Homopolymers, staining

Morphology. Ultrathin cast films of polystyrene and PTHF homopolymers stained by osmium tetroxide vapor were examined by electron microscopy. Only the PTHF was stained. 

In the transmission electron microscopic (TEM) studies, we found that it was exceedingly difficult to obtain ultramicrotomed sections of iPS-iPP blends, whereas the iPS-fo-iPP diblock copolymer could be cut with relative ease. This result exhibits one major difference between the diblock copolymer and the corresponding homopolymer blend. Unfortunately, owing to the difficulty of finding a selective staining technique, the sample of diblock copolymer did not display visible contrast or obvious structural features in the TEM studies. However, the results of SEM studies do reveal a clear difference between the blend and the diblock copolymer the macrophase separation is revealed on the etched surface of the blend and is not present in the copolymer (Figure 3). The diblock copolymer exhibits only a finely dispersed and continuous submicron structure throughout the field of view, as expected. 

Previous studies have reported silver staining with other amino acids. Heukeshoven and Dernick reported silver staining of the homopolymers of glycine, serine, proline and aspartic acid (4 ) while Nielsen and Brown reported the formation of colored silver complexes with aspartate, and tyrosine (45,). Staining of these homopolymers was not observed in the study of Merril and Pratt (32,), and prior metal binding studies failed to demonstrate metal interactions with the side-chain hydroxyl groups of serine, threonine or tyrosine... 

These discrepancies concerning the non-basic amino acids may be due to differences in the staining procedures employed the Heukeshoven and Dernick study stained homopolymers on polyacrylamide gel, Nielsen and Brown studied formation of silver-amino acid complexes in solution. Both of these studies used formaldehydye in an alkaline sodium carbonate solution for image development, while Merril and Pratt utilized acidic conditions and a combination of light, hydroquinone and formaldehyde for image formation (32). 

Libera [99] has presented an alternative for the study of polymer morphology avoiding the staining procedure as a way to induce amplitude contrast. EEe proposed the use of EELS to study different polymer systems to obtain several levels of resolution (related to the radiation sensitivity of the material) when studying interfaces, such as those in polystyrene-poly(2-vinyl pyridine) homopolymer blends, epoxy-alumina interfaces, and hydrated polymers. Polymers could be distinguished from each other on the basis of the energy-loss spectra in their low loss (valence) and core loss (elemental composition). 

The relative decrease in enthalpy should represent the extent of disorder at the interface of the two blocks, and has actually been directly correlated to the thickness of the interphase. That is, the AH of isotropization of lamellar PS-PChEMA (Scheme 26) containing pchEMA=0.56 is 81.4% of that of the homopolymer, indicating that the interphase should be approximately 18.6% of the liquid crystalline lamellae (12.5 nm). The calculated value of 2.3 nm corresponds very well to that measured by TEM following preferential staining of the interphase [207]. Nevertheless, variations in the extent of disorder at the interface as measured by decreased enthalpies of transitions may be due to variations in sample preparation and thermal history. For example, Gronski et al. s H-NMR experiments on deuterated PS-PBAz (Scheme 21) indicate that the disordered interphase present in powder samples is eliminated when the samples are oriented by shear for extensive time in the nematic mesophase [203]. 

Features Effective low vise., mod. reactive fonns flexible homopolymers of mod. tens, and elong. and exc. MEK and stain resist. 

Figure 4.20. Electron micrographs of 40/60 poly(styrene-h-isoprene) systematically diluted with polystyrene and polyisoprene homopolymers. The two homopolymers have the same molecular weights as their respective blocks, and are added in a 40/60 ratio in order to maintain the same overall composition. The major effect is a progressive increase in phase domain dimensions, which eventually approach those of the cast blend structure (Kawai and Inoue, 1970). Compositions are shown in Figure 4.21 films are cast from 5 % solutions in toluene and are stained with osmium tetroxide.

Transmission electron microscopy was performed on samples of thin films of copolymers and blends of homopolymers by means of JEOL JEMIOO electron microscope. The films were stained with OgO prior to examination. 

The study of thin films of copolymers and blends of homopolymers by transmission electron microscopy gives direct evidence for segregation into separate domains of both components in the case of blends. This can be clearly seen in Figure 5. The OsO stained cholesteryl moieties show as dark regions and indicate that PChMA separates into clusters of approximately iM. No separation was seen in films of the copolymer. 

Four series of IPNs were polymerized, the compositions of which are given in Table 5.2. The underlined polymer was polymerized first. This was always the elastomer PEA (normal IPNs), except for series I (inverse series), where the plastic homopolymer PS or PMMA was polymerized first. The B in PEAB indicates that the PEA contained 1% butadiene as a comonomer to permit staining for electron microscopy. The letters E, L, P, and I denote elastomeric, leathery, plastic, and inverse series, respectively. In compositions containing both S- and MMA-mers, a random copolymer was formed with the indicated composition. The actual compositions employed can be portrayed with the aid of a pseudoternary phase diagram, as shown in Figure 5.1 for the normal IPNs. Only the border compositions (no random... 

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