Poly chain motions

The classical example of a soUd organic polymer electrolyte and the first one found is the poly(ethylene oxide) (PEO)/salt system [593]. It has been studied extensively as an ionically conducting material and the PEO/hthium salt complexes are considered as reference polymer electrolytes. However, their ambient temperature ionic conductivity is poor, on the order of 10 S cm, due to the presence of crystalUne domains in the polymer which, by restricting polymer chain motions, inhibit the transport of ions. Consequently, they must be heated above about 80 °C to obtain isotropic molten polymers and a significant increase in ionic conductivity. 

The symbols have their usual meanings (] ). From measured values of NTj and ri on a poly (butene-1 sulfone) of degree of polymerization 700 the values of t (in nanosec.) shown in Table III are obtained. The discrepancy between the values of from NT and from ri, particularly marked for the side-chain motions, indicates the inadequacy of the single-Tg model. Nevertheless it is evident that the backbone motions are relatively rapid. (Comparison to polybutene-1 (jW) shows that SO2 groups retard the motion of the copolymer chains by a factor of about 50.) The question now becomes why are these rapid motions NMR-active but dielectrically inactive One possible type of motion which would account for this is shown in Fig. 9. Five backbone bonds and six main-chain atoms are involved, i.e. the sequence C-S-C-C-S-C, with concerted segmental transitions about two C-S bond, allowing interconversion... 

Correlation Times for Backbone and Side-Chain Motions in Poly(but-1-ene sulfone) of P = 700 as a 25% w/v Solution in Chloroform-d, Deduced from the Simple Isotropic Single-T Motional Model... 

It was straightforward to apply the TRMC technique to study on-chain charge transport to ladder-type poly-phenylene (LPPP) systems because covalent bridging between the phenylene rings planarizes the chain skeleton, eliminates ring torsions, and reduces static disorder. One can conjecture that in these systems intra-chain motion should be mostly limited by static disorder and chain ends. To confirm this... 

Disordering Chain Motions in Solid State Poly(Tetrafluoroethylene)... 

With the exception of local main-chain motions, the above-mentioned types of molecular motions have been investigated on a series of hydrophilic polymethacrylates and polyacrylates by means of dynamic mechanical measurements carried out with a torsional pendulum. For this purpose, the constitution of polymethacrylates was systematically altered and correlated with the dynamic mechanical response spectra. It was established for a series of copolymers of poly(2-hydroxyethyl methacrylate) that the temperature of the y relaxation (140 K 1 Hz), assigned to the motion of 2-hydroxyethyl... 

Section IA summarizes the molecular model of diffusion of Pace and Datyner (1 2) which proposes that the diffusion of gases in a polymeric matrix is determined by the cooperative main-chain motions of the polymer. In Section IB we report carbon-13 nmr relaxation measurement which show that the diffusion of gases in poly(vinyl chloride) (PVC) - tricresyl phosphate (TCP) systems is controlled by the cooperative motions of the polymer chains. The correlation of the phenomenological diffusion coefficients with the cooperative main-chain motions of the polymer provides an experimental verification for the molecular diffusion model. 

Poly(Propylene). In principle, resolution of individual carbon resonances in bulk polymers allows relaxation experiments to be performed which can be interpreted in terms of mainchain and side chain motions in the solid. This is a distinct advantage over the more common proton NMR relaxation experiments where efficient spin-diffusion usually results in the averaging of the relaxation behavior over the ensemble of protons. Thus, a direct... 

This leads to typical values at room temperature of 5xlO-6m2V-1sec-1 for films of soluble PPV polymers cast from solution. At 30 K a value of 3 x 10-4 m2V-lsec-1 was obtained for poly(2,3-dibutoxy-l,4-phenylenevinylene). Comparison with ESR data shows that in PAni the intra-chain motion of negative and positive polarons is similar but that negative polarons are more mobile between chains. j... 

