Slow monomer addition ethers

Quasiliving Polymerization of Methyl Vinyl Ether. Similarly to IBVE polymerization, MVE was polymerized with premixed p-DCC/AgSbF initiating systems in CH2CI2 solvent at -70°C by slow and continuous monomer addition. Polymer yields were vL00% at every reaction time. ... 

In the early 1980s, Kennedy and his co-workers reported quasiliving polymerizations, which are phenomenologically akin to living polymerizations [57]. These processes involved slow and continuous monomer addition to a stirred initiator solution kept at a relatively low temperature. The monomers used therein included a-methylstyrene, isobutene, styrene, and alkyl vinyl ethers. In most cases, the number-average molecular weights steadily increased with the weight of the added monomer and the formed polymers had relatively narrow MWDs. 

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 This monomer addition sequence can be reversed and repealed if the anion of each monomer sequence can initiate polymerization of the other monomer.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. 

By the technique of slow and continuous monomer addition, Sawamoto and Kennedy polymerized IBVE and methyl vinyl ether (MVE) > in conjunction with a difunctional initiating system consisting of />-dicumyl chloride and silver hexafluoro-antimonate (AgSbF ). This system may lead to a propagating species according to the reaction sequence shown in Eq. (32) ... 

If the rate of addition to monomer is low, primary radical termination may achieve greater importance. For example, in photoinitiation by the benzoin ether 12 both a fast initiating species (13, high k) and a slow initiating species (14, low... 

Anionic ring-opening polymerization of l,2,3,4-tetramethyl-l,2,3,4-tetraphenylcyclo-tetrasilane is quite effectively initiated by butyllithium or silyl potassium initiators. The process resembles the anionic polymerization of other monomers where solvent effects play an important role. In THF, the reaction takes place very rapidly but mainly cyclic live- and six-membered oligomers are formed. Polymerization is very slow in nonpolar media (toluene, benzene) however, reactions are accelerated by the addition of small amounts of THF or crown ethers. The stereochemical control leading to the formation of syndiotactic, heterotactic or isotactic polymers is poor in all cases. In order to improve the stereoselectivity of the polymerization reaction, more sluggish initiators like silyl cuprates are very effective. A possible reaction mechanism is discussed elsewhere49,52. 

With certain cyclic ethers (dioxolane, oxiranes, etc.), the use of particular conditions results in a limitation of the back-biting reactions and a certain control of the polymerization. For instance, in polymerizations carried out in the presence of an alcohol and with a very low instantaneous monomer concentration, obtained by a slow addition of the monomer solution, almost the totality of electrophilic entities carried by the initiator reacts with the monomer to give protonic species ( activated monomer) the latter then react with the nucleophilic sites that are the hydroxy groups of alcohols. Propagation occurs through nucleophilic attacks of hydroxyls onto activated monomer molecules ... 

Water is the ideal solvent from the cost and pollution viewpoints, but it is a non-solvent for many surface coating polymers. It will ssolve a small number of homopolymers, notably those derived from acrylamide, acrylic acid, itaconic acid, vinyl methyl ether, vinyl pyrrolidone and vinyl sulphonic acid, but none of these homopolymers forms flexible films of use in the coatings industry. While copolymers of acrylic or methacrylic acids with acrylate esters are generally insoluble in water, their salts are soluble when the acid content is over 5% (for hydrophilic monomers) and 12% (for hydrophobic monomers). Such polymers can be prepared in solution, or in emulsion, but not in aqueous solution. This is because the acrylate esters are insoluble in water. The acid is copolymerised in the un-ionised form because the ion is unreactive to free radicals. In emulsion polymerisation, care has to be taken to avoid homopolymerisation of the acrylic or methacrylic acid in the water phase. Suppression of homopolymerisation requires a low concentration of acid throughout the polymerisation process. This can be achieved by using a long reaction period and slow addition of monomer mixture, or by careful pH buffer selection. 

---