rela,,:ation in plasticized copolymers of styrene and acrylonitri le is s tudied dUring ~helr formatIOn as well as in t he fully polymerized copolymers b y measurements of dlelectn ? .constant and loss fa ctor at several frequencies from 100 cis to 100 kc/s . In t he p? lyme~'lzl!1g nuxture, t here occur, at an early stage of the reaction, sigmo id decrea es in t h e dlelectl'lc co nstan t at each frequency, accompanied by maxima in t he loss fa cto r when t hese vanables are plotted as ~ fun ction o~ reaction t im e. These changes are interpreted as res ultll1~ from the relaxatl?n of the mtnle groups. The. electrical properties of t he ful ly polymeI.lzed copolymer, as It goes .throu~h Its glass tran;ntIOn , are in semiquan t itativ e agreement ,,?th those of the polymerIZing mIXture at t he stao-e of t h e reaction referred to demonstratlllg the Occurrence of similar phenomena in each ~ase.'

The effects of various catalysts used to cure the resinous adhesives on the strength propertJes of plywood were investigated, particularly with regard to the degree of acidity developed by the catalysts in the resin film and in the plywood. The flexural, impact, and shear strengths, both initially and after aging, of birch plywoods bonded with urea-formaldehyde and phenol-formaldehyde resins definitely decrease as the acidity of the plywood increases, as evidenced by a decrease in pH. Only in the case of plywood bonded with casein and urea-formaldehyde resins had the deterioration at the bond progressed sufficiently in the roof-aging tests to make it impossible to carry out strength tests because of delamination. A correlation between decrease in strength on aging of plywood bonded with alkali-catalyzed phenolic acid and increase in alkalinity of the panel was observed. Because of the different absorption capacities of the phenolic resins for acids and alkalies, it is not possible to predict the pH of the plywood panel from the pH of the resin film.The susceptibility of birch wood, itself, to attack by acids and alkalies was determined in order to better understand the mechanism of the deterioration of resin-bonded plywood. A marked decrease in strengtn occurred when the pH of the wood was lowered below 2.0. In the range between pH 2.0 and 2.5, strong acids, such as hydrochlOrIc and sulfuric, had a more pronounced deteriorating effect than weak acids, such as hypophosphorous and nitranilic. A marked d ecrease in strength of the birch also occurred when the pH was raised to 8.8 by the absorption of an alkali, tetraethanolammonium hydroxide.

Structural adhesives are one of the more important developments in the adhesives field because they make possible bonded assemblies in lightweight structures which take full advantage of the strengths of the materials used. Structural adhesives can be divided into two classes. One class consists of hard brittle resins typified by unmodified epoxy adhesives which have high shear and tensile strengths but low peel strength. The second class consists of a combination of resins resulting in a more ductile type of adhesive which has high peel strength along with high shear and tensile strength. One application is described here in which an epoxy adhesive is used in a design which minimizes peel forces and which causes failure of the bonded assembly in the metal. The evaluation of this design showed it to be successful.