Summary Solid state NMR studies of molecular motions and network structure in poly(dimethylsiloxane) (PDMS) filled with hydrophilic and hydrophobic Aerosil are reviewed and compared with the results provided by other methods. It is shown that two microphases with significantly different local chain mobility are observed in filled PDMS above the glass transition, namely immobilized chain units adsorbed at the filler surface and mobile chain units outside this adsorption layer. The thickness of the adsorption layer is in the range of one to two diameters of the monomer unit ( 1 nm). Chain units in the adsorption layer are not rigidly linked to the surface of Aerosil. The chain motion in the adsorption layer depends significantly on temperature and on type of the filler surface. With increasing temperature, both the fiaction of less mobile adsorbed chain units and the lifetime of the chain units in the adsorbed state decrease. The lifetime of chain units in the adsorbed state approaches zero at approximately 200 K and 500 K for PDMS chains at the surface of hydrophobic and hydrophilic Aerosil, respectively. 

It should be taken into account that in very rigid chains, such as those of poly-(alkyl isocyanate)s and para-aromatic polyamides, apart from rotation about valence bonds another mechanism can contribute to flexibility the deformation of valence angles and bonds during thermal chain motion just as it should occur in ladder structures (p. 100). When several flexibility mechanisms exist, the resulting rigidity of the homopolymer chain can be evaluated if the flexibilities, resulting from different mechanisms, are considered to be additive and the following equations are used ... 

Extensive 13C NMR relaxation measurements on poly( -butyl methacrylate) were carried out at 45°C and at 90.6, 37.8 and 20.0 MHz in a variety of solvents and a semiquantitative relationship between polymer side-chain motion and the... 

A convenient way to get information about the dynamics of polymers is to measure Ti, Tip and T2 by H pulse NMR. Figure 7.15 shows the side chain length-dependence of the H T2 value measured at 80°C for the side chain of poly(y-n-alkyl L-glutamate)s [26]. As seen from this figure, T2 is almost constant for n = 5-9 and suddenly becomes double for n = 10. It is easy to find the discontinuity between n = 9 and n = 10. Based on BPP theory, T2 increases as the correlation time for the motion decreases. A sudden increment of T2 means that there is a large difference in the side chain mobility between n 9 and n 10. These polymers become a thermotropic liquid crystal if the number of carbon atoms in the alkyl side chain is more than... 

Therefore, this chapter presents preliminary evidence indicating the effect and interrelationship between primary and secondary molecular motions on thrombogenesis, independent of morphological order and/or crystallinity. The polymer selected for this study was an amorphous elastomeric hydrophobic polymer of poly[(trifluoroethoxy) (fluoroalkoxy)phosphazene] (PNF) I (5, 6). The salient aspects of this polymer are that (1) the onset of the secondary molecular motions occurs between -160° and - 120°C (2) the side chain motion can be altered by irradiation (ultraviolet, electron beam, or gamma) (3) no apparent ultrastructure morphology exists (4) the side chains can be derivatized (5) and (5) the polymer can be readily coated onto our extracorporeal test shafts (7) and irradiated accordingly. Additionally, contact angle measurements of the homopolymer (8) and the PNF (9), 19.7 and 15.0 dyn/cm2, respectively, indicated that the fluorinated side chains comprised the surface to be interfaced in the extracorporeal blood studies. 

The dielectric strength. As, which is proportional to the area under the loss peak, is much lower for the secondary processes, relative to the a relaxation analysed in the next section. This is a common pattern foimd in both polymer materials and glass formers. The P secondary process is even more depleted in linear polymers that contain the dipole moment rigidly attached to the m chmn, such as polycarbonate [78-80] and poly(vinyl chloride) (the behaviour of this polymer was revisited in ref [81] where the secondary relaxation motions are considered as precursors of the a-relaxation motions). Polymers with flexible polar side-groups, like poly(n-alkyl methacrylate)s, constitute a special class where the P relaxation is rather intense due to some coupling vnth main chain motions. 

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