1,3-Butadiene living anionic polymerization

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. 

The fairly broad most probable distribution for the rays may be considered as an undesirable imperfection of regular stars. Corresponding measurements with much narrower arm length distributions were made later, mainly by the research groups of Fetters [20, 30, 31] and Roovers [25, 26] which were obtained by living anionic polymerization of styrene, isoprene and butadiene respective-... 

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... 

A knife handle made of Kraton which is a block copolymer of styrene and butadiene that is made by living anionic polymerization (Source www.knifeoutlet.com). 

FIGURE 3-34 Schematic representation of the formation of a styrene/butadiene (SBR) triblock copolymer by living anionic polymerization. 

Since shortly after its discovery by Szwarc et al. [5] in the mid-1950s, living anionic polymerization has been recognized as an ideal route to styrenic block copolymers [6]. To date, living anionic polymerization remains the only commercially important technology for SBC synthesis. The anionic polymerization of styrene and common dienes such as butadiene and isoprene satisfies the criteria outlined above, particularly when carried out in a hydrocarbon solvent and initiated by an appropriate lithium alkyl. 

Recently, Ishizone d al. conducted a successful living anionic polymerization of 2-(l-adamantyl)-l,3-butadiene with sec-BuU in both THF and cyclohexane [62, 63]. Interestingly, the microstructure of the resulting polymer was predominantly regulated in 1,4-addition mode (88%, cis/trans=S2/lS), even in polar THF. Thus, the bulky adamantyl substituent significantly affected the stereoselectivity of the resultant polymer. 

Difunctional initiators such as sodium naphthalene can be employed to prepare triblock ABA block copolymers. Difunctional initiators produce "living pol3mieric dianions which are capable of adding a second monomer at each end. On the addition of a second monomer the ABA structure results. For example, consider the preparation of poly(butadiene-b-styrene-b-butadiene) by anionic polymerization initiated by sodium naphthalene. 

As indicated above, conventional free-radical poljnnerization is not very well suited for the synthesis of advanced polymer architectures. Even the synthesis of di- or triblock copolymers is hardly possible using this technique. The main reason is the continuous initiation and termination of chains. This results in the early generation of dead polymer chains that no longer participate in the polymerization process. The consecutive addition of monomers as employed in living anionic polymerization for the synthesis of eg poly(styrene-6Zoc -butadiene) will only lead to the synthesis of a mixture of two homopolymers. 

Living anionic polymerization can be used for the synthesis of AB block copolymers in which (a) or (b) is added to a living chain of the comonomer. The alternative procedure is limited due to the low reactivity of a chain end formed from (a) or (b). Block copolymers from butadiene and (a) or (b) show remarkable reduction of the cold flow [613,614]. ABA block copolymers are the result of the polymerization of butadiene (B) with a bifunctional initiator followed by the addition of (a) or (b) (A) [615]. AB block copolymers from... 

On of the most unique aspects of living anionic polymerizations is the ability to synthesize block copolymers by sequential monomer addition. Thus, the product of the alkyllithium-initiated polymerization of styrene (Scheme I) can be reacted with a diene such as butadiene or isoprene to produce a living diblock copolymer as shown in eq, 2 for butadiene. It is important to note that the alkyllithium-initiated poly-... 

In the early 1960 s, subsequent to the pioneering work of M. Szwarc on the living anionic polymerization of styrene and butadiene, extensive research on the anionic polymerization of methacrylate esters was undertaken by D. L. Glusker, W. E. Goode,... 

Recently, Gnanou et al reported that l,l-bis(4-bromophenyl)ethylene (4) can be used in a way similar to that for the above-mentioned TERMINI in the synthesis of dendrimer-like star-branched (PS)s and poly(1,3-butadiene)s (PB)s (Matmour and Gnanou, 2008). The synthetic outline is illustrated in Scheme 5.4. In each reaction step, 4 reacted with the terminal potassium alkoxide in a 1 1 addition manner to introduce two phenyl bromide moieties at the chain end, which was subsequently transformed into two phenyl lithiums by the Li-Br exchange reaction with sec-BuLi. Following the living anionic polymerization of styrene or 1,3-butadiene. 

The living anionic polymerization of 1,3-butadiene and isoprene is industrially important for the production of various synthetic elastomers, thermoplastic elastomers, and styrene-butadiene rubbers (SBRs). In addition, numerous alkyl- and aryl-substituted 1,3-diene monomers have been subjected to anionic polymerization to develop new elastomers. Unfortunately, the anionic polymerization of functional... 

---