Transmission electron microscopy copolymers

Interestingly, this behavior of the reaction mixture can be prevented by employing another principle of particle stabilization steric protection. Inclusion of pegylated comonomer (PEG-AEPD) into the reaction mixture did enable the formation of nonaggregating DNA particles. It also caused the particles to form worm -like structures (as judged by transmission electron microscopy) that have previously been observed with DNA complexes formed from block copolymers of PEL and PEG [98]. 

The use of lightly crosslinked polymers did result in hydrophilic surfaces (contact angle 50°, c-PI, 0.2 M PhTD). However, the surfaces displayed severe cracking after 5 days. Although qualitatively they appeared to remain hydrophilic, reliable contact angle measurements on these surfaces were impossible. Also, the use of a styrene-butadiene-styrene triblock copolymer thermoplastic elastomer did not show improved permanence of the hydrophilicity over other polydienes treated with PhTD. The block copolymer film was cast from toluene, and transmission electron microscopy showed that the continuous phase was the polybutadiene portion of the copolymer. Both polystyrene and polybutadiene domains are present at the surface. This would probably limit the maximum hydrophilicity obtainable since the RTD reagents are not expected to modify the polystyrene domains. 

Triblock terpolymers PS-b-PBd-b-P2VP and PBd-b-PS-b-P2VP, where PBd is polybutadiene (mostly 1,2-PBd), were prepared in order to study the microphase separation by transmission electron microscopy, TEM and SAXS. In the first case the triblocks were synthesized by the sequential addition of monomers in THF using s-BuLi as the initiator [26]. For the second type of copolymers, living PBd-b-PS diblocks were prepared in benzene at 40 °C in the presence of a small quantity of THF in order to obtain the desired 1,2-content and to accelerate the crossover reaction as well. DPE was then added to decrease the nucleophilicity of the active centers in order to avoid side reactions with the THF, which in combination with benzene was the solvent of the final step. 

Recently, Kroeze et al. prepared polymeric iniferter 34 including poly(BD) segments in the main chain [152]. They successfully synthesized poly(BD)-block-poly(SAN), which was characterized by gel permeation chromatography, elemental analysis, thermogravimetric analysis, NMR, dynamic mechanical thermal analysis, and transmission electron microscopy. By varying the polymerization time and iniferter concentration, the composition and the sequence length were controlled. The analysis confirmed the chain microphase separation in the multiblock copolymers. 

The phase morphology of block copolymers can also be visualized by transmission electron microscopy. Figure 10.8 shows the lamellar structure of Fluoro-PSB-IX. From diblock copolymers it is well known that the resulting microphase morphology depends on the volume fraction (< >) of the two phases. By simple adjustment of the relative block lengths we are able to synthesize block copolymers with specific structures.1718... 

A controversy has arisen as to whether the observations by POM and those by transmission electron microscopy reflect the same morphological features or not. In fact, Kim et al. [125] demonstrated that the same block copolymer can exhibit different morphologies depending on sample thickness, this being a possible reason for the sometimes contradictory results found in several works. Nevertheless, before this aspect can be properly treated in this section, we present a review of the morphological investigations carried out in semicrystalline ABC triblock copolymers at a nanoscopic scale. 

Goldraich M, Talmon Y (2000) Direct-imaging cryo-transmission electron microscopy in the study of colloids and polymer solutions. In Alexandridis P, Lindman B (eds) Amphiphilic block copolymers self assembly and applications. Elsevier, Amsterdam... 

Figure 2. Morphology of various cross-polybutadiene-in/er-cross-polystyrene sequential IPNs and graft copolymers via transmission electron microscopy. The double bonds in the polybutadiene phase are stained dark with osmium tetroxide. (Reproduced from ref. 15. Copyright 1976 American Chemical Society.)...

The resulting polymer foam composition is substantially of the closed cell type. This is evidenced by the fact that for equivalent densities, foams of EVA and acid copolymer are found to exhibit lower helium densities than foams of EVA alone. This is an indication that more of the cells in the EVA/acid copolymer foam are closed. Particularly for an acid copolymer content in the range of about 3-15%, the acid copolymer has been observed to be uniformly dispersed within the EVA in micron-sized particles when analyzed by transmission electron microscopy. 

Transmission electron microscopy (TEM) has been used to provide a direct image of block copolymer micelles that complements the indirect information obtained from scattering experiments. Because of the technical difficulties of obtaining electron micrographs from solutions it is not employed routinely. Price and co-workers (Booth et al. 1978 Price and Woods 1973) obtained specimens for TEM investigation by two methods. In the first (Price and Woods 1973),... 

Winey KI et al (1993) Morphology of a lamellar diblock copolymer aligned perpendicular to the sample plane - transmission electron-microscopy and small-angle X-ray-scattering. Macromolecules 26(16) 4373—4375... 

---