Disordered methylene chains

Considerable experimental evidence (1-6,11) suggests that the methylene chains inside of a spherical micelle are almost as disordered as in the bulk liquid state (i.e. they contain a significant proportion of gauche conformers). The FTTR spectra of micellar SDS support this assertion, exhibiting CH2 stretching and scissoring band frequencies which are comparable to those found in the spectra of liquid hydrocarbons (1-6,11). A recent quantitative analysis of the CH2 defect modes of SDS has shown that the disorder of me methylene tails is similar to that found in liquid tridecane (11). 

Solid-state 13C NMR experiments on extended-chain /7-C168H338 have shown the strong reversible thermal disordering of chain ends very clearly.95 The methyl and a-methylene signals are clearly distinguished from those of inner methylenes the respective crystalline (all-trans) signals are at 16.1, 25.7, and 33.6 ppm, while their amorphous (conforma-tionally averaged) counterparts are at 15.5, 24.2, and 31.5 ppm. The relative intensities of the crystalline component are shown in Table 2 for 27 and 87 °C. 

In the case of magic angle sample spinning, the average (Oave) of the principal values and the motionally conformation-averaged chemical shift (Oiso) listed in Table 1 are detectable. Examination of these Oave and Oiso values, as well as the relaxation phenomena associated with these chemical shifts provides information on the phase structure of samples in terms of molecular conformation and dynamics. As is known, the phase structure of LPE samples differs widely depending on the mode of crystallization. For example, when crystallized isothermally from dilute solution or from the melt, LPE usually exhibits a lamellar crystalline structure the thicknesses of lamellae are relatively limited, say ca 100-500 A, in comparison with the lateral dimensions of over several microns, and the crystalline methylene chains orients perpendicularly to the wide face of the lamellae with molecular chains inclined to lamellar normals at angles of up to 38°. These lamellar samples, crystallized either from the melt or dilute solution, contain a non-crystalline component. The problem of whether this non-crystalline component is in an isotropically disordered state or in a particular state due to the coexistence of lamellar crystallites has been extensively studied for a few decades. 

Kwok et al. have reported on the development of ULS-sensitive barrier membranes able to give a pulsatile drug release. A co-polymer of 2-hydroxyl methacrylate (HEMA) and PEG dimethacrylate was loaded with particulate insulin and PEG, after which the surface of the polymer was coated with methylene chains. Upon exposure to ultrasound the methylene chains became disordered, permitting the insulin to diffuse out of the matrix [100,101]. 

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