Dynamics crystalline poly

Farmer et al. evaluated the conformations and dynamics of poly(di- -hexylsilane). " - " The lowest energy conformer for a polymer containing eight silicon atoms was a helical arrangement with 30° torsional angles in the silane backbone. The authors also monitored different backbone and side chain torsions during dynamics simulations and concluded that the conformation present in the crystalline solid is controlled by intermolecular effects. 

Fig. 12. (a) Schematic representation of DQ exchange experiments for elucidation of slow molecular dynamics.45 (b) Calculated (black) and observed (gray) 13C-I3C DQ MAS NMR sideband patterns of crystalline poly(ethylene) yielding the dipolar coupling strength and DQ-DQ exchange sideband patterns for different jump angles. For details, see ref. 45. 

The polymer composed of 2-cyclohexenyl-l,4 units can exhibit high Tg (176 °C) when the tacticity is controlled well [62]. Recently, [( -allyl)NiBr]2, in conjunction with MAO, was found to initiate stereo- and regiospecific polymerization of 1,3-cyclohexadiene [63]. Although the polymer has too poor solubility in organic solvents to be analyzed by NMR spectroscopy, the copolymers of 1,3-cyclohexadiene with 1,3-butadiene and norbornene prepared by the Ni catalyst show NMR spectra that indicate the presence of the 2-cyclohexene- 1,4-diyl unit formed via 1,4-polymerization of 1,3-cyclohexadiene (Eq. 11). X-ray diffraction analysis of the crystalline poly( 1,3-cyclohexadiene) as well as studies by molecular dynamics confirmed the cis-syndiotactic structure of the polymer [64]. 

Although the dynamic mechanical properties and the stress-strain behavior iV of block copolymers have been studied extensively, very little creep data are available on these materials (1-17). A number of block copolymers are now commercially available as thermoplastic elastomers to replace crosslinked rubber formulations and other plastics (16). For applications in which the finished object must bear loads for extended periods of time, it is important to know how these new materials compare with conventional crosslinked rubbers and more rigid plastics in dimensional stability or creep behavior. The creep of five commercial block polymers was measured as a function of temperature and molding conditions. Four of the polymers had crystalline hard blocks, and one had a glassy polystyrene hard block. The soft blocks were various kinds of elastomeric materials. The creep of the block polymers was also compared with that of a normal, crosslinked natural rubber and crystalline poly(tetra-methylene terephthalate) (PTMT). 

Hiraoki et al. investigated the phenyl ring dynamics of poly(L-phenylalanine) using H-NMR, showing that it is characterized by a fairly broad distribution of correlation times. The mean correlation time of this distribution was 1.2 x 10 Hz at 25°C, which is close to that of the fast motional component of the B. mori and S.c. ricini silk fibroins. The Tyr ring flip in the pentapeptide [Leu ] enkephalin was reported to be 5.6 x 10 Hz at 25°C, which is close to that of the slow motional component observed here for silk fibroin. On the other hand, the ring motion in crystalline N-acetyl-L-Asp-L-Pro-L-Tyr-N -methylamide was found to be 1.1 X 10 Hz at 27°C, close to that of the fast motional component of the silk fibroins. 

Figure 3.16 Some experimental dynamic components, (a) Storage and loss compliance of crystalline polytetrafluoroethylene measured at different frequencies. [Data from E. R. Fitzgerald, J. Chem. Phys. 27 1 180 (1957).] (b) Storage modulus and loss tangent of poly(methyl acrylate) and poly(methyl methacrylate) measured at different temperatures. (Reprinted with permission from J. Heijboer in D. J. Meier (Ed.), Molecular Basis of Transitions and Relaxations, Gordon and Breach, New York, 1978.)...

First introduced to polymer chemistry by Schaefer and collaborators, CP-MAS spectroscopy has already yielded interesting results in both stractural and dynamic studies. The comparison of spectra in solution and in bulk permits identification of frozen conformations, distinction between spectra of crystalline and amorphous phases and measurement of the rate of several eonformational transitions. For example, the C spectrum of the poly(phenylene oxide), 74, in solution consists of five signals while the CP-MAS spectrum displays six. In the solid state the resonance of the aromatic CH appears split into two components. The phenomenon is attributed to the forbidden rotation of the benzene ring around the O. .. O axis, which makes the two carbon atoms indicated with an asterisk no longer equivalent. 

