Butadiene/styrene copolymers, sequence lengths

Another area in which both proton and carbon-13 nmr have proved very powerful is the determination of the structure of copolymers. This has a long history (ref. 6, Chap. X 15,16)9 beginning with the observations of butadiene-styrene copolymers in 1959, Again, the information content of the spectra has increased remarkably since these early reports. Although compositional sequence lengths and probabilities can be calculated from the copolymer equation using the traditional data of polymer composition vs. monomer feed composition, nmr allows direct measurement of the sequences and gives in addition much structural detail not available from overall composition alone. 

As previously mentioned, we are concerned in this chapter with essentially random copolymers of styrene and butadiene produced by solution polymerization. In terms of the distribution of styrene and butadiene units, random solution copolymers are considered as having only small variations in the sequence length distribution of the... 

Thus, the synthesis of a styrene-methyl methacrylate block polymer requires that styrene be the first monomer. Further, it is useful to decrease the nucleophilicity of polystyryl carbanions by adding a small amount of 1,1-diphenylethene to minimize attack at the ester function of MMA [Quirk et al., 2000]. Block copolymers of styrene with isoprene or 1,3-butadiene require no specific sequencing since crossover occurs either way. Block copolymers of MMA with isoprene or 1,3-butadiene require that the diene be the first monomer. The length of each segment in a block copolymer is controlled by the ratio of each monomer to initiator. The properties of the block copolymer vary with the block lengths of the different monomers. 

The properties of block copolymers are dependent on the length of the sequences of repeating units, or domains. The domains in typical commercial block copolymers of styrene and butadiene are sufficiently long such that the products are flexible plastics. They are called thermoplastic elastomers (TPE). It should be noted that although the Ts for random copolymers is between the T/s of the respective homopolymers, the repeating sequences in block copolymers exhibit their own characteristic Ff s. 

The chemical structure of block copolymers is given by the number of blocks, their sequence, and their length, as is discussed in Fig. 1.19 and Sect. 3.4.1. The structure of a diblock copolymer poly(styrene-fc/oc -l, 4-butadiene) of type AB, for example, can have the following chemical structure ... 

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