Microdomains, styrene-butadiene

Figures 4A and 4B are the ultra-thin cross-sections of OsOi+-stained two-stage (styrene//styrene-butadiene) and (styrene-butadiene/ /styrene) latex particles at the stage ratio of 50/50 (LS-10 and LS-11), respectively. Latex samples were mixed with a polymerizable monomer mix of butyl and methyl methacrylates, cured, and microtomed for examination. Figure 4A shows particle cross-sections much smaller than the actual particle size of LS-10. It appears that since the embedding monomer solution was a solvent for polystyrene, the continuous polystyrene phase was dissolved and small S/B copolymer microdomains were left behind. This is further evidence that the second-stage S-B copolymers phase-separated as microdomains within the first-stage polystyrene phase, as shown in Figures 1A and 1A. Figure 4B shows somewhat swollen and deformed particle cross-sections, suggesting that the first-stage cross-linked S-B copolymers were a continuous phase. Indeed, the former (LS-10) behaved like a hard latex, but the latter (LS-11) behaved like a soft latex.

The viscoelastic properties of concentrated solutions of styrene-butadiene star-block copolymers were studied by Masuda et al. [296] in good solvents for both blocks and in selective ones. A significant dependence of the loss and storage moduli on the strain amplitude was observed in the case of dibutylphthalate, a selectively good solvent for the PS blocks at temperatures below 60 °C, which indicates the presence of a microdomain structure due to self assembling of the insoluble blocks. At a certain value of the applied strain the microdomain structure in solution was disrupted. 

Figure 5.19 Small-angle neutron scattering intensity obtained with a styrene-butadiene diblock copolymer having spherical butadiene microdomains. The peaks at very small q are due to a body-centered cubic lattice structure of ordered microdomains. The solid curve is the calculated intensity of independent scattering from solid spheres of mean radius 124 A. (From Bates etal.34)...

The most extensively studied block copolymers prepared by anionic polymerization are the styrene-butadiene or styrene-isoprene rubbers. Shell Chemical Company s Kraton thermoplastic elastomers are ABA block copolymers of this type. Their elastomeric properties are excellent, yet they differ from other rubbers in that vulcanization is not required. These elastomers consist of a rubbery polybutadiene matrix with the styrene segments serving as anchors in thermoplastic microdomains. 

As mentioned above, the spm is mostly limited to sampling the near-sinface region of a polymer system. A new technique based on tmafm has been developed to enable volume imaging with the spm. This study tracked a series of height and phase images of a styrene-butadiene-styrene (SBS) triblock polymer microdomain as the surface was being removed 7.5 nm at a time with a plasma etcher. These data are illustrated in Figure 10 (65). 

The basic concept of 2D IR spectroscopy based on the correlation analysis of perturbation-induced time-dependent fluctuations of IR intensities could be readily extended to other areas of polymers spectroscopy. The 2D correlation analysis has been successfully applied to the time-dependent variations of small angle X-ray scattering intensity measurement [4], In this study, a small amplitude dynamic strain is applied a sheet of microphase-separated styrene-butadiene-styrene triblock copolymer sample. Intensity variation of scattered X-ray beam due to the strain-induced changes in the interdomain Bragg distances coupled with the reorientation of microdomain structures is analyzed by using the 2D correlation map. Similarly, the formal approach of 2D correlation analysis to time-dependent spectral intensity fluctuations has been extended to UV, Raman [63], and near-IR spectroscopy [64], There seems no intrinsic limitation to the application of this versatile technique in polymer spectroscopy. 

Fig. 16. Phase diagram of a mixture containing polystyrene (M = 2400) and styrene/butadiene diblock copolymer (27 % styrene, M = 28000). Liquid phases L, and Lj represent mixtures of disordered block copolymer and polystyrene. Mesophase M, consists of ordered microdomains of the block copolymer swollen with polystyrene. Mesophase Mj probably contains aggregates of block copolymer micelles within the medium of polystyrene. The features on the lower right, drawn in broken lines, are more speculative. (From Roe and Zin...

Second, the strain-softening phenomenon of a styrene-butadiene-styrene tri-block copolymer and its blend with polystyrene both having alternating lamellar microdomains of the two components i.e., "strain-induced plastic-to-rubber transition" is investigat-d in terms of change of the alternating lamellar microdomains to fragmented sty-... 

Drug Release from PHEMA-l-PIB Networks. Amphiphilic networks due to their distinct microphase separated hydrophobic-hydrophilic domain structure posses potential for biomedical applications. Similar microphase separated materials such as poly(HEMA- -styrene-6-HEMA), poly(HEMA-6-dimethylsiloxane- -HEMA), and poly(HEMA-6-butadiene- -HEMA) triblock copolymers have demonstrated better antithromogenic properties to any of the respective homopolymers (5-S). Amphiphilic networks are speculated to demonstrate better biocompatibility than either PIB or PHEMA because of their hydrophilic-hydrophobic microdomain structure. These unique structures may also be useful as swellable drug delivery matrices for both hydrophilic and lipophilic drugs due to their amphiphilic nature. Preliminary experiments with theophylline as a model for a water soluble drug were conducted to determine the release characteristics of the system. Experiments with lipophilic drugs are the subject of ongoing research. 

An isothermal morphology diagram of poly(styrene-fe/oc -butadiene) is shown in Fig. 19 as a function of molecular weight and copolymer composition the classic morphologies include spherical microdomains (0< a<0.15) packed in a body-centered cubic lattice, hexagonally packed cylindrical microdomains (0.15 <( a-0-3), and alternating lamellae of approximately symmetric diblocks (0.3 <0 -0-5). Sever-... 

Fig. 18, the most significance is that the microcrazes go through the dispersed particles of the block copolymer. It results in considerable local yielding and micronecking in the block copolymer particle. The microdomain structure of the particle is not of alternating lamellae of the two components, but of styrene rods dispersed in a butadiene matrix in the undeformed state. The domain structure of the dispersed rods of styrene in the butadiene matrix still... 

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