Polystyrene homopolymers

Polymers of a-methylstyrene have been marketed for various purposes but have not become of importance for mouldings and extrusions. On the other hand copolymers containing a-methylstyrene are currently marketed. Styrene-a -methylstyrene polymers are transparent, water-white materials with BS softening points of 104-106°C (c.f. 100°C for normal polystyrenes). These materials have melt viscosities slightly higher than that of heat-resistant polystyrene homopolymer. 

Polystyrene homopolymer produced by free radical initiators is highly amorphous (Tg = 100°C). The general purpose rubber (SBR), a block copolymer with 75% butadiene, is produced by anionic polymerization. 

This section deals with atactic polystyrene homopolymer, and high-impact polystyrene. The properties of SMA are included in Table 4.36 and are not otherwise detailed. 

Based on this approach Schouten et al. [254] attached a silane-functionalized styrene derivative (4-trichlorosilylstyrene) on colloidal silica as well as on flat glass substrates and silicon wafers and added a five-fold excess BuLi to create the active surface sites for LASIP in toluene as the solvent. With THF as the reaction medium, the BuLi was found to react not only with the vinyl groups of the styrene derivative but also with the siloxane groups of the substrate. It was found that even under optimized reaction conditions, LASIP from silica and especially from flat surfaces could not be performed in a reproducible manner. Free silanol groups at the surface as well as the ever-present impurities adsorbed on silica, impaired the anionic polymerization. However, living anionic polymerization behavior was found and the polymer load increased linearly with the polymerization time. Polystyrene homopolymer brushes as well as block copolymers of poly(styrene-f)lock-MMA) and poly(styrene-block-isoprene) could be prepared. 

Gold nanoparticles coated by short thiol end functional polystyrene homopolymers (PS-SH) can be incorporated into a poly(styrene-fo-2-vinylpyridine) diblock copolymer template (PS-NP2VP). It has been found that the surface density of PS chains on the gold particles is critical in controlling their location in block copolymer templates [95]. 

The observed Tgs of the polystyrene microphases in all of the work quoted above (1,2,3,4,5) were lower than those expected for polystyrene homopolymers having the same molecular weights as the blocks in the block copolymers. We present a detailed comparison of such data below. 

Fig. Z4a, b. Morphologies of the rooonstituled samples containing CSS particles and polystyrene homopolymer a) 15% particles from the spincast source (large particles) b) 15% particks from the static cast source (small particles)...

H-copolymer as shown in Scheme 73. This synthetic scheme is an extension of the one used for the preparation of H-shaped polystyrene homopolymers.160... 

Tensile testing was done using an Instron Model 1122 load frame and an Instron 1000 lb. maximum combination tension/com-presslon load cell. Samples were cut from films using ASTM 1822 Type D standard cutter for tensile samples. Crosshead speed was 5 Inches per minute for all samples. Prior to tensile testing, polystyrene homopolymer tensile samples were annealled at 85 C for 4 days in order to remove any additional Internal stresses introduced during the specimen cutting procedure. 

Figure 6. Variations of tensile strength as a function of composition of butadiene (BU) and styrene (ST)polymers and copolymers. Key A, polystyrene homopolymer B, 52/48 BU/ ST block copolymer C, 70/30 BU/ ST block copolymer D, 75/25 BU/ ST block copolymer E, 75/25 BU/ ST random copolymer F, butadiene homopolymer.

Figure 7. Effects of ozone exposure on oxygen/carbon ratio of butadiene (BU) and styrene (ST) polymer sand copolymers. Key , 75/25 BU/ST block copolymer Ci, 70/30 BU/ST block copolymer +, 52/48 BU/ST block copolymer and polystyrene homopolymer.

The agreement between the experimental and predicted values of the constant of the exponents was very good. The MPo of the SAN copolymer, as calculated by the extrudate expansion data, was 64,000. This value was higher than that for the polystyrene homopolymer. 

Figure 7. Intrinsic viscosity of polystyrene homopolymer vs. monomer conversion...

Grafting of vinyl chloride and of styrene in the presence of EPDM elastomers occurred under the described conditions with formation of graft copolymers of rubber and of poly (vinyl chloride) and polystyrene homopolymers. 

XPS was used to evaluate the surface composition of these copolymers in relation to the bulk composition (fractions of methyl acrylate and styrene). Surface composition was essentially identical to the bulk composition. Thus, for example, when the bulk composition is 40 mol % styrene, the surface percentage of styrene is about 40. Such a surface appears to be as active as polystyrene homopolymer. 

Because of its inherent brittleness, polystyrene homopolymer itself has limited application in blends. However, its impact modified version, viz., HIPS, is more widely used. HIPS itself is a reactor-made multiphase system with 5 to 13% polybutadiene ( cis -rich) dispersed as discrete particles in the polystyrene phase, with an optimum particle size of mean diameter of 2.5 fim. The rubber in HIPS is chemically grafted to some extent to the polystyrene. The effective volume of... 

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