Poly relaxation properties

A number of examples have been studied in recent years, including liquid sulfur [1-3,8] and selenium [4], poly(o -methylstyrene) [5-7], polymer-like micelles [9,11], and protein filaments [12]. Besides their importance for applications, EP pose a number of basic questions concerning phase transformations, conformational and relaxational properties, dynamics, etc. which distinguish them from conventional dead polymers in which the reaction of polymerization has been terminated. EP motivate intensive research activity in this field at present. 

Data of Figs 8-10 give a simple pattern of yield stress being independent of the viscosity of monodisperse polymers, indicating that yield stress is determined only by the structure of a filler. However, it turned out that if we go over from mono- to poly-disperse polymers of one row, yield stress estimated by a flow curve, changes by tens of times [7]. This result is quite unexpected and can be explained only presumably by some qualitative considerations. Since in case of both mono- and polydisperse polymers yield stress is independent of viscosity, probably, the decisive role is played by more fine effects. Here, possibly, the same qualitative differences of relaxation properties of mono- and polydisperse polymers, which are known as regards their viscosity properties [1]. 

The synthesis of organotin oligosteracrylate i.e. dimethylstannyl dimethacrylate, and the production of the cross-linked homopolymers on its basis have been reported. Morphology, mechanical and relaxation properties of poly(dimethyl-stannyl dimethacrylate) have been investigated 67). 

Aime et al. took advantage of the different redox states of manganese and of the difference in the related relaxation properties to design a p02 responsive contrast agent. The adducts formed between Mn /Mnn tpps complexes and poly-P-cyclodex-trin have considerably different relaxivities depending on the redox state of the metal, itself determined by the partial oxygen pressure of the solution (tpps — 5,10,15,20-tetrakis-(p-sulfonato-phenyl porphinate) (243). 

Because of the potential interest of these materials, Sanchis and coworkers [64] shows that it is interesting to know the dielectric behavior of two heterocyclic poly(methacrylate)s PTHFM and poly(3-methyl tetrahydrofurfuryl methacrylate) P3MTHFM, (see Scheme 2.9)and the comparison of the relaxation properties of these two polymers. 

Poly(n-butyl acrylate). A study of the relaxation properties of PBA was initiated for several reasons. There are two backbone carbons with directly bonded protons thus the effect of the side chain on backbone motion might be determined. Also, the CH carbon should more directly reflect the distribution of correlation times necessary to begin analysis of alkyl sidechain motion. Finally, the lack of the additional chain-CH3 groups significantly loosens motional constraints in PBA. The effect of this on the overall dynamics of PBA was of interest. 

The relaxation dynamics of junctions in polymer networks have not been well known until the advent of solid-state P NMR spin-lattice relaxation measurements in a series of poly(tetrahydrofuran) networks with tris(4-isocyanatophenyl)-thiophosphate junctions (Shi et al., 1993). The junction relaxation properties were studied in networks with molecular weights between crosslinks, Me, ranging from 250 to 2900. The dominant mechanism for P nuclear spin lattice relaxation times measured over a wide range of temperatures were fit satisfactorily by spectral density functions, 7([Pg.225]

In this brief review an attempt has been made to indicate how molecular weight and chemical structure can influence the relaxation properties of polymer molecules in solution. Other important effects which can be considered are those of tacticity in polymers such as a polyiiiHe styrene ( ZZ ) and poly methyl methacrylate 21 ) and solvent effects in segmental relaxation. 

Wan mimics the mechanical behavior of cardiovascular tissues, such as aorta and heart valve leaflets. The stress-strain properties for porcine aorta are matched by microbial cellulose-poly(vinyl alcohol) nanocomposite in both the circumferential and the axial tissue directions. Relaxation properties of the nanocomposite, which are important for cardiovascular applications, were also studied and found to relax at a faster rate and to a lower residual stress than the tissues they might replace. The study showed that this nanocomposite is a promising material for cardiovascular soft tissue replacement applications. The aim of a study by Mohammadi et al. was to mimic not only the nonlinear mechanical properties displayed by porcine heart valves, but also their anisotropic behavior, by applying a controlled strain to the samples while imdergoing low-temperature thermal cycling, in order to induce oriented mechanical properties. 

Thermoplastic poly(ether-imide) Ultem 1000 (Tg 217°C) is used as overlay adhesive for a Kapton film on which the interconnect is created [92]. This adhesive layer is disclosed to produce void-free lamination at approximately 300°C. Actual dielectric layers therefore consists of 25 xm thick Kapton over 12.5 xm thick adhesive film. The self-relaxation properties of Ultem 1000 tend to release... 

The time-temperature superpositioning principle was applied f to the maximum in dielectric loss factors measured on poly(vinyl acetate). Data collected at different temperatures were shifted to match at Tg = 28 C. The shift factors for the frequency (in hertz) at the maximum were found to obey the WLF equation in the following form log co + 6.9 = [ 19.6(T -28)]/[42 (T - 28)]. Estimate the fractional free volume at Tg and a. for the free volume from these data. Recalling from Chap. 3 that the loss factor for the mechanical properties occurs at cor = 1, estimate the relaxation time for poly(vinyl acetate) at 40 and 28.5 C. 

Poly(benzyl ether) dendrimers synthesized by Frechet el al. have been studied with many techniques in order to reveal their conformational properties. Size exclusion measurements performed by Mourey et al. [154], rotational-echo double resonance (REDOR) NMR studies by Wooley et al. [155] and spin lattice relaxation measurements by Gorman et al. [156] reveal that back-folding takes place and the end-groups can be found throughout the molecule. The observed trends are in qualitative agreement with the model of Lescanec and Muthukumar [54],... 

Summary In this chapter, a discussion of the viscoelastic properties of selected polymeric materials is performed. The basic concepts of viscoelasticity, dealing with the fact that polymers above glass-transition temperature exhibit high entropic elasticity, are described at beginner level. The analysis of stress-strain for some polymeric materials is shortly described. Dielectric and dynamic mechanical behavior of aliphatic, cyclic saturated and aromatic substituted poly(methacrylate)s is well explained. An interesting approach of the relaxational processes is presented under the experience of the authors in these polymeric systems. The viscoelastic behavior of poly(itaconate)s with mono- and disubstitutions and the effect of the substituents and the functional groups is extensively discussed. The behavior of viscoelastic behavior of different poly(thiocarbonate)s is also analyzed. 

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