Radial block copolymer

Kraus et al. (74,75) studied the steady flow and oscillatory flow behavior of linear triblocks of S-B-S and B-S-B and radial block copolymers of the type (B-S-) 3, (S-B-)3, and (S-B-)4. For block copolymers of the same molecular weight and composition, those with end blocks of PS always have higher viscosities. However, when compared with corresponding linear block copolymers, the viscosities of the radial block copolymers are generally lower. 

SB block copolymers are made anionically. These copolymers can be dlblocks, triblocks, and radial block copolymers with different degrees of tapering. Kraton was introduced in the mid-1960s by Shell. Another major manufacturer is Phillips with Solprene and K-Resins. These products can be used as thermoplastic elastomers or as impact modifiers. One of the most interesting aspects of these resins is the different types of morphologies that can be obtained as shown in Figure 6 (12-15). 

With both instruments, data can be plotted as a function of time or temperature to give dynamic mechanical spectra. An example is shown in Figure 32, where rigidity and damping from TBA experiments are shown as functions of temperature for a styrene-butadiene-styrene radial block copolymer (329). Such spectra are particularly useful for the study of polymers, including the identification of physical transitions and the onset and kinetics of cross-linking (323,330) or embrittlement (329), as well as for measuring various viscoelastic parameters. The... 

Modified acrylics have been reported to be good metal adhesives. Radial block copolymers , in addition to S-B block copol3miers, have been offered as new contact adhesives. Cyanoacrylates have found wide applications beyond their use as surgical... 

TroUsas, M., Hawker, C.J., Remenar, J.F. et al. (1998b) Highly branched radial block copolymers via dendritic initiation of aUphatic polyesters. Journal of Polymer Science Part A-Polymer Chemistry, 36,2793-2798. 

The development of the styrenic block copolymers has created special challenges for resin manufacturers. These block copolymers are of two basic types. The first are the triblock copolymers, consisting of an elastomeric midblock and thermoplastic polystyrene end-blocks. These can be either the linear triblock copolymers, such as the Kraton polymers from Shell Chemical Company or the Europrene polymers from Enichem, or radial block copolymers, initially produced by Phillips Petroleum and now available from Petrofine SA under the tradename Finaprene. The linear triblock copolymers are the most widely used in the adhesive industry. 

As discussed previously, thermoplastic elastomers are materials which have the functional properties of conventional vulcanized rubbers but which may be processed as normal thermoplastics (see section 2.9). Effects of this kind are shown by styrene-butadiene block copolymers. Two types of styrene-butadiene block copolymers are produced commercially, namely triblock and radial block copolymers. The triblock copolymers (denoted by SBS) consist of a centre block of butadiene units with two terminal blocks of styrene units. The radial block copolymers (denoted by (SB) X) consist of three or more styrene-butadiene diblock copolymers radiating from a central... 

The radial block copolymers are also prepared by anionic polymerization. Firstly, a styrene-butadiene diblock which is active at the butadiene end is formed. A polyfunctional coupling agent such as silicon tetrachloride is then added to produce the radial structure. The process may be represented as follows ... 

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