Hydrophobically modified contents

Recently, we surprisingly found that even hydrophobically modified PNIPAM-co-MACA comonomer chains can form stable mesoglobules at higher temperatures [142]. Moreover, opposite to our expectation, the PNIPAM copolymer with a higher content of hydrophobic comonomer could... 

Associative ASTs. Nonionic and anionic associative thickeners are presently considered state of the art in many important industrial applications. The anionic associative thickeners are a subclass of hydrophobically modified, water-soluble polymers (HWSPs), and are predominantly represented by hydrophobically modified ASTs (HASEs and HASNEs), the chemical architectures of which were previously described. Because these polymers are very similar to conventional ASTs in molecular weight and carboxyl content, thickening is by a dual mechanism hydrodynamically (a function of molecular weight, anionic content, cross-link density, and other... 

Hydrophobically modified glycol chitosan (HGC) with 5p cholanic acid has been extensively studied both in vitro and in vivo. This polymer was developed as a new Cremophor EL-free alternative carrier systems for docetaxel [74] and paclitaxel. Physical characteristics of the nanoparticules such as size, hydrophobic core, and stability depend on the degree of 5-p cholanic acid substitution. The maximum loading content of paclitaxel into HGC nanoparticles was 10 wt% and the loading efficiency was above 90% [120]. Cytotoxicity studies on MCF7 breast cancer cells showed that HGC nanoparticles were less toxic than Cremophor EL, and allowed a higher dose of paclitaxel administration. The survival rate of mice that received 50 mg/kg paclitaxel in HGC nanoparticles increased substantially compared to 20 mg/kg PTX in Cremophor EL-ethanol solutions [120]. 

The association of polymer-bound hydrophobes can occur either within a single polymer chain or between different polymer chains, or both at a time, depending on the type of amphiphilic polymer. In Ughly dilute aqueous solutions, in general, hydrophobic associations may occur witiiin a polymer chain, but with an increase in the polymer concentration, a tendency for inteipolymer association may increase. In the case of hydrophobically-modified nonionic polymers, tiie association of polymer-bound hydrophobes can occur even if the hydrophobe content in a polymer is very low (4-6). In the case of hydrophobically-modified polyelectrolytes, however, a relatively Ugh content of hydrophobes is necessaiy for the association to occur, because... 

On the other hand, and CNMR [31] has been successfully used to determine the hydrophobe level for hydrophobically modified poly(sodium acrylates) of lower molecular weights (i.e. < 10 g/mol) and high (up to 30%) hydrophobe contents, provided the pH = 8 and the alkyl group is kept small ( < Cg). A deaggregating but nonprecipitating solvent pair (i.e. D2O/CD3OD, to 70/30) is used to improve resolution. 

Finally, degradation/GC have been used to determine the hydrophobe content in certain hydrophobe modified natural polymers. For example, the hydrophobe content of hydrophobe modified HEC have been determined by exhaustive cleavage of the polymer by aqueous hydroiodic acid followed by GC analysis of the iodoalkane formed [3]. 

Modified Leverett Function Appropriate for Fuel Cell Media The standard Leverett function has been found to be appropriate for qualitative matching of the flow characteristics through the media however, actual measurements of PEFC diffusion media show different quantitative behavior. Kumbur et al. [47] presented a modified Leverett function appropriate for thin-film fuel cell DM to estimate the capillary pressure as a function of liquid saturation and hydrophobic additive content This empirical fit was derived from the direct measurement of capillary pressure-saturation for different types of DMs (cloth and paper) with PTFE content ranging from 0 to 20% of weight and a nnicrop-orous layer. Figure 5.35 depicts the measured capillary pressure (Pc) versus nonwetting liquid saturation for carbon paper DM tailored with 20% PTFE content. The nature of the capillary pressure-saturation curves exhibits a continuous S shape, rather than J shape, and yields four inflection points. For saturation leads under 0.5, the capillary pressure in the DM was fit to a modified Leverett function, appropriate for the hydrophobic pores ... 

There is a class of hydrophobically modified water-soluble polymers known as associative thickeners (AT polymers) that are used in cotmnercial applications for rheology control (11-22). AT polymers and their model polymers include copolymers of acrylamide or (meth)acrylic acid with associative comonomers containing an oligomeric ethylene oxide (EO) chain as a spacer between a polymerizable moiety and terminal hydrophobe (11-16,23), Associative comonomer units in such copolymers play a role as stickers in aqueous solutions. The content of associative comonomers in AT copolymers is usually veiy low (< 2 mol %) because AT polymers are... 

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