Microgels

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... 

Saunders B R and Vincent B 1999 Microgel particles as model colloids theory, properties and applications Adv. Colloid Interface Sol. 80 1 -25... 

Micro Flow cell Microfluidizers Microgel theory Microgravity Microhardness... 

Suspension- and emulsion-polymerized PVDF exhibit dissimilar behavior in solutions. The suspension resin type is readily soluble in many solvents even in good solvents, solutions of the emulsion resin type contain fractions of microgel, which contain more head-to-head chain defects than the soluble fraction of the resin (116). Concentrated solutions (15 wt %) and melt rheology of various PVDF types also display different behavior (132). The Mark-Houwink relation (rj = KM°-) for PVDF in A/-methylpyrrohdinone (NMP) containing 0.1 molar LiBr at 85°C, for the suspension (115) and emulsion... 

Porous membranes with selective permeabiUty to organic solvents have been prepared by the extraction of latex films prepared with moderate ratios of PVA—PVAc graft copolymer fractions. The extracted films are made up of a composite of spherical cells of PVA, PVAc microgel, and PVA—PVAc graft copolymers (113). 

A further deficiency of natural rubber, compared with the synthetics, is its very high molecular weight coupled with a variable microgel content. Whilst this is desirable in that it reduces the tendency of stacked bales of rubber to flatten out... 

The particle diameter of the GPC column stationary phase plays a role not just in determining the resolution of the column, but also in determining how well the column elutes insolubles or microgels that may be present. It is usually advisable to avoid the injection of insolubles or microgels that might block the frits or interstices of any GPC column, but in some instances the analysis of these materials by GPC is possible and even desirable. 

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]. 

The arm-first synthesis of star microgels by initiating polymerization or copolymerization of a divinyl monomer such as diviny lbenzene or a bis-maleimide with a polystyryl alkoxyamine was pioneered by Solomon and coworkers.692 693 The general approach had previously been used in anionic polymerization. The method has now been exploited in conjunction with NMP,692 6 ATRP69 700 and RAFT.449 701 702 The product contains dormant functionality in the core. This can be used as a core for subsequent polymerization of a monoene monomer to yield a mikto-arm star (NMP ATRP704). 

Elaissari A, Ganachaud F, Pichot C (2003) Biorelevant Latexes and Microgels for the Interaction with Nucleic Acids. 227 169-193... 

FIGURE 22.7 ScaUng behavior of the small-strain modulus of carbon black composites left) and microgel or siUca composites right). In aU cases an exponent close to 3.5 is found, indicating the universal character of the cluster-cluster aggregation model. (From Kliippel, M. and Heinrich, G., Kautschuk, Gummi, Kunststojfe, 58, 217, 2005. With permission.)... 

Yin et al. [73,74] prepared new microgel star amphiphiles and stndied the compression behavior at the air-water interface. Particles were prepared in a two-step process. First, the gel core was synthesized by copolymerization of styrene and divinylbenzene in diox-ane using benzoylperoxide as initiator. Microgel particles 20 run in diameter were obtained. Second, the gel core was grafted with acrylic or methacryUc acid by free radical polymerization, resulting in amphiphilic polymer particles. These particles were spread from a dimethylformamide/chloroform (1 4) solution at the air-water interface. tt-A cnrves indicated low compressibility above lOmNm and collapse pressnres larger than 40 mNm With increase of the hydrophilic component, the molecnlar area of the polymer and the collapse pressure increased. 

Poncelet, D. et ah. Formation of microgel beads by electrostatic dispersion of polymer solutions, AIChE /., 45, 2018, 2003. 

The supports are soluble microgels and pore diameter cannot be measured. 

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