Microgel crosslinking

Different ways of toughening thermosets may be employed such as the use of rubber block copolymers (Mulhaupt and Buchholz, 1996) or introduction of microgels (crosslinked microparticles) (Funke et al., 1998). 

A different class, in between polymer lattices and polymer solutions, is tliat of microgels, consisting of weakly crosslinked polymer networks. Just as for polymer solutions, small changes in tire solvency conditions may have large... 

The treatment of blends as a two phase system opened up an interesting field of modifying the composite properties by the use of a (third component within the interface boundaries, which is termed as compatibilizers [1]. Such modifications are still being extended to the formation of microgel out of the interaction between the two blend partners having a reactive for functionalities. This type of interchain crosslinking does not require any compatibilizer to enhance the blend properties and also allows the blends to be reprocessed by further addition of a curative to achieve still further improved properties [3,4]. Such interchain crosslinking is believed to reduce the viscoelastic mismatch between the blend partners and, thus, facilitates smooth extrusion [5,6]. 

Figure 3. Dependence of the size of microgel-stabilized Pd nanoclusters from the crosslinking degree of the microgel and from the nature of the nonfunctional comonomer.

Funke, Wa Microgels-Intramolecularly Crosslinked Macromolecules with a Globular Structure. VoL 136, pp. 137-232. 

Zweigle, M.L. and Lamphere, J.C. "Crosslinked, Water-Swellable Polymer Microgels," US Patent 4,172,066(1979). 

Vilgis TA (1992) Polymer Networks - Crosslinking, Rubbers, Microgels Ch. 33... 

Gel present in natural rubber when the crosslinked particles are at or below the limits of microscopic vision (0.1 ptm) the gel is known as microgel. The term is also applied to similar structures in synthetic rubber. 

The intrinsic viscosity of microgels described in [9] decreased with increasing fractions of the crosslinking monomer to about 8 ml/g which was still above the theoretical value for hard spheres of about 2.36 ml/g according to the Einstein equation and assuming a density of 1.1 g/ml. Obviously, due to the relatively low fraction of the crosslinking monomer, these microgels did not behave like hard spheres and were still swellable to some extent. 

For the formation of microgels the presence of a crosslinking monomer is not always necessary. Thus, microgels have also been detected in polymers prepared with bifunctional monomers, e.g. poly(acrylonitrile-co-vinylacetate) [39], polyethylene [40],poly(vinylchloride) [41] andpoly(vinylidenefluoride) [42].Obviously, the reason for the intramolecular crosslinking with the formation of microgels are side reactions. 

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