Self-associating Polymers

The low-k films are prepared by solution casting the methyl silsesquioxane and the triblock copolymers mixtures from butanol. The size and distribution of polymer domains in the film will depend on the degree to which the polymer self-associates. Figure 4 shows the solution proton NMR spectra of the P103 triblock copolymer (EOirPOgo-EOn) mixed with methyl silsesquioxane in butanol-dio. The important feature to note is the narrow line widths for the polymer methyl and main chain resonances. Both sets of peaks are narrower than the broad peaks shown in Figure 3 for the triblock... 

PER Persson, K., Wang, G., and Olofsson, G., Self-diffusion, thermal effects and viscosity of a monodisperse associative polymer self-association and interaction with surfactants, J. Chem. Soc., Faraday Trans., 90, 3555, 1994. 

The behavior of surface-active graft copolymers In aqueous solutions has been the subject of much interest and study by the authors [1-3] and others [4-8]. It has been shown that these polymers self-associate in aqueous solutions, forming micelle-like aggregates among the less water-soluble species on the chain. These aggregates may form either intra- or intermolecularly. The net effect of the latter process is the formation of hydrogels with dispersed hydrophobic microdomains. 

The slightly galactosylated mannans are essentially linear polymers. As a result of their cellulose-like (1 4)-/3-D-mannan backbone, they tend towards self-association, insolubility, and crystallinity. Crystallographic study of C. spectabilis seed GaM [180] with a Man Gal ratio 2.65 1 suggested an orthorhombic unit cell with lattice constants of a = 9.12, b = 25.63, and c = 10.28 the dimension b was shown to be sensitive to the degree of galactose substitution and the hydration conditions [180 and references therein, [191]]. 

Ascher and Nemny 495) found that residues of triphenyltin acetate on glass, resulting from the evaporation of acetone solutions thereof, were, on contact to houseflies, less toxic with rising concentration. As triphenyltin acetate is likely to be a self-associated polymer in the solid state [similar to trimethyltin acetate (355)] and in concentrated solutions, it was suggested 495) that the monomer, which exists in dilute solutions, is toxic to insects, and the polymer, nontoxic. Interestingly, in this connection, a triphenyltin methacrylate copolymer has 470) a very low mammalian toxicity (acute, oral LDso for mice >2000 mg/kg). 

In donating solvents the subtle effects determining the chemical shift in chloroform, benzene, and hexane are apparently masked. In hexane, which is considered a poor solvent, self-association is possible and would explain the appearance of the Sn spectrum. Chloroform and benzene are excellent solvents for organometallic polymers, and the structure and downfield position support a well-solvated, unassociated environment. 

Although these examples demonstrate the feasibility of using calculated values as estimates, several constraints and assumptions must be kept in mind. First, the diffusant molecules are assumed to be in the dilute range where Henry s law applies. Thus, the diffusant molecules are presumed to be in the unassociated form. Furthermore, it is assumed that other materials, such as surfactants, are not present. Self-association or interaction with other molecules will tend to lower the diffusion coefficient. There may be differences in the diffusion coefficient for molecules in the neutral or charged state, which these equations do not account for. Finally, these equations only relate diffusion to the bulk viscosity. Therefore, they do not apply to polymer solutions where microenvironmental viscosity plays a role in diffusion. 

The structural chemistry of the organotin halides is dominated by their Lewis acid properties and their propensity to form five- and six-coordinate complexes. Self-association may give oligomers or polymers in the solid state, which usually dissociate in solution. The structure of tricyclohexyltin chloride in the crystal is temperature-dependent. At 108 K, it has the form of a rod-like polymer with distorted trigonal-bipyramidal tin and Sn-Cl separations of 245.6(7) and 300.77(7) pm, but at 298 K, the structure is best regarded as consisting of near-tetrahedral discrete molecules.3... 

With a functional substituent in the alkyl group, the self-association may be intramolecular. Thus, in the tu-hydroxyalkyltin trihalides, HO(CI I2) SnGI3, when n 3 or 4, the molecules are intramolecularly coordinated, whereas when n = 5, they form a linear polymer.336 Similarly, MeC02(CH2) SnCl3 forms a cyclic monomer when n = 3, but a cyclic dimer when 11 = 2, and an oligomer when n = 4.337... 

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