Water-induced chain dynamics alterations are of paramount importance in many proteinbased polymers because they determine and affect to a great extent the temperature dependence of the end properties. In this study, the thermal behavior of the reversible unfolding and refolding of poly(Val-Pro-Gly-Val-Gly) and poly(Val-Pro-Ala-Val-Gly) and of their concurrent dehydration and hydration processes has been studied by differential scanning calorimetry (DSC) and turbidimetry. Contrary to the good reversibility shown by poly(Val-Pro-Gly-Val-Gly), the substitution of glycine by alanine in poly(Val-Pro-Ala-Val-Gly) perturbed to a large extent the process of chain unfolding. For the latter polymer, it was found that both chain unfolding and rehydration processes take place at large undercoolings, suggesting that both events occur far from equilibrium conditions and, therefore, are strongly dominated by kinetics. In this context, the existence of an hydration excess with a kinetic rather than a thermodynamic nature is a remarkable observation. The kinetics of folding and unfolding were also studied by using an isoconversional method of kinetic analysis, i.e., the model-free Friedmand's isoconversional method. As expected, the kinetics of the solvation of nonpolar moieties for both polymers indicated a complex and multistep process. Again, poly(Val-Pro-Ala-Val-Gly) showed a quite different pattern characterized by an acute hysteresis behavior which seems to govern the hydration process for this polymer. The differences observed between both polymers have been interpreted in terms of the hindrance provided by the methyl group in alanine during temperature-induced chain dynamics.

The extinction coefficient of a collection of polyolefin foams was investigated experimentally and theoretically. Transmittance spectra were measured with Fourier transform infrared spectroscopy (FTIR) for samples of various thicknesses and different chemical compositions, densities, colors and structural characteristics. The extinction coefficients were then calculated by applying Beer's law. The results showed that the extinction coefficient decreased with the mean cell size and that this was the main structural parameter influencing the extinction coefficient of the foams under study. The experimental results agreed well with the Glicksman model. Moreover, the total thermal conductivity was calculated in terms of the Rosseland equation with an accuracy of 5%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1608–1617, 2005

4-Chlorocoumarin has been shown to be a highly versatile starting material when treated with organometallic reagents. Thus, it has allowed the selective synthesis either directly, or through simple additional transformations, of 4-alkylcoumarins (with R,CuLi in Et,O, or Pr'Mg Br in TH F), 2-chloro-2-(0-hydroxyphenyl)allyl alcohols or their 4-chloro-2H-1 -benzopyran derivatives (with RMgX in TH F), 2-(o-hydroxyphenyl)prop-2-ynyt alcohols (when non-acid hydrolysis were used in the latter reactions) and 2,2,4-trialky1-2H-l -benzopyrans (when excess of RMgX or R,AI reagents were used).

3-Halogeno-2H-I -benzopyran-2-ones react with magnesium, lithium, aluminium and copper derivatives to give 3,4-dihydrocoumarins and 3-(0-hydroxyphenyl) propenols as major products. The nature and the ratio of the products in the final mixture depend on the solvent and on the organometallic reagent. Grignard derivatives yield 1,4-monoalkylation compounds in tetrahydrofuran (TH F) or 1,2-dialkylation derivatives in toluene. In some cases the dehalogenation competes with the 1,2-alkylation process in the reactions with alkyllithiums. The presence of the halogen at C-3 increases the reductive ability of organoaluminiums. In general, the reaction with lithium dialkylcuprates leads to complex mixtures of products. The 4-alkyl-3-halogeno-3,4-dihydrocoumarins obtained undergo dehydrohalogenation easily, and lead to 4-alkylcoumarins in good yields. The tandem alkylation-dehydrohalogenation of 3-halogeno-2H-I -benzopyran-2-ones constitutes a versatile synthesis of 4-alkylcoumarins.The reaction of coumarins with organometallic compounds is a very well known synthetic method to 2H-1-benzopyrans. We have now studied the reactivity of 3-chloro-and 3-bromocoumarins towards magnesium, lithium, aluminium and copper derivatives in order to confirm the influence of the halogen on the behaviour of these substrates.The Grignard derivatives react with 3-chlorocoumarin 1, 3-bromocoumarin 2, and 3-bromo-4-methylcoumarin 3 leading to dihydrocoumarins, chromen-2-ols, and open-chain compounds as a consequence of 1,4-and/or 1,2-addition or reduction processes (Scheme 1). The rate of reaction is intermediate between that with the organolithiums and that with organoaluminiums, and the solvent plays an important role in determining the ratio of the products in the final mixture ( Table 1).As previously described for 3-phenyl-and 3-ethoxycarbonyl~o u m a r i n , ' -~ in our case the 1P-addition process was favoured when the reactions were carried out in ether solvents (THF or diethyl ether) and with increasingly bulky groups R; the resulting 4-alkyl-3-halogeno-3,4-dihydrocoumarins 4 and 5 were obtained as a mixture of cis (80-90%) and trans (20-10%) isomers.Indeed a double 1,2-addition was the major process for 3-bromo-4-methylcoumarin or when benzene or toluene was used as solvent.The ratio of products in the final mixture also depends on the nature of the magnesium derivative; thus, EtMgI and EtMgBr led to the same mixture, but MeMgI did not produce 1,4-addition, and Pr'MgBr gave reduction products (E)-2-bromo-1-(o-hydroxyphenyl)-4-methylpent-l -en-3-01 12d and (E)-2-chloro-l-(o-hydroxyphenyl)-4-methylpent-1 -en-3-01 1 Id in 5 s 60% yield.On the other hand, 3-chloro-and 3-bromo-coumarin behave in similar fashion towards organometallics. Only in the case of phenylmagnesium bromide did 3-bromocoumarin lead to phenyl2,3-dihydro-3-phenylbenzofuranyl ketone 7f, whereas 3-chlorocoumarin yielded 3-chloro-3,4-dihydro-2,4-diphenyl-2H-l-benzopyran-2-016f, but both products derive from a common hydroxy ketone (acyloin) intermediate 6' that in the hydrol...

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