Polystyrene morphology

The diameter of as-spun fiber decreased from around 20-30 p,m to about 15 pm after drawing, while the size of the polystyrene morphology reduced about 10%. This indicates the drawing process did not effectively deform the solid dispersed phase, because it is difficult for the draw stress to transfer from the matrix to the dispersed phase through the solid interface, and the free space for the polystyrene phase deformation is limited. 

Both compounds are derivatives of triphenylamine, a well-known photoconductor. If thin films of TPD and TAPC are prepared by vacuum evaporation both compounds form metastable glasses. In such glasses carrier mobUities up to 10 cm A s for TPD [13] and 10 cm A s for TAPC [14] have been reported. But both TAPC and TPD glasses are metastable and have a strong tendency to crystallize. If the molecules are imbedded in a polymer matrix, e.g. polycarbonate or polystyrene, morphologically stable materials are formed, but the mobilities decrease drastically [13]. 

Figure4.2 and Figure 4.3 Impact polystyrene morphology as a function of agitation during polymerization (Fig.4.2-without agitation Fig.4.3-with agitation (reproduced (adapted) with permission of reference Wagner, E. R. and Robeson, L M., Rubber Chem. recf)r)o/.(1970)43,p.1129)...

Thermoplastic Elastomers. These represent a whole class of synthetic elastomers, developed siace the 1960s, that ate permanently and reversibly thermoplastic, but behave as cross-linked networks at ambient temperature. One of the first was the triblock copolymer of the polystyrene—polybutadiene—polystyrene type (SheU s Kraton) prepared by anionic polymerization with organoHthium initiator. The stmcture and morphology is shown schematically in Figure 3. The incompatibiHty of the polystyrene and polybutadiene blocks leads to a dispersion of the spherical polystyrene domains (ca 20—30 nm) in the mbbery matrix of polybutadiene. Since each polybutadiene chain is anchored at both ends to a polystyrene domain, a network results. However, at elevated temperatures where the polystyrene softens, the elastomer can be molded like any thermoplastic, yet behaves much like a vulcanized mbber on cooling (see Elastomers, synthetic-thermoplastic elastomers). 

Finally, block copolymers have been made in a two-step process. First a mixture of chloroprene and -xylenebis-Ai,Ar-diethyldithiocarbamate is photopolymerized to form a dithiocarbamate terminated polymer which is then photopolymerized with styrene to give the block copolymer. The block copolymer has the expected morphology, spheres of polystyrene domains in a polychloroprene matrix (46). 

Since the last edition several new materials have been aimounced. Many of these are based on metallocene catalyst technology. Besides the more obvious materials such as metallocene-catalysed polyethylene and polypropylene these also include syndiotactic polystyrenes, ethylene-styrene copolymers and cycloolefin polymers. Developments also continue with condensation polymers with several new polyester-type materials of interest for bottle-blowing and/or degradable plastics. New phenolic-type resins have also been announced. As with previous editions I have tried to explain the properties of these new materials in terms of their structure and morphology involving the principles laid down in the earlier chapters. 

Paine et al. [99] tried different stabilizers [i.e., hydroxy propylcellulose, poly(N-vinylpyrollidone), and poly(acrylic acid)] in the dispersion polymerization of styrene initiated with AIBN in the ethanol medium. The direct observation of the stained thin sections of the particles by transmission electron microscopy showed the existence of stabilizer layer in 10-20 nm thickness on the surface of the polystyrene particles. When the polystyrene latexes were dissolved in dioxane and precipitated with methanol, new latex particles with a similar surface stabilizer morphology were obtained. These results supported the grafting mechanism of stabilization during dispersion polymerization of styrene in polar solvents. 

Lactic acid and levulinic acid are two key intermediates prepared from carbohydrates [7]. Lipinsky [7] compared the properties of the lactide copolymers [130] obtained from lactic acid with those of polystyrene and polyvinyl chloride (see Scheme 4 and Table 5) and showed that the lactide polymer can effectively replace the synthetics if the cost of production of lactic acid is made viable. Poly(lactic acid) and poly(l-lactide) have been shown to be good candidates for biodegradeable biomaterials. Tsuji [131] and Kaspercejk [132] have recently reported studies concerning their microstructure and morphology. 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

Puskas J.E., Antony P., ElFray M., and Altstadt V. The effect of hard and soft segment composition and molecular architecture on the morphology and mechanical properties of polystyrene-polyisobutylene thermoplastic elastomeric block copolymers, Eur. Polym. J., 39, 2041, 2003. 

Antony, P., Puskas, J.E., Ott, H., Altstadt, V., Kovar, M., and Norton, P.R. Effect of Hard and Soft Segment Composition on the Morphology and Mechanical Properties of Polystyrene-Polyisobutylene Thermoplastic Elastomeric Block Copolymers. Proceedings of the Polymer Processing Society Meeting, May 21-24, Montreal, Canada, 2001. 

Hong, B. K. and Jo, W. H. (2000) Effects of molecular weight of SEBS triblock copolymer on the morphology, impact strength, and rheological property of syndiotactic polystyrene/ ethylene-propylene rubber blends. Polymer, 41, 2069-2079. 

Gong, Y., Hu, Z., Chen, Y, Huang, H. and He, X. (2005) Ring-shaped morphology in solution-cast polystyrene-poly(methyl methacrylate) block copolymer thin films. Langmuir 21, 11870-11877. 

Various techniques have been used for the determination of oligomers, including GC [135], HPLC [136-138], TLC for polystyrene and poly a-methyl-styrene [139] and SEC for polyesters [140,141]. GC and PyGC-MS can also profitably be used for the analysis of the compositions of volatile products formed using different flame retardants (FRs). Takeda [142] reported that volumes and compositions of the volatile products and morphology of the char were affected by FRs, polymers (PC, PPE, PBT) and their reactions from 300... 

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