Transmission electron copolymers

Figure 2 The transmission electron micrographs of samples cast from solution containing 1 wt% of polymer, (a) the block copolymer BCl, and (b) the microsphere, MCI [24].

Figure 7 The transmission electron micrograph of the block copolymer B1 for blend [36].

The microphase structure was clearly observed in transmission electron micrographs of the film of amphiphilic copolymers cast from aqueous solutions [29, 31]. An important finding was that no microphase structure was observed for the film cast from organic solutions. This difference indicates that a microphase structure is formed in aqueous solution, but not in organic solution. Different hydrophobic groups showed considerably different morphological features i.e. whether microphase separation leads to a secondary or higher structure depends on the type of hydrophobic units in the copolymers [31],... 

ABA type poly(hydroxyethyl methacrylate) (HEMA) and PDMS copolymers were synthesized by the coupling reactions of preformed a,co-isocyanate terminated PDMS oligomers and amine-terminated HEMA macromonomers312). Polymerization reactions were conducted in DMF solution at 0 °C. Products were purified by precipitation in diethyl ether to remove unreacted PDMS oligomers. After dissolving in DMF/toluene mixture, copolymers were reprecipitated in methanol/water mixture to remove unreacted HEMA oligomers. Microphase separated structures were observed under transmission electron microscope, using osmium tetroxide stained thin copolymer films. 

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. 

Recent developments have allowed atomic force microscopic (AFM) studies to follow the course of spherulite development and the internal lamellar structures as the spherulite evolves [206-209]. The major steps in spherulite formation were followed by AFM for poly(bisphenol) A octane ether [210,211] and more recently, as seen in the example of Figure 12 for a propylene 1-hexene copolymer [212] with 20 mol% comonomer. Accommodation of significant content of 1-hexene in the lattice allows formation and propagation of sheaf-like lamellar structure in this copolymer. The onset of sheave formation is clearly discerned in the micrographs of Figure 12 after crystallization for 10 h. Branching and development of the sheave are shown at later times. The direct observation of sheave and spherulitic formation by AFM supports the major features that have been deduced from transmission electron and optical microscopy. The fibrous internal spherulite structure could be directly observed by AFM. 

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. 

Figure 9.3. Characterization of mesoporous Ti02 films templated by Pluronics block copolymers using diverse characterization techniques XRD pattern (a), transmission electron microscope (TEM) image (b), dark-field TEM image (c), and isotherms of Kr adsorption (d).The Pluronic-templated Ti02 films were calcined at 400°C (solid points) and 600°C (open points). The films were prepared according to Alberius et al. (Ref. 14).

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... 

Transmission electron microscope photograph of 2-methyl re-sorcinol-PDMSX copolymers using (a) 4400 g/mole PDMSX and (b) 510 g/mole PDMSX. 

Transmission electron microscope photograph of poly (hydroxy-styrene)-PDMSX copolymer. 

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... 

Some typical transmission electron micrographs of these polystyrene lattices are shown (Sample 2 and Sample 3) in Figure 10.6. The effects ofthe amount of stabilizer S is the relative amount of stabilizer) on the particle size is strong the more stabilizer applied, the smaller the particles are. It must be emphasized that this effective stabilization of nanopowders by our fluorinated block copolymers is not restricted to polymerization processes, but can be generalized to the fabrication of all organic nanopowders in media with low cohesion energy density, e.g., to the dispersion of dyes, explosives, or drugs. 

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