Copolymers, block living anionic polymerization

HIR Hirao, A., Inushima, R., Nakayama, T., Watanabe, T., Yoo, H.-S., Ishizone, T., Sugiyama, K., Kakuchi, T., Carlotti, S., and Deffieux, A., Precise synthesis of thermo-responsive and water-soluble star-branched polymers and star block copolymers by living anionic polymerization, Eur. Polym. J., 47, 713, 2011. 

A brief review has appeared covering the use of metal-free initiators in living anionic polymerizations of acrylates and a comparison with Du Font s group-transfer polymerization method (149). Tetrabutylammonium thiolates mn room temperature polymerizations to quantitative conversions yielding polymers of narrow molecular weight distributions in dipolar aprotic solvents. Block copolymers are accessible through sequential monomer additions (149—151) and interfacial polymerizations (152,153). 

The earliest SIS block copolymers used in PSAs were nominally 15 wt% styrene, with an overall molecular weight on the order of 200,000 Da. The preparation by living anionic polymerization starts with the formation of polystyryl lithium, followed by isoprene addition to form the diblock anion, which is then coupled with a difunctional agent, such as 1,2-dibromoethane to form the triblock (Fig. 5a, path i). Some diblock material is inherently present in the final polymer due to inefficient coupling. The diblock is compatible with the triblock and acts... 

Though living anionic polymerization is the most widely used technique for synthesizing many commercially available TPEs based on styrenic block copolymers, living carbocationic polymerization has also been developed in recent years for such purposes [10,11], Polyisobutylene (PlB)-based TPEs, one of the most recently developed classes, are synthesized by living carbocationic polymerization with sequential monomer addition and consists of two basic steps [10] as follows ... 

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... 

Polymer Synthesis and Characterization. This topic has been extensively discussed in preceeding papers.(2,23,24) However, we will briefly outline the preparative route. The block copolymers were synthesized via the sequential addition method. "Living" anionic polymerization of butadiene, followed by isoprene and more butadiene, was conducted using sec-butyl lithium as the initiator in hydrocarbon solvents under high vacuum. Under these conditions, the mode of addition of butadiene is predominantly 1,4, with between 5-8 mole percent of 1,2 structure.(18) Exhaustive hydrogenation of polymers were carried out in the presence of p-toluenesulfonylhydrazide (19,25) in refluxing xylene. The relative block composition of the polymers were determined via NMR. 

Hyperbranched polymers have also been prepared via living anionic polymerization. The reaction of poly(4-methylstyrene)-fo-polystyrene lithium with a small amount of divinylbenzene, afforded a star-block copolymer with 4-methylstyrene units in the periphery [200]. The methyl groups were subsequently metalated with s-butyllithium/tetramethylethylenediamine. The produced anions initiated the polymerization of a-methylstyrene (Scheme 109). From the radius of gyration to hydrodynamic radius ratio (0.96-1.1) it was concluded that the second generation polymers behaved like soft spheres. 

Siloxane containing block or segmented copolymers can be synthesized either by living anionic polymerization of the cyclic organosiloxane trimers with appropriate vinyl monomer(, 4 ) or by step-growth or condensation copolymerization of preformed a,w-difunctional siloxane oligomers with conventional difunctional... 

Based on this approach Schouten et al. [254] attached a silane-functionalized styrene derivative (4-trichlorosilylstyrene) on colloidal silica as well as on flat glass substrates and silicon wafers and added a five-fold excess BuLi to create the active surface sites for LASIP in toluene as the solvent. With THF as the reaction medium, the BuLi was found to react not only with the vinyl groups of the styrene derivative but also with the siloxane groups of the substrate. It was found that even under optimized reaction conditions, LASIP from silica and especially from flat surfaces could not be performed in a reproducible manner. Free silanol groups at the surface as well as the ever-present impurities adsorbed on silica, impaired the anionic polymerization. However, living anionic polymerization behavior was found and the polymer load increased linearly with the polymerization time. Polystyrene homopolymer brushes as well as block copolymers of poly(styrene-f)lock-MMA) and poly(styrene-block-isoprene) could be prepared. 

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. 

In addition to the triblock thermoplastic elastomers, other useful copolymers of styrene with a diene are produced commerically by living anionic polymerization. These include di-and multiblock copolymers, random copolymers, and tapered block copolymers. A tapered (gradient) copolymer has a variation in composition along the polymer chain. For example, S-S/D-D is a tapered block polymer that tapers from a polystyrene block to a styrene-diene random copolymer to polydiene block. (Tapered polymers need not have pure blocks at their ends. One can have a continuously tapered composition from styrene to diene by... 

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... 

By using the aluminum porphyrin-Lewis acid system, we attempted the synthesis of a narrow MWD block copolymer from oxetane and methyl methacrylate (MMA). Methacrylic monomers can be polymerized radically and anioni-cally but not cationically, so a block copolymer of oxetane and methyl methacrylate has never been synthesized. As already reported, methacrylic monomers undergo accelerated living anionic polymerization with the (TPP)AlMe (1, X= Me)-3e system via a (porphinato)aluminum enolate as the growing species. 

Fast growing Interest in block copolymers originates from the Intramolecular phase separation, which Is responsible for some unique properties involving many potential applications. In this field again major progress has been accomplished due to the availability of the "living" anionic polymerization techniques. 

The nonterminating nature of living anionic polymerization allows the synthesis of block copolymers,480,481 which are useful thermoplastic elastomers. They have many properties of rubber (softness, flexibility, resilience) but in contrast to rubber can be processed as thermoplastics 482,483 Block copolymers can be manufactured by polymerizing a mixture of two monomers or by using sequential polymerization. 

One of the most useful features of living polymerizations, which proceed in the absence of chain transfer to monomer and irreversible termination, is the ability to prepare block copolymers. Compared with living anionic polymerization the development of living cationic polymerization is rather re-... 

The combination of living cationic and living anionic polymerizations provides a unique approach to the synthesis of block copolymers not available by a single method. Coupling of living anionic and cationic polymers is conceptually simple, but few examples have been reported so far. This is most likely due to the different reaction conditions required for living cationic and anionic polymerizations. 

Living Anionic Polymerization with PO Macroinitiator For Block Copolymers ... 

There are essentially two methods used for the production of commercial FTPEs. The first is referred to as iodine transfer polymerization, which is similar to the living anionic polymerization used to make block copolymers such as styrene-butadiene-styrene (e.g., Kraton ). The difference is that this living polymerization is based on a free radical mechanism. The products consist of soft segments based on copolymers of vinylidene fluoride (VDF) with hexafluoropropylene (HFP) and... 

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... 

Block copolymers were developed rapidly in the 1960s when living anionic polymerization was first utilized to synthesize triblock thermoplastic elastomers or elastoplastics. At the same time, step or condensation polymerization to produce thermoplastic polyurethanes, urea-urethane spandex fibers, and later more specialized materials, such as the semicrystalline polyester-polyether copolymers were developed [10]. Imide block or segmented copolymers utilizing... 

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