Radial block polymers

Radial styrenic block polymers, PholUps (Solprene)... 

Elastomeric block polymers of styrene and butadiene or iso-prene and their products of hydrogenation are finding increasing use in a variety of fields.44. Linear and radial block polymers are used extensively in injection molded rubber goods, footwear, pressure sensitive and hot melt adhesives and in mechanical rubber goods such as hose, tubing, cove base, toys, drug sundries, rubber bands, stoppers, erasers, etc. 

Blends of butadiene-styrene block polymers with polyolefins, particularly polypropylene are mentioned in literature to improve the impact strength of the latter. Since similar improvements can be realized from the use of polyolefin block polymers, the blends have not gained much recognition. However, butadiene-styrene radial teleblock polymers are blended into polyethylene film, to increase the tear resistance and tensile impact. ... 

Block polymers were prepared by organolithium-initiated polymerization in cyclohexane solution by using the sequential monomer addition technique (3). Polymers were both of the linear-SBS and radial -branched (SB) type. Blends were prepared in cyclohexane solution, either before or after coupling the initially linear SBLi precursor. Coupling agents investigated were ethyl acetate (for linear coupling), epoxi-aized soybean oil (ESO), and SiCh. 

The contribution from the shell consisting of A-block polymers with concentration rj, homogeneously distributed in the radial direction, is written in the form ... 

Several structural arrango ents of butadiene-styrene copolymers are listed in Figure 1. As indicated, polymers with multiple blocks can be structured in several ways. Che important distinction that can be made is betweoi linear polymers and radial, branched polymers. Structures of these are further illustrated in Figure 2 Figure 3 demonstrates aggregations of several molecules of simple, linear and radial block polymers. 

Properties of seme ccmmercially available radial block polymers based on butadiene and styrene are shown in Table I. 

Radial Block Polymer-Oil Basteii>atch I50 Whiting 80... 

The response of melt viscosity to changes in shear rate over the range normally encountered in mixing, extrusion and injection molding is generally similar to that of thermoplastics such as polyethylene or polystyrene. Melt viscosities for a radial block polymer based on butadiene and styrene, an oil masterbatch and a compound based cn the masterbatch are shown in Figure 8. 

Polyether-b-polyester dendrimer 3,5-dihydroxybenzyl alcohol as monomer for ether-linked fragments and 2,2,2-trichloroethyl 3,5-dihydroxybenzoate for ester linked fragments radially alternating the dendritic segments produced segmented-block polymer and concentric alternation gave layer-block polymer spectroscopy, thermal characterization described. [269]... 

Triblock polymers and radial block polymers of styrene and butadiene (or isoprene) are successful commercial thermoplastic elastomers pioneered by the Shell Chemical Company and the Phillips Petroleum Company. The low diene and high styrene block polymers are clear impact resisting plastics marketed by the Phillips Petroleum Company under the trade name K-Resins. One common deficiency of these polymers is the relatively low glass temperature (Tg) of the polystyrene end blocks. For the thermoplastic elastomers the service temperatures are limited to below 65°C. The Vicat softening... 

In this paper we describe the preparation and the properties of the title triblock with a low vinyl-1,2 (or 3,4 in the case of polyisoprene) polydiene center block. Two different solvent systems were used as the media of polymerization. In the first system, the polydiene center block was prepared in cyclohexane. Alpha-methylstyrene (AMS) and a polar solvent tetrahydrofuran (THF) were then added. This was followed by a slow and continuous styrene addition to complete the end block preparation. In the second system, AMS itself was used as the solvent with no other solvent added. The second solvent system enabled us to use several different polymerization schemes. The center block could be prepared first to form a tapered or untapered triblock. The end block copolymer also could be prepared first and then the diblock and then coupled to form a tri- or a radial block polymer. Instead of coupling, more styrene could be added to complete the triblock. All these different routes of preparation were used in this work. 

One area of current active research is where there are at least three blocks linked together at a common point. The three-armed materials have been referred to as T-block polymers and where there are more blocks commonly linked the terms radial and star polymer have been used (Fig. 17.1). 

Transparent toughened polystyrene polymers are produced by blending polystyrene with SBS block copolymers (see Section 11.8). During the 1970s and 1980s most development was with block copolymers with a radial (or star) shape. Two types were developed block copolymers with a central butadiene block, and block copolymers with a central polystyrene block. 

Block copolymer chemistry and architecture is well described in polymer textbooks and monographs [40]. The block copolymers of PSA interest consist of anionically polymerized styrene-isoprene or styrene-butadiene diblocks usually terminating with a second styrene block to form an SIS or SBS triblock, or terminating at a central nucleus to form a radial or star polymer (SI) . Representative structures are shown in Fig. 5. For most PSA formulations the softer SIS is preferred over SBS. In many respects, SIS may be treated as a thermoplastic, thermoprocessible natural rubber with a somewhat higher modulus due to filler effect of the polystyrene fraction. Two longer reviews [41,42] of styrenic block copolymer PSAs have been published. 

A schematic view of an extruder is shown in figure 1. The extruder barrel is essentially a ferrous alloy cylinder, with aluminum block heaters attached to the outside. There are several temperature control zones along the length of the extruder. Measurement thermocouples are installed in the extruder barrel itself. Barrel temperature is used to control the temperature of the polymer melt. Energy from the heaters is conducted both radially and axially in the barrel. Below, figure 2 shows a sketch of the extruder barrel, with the heaters and the temperature measurement points used in this paper marked. 

It is usually assumed that the micellar corona is a continuous phase extending from the micellar core to the micellar radius Rm. The internal structure of the micelle can be described by a density profile as shown in Fig. 8. The micellar core is a homogeneous melt or glass of insoluble polymer blocks. For hydrophobic blocks in aqueous solutions, the polymer volume fraction in the micellar core is 0C 1. The micellar shell is swollen with water or aqueous salt solution and has a polymer segment density that is expected to decrease in the radial direction as 0(r) r-a as typical for star polymers or... 

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. 

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