Polystyrene microgels

Clarke and Vincent in these studies established the phase diagrams for the free polystyrene-microgel-ethyl benzene systems, two of which are displayed in Fig. 16.2a and b. In all cases, only the stability/instability boun ry is shown. These lines correspond to the locus of the critical volume fraction of free polymer required to induce flocculation (vj ) as a function of the volume fraction of the microgel particles (< 3). 

Fig. 16.2. Three component diagrams at 25 °C for polystyrene microgel particles (M) in ethylbenzene (S) in the presence of free polystyrene (P) (a) free polystyrene of various molecular weights curves 1, 1 800 2, 18 000 3, 2 x lO (b) different particle sizes curves 1, 520 nm 2, 460 nm 3, 403 nm (after Clarke and Vincent, 1981b).

In addition to the above-mentioned, rather painstaking, techniques of polypeptide syntheses, a very elegant technique was developed by Merrifield. This solid-phase peptide synthesis automates the reaction sequences. The method makes use of an insoluble crosslinked polymer substrate with pendant reactive groups for attachment of peptide chains. Chloromethylated polystyrene microgels are often used (see Chapter 8 for more discussions on the use of chloromethylated polystyrene for reactions of polymers). The chloromethyl moieties serve as the initiating sites for formation of the polypeptides ... 

Vincent (7) investigating the effect of non-adsorbing polystyrene on polystyrene microgels reported the critical flocculation concentration (CFC) of polymer increased... 

Microgel Polystyrenes. Microgels are soluble polymers with a certain degree of cross-linking, but can be precipitated using an appropriate solvent (51). Beads with a diameter of 5-25 /um can be prepared by radical dispersion polymerization in the presence of a surfactant. 

Fig. 14 The relationship between translational diffusion coefficient and gel concentration of polystyrene microgel at the swelling state [39].

Figure 10.10 Normalized storage and storage moduli G a))/a) and G"( >)/ ) of (a) 187, (b) 1030, and (c) 39 200 kDa spherical polystyrene microgel melts and tits including as appropriate an initial stretched exponential and a terminal (i) power law or (ii) sum of a power law and late stretched exponential and a high frequency baseline, based on measurements of Antonietti, et al.(60).

The concentration dependence of q of hard-sphere suspensions is the same as the concentration dependence of q found in many polymer solutions, namely t](c) is a stretched exponential in c at smaller c and a power law in c for larger c. The frequency dependences of G (a>) and G"(co) for a colloid suspension and for a polymer solution are also very nearly the same, namely a stretched exponential in (o at smaller a>, a power law in co at large a> and various high-frequency small additive components. At the extreme large-concentration limit, the dynamic moduli of a soft-sphere melt composed of polystyrene microgel particles have very nearly... 

M. Antonietti, T. Pakula, and W. Bremser. Rheology of small spherical polystyrene microgels A direct proof for a new transport mechanism in bulk polymers besides reptation. Macromolecules, 28 (1995), 4227-4233. 

The first report on the preparation of microgel-stabilized metal nanoclusters was published in 1997 by Antonietti et al. [11a], who utilized polystyrene-based microgels prepared... 

As maybe seen in Figs. 28 and 29, values for [r ] of various microgels from UP and S resp. 1,4-DVB and EDM A are only as low as about 4-8 ml/g and depend little on the molar mass over a range of about 0.5 X106 to 40 X106 g/mol. As compared with these values, the [r ] of linear polystyrene for the same range of molar... 

Fig. 33. Dependence of viscosity on the shear rate of microgel solutions in C2H5OC2 H4OCOCCH3. EUP(MA+HD), c/t 70/30, EUP/S and EUP/EDMA(D), AIBN, P.-S. polystyrene [136].

Fig. 44. Schematic representation of Dd/JV plots for microgels formed in emulsion (solid lines) and in solution (dashed line). Solvent = toluene. Temperature = 25°C. The dotted line represents the plot of linear polystyrene. The 1,4-DVB contents are given in the figure. E = Einstein equation.

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].

Fig. 55. Gel-permeation chromatogram(GPC) of a microgel sample of Mw = 10X106 g/mol obtained in the anionic polymerization of EDMA in toluene. Microgel concentration = 1 g/L solvent = butyl acetate elution temperature = 70 °C is the weight-average molar mass of linear polystyrene used for comparison. [Reproduced from Ref. 256 with permission, Huthig Wepf Publ., Zug, Switzerland].

An interesting way to prepare shock-resistant coatings [381] follows the synthesis of the ABS-terpolymers, e.g. shock-resistant polystyrene, where a soft, elastomeric phase is incorporated in a hard polymer matrix via covalent bonds. Because organic coatings solidify in situ, elastomeric microgels have been synthesized and mixed to a binder which forms the hard matrix phase before the application of this mixture as a coating material. 

Figure 20. Model of two consecutive growth stages for the polystyrene phase. (1) Early stages microgels of increasing size. (2) Intermediate to final stages Domains become wormlike cylinders and then interconnected cylinders that exhibit dualphase continuity 41).

In a related application, polyelectrolyte microgels based on crosslinked cationic poly(allyl amine) and anionic polyfmethacrylic acid-co-epoxypropyl methacrylate) were studied by potentiometry, conductometry and turbidimetry [349]. In their neutralized (salt) form, the microgels fully complexed with linear polyelectrolytes (poly(acrylic acid), poly(acrylic acid-co-acrylamide), and polystyrene sulfonate)) as if the gels were themselves linear. However, if an acid/base reaction occurs between the linear polymers and the gels, it appears that only the surfaces of the gels form complexes. Previous work has addressed the fundamental characteristics of these complexes [350, 351] and has shown preferential complexation of cationic polyelectrolytes with crosslinked car-boxymethyl cellulose versus linear CMC [350], The departure from the 1 1 stoichiometry with the non-neutralized microgels may be due to the collapsed nature of these networks which prevents penetration of water soluble polyelectrolyte. 

M. Rasmusson, A. Routh, and B. Vincent, Flocculation of microgel particles with sodium chloride and sodium polystyrene sulfonate) as a function of temperature, Langmuir 20, 3536-3542 (2004). 

In reactions with polymer-bound catalysts, a mass-transfer limitation often results in slowing down the rate of the reaction. To avoid this disadvantage, homogenous organic-soluble polymers have been utilized as catalyst supports. Oxazaborolidine 5, supported on linear polystyrene, was used as a soluble immobilized catalyst for the hydroboration of aromatic ketones in THF to afford chiral alcohols with an ee of up to 99% [40]. The catalyst was separated from the products with a nanofiltration membrane and then was used repeatedly. The total turnover number of the catalyst reached as high as 560. An intramolecularly cross-linked polymer molecule (microgel) was also applicable as a soluble support [41]. 

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