Transitions temperature, hydrophobic

To strengthen mechanical properties and vary the transition temperature, hydrophobic monomers such as BMA were introduced into poly(IPAAm). The unique swelling properties with varying BMA composition are shown in Figure 11. 

We have been interested for some time in the chemistry and structure of polysiloxane containing systems. We suggest that some of the important characteristics of siloxane structures, such as their thermal and oxidative stability, low glass transition temperature, hydrophobic character and low surface energies could perhaps render them useful as epoxy modifiers, order to do so, however, one would have to consider the questions of functionality, both with respect to type and concentration and also the miscibility or solubility of such hydrophobic nonpolar materials in the typically aromatic based epoxy precursors. 

Carbon Cha.in Backbone Polymers. These polymers may be represented by (4) and considered derivatives of polyethylene, where n is the degree of polymeriza tion and R is (an alkyl group or) a functional group hydrogen (polyethylene), methyl (polypropylene), carboxyl (poly(acryhc acid)), chlorine (poly(vinyl chloride)), phenyl (polystyrene) hydroxyl (poly(vinyl alcohol)), ester (poly(vinyl acetate)), nitrile (polyacrylonitrile), vinyl (polybutadiene), etc. The functional groups and the molecular weight of the polymers, control thek properties which vary in hydrophobicity, solubiUty characteristics, glass-transition temperature, and crystallinity. 

Extremely low Glass Transition Temperatures —123 °C) Very low Surface Energies (20-21 dynes/cm) Hydrophobicity... 

Figure 8a shows the turbidity measurements for different guest residues in ELP [VgX2l. Lower transition temperatures (Tt) correlate with increased hydrophobicity of the guest residue [24, 25]. This data was extrapolated to other ratios of VahXaa (Fig. 8b). The transition temperature could also be influenced by the molecular weight of the ELP. The Tt was shown to increase with decreasing polymer length (Fig. 8c) [23, 26].

Micellar nanocarriers have already been applied successfully for delivery of hydro-phobic drugs [86]. These carriers are usually the product of self-assembled block copolymers, consisting of a hydrophilic block and a hydrophobic block. Generally, an ELP with a transition temperature below body temperature is used as hydrophobic block and the hydrophilic block can be an ELP with a transition temperature above body temperature or another peptide or protein. The EPR effect also directs these types of carriers towards tumor tissue. 

ELP-based triblock copolypeptides have also been used to produce stimulus-responsive micelles, and Chaikof and coworkers envisioned the possible application of these micelles as controlled drug delivery vehicles. These amphiphilic triblock copolymers were constructed from two identical hydrophobic ELP endblocks and a hydrophilic ELP midblock. Below the transition temperature, loose and monodispersed micelles were formed that reversibly contracted upon heating, leading to more compact micelles with a reduced size [90]. 

Recently, due to increased interest in membrane raft domains, extensive attention has been paid to the cholesterol-dependent liquid-ordered phase in the membrane (Subczynski and Kusumi 2003). The pulse EPR spin-labeling DOT method detected two coexisting phases in the DMPC/cholesterol membranes the liquid-ordered and the liquid-disordered domains above the phase-transition temperature (Subczynski et al. 2007b). However, using the same method for DMPC/lutein (zeaxanthin) membranes, only the liquid-ordered-like phase was detected above the phase-transition temperature (Widomska, Wisniewska, and Subczynski, unpublished data). No significant differences were found in the effects of lutein and zeaxanthin on the lateral organization of lipid bilayer membranes. We can conclude that lutein and zeaxanthin—macular xanthophylls that parallel cholesterol in its function as a regulator of both membrane fluidity and hydrophobicity—cannot parallel the ability of cholesterol to induce liquid-ordered-disordered phase separation. 

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