Styrenes, controlled/living anionic

Novel sulfonated and carboxylated ionomers having "blocky" structures were synthesized via two completely different methods. Sulfonated ionomers were prepared by a fairly complex emulsion copolymerization of n-butyl acrylate and sulfonated styrene (Na or K salt) using a water soluble initiator system. Carboxylated ionomers were obtained by the hydrolysis of styrene-isobutyl-methacrylate block copolymers which have been produced by carefully controlled living anionic polymerization. Characterization of these materials showed the formation of novel ionomeric structures with dramatic improvements in the modulus-temperature behavior and also, in some cases, the stress-strain properties. However no change was observed in the glass transition temperature (DSC) of the ionomers when compared with their non-ionic counterparts, which is a strong indication of the formation of blocky structures. 

Controlled/Living Anionic Polymerization of Styrenes in Polar Solvent Using Flow Microreactor Systems [145]... 

Controlled/Living Anionic Block Copolymerization of Styrenes and Alkyl Methacrylates Using Integrated Flow Microreactor Systems... 

PS macromonomers have been efficiently applied to the synthesis of well-defined polymer hybrids with controlled length of grafts. They are, in general, prepared via living anionic polymerization of styrene monomers and their treatment with vinyl compounds, such as -allyl, -undecenyl, and styryl compounds. 

The synthetic procedure for the synthesis of the inverse starblock copolymers is given in Scheme 25. Diblock arms (I) having the living end at the PS chain end were prepared by anionic polymerization with sequential addition of monomers. In order to accelerate the crossover reaction from the PILi to the PSLi chain end a small quantity of THF was added prior the addition of styrene. The living diblock (I) solution was added dropwise to a stoichiometric amount of SiCl4 until two arms are linked to the silane. This step was monitored by SEC and is similar to a titration process. The end point of the titration was determined by the appearance of a small quantity ( 1%) of trimer in the SEC trace. The diblock (I) was selected over the diblock (II) due to the increased steric hindrance of the styryl anion over the isoprenyl anion, which makes easier the control of the incorporation of only two arms into the silane. 

In a similar manner, Yoshida and Osagawa [436] synthesized poly(s-caprolactone) with 2,2,6,6-tetramethylpiperdine-l-oxyl (TEMPO) at one end by anionic polymerization of caprolactone using an aluminum tri(4-oxy-TEMPO) initiator. The TEMPO-supported polycaprolactone behaved as a polymeric counter radical for a controlled/ living radical polymerization of styrene to form block copolymers [436]. 

Ramakrishnan, A., and Dhamodharan, R. (2000). A novel and simple method of preparation of poly(styrene-b-2-vinylpyridine) block copolymer of narrow molecular weight distribution living anionic polymerization followed by mechanism transfer to controlled/iivingc radical polymerization (ATRP). J. Macromol. ScL, Pure Appl. Chem., A37(6) 621-631. 

The synthesis of block copolymers of controlled structures is most conventionally accomplished through the use of living anionic polymerization. One can easily imagine, however, desirable block copolymers derived from monomers which are inert to anionic polymerization conditions, or which do not share any common mode of polymerization. In a recent series of papers (24-34), Richards and coworkers have addressed this problem in a general way, and have developed methods which convert one kind of active center into another. Within the context of cyclic ether polymerizations, Richards has focused on the preparation of block copolymers of styrene and tetrahydrofuran (THF) several methods of accomplishing this copolymerization are described in the following paragraphs. 

For carbon-based vinyl monomers, controlled polymerization has been traditionally achieved by ionic mechanisms [174]. The living anionic polymerizations of styrene and methyl methacrylate are quite common, resulting in preservation of the polymer functionality. However, alike the inorganic analogues the ionic polymerization mechanism is limited to a rather narrow class of monomers, under conditions of the most stringent purity. Therefore, the aim to develop a controlled free radical... 

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