Poly caution

Bi- and poly-thioethers with aliphatic backbones are produced by attack of RS on the appropriate haloalkane. This is the method of choice for RS(CH2)raSR (R = Me or Ph),26 MeC(CH2SR)3,27,28 MeS(CH2)raS(CH2)raSMe (n = 2 or 3) and MeS(CH2)raS(CH2) S(CH2) SMe.28,29 [Caution Some of these syntheses involve sulfur mustard derivatives as intermediates - these are very powerful vesicants and should be handled only with extreme care.] The other tridentates RS(CH2)3S(CH2)3SR (R = Et, Pr or Ph) may be obtained from nucleophilic attack by RS on the ditosylate TsO(CH2)3S(CH2)3OTs.30 Tetra-dentate thioethers involving o-phenylene interdonor linkages are also known.31 More recently the preparation and coordination chemistry of the silicon-apex derivative MeSi(CH2SMe)3 has been described.32... 

A word of caution about toxicity. Many of these compounds are so malodorous it is unlikely anyone could tolerate lethal concentrations of them. Just the same, one should remember that they are toxic and that exposure to them should be minimized. They should only be handled in hoods with good drafts. On human skin, poly(thioformaldehyde) causes dermatitis. Its LDS0 in rats is 365 11 mg/kg (21). 

Coleman et al. 2471 reported the spectra of different proportions of poly(vinylidene fluoride) PVDF and atactic poly(methyl methacrylate) PMMA. At a level of 75/25 PVDF/PMMA the blend is incompatible and the spectra of the blend can be synthesized by addition of the spectra of the pure components in the appropriate amounts. On the other hand, a blend composition of 39 61 had an infrared spectrum which could not be approximated by absorbance addition of the two pure spectra. A carbonyl band at 1718cm-1 was observed and indicates a distinct interaction involving the carbonyl groups. The spectra of the PVDF shows that a conformational change has been induced in the compatible blend but only a fraction of the PVDF is involved in the conformational change. Allara M9 250 251) cautioned that some of these spectroscopic effects in polymer blends may arise from dispersion effects in the difference spectra rather than chemical effects. Refractive index differences between the pure component and the blend can alter the band shapes and lead to frequency shifts to lower frequencies and in general the frequency shifts are to lower frequencies. 

A variety of useful protein tags are available. A common one is a histidine tag, often just a string of six His residues. A poly-His sequence binds quite tightly to metals such as nickel. If a protein is cloned so that its sequence is contiguous with a His tag, it will have the extra His residues at its carboxyl terminus. The protein can then be purified by chromatography on columns with immobilized nickel. These procedures are convenient but require caution, because the additional amino acid residues in an epitope or His tag can affect protein activity. 

Spin-lattice relaxation times and 13C chemical shifts were used to study conformational changes of poly-L-lysine, which undergoes a coil-helix transition in a pH range from 9 to 11. In order to adopt a stable helical structure, a minimum number of residues for the formation of hydrogen bonds between the C = 0 and NH backbone groups is necessary therefore for the polypeptide dodecalysine no helix formation was observed. Comparison of the pH-dependences of the 13C chemical shifts of the carbons of poly-L-lysine and (L-Lys)12 shows very similar values for both compounds therefore downfield shifts of the a, / and peptide carbonyl carbons can only be correlated with caution with helix formation and are mainly due to deprotonation effects. On the other hand, a sharp decrease of the 7] values of the carbonyl and some of the side chain carbons is indicative for helix formation [854]. 

Information on the crystal to liquid crystal transitions is scarce and is to be treated with caution since partial crystallization is prominent and polymorphism of the smectic phase is frequent. Only the data on poly(acryloyloxybenzoic acid) (entry 2 of Table 5) have been extrapolated to 100% crystallinity. As with the low molecular weight liquid crystals, the total heat of transition is lower than expected for fully ordered crystals. Various combinations of two phase structures as suggested by Fig. 3 could be produced for the poly(acryloyloxybenzoic acid)21>. 

The photophysical behavior of poly(vinyl aromatics) has stimulated much interest from both practical and theoretical points of view. The proposal that such molecules exhibit electronic energy migration, e.e.m., resulted in, among other things, development of the concept of synthetic antennae macromolecules (1 ). The object of this paper is to introduce a note of caution to interpretation of observed photophysical phenomena. The bulk of the discussion is concerned with polystyrene, although the behaviour of poly(vinyl naphthalene) will also be considered. 

The most direct way of looking at the specific interactions is by using spectroscopic measurements. Infra-red spectroscopy is the technique which has been most commonly used to study mixtures involving polymers. Studies of blends of PVC with polycaprolactone showed shifts of 4-6 cm 1 in the carbonyl band of polycapro-lactone relative to the pure polymer 99 l00), but this Figure should be treated with caution as the peak probably consists of the sum of a shifted and an unshifted peak and it is difficult to say what the frequency of the shifted peak would be, or what fraction of the carbonyl groups are, or can be, involved in the interaction. Frequency shifts have also been shown to exist in blends of poly(methyl methacrylate) with poly(vinylidene fluoride)63). 

USE Intermediate in the production of vinylidene poly mer plastics such as Saran and Veton, Caution Irritant to skin, mucous membranes narcotic in high concentrations has caused liver, kidney injury in exptl animals Irish in Industrial Hygiene and Toxicology vol. 2, F. A. Patty, Ed. (Interscience, New York, 2nd ed-, 1962) pp 1305-1307 Prendergast et at.. Toxicol AppL Pharmacol. 10, 270 (1967). 

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