Density styrene-divinylbenzene networks

The "uncrosslinked limit" of many crosslinked polymers can be defined quite easily. For example, polystyrene is the uncrosslinked limit of styrene-divinylbenzene copolymers. On the other hand, the uncrosslinked limit of many other crosslinked polymers cannot be defined unambiguously, and is an idealization. In such cases, there is no unique uncrosslinked limit for a densely crosslinked polymer synthesized from a monomer or monomers with functionalities able to react by several mechanisms. DVS-BCB2 is an example of such a complicated network polymer. However, even for such cases, reasonable choices of uncrosslinked limit can be made. Furthermore, the general form for the dependence of Tg on the crosslink density can be combined with a very small amount of data (such as one or two data points) to give the proper scale for the Tg values and to provide a good estimate for Tg at other crosslink densities. 

J. R. Millar, Interpenetrating Polymer Networks—Styrene-Divinylbenzene Copolymers with Two and Three Interpenetrating Networks, and Their Sulphonates, J. Chem. Soc., 1311 (1960). Synthesis of IPNs. Swelling Behavior of IPNs. vs. crosslink density. 

An obvious extension of polyhedral silsesquioxane materials chemistry would be the incorporation of suitably functionalized POSS cages into important classes of thermoset resins, such as epoxy, phenolic, vinyl ester, styrene/divinylbenzene, acrylic resins and hydrocarbon networks. However, little has appeared in the literature, except for a few examples already discussed. This is an area in which our laboratory has become quite active. Two general types of substituted POSS monomers can be chemically incorporated into such resins. First, monofunctional monomers can be used. Alternatively, difunctional or polyfunctional POSS monomers can be used. Incorporating a monofunctional POSS monomer can actually lower flie resulting resin s crosslink density if the amoimt of the monofunctional POSS monomers in the commercial resin s monomer mixture is held constant. The POSS cages with organic functions attached to its comers have typical diameters of 1.2-1.5 run. Therefore, each POSS monomer occupies a substantial voliune. When that POSS... 

The term IPN was first used in 1960 to describe the apparently homogeneous product obtained from styrene crosslinked with divinylbenzene. IPNs were prepared from this system by taking a crosslinked poly(styrene) network and allowing it to absorb a controlled amount of styrene and a 50% divinylbenzene-toluene solution containing initiator. Polymerisation of this latter component led to the formation of an IPN, the density of which was... 

B. N. Kolarz, Ion Exchangers XIX. Some Properties of the Carboxylic Cation Exchangers Obtained by Intermesh Polymerization of Methacrylic Acid into Styrene and Divinylbenzene Porous Copolymers, /. Polym. Sci. 47C, 197 (1974). PS/PMA IPNs. Both polymers crosslinked with DVB. Effect of porosity of network I. Effect of crosslink density of network I. Ion exchange properties. 

It is of interest that the phenomena discussed above are most clearly manifested for linear polymers. When passing over to cross-linked polymers (eg copolymers of styrene and divinylbenzene), the effect of the surface on the relaxation time becomes less perceptible as the network density increases. This is due to the fact fiiat the reduction in the mobility of large segment of the chains caused by cross-linking excludes them from participation in the relaxation process, thus leveling the effect of the surface on their mobility. 

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