Local segmental motion

For the investigation of polymer systems under spatial confinement, fluorescence microscopy is a powerful method providing valuable information with high sensitivity. A fluorescence microscopy technique with nanometric spatial resolution and nanosecond temporal resolution has been developed, and was used to study the structure and dynamics of polymer chains under spatial confinement a polymer chain in an ultra-thin film and a chain grafted on a solid substrate. Studies on the conformation of the single polymer chain in a thin film and the local segmental motion of the graft polymer chain are described herein. 

The rate of growth of polymer-salt complexes can provide fundamentally important information that is difficult to determine otherwise. The rate of crystal growth of (PEO)3 NaSCN from its undercooled liquid was measured and used to determine values for the diffusion coefficients of Na" " and SCN (Lee, Sudarsana and Crist, 1991). Also it was shown that the rate of the salt diffusion is independent of the molecular weight of the polymer for PEO molecular weights above 10. This result is fully consistent with the concept that ion motion is due to local segmental motion of the polymer. 

Carbon-13 spin-lattice relaxation times TL (Section 3.3) are relatively insensitive to the chain length of polymers [531]. The influence of local segmental motions predominates, as shown for low-density polyethylenes in which Tx values are one to two seconds for the main chain but up to seven seconds for peripheral side-chain carbon nuclei at 120 C [532] due to segmental mobility (Section 3.3.3.4). To conclude, quantitative evaluation of polymer carbon-13 spectra as necessary for side-chain determination requires the knowledge of spin-lattice relaxation times. 

The relationship between the structure of a polymer chain and it dynamics has long been a focus for work in polymer science. It is on the local level that the dynamics of a polymer chain are most directly linked to the monomer structure. The techniques of time-resolved optical spectroscopy provide a uniquely detailed picture of local segmental motions. This is accomplished through the direct observation of the time dependence of the orientation autocorrelation function of a bond in the polymer chain. Optical techniques include fluorescence anisotropy decay experiments (J ) and transient absorption measurements(7 ). A common feature of these methods is the use of polymer chains with chromophore labels attached. The transition dipole of the attached chromophore defines the vector whose reorientation is observed in the experiment. A common labeling scheme is to bond the chromophore into the polymer chain such that the transition dipole is rigidly affixed either para 1 lei (1-7) or perpendicular(8,9) to the chain backbone. 

Our experimental measurements of the orientation autocorrelation function on sub-nanosecond time scales are consistent with the theoretical models for backbone motions proposed by Hall and Helfand(ll) and by Bendler and Yaris(12). The correlation functions observed in three different solvents at various temperatures have the same shape within experimental error. This implies that the fundamental character of the local segmental dynamics is the same in the different environments investigated. Analysis of the temperature dependence of the correlation function yields an activation energy of 7 kJ/mole for local segmental motions. 

Theoretical Models for Local Segmental Motions. The second order orientation autocorrelation function measured in this experiment is defined by ... 

Temperature Dependence of Local Segmental Motions. In this paper, our major focus is on the temperature and viscosity dependence of... 

In this paper, we have shown the utility of time-resolved optical techniques for the investigation of local segmental motions in polymer chains on a sub-nanosecond time scale. Detailed information about chain motions is contained in the time dependence of the orientation autocorrelation function of a backbone bond. 

The constant shape of the correlation function in various solvents at different temperatures implies that the same mechanisms are involved in local motions under all conditions investigated. In terms of the Hall-Helfand model, the ratio of correlated to uncorrelated transitions is constant. Analysis of the temperature dependence of the labeled polyisoprene yields an activation energy of 7.4 kJ/mole for local segmental motions. 

Resistance to flow in polymer systems is greater than in low molar mass fluids, because now the molecules are covalently bonded into long chains, which are coiled and entangled, and translational motion must, of necessity, be a cooperative process. It would be unreasonable to expect easy cooperative motion along the entire polymer chain, but as there is normally some degree of flexibility in the chain, local segmental motion can take place more readily. The polymer can then be considered as a sraies of kinetic units each of these moves in an independent manner and involves the cooperative movement of a munber of consecutive chain atoms. 

Musculoskeletal—for great forces Cardiopulmonary—for medium to low forces General body posture Body motion Local segmental motion Local segmental configuration Anthropometry... 

This study compared methacrylate and acrylate polymers to structural analogs with fluorinated ester groups. Two types of relaxations were characterized, the primary relaxation associated with the glass transition and secondary relaxations associated with side group motion and localized segmental motion. Dielectric analysis was used to characterize the response of dipoles to an electric field as a fimction of temperature. Mechanical properties were analyzed via dynamic mechanical analysis and stress relaxation measurements. Relaxation behavior was interpreted in terms of intermolecular and intramolecular mechanisms. 

In our laboratory, we have found that the use of deuterium NMR relaxation times could provide a convenient probe of local segmental motions in concentrated solutions. The overlap of different moieties can be avoided through the use of specific labeling. The low natural abxmdance of deuterium means that only the labeled sites will give any appreciable amount of signal. The moderate size quadrupole moment of the deuteron means that the relaxation of deuterons attached to carbons can be interpreted in terms of the reorientation of the C-D bond vector. Additionally, the relaxation times of deuterons on polymers tend to be quite rapid so that the experiments can be done quickly. 

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