Network formation diluent

These excesses diminished for those networks with diluent present during network formation or with low extents of the network formation reaction. 

Networks Formed in the Presence of Diluent, s>0.9. A series of six networks were prepared both in bulk and in the presence of oligomeric PDMS (Mn = 1170, no vinyl groups) using as junctions a 0 = 43.9 linear PMHS and as chains a,o>-divinyl PDMS ranging in Mn from 9,320 to 28,600 g mol . The volume fraction of solvent present during network formation, v s, was 0.30 for all six networks and was calculated assuming simple additivity of volumes. The tensile behavior of the networks formed in bulk was measured in bulk, vt = Vf/V = 1. The tensile behavior of the networks formed in solution was measured both on networks with solvent present (vt =1) and on networks from which the oligomeric PDMS had been extracted (vt 1.47). 

A quantitative analysis of Eq. (6) shows that also conditions at network formation affect the magnitude and appearance of phase transition. Both the increasing concentration of the crosslinker (increasing vd) and decreasing amount of the diluent at network formation (increasing critical value of -For networks with vd > 20 x 10-5molcm-3 (at ° > 0.2 (at vrf = 5 x 10 5 mol cm"3) and i = 0.012 the phase transition does not exist any more [34]. 

The Effect of the Concentration of the Crosslinking Agent and Amount of Diluent at Network Formation... 

Since a change in the elastic energy of the network (see Eq. (3)) is operative in the swelling pressure (Eq. (1)) of the network, one can expect that the occurrence and extent of phase transition will be affected also by the concentration of the crosslinking agent and by the amount of diluent at network formation. We measured [26] six series of networks - A, B, C, D, E and F with varying content... 

Chapter II describes the various kinds of network structures which may exist before or arise during its formation. Of these, the various network defects resulting from the crosslinking statistics, have received far more attention in the literature than the effects of inhomogeneous network formation and syneresis (separation in a gel + diluent phase). This is reflected in this review (Chapter II, section 2) although a special emphasis is also laid on the latter aspect (Chapter II, section 3 and 4). 

Elliot, J. R. and Cheung, H. M. (1993) Light scattering study of polymer network formation in supercritical diluent, in Supercritical Fluid Engineering Science, Kiran, E. and Brennecke, J. M., Eds., ACS Symposium Series 514, pp. 271-280. 

So far, the role of phase separation in gelation has been limited to polymers which are regarded as flexible in solution. Thermoreversible gels can be formed from solutions of many rod-like polymers. " Miller et have reviewed the phase separation and networks formed by some rod-like polymers. The nature of the restoring force in such networks of rods must clearly be different from that of a rubber-like, flexible polymer network. However, that network formation occurs via a phase separation remains a possibility. Flory has developed a detailed theory for the liquid crystal-isotropic phase behaviour of rod-like particles in a diluent. 

Precipitation of the growing polymer from the initial solution of styrene and DVB in an inert diluent during crosshnking copolymerization results in the formation of a two-phase heterogeneous network, in which one phase is presented hy the highly crosshnked and rigid polymer, while the rejected diluent forms another phase. After removing the diluent, permanent voids remain in the copolymer beads. The total pore volume, and the inner surface area, S, are the major characteristics of the porous structure these are intimately related to pore size and pore size distribution. These parameters determine the practical apphcation frelds of the polymeric adsorbent resins therefore, a precise quantitative characterization of resin porosity becomes an important task. 

Chung et al. [313] tried to find an explanation for such variations in network morphology by considering the sequence of three critical events taking place during copolymerization (i) formation of an insoluble gel that is affected largely by the DVB content and, to a lesser extent, by the amount of the diluent (ii) phase separation occurring when the polymer—environment... 

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