Interparticle crosslinking

Carboxylic monomers, such as acrylic or methacrylic acid, are included in emulsion polymerisation formulations for several reasons to increase the stability of latex particles, to improve the adhesion of resultant films to various substrates, to provide functional groups for interparticle crosslinking reactions and to control the viscosity of latex via neutralisation. Acrylic latices with and without incorporation of carboxylic groups, together with addition of various amounts of anionic surfactant, are used to investigate rheological and drying behaviours of the latices. 9 refs. 

In this context it is worthwile to report experiments carried out by W. Muller in our laboratory by which it was shown, that free standing films may be prepared from a suspension of individual particles and that the mechanical strength as well as the electrical properties are linked to a interparticle crosslinking reaction which seems to occur during the drying of the particle suspension. 

C.J. Berg, F.H. Lahrman, and D.C. Roe, Particulate, absorbent, polymeric compositions containing interparticle crosslinked aggregates, US Patent 5300565, assigned to The Procter Gamble Company (Cincinnati, OH), April 5,1994. 

Micro-gel fractions are a common feature of emulsion polymers because of intraparticle crosslinking. On the other hand, interparticle crosslinking, which occurs after film formation, significantly reduces the solubility of the polymer film. In this latter case, crosslinking is characterized by performing swelling experiments in organic solvents. 

Very recently, the formation of clusters and filler network structures via interparticle interaction has also been observed in composites containing monodis-perse size crosslinked polystyrene particles [108]. 

Fig. 6 (a) Structural model showing organic (polymer)-inorganic (clay) networks in the NC gel. Dio is the interparticle distance of exfoliated clay sheets. /, gi, and g2 represoit crosslinked chain, grafted chain, and looped chain, respectively. In the model, only a small number of polymer chains are depicted for simplicity [19, 20, 54]. (b) Decorated clay platelet sandwiched by polymer layer [52]. (a) Reprinted from Haraguchi and Li [54], Copyright 2009, with permission of Wiley... 

Table 13.3 summarizes the polymeric systems that have been applied to silica. In effect, the underlying inorganic framework plays the role of a structure-directing agent (template). The mechanical property improvement is attributed to reinforcement of the interparticle necks, which are the weak points of the aerogel skeletal framework. In turn, the stabilization provided by the crosslinking polymer is attributed to the extra chemical bonds created by the interparticle polymeric tethers. 

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