Polyacrylate chains

It has been suggested by Ikegami (1968) that the carboxylate groups of a polyacrylate chain are each surrounded by a primary local sphere of oriented water molecules, and that the polyacrylate chain itself is surrounded by a secondary sheath of water molecules. This secondary sheath is maintained as a result of the cooperative action of the charged functional groups on the backbone of the molecule. The monovalent ions Li", Na and are able to penetrate only this secondary hydration sheath, and thereby form a solvent-separated ion-pair, rather than a contact ion-pair. Divalent ions, such as Mg " or Ba +, cause a much greater disruption to the secondary hydration sheath. 

At the molecular level, a number of features are associated with the phenomenon of gelation or precipitation. In particular the disruption of the secondary hydration sheaths around the polyacrylate chains appears... 

The precise nature of the adhesion of the polyelectrolyte cements to untreated dental enamel and dentine has yet to be established. The earliest theory was due to Smith (1968) who speculated that the polyacrylate chains of the cement formed a chelate with calcium ions contained in the hydroxyapatite-like mineral in enamel and dentine. Beech (1973) considered this unhkely since it involved the formation of an eight-membered ring. Beech studied the interaction between PAA and hydroxyapatite, identified the formation of polyacrylate and so considered that adsorption was due to ionic attraction. 

Figure 7 shows the effect of polymer dose on the measured zeta potential. Zeta potential continues to rise quite steeply through regions 1 and 2, but then decreases rapidly in region 3. This sharp decrease could be a result of the reduction in ionisation of the polymer as the adsorption density rises however, recently published studies on tethered polyacrylate chains at various surface... 

Reaction-induced phase separation is certainly also the reason for which an inhomogeneous structure is observed for photocured polyurethane acrylate networks based on polypropylene oxide (Barbeau et al., 1999). TEM analysis demonstrates the presence of inhomogeneities on the length scale of 10-200 nm, mostly constituted by clusters of small hard units (the diacrylated diisocyanate) connected by polyacrylate chains. In addition, a suborganization of the reacted diisocyanate hard segments inside the polyurethane acrylate matrix is revealed by SAXS measurements. Post-reaction increases the crosslink density inside the hard domains. The bimodal shape of the dynamic mechanical relaxation spectra corroborates the presence of a two-phase structure. 

In the poly(ethyl acrylate)rubbers described above spirobenzopyran and aromatic azo chromophores were incorporated in the cross-links between the polyacrylic chains. In contrast, Matejika and al. studied cross-linked systems with azo side groups they considered especially the relative importance of the thermal effects occurring during photomechanical conversion. Most interesting are their results on copolymers ccmtaining low concentrations of chromophore (for which heat effects are less important), namely copolymers of )8-hydroxyethyl methacrylate (0.99) and azonaphthol methacrylate (XII) (0.01) swollen in water... 

Polymeric substances may show enhanced viscosity in H bonding solvents. Edelson and Fuoss (576) show that the greatly increased effect of water as a solvent (even compared to methanol) results from its bifunctional H bonding character which helps hold polyacrylate chains together. 

The unperturbed average dimensions of polyacrylate chains would thus be only slightly dependent upon ionic strength, the characteristic ratio, value at 15° ranging from about 11 to 13 going from... 

The results obtained by Buscall (1981) for the stabilization of polystyrene latices by well-anchored polyacrylate chains, of molecular weight 16000, support the prediction that the steric mechanism is dominant at high ionic strengths. Up to a degree of neutralization of ca 0-5, the polyacrylate stabilized latices when dispersed in an aqueous solution of sodium chloride at a concentration in excess of 1 M, could be flocculated by cooling. A comparison is presented in Fig. 6.7 of the LCFTs and the corresponding 0y-temperature for these systems as a function of the degree of neutralization. The dispersion medium was 1 -6 M NaCl. 

Table 5 lists the number of monomer units in a segment s =A/x, where X is the length of projection of the monomer unit on the axis of the molecule. For polyacrylic chains, X is 2.5 A. In the series presented in the Table, the value of optical anisotropy increases sharply thirty-fold. As shown previously, this reflects the generation of orientational order in the molecule. In this case, attention is drawn to the fact that the increase in... 

Scheme 30 Radical addition of allyl alcohol and 1,2-epoxy-5-hexene to polyacrylate chain end.

SCH Schweins, R., Hollmann, J., and Huber, K., Dilute solution behaviour of sodium polyacrylate chains in aqueous NaCl solutions, Polymer, 44, 7131, 2003. 

If both components are mixed together, an ion-exehange process takes place between the ions liberated by the dissociation of the earboxylie gronp and the Ca and Al ions of the glass. These ions subsequently form bridges between the carboxylic groups of neighboring polyacrylate chains ... 

The three-dimensional crosslinked network which is formed upon curing (Scheme 16.27) consists of two main segments the polyacrylate chain and the polymer, to which some acrylate groups are attached. This schematic picture clearly illustrates the methods by which the properties of the network can be adjusted the polyacrylate chain, the side groups, the number of crosslinks, and the acrylate-functional polymer. 

In addition to providing strong evidence that the electrografted polyacrylate chains are tethered to the surface and form a... 

Huber, K., 1993. Calcium-induced shrinking of polyacrylate chains in aqueous solution, J. Phys. Chem., 97, 9825-9830. 

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