58 FUNDAMENTALS OF SUBMICROSCOPIC MORPHOLOGY I 



§ 3. Structure of Gels 



a. Chemistry of High Polymers 



Polymerisation and condensation. In about 1920 Staudinger drew 

 attention to the fact that in the high-polymer natural substances the struc- 

 tural units which can be obtained from them by hydrolysis are interlinked 

 by primary valency bonds (Kekule bonds). He first proved the correctness 



Monomer 

 H 



H 



Polymer chain 

 H H H 



H 



c=o 



-C— O— C— O— C— O— C— O— C— o 



H 



Formaldehyde 

 (oxymethylene) 



CH = CH., 



H H H H H 



Polyoxymethylene 



_CH— CH,— CH— CH.,— CH— CH,— CH— CH,— CH— 



Styrene 



/ 



Polystyrene 



CH2=C— CH-CH„ 



— CH,— C = CH— CH„— CH,— C = CH— CH,— CH^— 



CH3 

 Isoprene 



CH3 CH3 



Caoutchouc (polyprene) 



Fig. 49. Polvmerization 



of this point of view in synthetic products. Fig. 49 shows some of his 

 polymerizations. It is seen that the monomer molecules always contain 

 double bonds, one of which interacts with another molecule and thus links 

 two monomer molecules together. If this process is repeated, long chain 

 molecules are formed whose growth would be theoretically unlimited if the 

 possibility of further addition did not diminish with increasing chain length 

 and the sensitivity to oxygen (and the like) of the giant molecules formed 

 did not become considerably enhanced. For the present, however, the 

 factors limiting the chain length will not be considered, and the polymer 

 chains will simply be denoted by "open" formulae. Polymerization pro- 

 cesses are particularly successful if the monomer contains a system of 

 conjugated double bonds, as e.g., in isoprene, i.e., if double bonds alternate 

 with single bonds. The terminal double bonds may then give rise to inter- 

 linking with those of neighbouring monomer molecules, while the central 

 single bond is converted into a double bond. In this manner unsaturated 



