2 edition of Termination of anionic ends in polymers found in the catalog.
Termination of anionic ends in polymers
Malcolm David Glasse
Thesis (Ph.D.) - Leicester Polytechnic, Leicester 1978.
|Statement||Malcolm David Glasse.|
Data on sulfur analysis indicated that the resulting polymers had nearly two initiator fragments (5 in eq 4) at the chain ends, as is shown in Table I. 13 Therefore, the polymerization of the monomer (M) with 1 proceeds via the dissociation of 1, initiation, propagation, primary radical (PR) termination, and chain transfer (CT) to 1, according. During the propagation step, the anionic active living ends are quickly transferred among all the propagating polymer chains [species (c) and (d) in Fig. 2]. The product polymers have high molecular weight and narrow molecular weight distribution (Nobori et al., ; Takaki et al., ). However, details of the reaction mechanism such as.
Initiator, a source of any chemical species that reacts with a monomer (single molecule that can form chemical bonds) to form an intermediate compound capable of linking successively with a large number of other monomers into a polymeric compound. The most widely used initiators produce free. In a free radical polymerization, high molecular weight polymers are initially formed and the molecular weights are independent of the rate of reaction. Ionic polymerization involves anionic and cationic polymerizations dependent on ionic species at their propagating ends.
Anionic Vinyl Polymerization In this process, the anions are introduced to make the monomers reactive. These reactive anions (Usually formed when a strong Lewis base or a nucleophile transfers its charge to the reacting monomers) then react with other monomers resulting in the propagation of the chain and forming the required polymers. Step-growth polymers, also called condensation polymers, Anionic initiation, requires the R group to. be electron withdrawing in order to. promote the formation of a stable. carbanion (ie, -M and -I effects help. ends in the inactive association state, gives rise to the.
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Anionic polymerization involves the polymerization of vinyl monomers possessing strong electronegative groups. The polymerization proceeds by formation of carbanions at polymer chain ends. Anionic polymerizations can be divided into initiation, propagation, and termination (chain transfer does not occur to any appreciable extent), and thus.
Anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of monomers initiated with anions. The type of reaction has many manifestations, but traditionally vinyl monomers are used.
Often anionic polymerization involves living polymerizations, which allows control of structure and composition. The methodology of living anionic polymerization is particularly suitable for syntheses of functionalized polymers with well-defined structures in certain systems which proceed in the absence of chain termination and chain transfer reactions.
15,21–28 A variety of linear, branched and cyclic molecular architectures can be prepared with control of structural variables such as molecular weight. Part of the Advances in Polymer Science book series H., D. Richards and M. Szwarc: Association of polymers with ionized ends. Effect of charge density on the degree of association.
Chem. and Ind. 45, Termination of anionic polymerization. In: Fortschritte Der Hochpolymeren-Forschung. Advances in Polymer Science, vol 2/2 Cited by: A solution of "living" polymers is in a state of dynamic equilibrium, because lack of termination reaction leaves the ends perpetually active.
The equilibrium molecular weight distribution of Author: M. Szwarc. The anionic ends of \(2\) are equivalent and can add ethenylbenzene molecules to form a long-chain polymer with anionic end groups, \(3\): If moisture and oxygen are rigorously excluded, the anionic groups are stable indefinitely, and if more monomer is added polymerization will continue.
As early asKarl Ziegler proposed that anionic polymerization of styrene and butadiene by consecutive addition of monomer to an alkyl lithium initiator occurred without chain transfer or termination. Twenty years later, living polymerization was demonstrated by Szwarc through the anionic polymerization of styrene in THF using sodium naphthalenide as an initiator.
Under certain conditions, anionic and coordination polymerizations can be carried out without the Termination Step to generate so-called “living” polymers.
