Copolymers, triblock styrene production

The most commonly used compatibilizers for PP/PS blends are also di- or triblock copolymers of styrene and butadiene (SB and SBS) and their hydrogenated products (SEB and SEBS) (160-164). They form dispersed phases in both pure PP and PS. In PP/PS blends, they locate at the interface to connect both PP and PS phase together. Thus, the interfacial tension is decreased and the dispersed phase sizes are greatly decreased. 

Polymer alloys are commercial polymer blends with improvanent in property balance with the use of compatibilizers. Texas A M University [1] has patented a com-patibilizer that can result in a product with high impact resistance as well as scratch resistance. The blend is composed of HIPS or polypropylene (PP) and a compati-bilizer made of a triblock copolymer of styrene-ethylene-propylene. Udipi [2] discovered that polymer blends composed of PC, a copolyester of PETG, and nitrile rubber exhibit a superior balance of properties. Reactive compatibilization of PC/ SAN blends at various AN compositions were conducted by Wildes et al. [3] using a SAN-amine compatibilizer. PC and SAN were found to be miscible over a range of AN composition by Mendelson [5]. Nylon/ABS blends can be compatibilized by use of SAN-maleic acid (Lavengood et al. [6]). Styrene-GMA copolymers can be used as compatibilizers for PS/PA, PS/PBT, PS/PET, and PPO/PBT blends. 

With this in mind, Tanaka and co-workers [43] proposed a new method for the characterisation of the sequence distribution of styrene units in styrene-butadiene copolymers by a combination of selective ozonolysis of the double bonds in butadiene units and GPC measurements of the resulting products. His method is based upon high resolution GPC analysis of the alcohols corresponding to styrene sequences obtained by scission of all the carbon-carbon double bonds of butadiene units. The ozonolysis-GPC method has already been proven to be a very powerful tool to characterise the sequence distribution of styrene units and the tacticity in random, partially blocked, and triblock styrene-butadiene copolymers [39, 44-48] in this study a new analytical method of the sequence distribution of 1,2 units in polybutadiene was investigated on the basis of the ozonolysis-GPC method. 

Bipyridine-centered triblock copolymers of the type BA-bpy-AB were prepared by a combination of ATRP and ROMP [159]. 4,4 -Bis(hydroxymelhyl)-2,2/-bipyridine was employed for the polymerization of lactic acid, LA or CL in the presence of Sn(Oct)2 in bulk at 130 and 110°C, respectively. The hydroxyl end groups were converted to tertiary or secondary bromo esters by reaction with 2-bromoisobutyryl bromide or 2-bromopropionyl bromide. The reaction yields were very high (> 80%) but not quantitative. These products were used as macroinitiators for the ATRP of MMA or tBuA in the presence of CuBr/HMTETA. 4,4/-bis(Chloromethyl)-2,2 -bipyridine was employed to promote the ATRP of MMA or styrene followed by the addition... 

A second route is termed sequential anionic polymerization. More recently, also controlled radical techniques can be applied successfully for the sequential preparation of block copolymers but still with a less narrow molar mass distribution of the segments and the final product. In both cases, one starts with the polymerization of monomer A. After it is finished, monomer B is added and after this monomer is polymerized completely again monomer A is fed into the reaction mixture. This procedure is applied for the production of styrene/buta-diene/styrene and styrene/isoprene/styrene triblock copolymers on industrial scale. It can also be used for the preparation of multiblock copolymers. 

Gitsov and Frechet [11] reported the syntheses of novel linear-dendritic triblock copolymers achieved via anionic polymerization of styrene and final quenching with reactive dendrimers. For the characterization of the products in the reaction mixture, SEC with double detection was performed at 45°C on a chromatography line consisting of a 510 pump, a U6K universal injector, three Ultrastyragel columns with... 

Styrene and isoprene also may copolymerize and give a variety of products including random, diblock, triblock and star copolymers. These copolymers also are used as elastomers in the tire industry, but are less common compared to SBR. 

