Abstracts of Technical Articles by Bell System Authors 



Paracon — A New Polyester Rubber} B. S. Biggs and C. S. Fuller. 

 Paracons are high molecular weight linear polyesters which are soft enough 

 to be rubbery and are capable of undergoing a vulcanization reaction. They 

 are prepared by the condensation of dibasic acids with glycols or by the self 

 condensation of hydroxy acids, and the name is intended to signify "conden- 

 sation rubber." Paracon looks and feels like rubber, and in comparison 

 with other rubbers it has some distinct advantages and some definite limita- 

 tions. Its outstanding properties are oil resistance, high heat and light 

 resistance, lack of odor and fast curing cycle. Tensile strength ranges from 

 1500 to 3000 pounds per square inch with elongations of 400 to 600 per cent. 



Rubber pigments and compounding techniques may be used with it but 

 vulcanization is accomplished in most cases by the action of benzoyl peroxide 

 rather than sulfur. 



Aside from its practical aspects the development of paracon is of theoreti- 

 cal interest because of the light it throws on rubber structure and the 

 mechanism of vulcanization processes. 



Unsaturation oj Butadiene and Related Polymers as Determined by Iodine 

 Chloride Addition? A. R. Kemp and Henry Peters. This paper de- 

 scribes procedures which have been developed to determine the unsaturation 

 of various butadiene and related polymers and copolymers, as well as mixed 

 vulcanizates of Buna S and rubber. These methods are based on the use of 

 ^-dichlorobenzene as a solvent and iodine chloride as the addition agent, fol- 

 lowing the general technique employed in the standard Kemp-Wijs method 

 for the determination of the unsaturation of natural rubber. 



The ratio of butadiene to styrene in copolymers has been calculated from 

 the iodine value and from the carbon-hydrogen ratio; however, the accuracy 

 of these procedures is subject to several variables which are discussed. 



Unsaturation data are presented on highly purified emulsion-type poly- 

 mers of butadiene-isoprene and butadiene-styrene which agree closely with 

 the presence of one double bond for each diolefin molecule present. The 

 reaction rate of Buna S with halogens is shown to agree closely to that of 

 natural rubber hydrocarbon. 



Brittle Temperature of Rubber under Variable Stress? A. R. Kemp, F. S. 

 Malm and G. G. Winspear. This paper supplies the need for a method to 



1 Chem. and Engg. News, June 25, 1943. 



2 Indus. & Engg. Chemistry, Analytical Edition, July 1943. 

 2 Indus. & Engg. Chem., April 1943. 



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