Molecular motion of polymers

The aim of this work was to find out how to get more information about stereochemistry and molecular motion of polymer methyl- and methyl-phenyl-siloxanes by measuring longitudinal relaxation times, Tj, and nuclear Overhauser effects, NOE, of the individual building blocks. 

Hikichi.K. Molecular motions of polymers having helical conformation. II. J. Phys. Soc. Japan 19,2169 (1964). 

TABLE 18.1. Molecular Motions of Polymers with Increasing Thermal Energy... 

In addition to spin relaxation, there are the methods that measure molecular motion. The spectra reflecting the quadrupolar interaction are sensitive to the mid-range of frequencies. Therefore, NMR spectroscopy is a powerful tool to examine the molecular motion of polymers in the solid state. Different types of motion can be di.scriminated on the basis of their time scale and their exchange geometry. The one-dimensional quadrupole echo lineshape of "H NMR is sensitive to dynamics in the range 10 s < r < 10 s. where is the... 

Abstract ESR spectroscopic applications to polymer science are presented. ESR parameters used for the molecular and material characterization of polymer materials are reviewed. It is emphasized that ESR studies of the polymer science are particularly effective in three areas. (1) Intermediate species such as free radicals produced in chemical reactions of polymer materials can be directly detected. (2) The temperature dependent ESR spectra of free radicals trapped in the polymer matrices are very effective for the evaluation of molecular mobility (molecular motion) of polymer chains. (3) The mobility of electron, the structure of solitons, and the doping behavior in conduction polymers can be observed in detail in order to clarify the mechanism of conduction. 

In this chapter, we present typical applications of ESR spectroscopy to polymer science, whieh include structures and molecular motions of polymer chains and chemical reactions in the polymer material. The first part deals with ESR parameters derived from speetra and the molecular information of polymer chains. In the second part, examples of applications to polymer science are introduced. In the following section, the close relations between structure, molecular motion and chemical reactions are discussed. The narrative will illustrate how these studies have made a considerable contribution to polymer physics and chemistry especially describing mechanisms of deteriorations, polymerization and relaxation phenomena of solid polymers. 

B-2) Molecular motion of polymer chains in crystalline and non-crystalline regions and in polymer alloys and polymer blends. 

We can relate structure and molecular motion of polymer chain to chemical reaction in solid polymers by the ESR method. In this chapter, we present ESR studies that are particularly effective in three areas of polymer science. 

The evaluation of molecular mobility (molecular motion) of polymer chains, (a) The decay of the radicals trapped in polyethylene can be interpreted in terms of a diffusion controlled reaction. The decay reaction is closely related to the molecular motion of polymer chains in the crystalline region, attributed to so-called a-relaxation because the time constants of the molecular motion agree with those of the diffusion, (b) The high molecular mobility of isolated polyethylene chains tethered on polytetrafluoroethylene surfaces has been identified. 

Abstract Measurements of temperature dependent ESR spectra of spin labels trapped in the polymer matrices is very effective for the evaluation of molecular mobility (molecular motion) of polymer chains. We can characterize the molecular motion of the particular sites in different region by the ESR method. It is possible to detect the mobility of polymer material at the segment or atomic level. ESR studies help to relate the features of the nanometer scale to macroscopic properties of the polymer materials. We present examples of spin labeling studies in the polymer science to help readers new to the field understand how and for what areas the method is effective. In the first part, we give a simple review of the spin labeling method and present applications in the polymer physics related to relaxation phenomena in various systems. In the second part applications to biopolymer system are introduced to help the clarification of various mechanisms of bio-membranes. 

Mechanical properties of polymers depend on the frequency and temperature, and the dynamic viscoelastic parameters are important to understand the morphology, structure, and molecular motion of polymers as described above. Because chemical reactions, such as curing and degradation, change the chemical structure of polymers, the mechanical properties may also be changed. In this section, we describe changes in the dynamic viscoelastic properties during chemical reactions. 

Kawaguchi et al [839] have reviewed the application of ESR for studies of reaction mechanisms of polymer additives (light stabilisers, antioxidants, carbon-black/rubber coupling agent), and of molecular motions of polymers. More recently, more general ESR applications have been reviewed [840]. Various books deal with applications of ESR [841], in particular also in relation to polymer research [842]. 

Molecular Motion. Spin-lattice relaxation times, T, determined using solid-state NMR provide a practical method to characterize molecular motion of polymers in the solid state. In diis regard. Figure 4 presents Si T, values for as-cast and aged PTMSP membranes. Based on the results in this table, the spin lattice relaxation time is not sensitive to aging for PTMSP synthesized with the thrw catalysts considered in this study. 

Because sporting goods are used by humans, they must be stable at the temperatures at which they will be used. If glass transition temperature (which is due to the molecular motion of polymer chains) is to he used as the energy absorption mechanism, the sudden change in modulus at the glass transition often causes unstable properties. If other viscoelastic properties are to be used for energy absorption, it is necessary either to copolymerize monomers or to mix polymers of different mohilities [6] (see Fig. 5) [7]. 

Many solid polymers are sensitive to heat stimulation and show characteristic REVERSIBLE PHASE TRANSITIONS at the GLASS TRANSITION TEMPERATURE and MELTING TEMPERATURE depending mainly on their own primary structure. This thermal sensitive property is being used in the fabrication of thermoplastic materials into any desired form in a similar means to that of fibers in the case of nylon, polyesters or films and other three dimensional products. In addition to the thermoplastic properties of polymers in the solid state, the molecular motion of polymers in solution is also achieved by thermal stimulation and has extensively been studied after pioneering works of Flory-Huggins. The effects of such thermal stimulation were detected experimantally as "sol-gel transformation", "viscosity changes", "phase separation" and so on. Egg-white and other aqueous solutions of natural proteins such as enzymes and hormones show such detectable behavior in the form of... 

In this section a series of experimental NMR studies based on the techniques described above will be compared with predictions of the model theories. Of course, any model is based on idealizations approaching reality only under certain conditions. The objective of the first few paragraphs will therefore be to demonstrate the rich variety of phenomena that can influence polymer dynamics. It will be elucidated under what circumstances the essence of the model theories and their predicted limits comes to light. We will first consider three basic features of polymer dynamics, namely the three dynamic components governing molecular motions of polymer chains, the dynamics of chain-end blocks in contrast to the central segment block, and how free volume and voids influence dynamics and the appearance of NMR measur-ands. 

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