In this paper, we report our unexpected finding about
the correlation between Lewis acid−base surface
interaction components and linear solvation energy relationship (LSER)
solvatochromic parameters α and
β. In 1987, van Oss, Chaudhury, and Good proposed to split the
asymmetric acid−base parts of a bipolar
system into separate surface tension components: Lewis acid (electron
acceptor) γ+ and Lewis base (electron
donor) γ-. It was assumed that the ratio of
γ+ and γ- for water at 20 °C was to
be 1.0. With that ratio
as a reference, the base components, γ- for other
liquids, biopolymers, polymers, and solids appeared to
be overestimated. Recently, we unexpectedly found a correlation
for liquids between γ+ and γ-, and
α
(solvent hydrogen-bond-donating ability) and β (solvent
hydrogen-bond-accepting ability) introduced since
1976 by Taft and Kamlet. From that correlation, we obtained a more
realistic ratio for the normalized
α and β values for water at ambient temperature to be 1.8 instead
of 1.0. Based on this new ratio, we
calculated total surface tensions for related materials at 20 °C.
They are generally unchanged as expected,
despite the considerable, favorable change in the γ+
and γ- values in the direction of lowering the
Lewis
basicity. The predicability of solubility with interfacial tension
is also unaffected. For example, the sign
of those negative interfacial tensions that favor solubility remains
the same. In addition, the implications
of other LSER parameters, e.g. Π* and δH
2,
on surface properties will be briefly mentioned.
The thermal degradation of uncured and cured epoxy resins was studied. By the use of the thermogravimetric analysis, the thermal stability of the cured epoxy resins, D.E.N. 438 and D.E.R. 331 resins, was compared with those of polycarbonate and polyphenylene sulfide. The resins, including novolac resin and D.E.R. 669 resins, were pyrolyzed, and their volatiles were determined with a mass spectrometer. The experimental results showed that the phenolic compounds were the major volatile products. Thus, the data do not support the degradation scheme proposed by Neiman and co‐workers. Several degradation schemes for epoxides are proposed based on the principles of the cleavage of simple ethers and the products obtained from the pyrolysis study.
Bisphenol‐A polycarbonate gradually degrades at temperatures above 310°C. as detected by differential thermal analysis. The first stage of degradation of the dry and purified resin is induced by oxygen. In connection with oxidation, zinc stearate causes a notable degradation. This compound may act partly as an oxidation catalyst. The initial site attacked by oxygen is presumably the isopropylidene linkage of the polymer. The second stage of degradation shows a characteristic endothermic peak between 340 and 380°C. This stage is chiefly associated with depolymerization since only a small amount of volatiles is detectable. Depolymerization can be caused by hydroperoxide cleavage, hydrolysis, alcoholysis and bisphenol cleavage. Bisphenol‐A can decompose in the presence of acid into phenol and isopropenylphenol. The latter compound is a color‐forming material. As temperature increases above 400°C., volatilization rate gradually increases. The last stage of degradation becomes uncontrollable above 500°C. At this stage, decarboxylation, dehydration, hydrolysis, hydrogen abstraction, ether cleavage, crosslinking as well as chain scission interact to yield aromatic hydrocarbons, phenolic compounds, and tar. The quantity of aromatic hydrocarbons is determined by the intensity of the thermal degradation.
SynopsisData on wettability of elastomers should be considered basic to the understanding of all phases of elastomer adhesion. However, no such data in the form of critical surface tensions were available for elastomers other than polydimethylsiloxane. For this study, 18 elastomers were selected to determine the effects of functional groups, of geometrical and structural isomerisms, of copolymerization, and of the induced orientation upon wettability. Most results support the constitutive law of wettability established by Shafrin and Zisman. The effect of structural isomerisms in the form of a vinyl side group and cyclization is discussed. An equation for the calculation of critical surface tension of a copolymer or of a mixture of isomers is proposed as follows:where Ng is the mole-fraction of the individual monomer in the copolymer and ycf is the critical surface tension of each homopolymer. Most elastomer adhesion studies conducted in the past were concerned with the diffusion theory of adhesion. This study further supports the conclusion on the role of diffusion and adsorption in adhesion advanced in Part I, especially with respect to the physical state of polymer at the time of application. The wettability data in this study could shed some light upon major basic mechanisms involved in elastomer reinforcement. m 1
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