small in the metal-catalyzed polymerizations in comparison to the ionic counterparts. Random copolymer R-6 is of this category, synthesized from styrene and />acetoxystyrene.372 It can be transformed into styrene// -vinylphenol copolymers by hydrolysis.380 The benzyl acetate and the benzyl ether groups randomly distributed in R-7 and R-8 were transformed into benzyl bromide, which can initiate the controlled radical polymerizations of styrene in the presence of copper catalysts to give graft copolymers.209 Epoxy groups can be introduced, as in R-9, by the copper-catalyzed copolymerizations without loss of epoxy functions, while the nitroxide-mediated systems suffer from side reactions due to the high-temperature reaction.317... 

In this category of injectable biomaterials, the gel is formed between the liquid monomers or macromers and a suitable polymerization/crosslinker initiator in response to either ionic or pH changes. Advantages of these kinds of materials include easy placement and subsequent polymerization to fill complex shaped defects that otherwise would be difficult to fill, improved adhesion of the polymer to the surrounding tissue due to close mechanical interlocking with the micro-roughened surface of the tissue. 

The excipients used in solid dispersions can be broadly classified as (a) polymeric and (b) non-polymeric excipients. Polymeric excipients are the primary excipients, whereas the non-polymeric ones are the auxiliary excipients. Polymeric excipients are further classified based on their charge into the following categories (a) nonionic or non-pH-dependent and (b) ionic or pH-dependent polymers. Further, nonionic polymers are classified as polyvinyllactam polymers and cellulose ethers. The ionic polymers are further classified as cationic and anionic polymers (Fig. 4.2). 

Solubility parameter calculated by Molecular Modeling Pro Plus from ChemSW Inc. Polymeric excipients are categorized into two main categories (1) nonionic/non-pH dependent polymers and (2) ionic/pH dependent polymers... 

Hydrides can be categorized in various classes according to the nature of the bond that links the metal and hydrogen. The following categories can usually be found in the literature ionic hydrides (hydrides with group 1 and 2 elements), covalent hydrides, polymeric hydrides, metallic hydrides, borderline hydrides, and transitirai metal complex hydrides. Here the reaction of ionic hydrides with carbon dioxide (CO2) is considered. Transition metal hydrides with the formula L M-H are discussed in Chap. 4, where the interaction of CO2 with analogous E-X systems (where E and X are different elements) is discussed. 

---