Elasticity of nonionic and weakly ionized acrylamide-based
hydrogels was studied as a
function of swelling degree Q and initial total monomer
concentration c
0. The shear modulus
decreases
as Q
-
m
at low
Q and then increases steeply because network chains no
longer obey Gaussian statistics.
The exponent m decreases from 0.7 to
1/3 as c
0 increases from
5 to 30 wt %. Ionization of network leads
to a decrease in the modulus, and this effect disappears at high
concentrations of added salt, as predicted
by a recent model. At swelling equilibrium, the modulus provides
an “effective” measure of the osmotic
pressure. The upturn in the modulus is described using the inverse
Langevin function that allows
estimation of an average network chain length. This length was
compared with that of a perfect network
chain, and the network density was evaluated from the modulus in the
preparation state. This indicates
that networks prepared with low c
0 contain a
large amount of elastically ineffective segments.
Their
“chains” apparently have architecture typical of ideal
random-branched macromolecules without loops.
At high c
0, “effective” perfect
networks with insignificant number of interchain trapped
entanglements
are formed.
For a study of the mechanism of catalysis of polymerization of diene hydrocarbons and also for investigation of the process of catalysis of copolymerization the following hydrocarbons tagged with C14 were synthesized: benzene, toluene and isoprene. The simplest ordinary methods possible were used for these syntheses to obtain pure active preparations in good yields from starting materials containing radioactive carbon.
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