Polymerizations living anionic type

A polymer-bound hindered amine light stabilizer [P-HALS] has been synthesized by terminating the living anionic polymerization of isoprene with 4(2,3-epoxy pro-poxy)-1,2,2,6,6-pentamethylpiperidine followed by hydrogenation of the resulting polymer to E-P copolymer using Zeigler type catalyst [40] ... 

Sequential addition of different monomer charges to a living anionic polymerization system is useful for producing well-defined block copolymers. Thermoplastic elastomers of the triblock type are the most important commercial application. For example, a styrene-isoprene-styrene triblock copolymer is synthesized by the sequence... 

Narrowly distributed Pl-ft-PS-i-PI triblock copolymer chains with both of their ends capped with bromobutyl groups were prepared by sequential addition of living anionic polymerization and terminated by excess of 1,4-dibromobutane (PS block Mw = 3.5 x 103 g/mol PI blocks Mw = 3.1 x 103 g/mol Mw/Mn = 1.12 The degree of end-functionalization was 92% characterized by HNMR). Figure 6 shows the SEC profile of such prepared triblock copolymer chains. The small but a detectable amount ( 5%) of Pl-i-PS-i-PI dimers, PI-Z>-PS-Z>-PI-c-PI-Z>-PS-Z>-PI, is presumably formed via the Wurtz-type coupling reaction. 

The range of monomers that can be incorporated into block copolymers by the living anionic route includes not only the carbon-carbon double-bond monomers susceptible to anionic polymerization but also certain cyclic monomers, such as ethylene oxide, propylene sulfide, lactams, lactones, and cyclic siloxanes (Chap. 7). Thus one can synthesize block copolymers involving each of the two types of monomers. Some of these combinations require an appropriate adjustment of the propagating center prior to the addition of the cyclic monomer. For example, carbanions from monomers such as styrene or methyl methacrylate are not sufficiently nucleophilic to polymerize lactones. The block copolymer with a lactone can be synthesized if one adds a small amount of ethylene oxide to the living polystyryl system to convert propagating centers to alkoxide ions prior to adding the lactone monomer. 

Another approach to block copolymers involves changing the type of propagating center part way through the synthesis via a transformation reaction [Burgess et al., 1977 Richards, 1980 Souel et al., 1977 Tung et al., 1985]. For example, after completion of the living anionic polymerization of monomer A, the carbanion centers are transformed into carbocations... 

Norbornenyl-ended macromonomers from poly(ethylene oxide) (PEO), 15, as well as from PEO-b-PSt or PSt-b-PEO block copolymers, 16a, 16b, have been prepared by the initiation or termination method of living anionic polymerization [22, 23]. The ROMP of 16 afforded various types of controlled, core-shell... 

The deciding factor which aroused increased interest in block copolymer production was the discovery of living anionic polymerization. New types of materials could be prepared by stepwise polymerization of several monomers. 

The number of copolymer types accessible in this way is only limited by the number of monomers able to polymerize by the living anionic mechanism. Similarly block copolymers can also be formed by living cationic polymerization [274-276],... 

ABA-type block copolymers B-12 with a hard PMMA as the outer segment (A) and a soft poly(nBA) as the inner segment (B) are expected as all-acrylic thermoplastic elastomers. Examples of B-12 have been prepared with copper and nickel catalysts via bifunctional initiation.359-364 Unfortunately, the copolymers by R—Br/Ni-2 via the macroinitiator method were reported to be inferior as thermoplastic elastomers to those by living anionic polymerizations. A possible reason is the presence of short PMMA seg-... 

Using this method asymmetric stars of the type (PSa) (PSb)/7 were prepared.77 Living PS chains were obtained by s-BuLi initiation and reacted with a small amount of DVB to give a living star polymer. The anionic sites of the star core were subsequently used to initiate the polymerization of a new quantity of styrene. This initiation step was accelerated by the addition of a small quantity of THF. It was revealed by SEC analysis that high molecular weight species were also present, probably due to the formation of linked stars. These structures can be obtained when living anionic branches of one star react with the residual double bonds of the DVB-linked core of another star. 

This method for the preparation of poly(styrene-fc-tBuA) is based upon the procedure described by Jerome et al. Teyssie and co-workers demonstrated that the addition of LiCl can be effective in the living anionic polymerization of the acrylic monomers, because a p,-type complex" is formed between LiCl and the growing site. This complex prevents the occurrence of side-reactions at the propagating site, thus markedly narrowing the molecular weight distribution. 

Miura et aL terminated a living anionic polymerization of BD with several different types of nitroxides to prepare CRP initiators [283]. The bulk polymerization of St initiated by four different nitroxide moieties proceeded with a linear increase of the molecular weight with monomer conversion and molecular weight distributions <1.2. To synthesize the macroinitiators for preparation of... 

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. 

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