The zero-shear viscosity r 0 has been measured for isotropic solutions of various liquid-crystalline polymers over wide ranges of polymer concentration and molecular weight [70,128,132-139]. This quantity is convenient for studying the stiff-chain dynamics in concentrated solution, because its measurement is relatively easy and it is less sensitive to the molecular weight distribution (see below). Here we deal with four stiff-chain polymers well characterized molecu-larly schizophyllan (a triple-helical polysaccharide), xanthan (double-helical ionic polysaccharide), PBLG, and poly (p-phenylene terephthalamide) (PPTA Kevlar). The wormlike chain parameters of these polymers are listed in Tables... 

Pochan, J. M., Hinman, D. F. and Froix, M. F. Morphological studies on the viscous crystalline phase of poly(diethylsiloxane) including the dynamics of phase formation and the relationship of viscous crystalline structure and crystalline structure. Macromolecules 9, 611 (1976)... 

Crystallization from the melt often leads to a distinct (usually lamellar) structure, with a different periodicity from the melt. Crystallization from solution can lead to non-lamellar crystalline structures, although these may often be trapped non-equilibrium morphologies. In addition to the formation of extended or folded chains, crystallization may also lead to gross orientational changes of chains. For example, chain folding with stems parallel to the lamellar interface has been observed for block copolymers containing poly(ethylene), whilst tilted structures may be formed by other crystalline block copolymers. The kinetics of crystallization have been studied in some detail, and appear to be largely similar to the crystallization dynamics of homopolymers. 

Rather recently, we have studied the solid-state structure of various polymers, such as polyethylene crystallized under different conditions [17-21], poly (tetramethylene oxide) [22], polyvinyl alcohol [23], isotactic and syndiotactic polypropylene [24,25],cellulose [26-30],and amylose [31] with solid-state high-resolution X3C NMR with supplementary use of other methods, such as X-ray diffraction and IR spectroscopy. Through these studies, the high resolution solid-state X3C NMR has proved very powerful for elucidating the solid-state structure of polymers in order of molecules, that is, in terms of molecular chain conformation and dynamics, not only on the crystalline component but also on the noncrystalline components via the chemical shift and magnetic relaxation. In this chapter we will review briefly these studies, focusing particular attention on the molecular chain conformation and dynamics in the crystalline-amorphous interfacial region. 

The compatibility of blends of poly (vinyl chloride) (PVC) and a terpolymer (TP) of ethylene, vinyl acetate, and carbon monoxide was investigated by dynamic mechanical, dielectric, and calorimetric studies. Each technique showed a single glass transition and that transition temperature, as defined by the initial rise in E" at 110 Hz, c" at 100 Hz, and Cp at 20°C/min, agreed to within 5°C. PVC acted as a polymeric diluent which lowered the crystallization temperature, Tc, of the terpolymer such that Tc decreased with increasing PVC content while Tg increased. In this manner, terpolymer crystallization is inhibited in blends whose value of (Tc — Tg) was negative. Thus, all blends which contained 60% or more PVC showed little or no crystallinity unless solvent was added. 

The compatibility, mechanical properties, and segmental orientation characteristics of poly-e-caprolactone (PCL) blended with poly (vinyl chloride) (PVC) and nitrocellulose (NC) are described in this study. In PVC blends, the amorphous components were compatible from 0-100% PCL concentration, while in the NC system compatibility teas achieved in the range 50-100% PCL. Above 50% PCL concentration, PCL crystallinity was present in both blend systems. Differential IR dichroism was used to follow the dynamic strain-induced orientation of the constituent chains in the blends. It was found for amorphous compatible blends that the PCL oriented in essentially the same manner as NC and the isotactic segments of PVC. Syndio-tactic PVC segments showed higher orientation functions, implying a microcrystalline PVC phase. 

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