Microgel structure

The structure of homopolymer microgels for example poly(NIPAM) has been shown to be non-uniform with respect to cross-linker distribution within the particles. In the reaction of NIPAM with BA by SFEP, BA has been shown to be consumed faster than NIPAM [6], inferring a particle consisting of a core with a higher cross-link density than the periphery of the particle. Recent SANS studies concerning microgels have reported that the particles have inhomogeneous structures with respect to cross-linker distribution which is shown to be concentrated in the core of the particle [86]. 

Keiding et al. [88] developed an indirect method to evaluate the compositional distribution of AA residues in the poly(NIPAM-AA) microgel network. A two-phase model based on the Dorman concept has been developed to predict p PP values as a function of a. In the 

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Fig.46. Dependence of [r ] on theMn of polymers prepared by anionic polymerization of 1,4-DVB in THF. The symbols represent linear ( ) branched (V) and microgel ( ) structures. The dashed line represents the [iq]/Mn relationship of anionically prepared polystyrene. [Reproduced from Ref. 231 with permission, Hiithig Wepf Publ., Zug, Switzerland].

The presence of the grafted PEG chains improves the colloidal stability of the microgels. The incorporation of the PEG macromonomers into the microgel structure decreases the swelling degree and induces a shift of the VPTT to higher temperatures. 

Precipitation polymerization can be used for integration of inorganic NPs into microgel structures. An interesting approach for the preparation of the hybrid microgels is encapsulation of the NPs during precipitation polymerization. To demonstrate the efficiency of this method, LaF3 Eu NPs modified with a mixed... 

Fig. 20 Selective AuNPs deposition on PEDOT nanorods in microgel structures (a) PEDOT nanorods are not fully oxidized and attract a small amount of counterions (green circles). The small amount of positively charged groups (red circles) are due to the incorporation of initiator residues into polymer chains of microgel. (b) After addition of H+, [AuCU]- PEDOT nanorods become oxidized in acidic pH and [AuCLt]" anions (yellow circles) are drawn into the microgel to compensate for a charge on the nanorod surface (white circles), (c) After addition of NaBH4 and a reduction process, AuNPs are predominantly formed on the PEDOT nanorod surface. Taken from [148], Copyright Wiley-VCH. Reproduced with permission...

A striking advantage of the second approach is that no unreacted monomers remain in the microgel structure, which is an essential requirement for biomedical applications. Therefore, only examples of polymer cross-linking will be discussed here. 

Hellweg T, Dewhurst CD, Eimer W, Kratz K (2004) PNIPAM-co-polystyrene core-shell microgels structure, swelling behaviour and crystallisation. Langmuir 20 4330-4335... 

Change of Microgel Structure on Curing Epoxy Polymers in Fractal Space... 

This chapter considers the reasons for a variation of microgel structure characterised by its fractal dimension, D, formed in the cure of epoxy resin systems. Quantitatively, change of D during the increase of reaction time is well described within the framework of mechanism of aggregation cluster - cluster. The fractal space, in which the reaction curing proceeds, is formed by a structure of the greatest cluster in system. 

Let us note in conclusion the strong dependence of k on the microgels structure, characterized by the fractal dimension Z) (Fig. 66). As it follows... 

Kozlov, G. V. Bejev, A. A. Dolbin, I. V. Change of microgel structures at curing epoxy polymers in fractal space. J. Balkan Tribological Association, 2004, 10(1), 31-35. 

Now it is possible to calculate value using the reaction rate constants k, obtained according to the described above experimental methods as function of t or Q. The calculation has shown the principal distinction of behavior D, which is the microgels structure characteristic, for the systems 2DPP+HCE/DDM and EPS-4/DDM. For the first from the indicated systems the value D. does not depend on t at the initial part of the curve but is the function of Tcur. So, at T = 353 and 373 KD, 1.5, atT = 393 D. 1.7andatT = 513 KD, 2.3. It means... 

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