Butadiene living anionic

Making use of the higher reactivity of butadiene in anionic polymerisation y <1, 2 > 1) to get the triblock SBS copolymer in two steps. The first step is the synthesis of a PS sequence with a living end, then, upon addition of a mixture of styrene and butadiene, butadiene will add first, building a "pure" PB sequence, and styrene will finally build the third sequence (two steps). 

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-... 

In the last few years the use of more rational synthetic methods based on living anionic polymers has become quite common. These polymers, usually of styrene or a-methylstyrene but sometimes of butadiene or styrene-butadiene mixtures, are initiated by metal alkyls and possess one reactive anionic end-... 

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... 

The linear polymers, as shown above, can be built up by the sequential addition of monomer or by coupling the living anionic chains using compounds like dichloro dimethylsilane. Hence, the base polymer would have styrene polymerized first, followed by butadiene, and then addition of the coupling agent. If a multifunctional coupling agent such as silicon tetrachloride is used, a radial block or star-branched SBS is formed. 

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. 

Two related procedures have been developed to effect this transformation. Both Involve the Initial synthesis of mono- or dlfunctlonal living anionic polymers of styrene, butadiene, or block copolymers of both. They are then reacted via Grlgnard Intermediates (7 ) with either excess bromine or with excess m-xylylyl dlbromlde (8-10) to yield polymers with reactive halide terminal groups (benzyllc or allyllc depending upon the polymer and terminating agent). The reactions for polystyrene are shown In equations 2 and 3. 

The seminal work of Schulz and co-workers on anionic polymer initiators which contain protected hydroxyl functionality was reported in 1974." These researchers prepared 2-(6-lithio- -hexyloxy)tetrahydopyran by metal-halogen exchange in diethyl ether, see Figure 1. The lithium chloride co-product was removed by filtration. This initiator was successfully employed in the polymerization of 1,3-butadiene. The resultant functionalized living anion was subsequently functionalized with ethylene oxide or coupled with dimethyldichlorosilane. Mild acid hydrolysis with dichloroacetic acid liberated the telechelic dihydroxy polybutadiene. The polybutadienes produced with this initiator exhibited narrow molecular weight distributions = 1.05-1.08). 

The kinetics of copolymerization provides a partial explanation for the copolymerization behavior of styrenes with dienes. One useful aspect of living anionic copolymerizations is that stable carbanionic chain ends can be generated and the rates of their crossover reactions with other monomers measured independently of the copolymerization reaction. Two of the four rate constants involved in copolymerization correspond at least superficially to the two homopolymerization reactions of butadiene and styrene, for example, and k, respectively. The other... 

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. 

A tadpole polybutadiene with two linear PS chains has been prepared by Quirck and Ma living anionic poly(styryl) lithium chains were first coupled by reacting the living ends with the double diphenylethylene. Then the resulting polymer bearing two reactive catbanionic centers located in the middle of the chain was used as a bifimcdonal macroinitiator to initiate the anionic polymerization of butadiene. The two... 

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