Fractionation, anionic poly

Figure 9.33. (a) Schematic description of the effects of ionic strength (I) and pH on the conformations of a humic molecule in solution and at a surface. Rh denotes the hydrodynamic radius of the molecule in solution and 6h denotes the hydrodynamic thickness of the adsorbed anionic poly electrolyte. (Adapted from Yokoyama et al., 1989 and O Melia, 1991). (b) The influence of ionic strength of pH on diffusion coefficient, Dl, and on Stokes-Einstein radius of a humic acid fraction of 50,000-100,000 Dalton. (From Cornel et al., 1986). 

Figure 11. Integral distribution functions obtained by BW fractionation of anionic poly(methyl methacrylate)s prepared at different reaction temperatures under otherwise identical reaction conditions initiator, cumylcesium in the presence of about 10 3 mole/1 cesium triphenylcyanoborate (19)...

PE is obtained by anionic polymerization from hydrogenating a precursor 1,4-PB polymer. Since 1,4-PB contains a small fraction of 1,2-nnits the PE stndied here has two ethylene side branches per 100 backbone carbons. alt-PEP Essentially alternating poly(ethylene co-l-butene). 

Note 1 If a substantial fraction of constitutional units carries negative charges, then an anionic polymer is a poly electrolyte. 

As explained in Sections 16.3.4, 6.4.1, and 16.4.2, SEC is a nonabsolute method, which needs calibration. The most popular calibration materials are narrow molar mass distribution polystyrenes (PS). Their molar mass averages are determined by the classical absolute methods—or by SEC applying either the absolute detection or the previously calibrated equipment. The latter approach may bring about the transfer and even the augmentation of errors. Therefore, it is recommended to apply exclusively the certified well-characterized materials for calibrations. These are often called PS calibration standards and are readily available from numerous companies in the molar mass range from about 600 to over 30,000,000g moL. Their prices are reasonable and on average (much) lower than the cost of other narrow MMD polymers. Other available homopolymer calibration materials include various poly(acrylate)s and poly(methacrylate)s. They are, similar to PS, synthesized by anionic polymerization. Some calibration materials are prepared by the methods of preparative fractionation, for example, poly(isobutylene)s and poly(vinylchloride)s. 

Fraction DII is a polystyrene containing 2.2 branches per molecule. DII has been prepared together with the absolutely linear fraction D IV by Henrici-Oliv and Oliv6 (120). Apparently, the effect of the poly-dispersity of sample D II prevails over the opposite effect of branching. In this respect the investigation of anionic star-molecules would be extremely interesting. 

Table 16. Superoxide anion production from human neutrophils activated by fractionated poly(VAd) (5000 < MW < 10,000)...

It seems, however, that only polyanions are chiefly concerned in the interferon induction. Further polymers having anionic groups have been investigated besides poly(nucleic acid)s and co-(cyclopolymers) 8, for which a partial hydrolysis of the anhydride moiety is supposed. Thus, poly(vinylsulfonate)s or polyacrylates have been found to be active, but, polymethacrylates inactive. It has been shown that in the case of acrylic acid copolymers the molecular weight is also of importance in addition to the structure of the polymer chain and the fraction of carboxy groups. The influence of these various parameters has been discussed in detail by De Somer (45). 

The use of supercritical-fluid-extraction techniques in the fractionation of polysiloxanes has been demonstrated by the data presented. The poly-dispersities of the fractions were comparable with those generally attainable only by anionic-polymerization techniques, with which the incorporation of two functional groups is often difficult to attain. The ability to isolate these well-defined fractions will lead to important fundamental studies on structure-property relationships in multiphase copolymer systems. 

Noda, Kato, Kitano, and Nagasawa23 have made systematic measurements of the osmotic pressure in order to verify (15.4.21). They used seven samples of poly(a-methyl) styrene of different molecular masses (see Table 15.13). Each sample was obtained by anionic polymerization, followed by a fractionation aimed at a reduction of polydispersity. The latter is characterized by the ratio Mw/Afn < 1.01. The solvent used was toluene. The interaction b for poly(a-methyl)styrene in toluene, experimentally determined, is about 1.5 nm1. 

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