Cross-link agglomerations

Fig. 16 Sketch of a heterogeneous polymer network consisting of domains (cross-link agglomerations) of different sizes...

Thus, we again find for inhomogeneously cross-linked gels a stretched exponential decay of the relaxation modulus G(t) on scales larger than the average size of the structmal inhomogeneities (cross-link agglomerations). Remarkably, the stretched exponential index here, 1 /3, coincides with that foimd by Sommer for polydisperse polymer networks [142], see Sect. 7.4. This is an expected result, since a ladder model is equivalent to a linear Rouse chain, see Sect. 6.2. 

The segments derived from the condensation reaction of the butanediol and the diisocyanate agglomerate into separate phases, which are hard and crystalline. The elastomeric chains are thus cross-linked to form a network similar in many ways to that given by the simple... 

Some elucidation of the mechanism of elastomer reinforcement is being obtained by precipitating chemically-generated fillers into network structures rather than blending badly agglomerated filler particles into elastomers prior to their cross-linking. This has been done for a variety of fillers, for example, silica by hydrolysis of organosilicates, titania from titanates, alumina from aluminates, etc. [85-87], A typical, and important, reaction is the acid- or base-catalyzed hydrolysis of tetraethylorthosilicate ... 

The tensile strength of cross-linked polysiloxane elastomers is low, but can be markedly improved by reinforcement with a filler. The material of choice is fumed silica with high surface area, which can increase the strength by a factor of 20. It is thought that the silica particles agglomerate to form a three-dimensional network within the siloxane, greatly reinforcing the stmcture. 

The first reported preparation of capillary columns containing MIPs utilised a thermally initiated dispersion polymerisation procedure [58], The functional monomer MAA and the cross-linking monomer EDM A were used. Agglomerates of micrometre-sized globular polymer particles were claimed to be prepared in situ in the capillary. Molecular imprinting of L-phenylalanine anilide, pentamidine and benzamidine was undertaken. A pH-dependent retardation of pentamidine over benzamidine in the pentamidine capillary was observed, while the opposite. 

Fig. 13 Ludipress (93% a-lactose monohydrate, 3.5% soluble povidone, 3.5% cross-linked povidone) (A), Cellactose (75% a-lactose monohydrate, 25% powdered cellulose) (B), and Avicel PH 200 (agglomerated microcrystalline cellulose) (C).

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