Butadiene anionic polymerisation

Closely related to these but thermoplastic rather than rubber-like in character are the K-resins developed hy Phillips. These resins comprise star-shaped butadiene-styrene block copolymers containing about 75% styrene and, like SBS thermoplastic elastomers, are produced by sequential anionic polymerisation (see Chapter 2). 

Synthesis of vinyl block copolymers is accomplished by living polymerisation, mostly by anionic polymerisation. Several strategies can be used, illustrated here by the example of the Styrene-Butadiene-Styrene (or SBS) triblock copolymer. 

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). 

It is possible to produce a block copolymer by the anionic polymerisation of styrene and butadiene as depicted below. The polystyrene and polybutadiene are mutually incompatible and hence phase separate to give the morphology also depicted below ... 

Anionic polymerisation was known for many years before the nature of the polymerisation was predicted. The production of buna type synthetic rubbers in Germany and Russia by the polymerisation of butadiene with the sodium or potassium as the catalyst was known. 

It became apparent that the mechanism of anionic polymerisation induced by the alkali metals should also involve initiation by electron transfer from the metal to the monomer. For example, in the Lithium initiated polymerisation of butadiene, we have,... 

Starting Material. 1,2-polybutadiene (PB) and the A-polystyrene-B-1,2-poly-butadiene block copolymer (PSPB) were obtained by "living 1 anionic polymerisation under high-vacuum conditions at -78°C with sec-buthyllithium as initiator. 

Synthesis of Polybutadiene Polyols by Anionic Polymerisation of Butadiene [16-24]... 

Another variant for the synthesis of hydroxy telechelic polybutadiene is based on the anionic living polymerisation of butadiene, using sodium naphthalene as catalyst [16]. Sodium naphthalene generates, by reaction with butadiene, a radical anion (9.8). If two of these radicals are coupled together, they generate a dianion (9.9), which is an ideal bifunctional initiator for the synthesis of perfectly bifunctional polybutadiene by anionic polymerisation. 

No. 16,1996, p.3665-73 ANIONIC POLYMERISATION OF STYRENE AND BUTADIENE INITIATED BYN-BUTYLLITHIUM IN ETHYLBENZENE DETERMINATION OF THE PROPAGATION RATE CONSTANTS USING RAMAN SPECTROSCOPY AND GEL PERMEATION CHROMATOGRAPHY... 

The nomenclature poly (M1-6-M2) is used where Mj and M2 are the monomer names for example poly (styrene-b-butadiene). To make block copolymers, the polymer chains must have the ability to propagate [living polymers) when the first monomer is replaced by the second. In conventional addition polymerisation the chain termination and transfer processes make the lifetime of a growing polymer chain too short. Consequently, special ionic polymerisation catalysts were developed. A fixed number of di-anions such as [C6H5CHCH2CH2CHC6H5] are introduced into an inert solvent. These propagate from both ends if a suitable monomer is introduced. As there are no termination or transfer reactions, once the first monomer has been consumed, a second monomer can be introduced to produce a triblock copolymer such as styrene-butadiene-styrene. Each block has a precisely defined molecular weight. These materials undergo phase separation (Chapter 4) and act as thermoplastic rubbers. 

B CgH3(CF3>2 4 anions i are piefened for butadiene polymerisations. With these non-coordinating anions high molecular weights are realised (M - 75,000). Dicationic [Pd(MeCN)4][BF4]2 is effective for norboroene polymerisation (M 50,000 < 1.4), ... 

Styrene-butadiene latices were prepared by emulsion-free polymerisation in the presence of N,N-diethylaminoethyl methacrylate to supply a positive charge and their colloidal behaviour and interaction with anionic pulp fibres investigated. It was found that the latices were positively charged and stabilised by electrostatic repulsion and deposited readily on anionic fibres suspended in water, forming a monolayer on the fibre surface. Dewatering and drying resulted in coalescence of the particles and fibres covered with a polymeric film, which improves the bonding between the fibres. 9 refs. CANADA... 

Even so, the solution has sufiicient anionic strength to determine stereo-specific polymerisation of isoprene and butadiene. 

S-SBR made from initiators other than anionic has a broader MW distribution, which depends upon the polymerisation conditions. The branching probability is much less than that in the emulsion polymerisation primarily because of the lower local concentration of polymer. The mechanisms of the long branch-formation are different for different initiator (catalyst) systems. This aspect will be discussed with butadiene (BR) polymerisation. 

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