Styrene microdomains

The distribution of styrene crosslinks in cured unsaturated polyesters based on maleic anhydride, phthalic anhydride, propylene glycol and dipropylene glycol is found to be dependent on the molar ratio of styrene vs. maleic/fumaric unit. If the molar ratio is higher than 1, the dyad distribution is predominant lower molar ratios yield mostly styrene microdomains, i.e. n-ads with more than 2 styrene repeating units 232>. 

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. 

A series of polymine-graft copolymers of styrene [92-95] and hydroxyethyl methacrylate [96-98] were found to form a microdomain structure and exhibit unique biomedical behavior at the interface with living cells, such as blood platelets and lymphocytes. The most intensive studies were made with poly(hydroxyethyl methacryIate)-0ra/t-polyamine copolymers (HA) ... 

Cohen et al. (1990) studied a poly(styrene)-poly(ethylene) (PS-PE) diblock that was solvent cast from toluene. Crystallization within microphase-separated PE spheres occurred when solvent-casting was done above the PE block melting temperature, Tm (see Fig. 5.2). When solvent was removed below Tm crystallization did not occur within spherical microdomains, instead TEM and SANS experiments suggested an irregular structure. Nojima et al. (1994) suggest that crystallization from the melt in this sample occurred within the microphase-separated block in the former case due to the high molecular weight of the... 

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.

Hashimoto T., Fujimura M. and Kawai H., Domain-boundary structure of styrene-isoprene block copolymer films cast from solutions 5. molecular-weight dependence of spherical microdomains. Macromolecules 13 (1980) pp. 1660-1669. 

In contrast, the foams derived from the a-methylstyrene and styrene-based copolymers showed pore sizes ranging from 200 to -1800 A, values which are considerably larger than the size of the microdomains of the initial copolymer (Fig. 13). Furthermore, the pores in these samples appear to be more interconnected than those obtained from the fully imidized copolymers. Finally, the... 

Experimentally, Thomas and coworkers found that hydrocarbon-coated gold nanoparticles, with a diameter of 3.5 nm, segregated to the interface between the microdomains of poly(styrene-btock-ethylene propylene) (PS-fe-PEP) copolymer, whereas larger hydrocarbon-coated silica nanoparticles (21.5nm in diameter) were located at the center of the PEP domains [79], In the absence of specific enthalpic interactions between the two types of nanoparticles and the polymer matrix, the result suggests a profound influence of entropic contributions to the self-organization process. For large particles, the decrease in conformational entropy of the respective polymer subchains after particle sequestration is dominant, whereas for smaller particles, the decrease in entropy is outweighed by the particle translational entropy. 

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)...

Synthetic weak polyelectrolytes provide hydrophobic microdomains in the low pH range. Typical examples are poly(methacrylic acid) (PMA) (i-3), copolymers of maleic anhydride and n-alkylvinyl ethers (n = 4-9) 4, 5), and copolymers of maleic anhydride and styrene or methylstyrene (6). The compact polymer coils are formed only in acidic solution, but the compact conformation is converted into the extended rod or coil form at high pH because of repulsion of ionized carboxyl groups. At low pH, many hydrophobic molecules can be hosted by the polymer coils, a condition that disappears at high pH. However, a hydrophobic environment is required... 

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-... 

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