The following are several general characteristics of this type of polymerization: 1) Once initiation occurs, the polymer chain forms very quickly, i.e., 10"1 23*to 10~6 sec. 2 1 Anionic Vinyl Polymerization Scheme Anionic polymerization of styrene using sodium naphthalene as initiator in THF. Scheme Anionic polymerization of styrene using sec-butyllithium as initiator.
their reactivity for a sufﬁcient time enabling continued propagation without termination and transfer reactions. Szwarc’s ﬁrst report of living anionic polymerization of styrene free from. both cationic and anionic polymerization.
•Formation of relatively stable ions is necessary in order to have reasonable lifetimes for propagation. This is accomplished by using low temperatures ( to 50 °C) to suppress termination and transfer and mildly polar.
synthesis offunctional-ended polymers byselective termination of living ends with appropriate reagents. The main architectural fea-tures available starting with these two basic themes are listed in Table 1 along with applications for the various polymer types.
Although living polymerization ofonly a. A review of anionic copolymerization, covering the material available inwas published by one of us.1 It dealt with the question of how to modify the concept of reactivity ratios to make it.
End groups are an important aspect of polymer synthesis and characterization. In polymer chemistry, end groups are functionalities or constitutional units that are at the extremity of a macromolecule or oligomer ().
In polymer synthesis, like condensation polymerization and free-radical types of polymerization, end-groups are commonly used and can be analyzed for example by nuclear magnetic.
DOI link for Functional Polymers. Functional Polymers book. Design, Synthesis, and Applications. Functional Polymers. DOI link for Functional Polymers. Functional Polymers book. Design, Synthesis, and Applications. Edited By Raja Shunmugam. Edition 1st Edition.
First Published This book presents these important facts: a) The mechanism of anionic polymerization, a more than year challenge in polymer chemistry, has now become better understood; b) Precise synthesis of many polymers with novel architectures (triblock, multi-block, graft, exact graft, comb, cyclic, many armed stars with multi-components, dendrimer-like hyper-branched, and their structural mixed (co.
The reversible transformation between the halide and living anionic chain end, which was used for initiation or termination, enables efficient end-functionalization of stereoregular polymethacrylates, which can be further utilized for the construction of structurally controlled polymers.
Free-radical polymerization (FRP) is a method of polymerization by which a polymer forms by the successive addition of free-radical building blocks. Free radicals can be formed by a number of different mechanisms, usually involving separate initiator molecules.
Following its generation, the initiating free radical adds (nonradical) monomer units, thereby growing the polymer chain. Living polymerization discovered by Professor Szwarc is known well to all chemists.
Some of the living polymerizations involve dormancy, a process in which there is an equilibrium (or at least exchange) between two types of living polymers, namely active at the given moment and dormant at this moment and becoming active in the process of activation.
These processes are at least equally. Polymerization ceases when the active centre destroyed by termination reaction(s). Introduction to Polymers 16 Chain polymerizationChain polymerization Introduction to Polymers 17 Chain polymerization – anionic polymerization ofChain polymerization – anionic polymerization of styrenestyrene But, the following is NOT possible Termination steps depend on the collision between two species that are both held at relatively low concentration, whether it is a cationic chain end and an anionic base or two different growing chains.
Propagation depends on the concentration of reactive chain ends. Polymer synthesis 3 • Polymers may be formed by two major kinetic schemes. polymerization polymerization (Faster) • Free radical polymerization Initiation Propagation Termination • Anionic polymerization • Cationic polymerization 4.
Step-growth mechanism 4 5. Step-growth polymerization 5 +𝐻𝐶𝑙 6.This new book covers the synthetic as well application aspects of functional polymers.
It highlights modern trends in the field and showcases the recent characterization techniques that are being employed in the field of polymer science. The chapters are written by top-notch scientists who are internationally recognized in the field.The building block through which any polymer molecule is built is known as a monomer.
These monomers are generally very reactive molecules. The process in which monomers are all linked together to form the long-chain polymers is called a polymerization reaction or polymerization process. Classification of Polymerization Reaction.