STRUCTURE OF GELS 



65 



VIII 



(ACCORDING TO STAUDINGER, 1936b, 1937^) 



rule. Whether this applies to the whole range from looo to 2000 chain 

 links cannot be decided. Furthermore, it has been questioned whether 

 chain molecules of such liighly polymeric substances can be completely 

 dispersed in a micromolecular solvent at all (Lieser, 1940, 1 941). On 

 the other hand, it is possible that native fibres contain still longer chains 

 which may be degraded on dissolution in cuprammonium. The value 

 of 2000 for the degree of polymerization of the fibre cellulose is, 

 therefore, not reliable ; but it is the only value which can be determined 

 at present experimentally and, for the time being, we must refer to it. 

 Its magnitude is impressive enough, seeing that a degree of poly- 

 merization of 2000 corresponds to a chain length of i /(, each glucose 

 residue measuring 5 A. This means that the cellulose molecules have 

 microscopic lengths. Nevertheless, they remain invisible because their 

 thickness is amicroscopic. 



Chain molecules of a given structural type but different chain lengths 

 are called a homologous polymeric series. The polyglucosans mentioned 

 represent the polymeric homologues of the celluloses. In such a 

 series the physical properties change with increasing molecular weight 

 according to certain laws. Table VIII gives data for cellulose. Not only 

 does the solubility decrease and the viscosity of the solutions increase, 

 but the fibrous character and the capacity for film formation, which 



