Coils trapped in a network

Here we look at a system which is simpler than a polymer melt but which still shows some nontrivial entanglement effects. This corresponds to a single, ideal, polymeric chain P (withA monomers) trapped in a three-dimensional network. 

Incorporation of the chain into the network is difficult. It is not enough to put a swollen gel into contact with a solution of chains. Even if thermodynamic eqitilibrium allows for a finite concentration of chains in the gel, the kinetics of chain diffusion ate usually too slow. However, it is possible to prepare a mixture of chains P with other chains C, and to crosslink the C chains in a second stage. This was done by the Wisconsin group using two different pathways 1) with P = polyisobutylene and C = butyl rubber, and 2) with P = saturated ethylene propylene copolymer, C = ethylene propylene terpolymer [+ crosslinking agent (sulfiir)].  

Another pos bility is obtained with block copolymers AB to which one adds some chains (P) which are chemically identical to the A group. Starting with a disordered solution or melt, by siritable changes in temperature or solvent concentration, one can reach a final state where the B group segregates into mkronodules. The A chains are then crosslinked by these nodules, and the P chains are trapped in a network.  

The best idea is probably to replace the network by a melt of chains that 

In all these processes, it is essential that the P chains never become attached to the netwoiic. As shown later, the behavior of a long chain which is attached at one end is very different fiom that of an unattached chain. It is also important (for similar reasons) that the P chain be unbranched. 

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