THEORY OF THE VARIATION OF RELAXATIONAL PROPERTIES OF POLYMERS DURING NETWORK FORMATION

Recent work on the change of mechanical and dielectric relaxational properties accompanying the formation of a polymer network from reactive oligomers is reviewed. The theoretical considerations cover the essential features of the behaviour observed in different polymer systems. The theory offers new possibilities for obtaining information about the chemical kinetics, physical structure, and structure formation during crosslinking, by means of relaxation studies. Analysis of the theory of the kinetics of structure formation suggests the following picture of the process of crosslinking. Shortlv before the gel point, there appears a state of 'kinetic entanglement', which is completed at gel; chemical crosslinks then start to form. Beyond the gel point the contribution of entanglements to the mechanical behaviour is insignificant. However, fluctuation restrictions on crosslinks, and the topological restrictions on network chains play an important role in the reduction of the front-factor and in the increase of the Mooney-Rivlin C2-term during network formation. © 1979.