Graft copolymers of A and B monomers are named poly(A-g-B) or poly A-grafi-poly B with the backbone polymer -(-A-)/j— mentioned before the branch polymer. Some examples are poly(ethylene-g-styrene) or polyethylene-grq/i-poly styrene and starch-grayi-poly(methyl methacrylate). In the nomenclature of block copolymers, b or block is used in place of g or graft, e.g., poly(A- -B) or poly A-block-po y B, poly(A-b-B-b-A) or poly A-block-po y B-block-po y A, poly(A-b-B-b-C) or poly A-block-poly B-block-poly C, and so on. Thus the triblock polymer (XX) is called poly(styrene- -butadiene-i -styrene) or polystyrene- /cck-polybutadiene-b/ock-polystyrene. For commercial products, such polymers are usually designated by the monomer initials thus, structure (XX) is named SBS block copolymer. 

The product is an ABA-type triblock thermoplastic elastomer. Styrene is polymerized first since styryl initiation of isoprene is faster than the reverse reaction. The reaction is carried out in a nonpolar solvent with Li as the counterion to enable a block of cis-1,4-polyisoprene to be formed in the second growth stage. The living polystyrene-6-polyisoprene AB di-block copolymer thus formed is then coupled by a double nucleophilic displacement of Cl ions from dichloromethane to give a polystyrene-Z -polyisoprene- i-polystyrene triblock copolymer. (Note that the mole ratio of living diblock chain to dichloromethane is 2 1.)... 

KRATON polymers are high-performance elastomers used to improve the properties of a wide range of end products. KRATON G polymers are triblock copolymers, with a random ethylene/propylene copolymer forming the saturated midblock and styrene forming the two other blocks (styrene-ethylene/propylene-styrene, SEPS). 

The discovery of living cationic polymerization has provided methods and technology for the synthesis of useful block copolymers, especially those based on elastomeric polyisobutylene (Kennedy and Puskas, 2004). It is noteworthy that isobutylene can only be polymerized by a cationic mechanism. One of the most useful thermoplastic elastomers prepared by cationic polymerization is the polystyrene-f -polyisobutylene-(>-polystyrene (SIBS) triblock copolymer. This polymer imbibed with anti-inflammatory dmgs was one of the first polymers used to coat metal stents as a treatment for blocked arteries (Sipos et al., 2005). The SIBS polymers possess an oxidatively stable, elastomeric polyisobutylene center block and exhibit the critical enabling properties for this application including processing, vascular compatibility, and biostability (Faust, 2012). As illustrated below, SIBS polymers can be prepared by sequential monomer addition using a difunctional initiator with titanium tetrachloride in a mixed solvent (methylene chloride/methylcyclohexane) at low temperature (-70 to -90°C) in the presence of a proton trap (2,6-dt-f-butylpyridine). To prevent formation of coupled products formed by intermolecular alkylation, the polymerization is terminated prior to complete consumption of styrene. These SIBS polymers exhibit tensile properties essentially the same as those of... 

Block copolymers can also be hydrogenated to produce unique products. Hydrogenated triblock copolymers of poly(styrene-co-butadiene-co-styrene) (SBS) are commercially available from the Shell Company under the trade name Kraton G. The middle block is usually a mixed microstructure of poly( 1,2-butadiene) and poly( 1,4-butadiene) units. The resulting product is a hydrogenated unsaturated polymer, which exhibits greater thermal and oxidative properties than the parent SBS triblock. 

The convenience of this technique has led to the development of many commercial products, including thermoplastic elastomers based on triblocks of styrene, butadiene, and isoprene. The initiator used in these systems is based on hydrocarbon-soluble organolithium initiators. In some cases, a hydrocarbon-soluble dilithio initiator has been employed in the preparation of multiblock copolymers. Several techniques are used to prepare thermoplastic elastomers of the ABA type. All these are discussed in detail in Chapter 2. A short summary of these techniques is given here. 

The control of chain structure and molecular weight afforded by the organolithium polymerization of dienes, has, of course, been of great technological interest [161,162,209]. Such product developments have been mainly in the form of (1) polybutadiene elastomers of various chain structures [162, 198,209] and functional end groups [210], (2) liquid polybutadienes [211], (3) butadiene-styrene copolymers (solution SBR) [69, 161, 162, 209], and (4) styrene-diene triblock copolymers (thermoplastic elastomers) [212]. 

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