Anionic polymerization monofunctional

To the first category belong the homo- and copolymerization of macromonomers. For this purpose, macromolecules with only one polymerizable end group are needed. Such macromonomers are made, for example, by anionic polymerization where the reactive chain end is modified with a reactive vinyl monomer. Also methacrylic acid esters of long-chain aliphatic alcohols or monofunctional polyethylene oxides or polytetrahydrofurane belong to the class of macromonomers. 

The terms in Equation 1.3 (Malkin s autocatalytic model) are described in Nomenclature. In Malkin s autocatalytic model, the concentration of the activator, [A], is defined as the concentration of the initiator times the functionality of the initiator. For a difimctional initiator [e.g., isophthaloyl-bis-caprolactam, the concentration of the activator (acyllactam) is twice the concentration of the initiator]. The term [C] is defined as the concentration of the metal ion that catalyzes the anionic polymerization of caprolactam. In a magnesium-bromide catalyzed system, the concentration of the metal ion is the same as the concentration of the caprolactam-magnesium-bromide (catalyst) because the latter is monofunctional. 

Polyethylene oxide)macromonomers have thus been synthesized by two-step processes. Poly(oxyethylene)mo nomethyl ethers with widely varying molecular weights are commercially available. They are obtained by anionic polymerization of oxirane initiated by monofunctional alkoxides261 such as potassium 2-methoxyethanol. 

Monofunctional siloxanes are readily prepared by anionic polymerization of hexamethylcyclo-trisiloxane (D3) following the route illustrated in Fig. 1 [1]. 

Most interesting from the standpoint of commercial development is the formation of block copolymers by the living polymer method. Sequential addition of monomers to a living anionic polymerization system is at present the most useful method of synthesizing well-defined block copolymers. Depending on whether monofunctional or difunctional initiators are used, one or both chain ends remain active after monomer A has completely reacted. Monomer B is then added, and its polymerization is initiated by the living polymeric carbanion of polymer A. This method of sequential monomer addition can be used to produce block copolymers of several different types. 

PEO prepared by anionic polymerization using the monofunctional initiator ((diphenylmethyl)potassium) has one -OH end group leading to the formation of linear-dendritic diblock copolymers (Scheme 102). 

Block Copolymer Synthesis by Three-Step Sequential Monomer Addition The preparation of block copolymers by sequential addition of monomers using living anionic polymerization and a monofunctional initiator is the most direct method for preparing well-defined block copolymers. Detailed laboratory procedures for anionic synthesis of block copolymers are available [37, 230], Several important aspects of these syntheses can be illustrated by considering the preparation of an important class of block copolymers (Scheme 7.22), the polystyrene-fe-polydiene-( -polystyrene triblock copolymers. 

Sequential monomer addition by using a monofunctional initiator (Figure 3(c)) could be followed only if the reactivity of both monomers is almost the same. The maaoinitiator formed from monomer A can polymerize monomer B and vice versa. Styrene (St) and dienes in anionic polymerization and various methacrylates in anionic or GTP are characteristic examples of this method. The sequential monomer addition route, due to partial termination and/or deactivation reactions, proposed from the addition of three different quantities of monomer allows the synthesis of asymmetric ABA ttiblock copolymers, where the two end blocks exhibit different molecular characteristics. 

With a similar approach it is also possible to obtain model networks with controlled amounts of very well defined pendant chains. Adding monofunctional B chains to the initial mixture of pre-polymer and crosslinker an + B + B, reaction is generated. This will result in the formation of linear pendant chains of length equal to that of the B, s. Furthermore, thanks to modem anionic polymerization procedures [12,14,15] it is possible to synthesize telequelic monodisperse chains of type B, and B that can be used to build model networks with elastic and pendant chains of any desirable molecular weight and narrow molecular weight distribution. 

In the first way, the polyvinyl block is obtained by anionic polymerization as described before except that the monofunctional initiator (cumylpotassium) is replaced by a bifunctional initiator (dimer dianion of a-methyl-styrene/K). Then the amination of the two living ends and the synthesis of the polypeptide blocks are performed as described before for AB copolymers. 

