Poly compositional heterogeneity

A 50% functionalization evokes the interesting question, bearing in mind facile transesterification, of how the fluoroalkyl chains will be distributed over the molecules and how they will be distributed on one particular molecule This question has been examined in detail for dendrimers of the poly(propyleneimine) type functionalized with stearic acid [33]. It was proven that the compositional heterogeneity (distribution of degree of substitution) is random, but the positional heterogeneity (spatial distribution of the substituents over the dendrimer molecule) is not random. However, due to flexibility, no particular effect of the spatial distribution can be observed. Unlike the dendrimers, we expect the hyperbranched polyesteramides to be stiffer, so that spatial distribution could lead to interesting effects if the molecule were composed of a functionalized side and a non-func-tionalized side (Fig. 28), as shown possible for dendrimers via a convergent synthesis [34]. 

Complexes between polyvinylpyrrolidone and poly(acrylic acid)s are also possible (IV). Such macromolecular reactions are highly selective and strongly dependent on molecular size and conformation. On mixing, some of the macromolecules might be involved in the complex while the rest will be free. The reason for compositional heterogeneity of the products could be the conformational transitions of macromolecules in the course of complex formation. 

Poly sty rene-polydimethylsiloxane block copolymer PS-PDMS (polysimethylsiloxane) blend Four 30 cm 10 pm packings (Polymer Laboratories 10, 105, 1Q4 103 C,H,C1, (tetrachloroethylene) quoted pore size concentration 5 x 10"3 g/cm 3 or less RI, FALLS (dual detector) Compositional heterogeneity correlation with MWD 54... 

Domain sizes and compositional heterogeneities in poly-3-hexyl-thiophene phenyl C61-butyric acid methyl ester bulk heterojunction thin films are studied by spin diffusion Solid-state Si, Al, C,... 

More recently, compositional heterogeneity has also been detected for various PUs, such as those based on poly(caprolactone) glycol PCL/PET polyesters [172] or MDI PCL BDO based PUs [162], by means of gel permeation chromatography and thin layer chromatography. 

The particles have a relatively uniform density of about 0.95 g cm-3 and hence a content of poly(butadiene) of 59 percent (ratio of the weight styrene/ acrylonitrile = 88/12). With this gradient system the investigation of the chemical composition and heterogeneity of nearly all butadiene copolymer latices is possible. The experiment needs about 1 hour. 

Wang, N. Wu, X.S. Li, J.K. A heterogeneously structured composite based on poly(lactic-co-glycolic acid) micro-spheres and poly(vinyl alcohol) hydrogel nanoparticles for long-term protein drug dehvery. Pharm. Res. 1999, 16 (9), 1430-1435. 

The methods described above correspond to those attainable with conventional sol-gel chemistry. This strategy is simple, low cost, and yields amorphous hybrid materials, which can contain specific organic molecules, biocomponents or polyfunctional cross-linkable polymers (e.g., telechelic polymers). These materials exhibit an infinity of microstructures, can be transparent, and easily shaped as films or bulks (Fig. 2, Route A). However, they are generally poly-disperse in size and locally heterogenous in chemical composition. 

The rotating-frame spin-lattice relaxation time for protons, Tip,( H), was measured indirectly from CPMAS/DD NMR to probe possible molecular scales of heterogeneity in the miscible poly(benzyl methacrylate)/poly(ethylene oxide) blend over the whole composition range. ... 

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