Abstracts of Technical Articles by Bell System Authors 



Gross-linkage of Linear Polyesters by Free Radicals} W. O. Baker. Re- 

 actions fundamental to the use of the new low pressure laminating or casting 

 resins have been studied. The striking property of these plastics, which are 

 usually based on some polyester and a vinyl monomer, is their rapid and 

 easy curing, leading to unique ease of fabrication. This curing, the forma- 

 tion of a permanent three-dimensional polymer network, or gel, is achieved 

 by reaction with a source of free radicals, such as from an organic peroxide. 

 These agents cause polymerization of the vinyl monomer, as was previously 

 understood, but they also seem to incorporate the polyester into the network, 

 even if the polyester contains little or no unsaturation. 



Investigation of a series of simple polyesters, the polyundecanoates, 

 showed that free radicals, such as come from the decomposition of benzoyl 

 peroxide, could cross-link or gel the linear, saturated, chains. Apparently 

 the hydrogen atoms in methylene groups next to polar groups like the car- 

 bonyl, i.e., the a-hydrogens, are removed by the free radicals. The resulting 

 chain radical attacks an adjacent chain, and a cross-link is formed. The 

 effects of cross-links thus produced on solubility, dilute solution viscosity, 

 melt viscosity and, finally, stress relaxation of the cured solid were examined. 

 Probably the similar activity of a -hydrogen atoms is important in the chemi- 

 cal aging or weathering of plastics and rubbers. It is likewise significant for 

 the vulcanization of many synthetic rubbers. 



Rubberlike Products from Linear Polyesters.^ B. S. Biggs, R. H. Erick- 

 SON and C. S. Fuller. The polymers which result from the condensation 

 of dibasic acids with propylene glycol are viscous gums which can be vulcan- 

 ized to rubberlike products. In the unpigmented condition these rubbers are 

 quite weak, but when reinforced with suitable pigments their strength and 

 elongation compare favorably with other synthetic rubbers. Because poly- 

 esters of known structure and molecular weight can be easily synthesized, 

 these polymers are useful for the study of the relations between structure and 

 properties in rubberlike materials in general. Factors affecting tensile 

 strength, oil resistance, brittle temperature, and stability are discussed. 



Pulse Code Modulation.^ H. S. Black and J. O. Edson. A radically new 

 modulation technique for multichannel telephony has been developed which 

 involves the conversion of speech waves into coded pulses. This new tech- 



1 



Jotir. Amer. Chemical Soc, May 1947. 



2 Indus. & Engg. Chem., September 1947. 



3 Telephony, August 30, 1947. * 



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