More recently, the monofunctional cyanopentadienoates (2) were shown to improve the heat resistance of cyanoacrylate adhesives. In one case, when more than 50 weight % of 2 was combined with a standard cyanoacrylate monomer, the impact, peel, heat, and water resistance were greatly improved. " The improved heat resistance was attributed to the crosslinking of the residual olefin (28) after the anionic polymerization of 2 (see Eq. 8). The cyanopentadienoate was used in 50-90% concentration. The slow cure rate of the dienoate was overcome by the addition of an accelerator, in this case, a small quantity of an alcohol. Improvements in the heat, water, and water vapor resistance of alkyl cyanoacrylates can also... 

Varshney, S.K., Hautekeer, J.P., Fayt, R. et al. (1990) Anionic polymerization of (meth)acrylic monomers. 4. Effect of lithium salts as Ugands on the Uving polymerization of methyl methacrylate using monofunctional initiators. Macromolecules, 23,2618-2622. 

The number of possible activators for the lactam anionic polymerization is extraordinarily large. In Scheme 22, some examples of the various types of activators are reported. The activators can be monofunctional or multifunaional and can be divided in two main categories ... 

Kraton 1102 contains about 20 wt % uncoupled SB diblocks. This is because a coupling method was used to produce SBS triblock copolymer from SB diblock copolymer that was synthesized, via anionic polymerization, using a monofunctional initiator. 

A final arm-first method based on the preparation via anionic polymerization of star-shaped polymers will be mentioned. Here the anionic polymerization is only used to prepare a linear (D-fimctional polymer of controlled molar mass and functionality and not for the coupling reaction. In many cases, anionic polymerization is the only way to access these well-defined monofunctional precursor chains. In a second step, these functional polymers were reacted with plurifunctional compounds exhibiting antagonist functions. Some examples are given below. 

A monofunctional poly(dimethyl)siloxane (PDMS) chain fitted wifli a SiH end group is reacted under appropriate conditions with a low-molar-mass compound exhibiting antagonist Si-vinyl functions or the reverse [41] (Scheme 3). That method has also been used successfully in combination with anionic polymerization to prepare polyst5n-ene-arm-styrene-arm-2-vinylpyridine star copolymers [42]. 

More detailed studies were devoted to the mechanism of electrochemical polymerization applied to Fe(II), Ru(II) and Os(II) complexes containing 2,2 -dipyridyl and monofunctional monomer (L) such as 4-VP, bis(4-pyridyl)ethylene, trans-4-stilbazole or N-(4-pyridyl)acrylamide [86], The first stage of electrochemical polymerization is shown to be the formation of a radical-anion, e. g. by the following scheme... 

Monofunctional Initiators. AB, ABA, and multiblock copolymers can be synthesized by initiation of one monomer with a monofunctional initiator like n-butyl lithium. When the first monomer has been reacted, a second monomer can be added and polymerized. This monomer addition sequence can be reversed and repealed if the anion of each monomer sequence can initiate polymerization of the other monomer. The length of each block is determined by the amount of the corresponding monomer which was provided. Styrene-isoprene-styrene block copolymers can be made by this method by polymerizing in benzene solution and adding the styrene first. Addition of a small amount of ether accelerates the slow attack of dienyl lithium on styrene. 

Coupling Reactions. In this technique, a living AB block copolymer is made by monofunctional initiation and is then terminated with a bifunctional coupling agent likeadihaloalkane. ABA copolymers can be madeby joining AB polymeric anions ... 

Almost all fimctional silicone fluids of today s industrial production are either of a cyclic nature, containing the appropriate residues, or are linear oils bearing reactive functionalities at both ends or in the chain. The chemical nature of silicone synthesis done by equilibration and condensation is prohibitive for formation of asymmetrical silicones, in contrast to organic molecules like oleic acid or even ethanol. Currently there is only one way of preparing monofunctional silicone fluids, which is through kinetic anionic ring opening polymerization of the cyclic silicone monomer hexamethyl-cyclotrisiloxane (D3). 

Synthesis of monofunctional fluids usually proceeds via anionic ring opening of D3 by butyl lithium in an aptotic solvent (for example THF) and subsequent polymerization to a lithium polydimethylsiloxanolate. This may be neutralized to a silanol functional fluid by acids or terminated with chlorosilanes to the corresponding functional fluids. 

Acrylonitrile. Acrylonitrile is usually considered to be monofunctional in polymerization—Le., it reacts normally with free-radical and anionic catalysts. It has been reported, however, that irradiation with x-rays at —78°C. results in partial formation of keteneimine groups (7), as shown in Reaction 21. 

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