Polymer thermoelastic

Finally, we turn from solutions to the bulk state of amorphous polymers, specifically the thermoelastic properties of the rubbery state. The contrasting behavior of rubber, as compared with other solids, such as the temperature decrease upon adiabatic extension, the contraction upon heating under load, and the positive temperature coefficient of stress under constant elongation, had been observed in the nineteenth century by Gough and Joule. The latter was able to interpret these experiments in terms of the second law of thermodynamics, which revealed the connection between the different phenomena observed. One could conclude the primary effect to be a reduction of entropy... 

Nairn, J.A. (1985). Thermoelastic analysis of residual stresses in unidirectional high-performance composites. Polym. Composites 6, 123-130. 

Values of the dipole moment ratio of PNS are obtained from dielectric measurements. From thermoelastic experiments, performed on polymer networks, the temperature coefficient of the unperturbed dimensions is determined. Analysis of these results using the RIS model is performed leading to the parameters given above. 

Theoretical Study of the Thermoelastic Properties of Eiastin Model Chains DeBolt, L. C. Mark, J. E. Polymer 1987, 28, 416. 

These expressions show that a deformed polymer network is an extremely anisotropic body and possesses a negative thermal expansivity along the orientation axis of the order of the thermal expansivity of gases, about two orders higher than that of macromolecules incorporated in a crystalline lattice (see 2.2.3). In spite of the large anisotropy of the linear thermal expansivity, the volume coefficient of thermal expansion of a deformed network is the same as of the undeformed one. As one can see from Eqs. (50) and (51) Pn + 2(iL = a. Equation (50) shows also that the thermoelastic inversion of P must occur at Xim (sinv) 1 + (1/3) cxT. It coincides with F for isoenergetic chains [see Eq. (46)]. 

Three types of measurements were used for investigation of reversible thermomechanical effects in glassy polymers. They include (i) thermoelastic temperature changes at elevated hydrostatic pressure 65,66), (fi) thermoelastic temperature changes... 

Hoeve, C. A. J.., and A. Ciferri Limitations of the application to semi-crystalline fibers of thermoelastic relations for high elastic materials A reply to W. Prins. J. Polymer Sci. 60, 68 (1962). 

Opschoor, A., and W. Prins Thermoelasticity and conformational behaviour of polyethylene and ethylene-propylene copolymers. J. Polymer Sci., Pt. C16, 1095 (1967). 

These experimental results give only a first insight into the fascinating properties of these very new l.c. elastomers. Further detailed studies have to come to a more profound understanding of the interactions of polymer networks and l.c. order of the mesogenic side chains. The exceptional photoelastic and thermoelastic properties promise to open up a new scientific and technological field of interest. 

The constitutive model makes use of the decomposition of the rate of deformation D into an elastic, De, and a plastic part, Dp, as D = De + Dp. Prior to yielding, no plasticity takes place and Dp = 0. In this regime, most amorphous polymers exhibit viscoelastic effects, but these are neglected here since we are primarily interested in those of the bulk plasticity. Assuming the elastic strains and the temperature differences (relative to a reference temperature T0) remain small, the thermoelastic part of the response is expressed by the hypoelastic law... 

Other studies of interest include the modification of polysulphone membranes using crosslinking agents, thermoelastic properties of network polymers, and the effects of coating thickness on initiator activity for oligourethane acrylates and triethylene glycol dimethacrylate. ... 

The remainder of this chapter will focus on the thermal conductivities of amorphous polymers (or the amorphous phase, in the case of semicrystalline polymers). See Chapter 20 for a discussion of methods for the prediction of the thermal conductivities of heterogeneous materials (such as blends and composites) in the much broader context of the prediction of both the thermoelastic and the transport properties of such materials. 

The properties of block copolymers, on the other hand, cannot be calculated without additional information concerning the block sizes, and whether or not the different blocks aggregate into domains. The results of calculations using the methods developed in this book can be inserted as input parameters into models for the thermoelastic and transport properties of multiphase polymeric systems such as blends and block copolymers of immiscible polymers, semicrystalline polymers, and polymers containing various types of fillers. A review of the morphologies and properties of multiphase materials, and of some composite models which we have found to be useful in such applications, will be postponed to Chapter 19 and Chapter 20, where the most likely future directions for research on such materials will also be pointed out. 

Metal sulfonate-containing ethylene-propylene-diolefin ter-polymers (EPDM) were plasticized with stearic acid and derivatives for the reduction of the melt viscosities of these ionomers through interaction with the very strong ionic associations. Substantial improvements in melt flow were achieved with stearic acid and the zinc, lead, and ammonium stearates, while other metal stearates were ineffective. Zinc stearate and lead stearate not only markedly improved melt flow but, remarkably, also enhanced the mechanical properties of the plasticized systems. These unique additives were fully compatible with the EPDM ionomers and provided thermoelastic systems with excellent physical properties and ready processability. 

A third source of stress waves derives from the expansion of any gases (CO, CN, N2, CH3 etc.) produced by thermal or photochemical decomposition within the substrate [104]. This factor, for instance, has been invoked to account for the transient stresses of about 0.1 MPa detected in the UV irradiation of polyimide below the ablation threshold [106]. In the case of doped PMMA, irradiation with 150-ps pulses at 1064 nm, Hare et al. [104] estimate that at the ablation threshold, the thermoelastic mechanism and the expansion of the decomposition products contribute about equally to the generated pressure. For specifically designed polymers that upon irradiation form a high enough concentration of volatile products, the generated pressure has been suggested to be the primary cause of material ejection [68-69]. 

As far as the thermoelasticity performance of a polymer network k concerned, it is generally true that the hi er the concentration of crosslinks or the lower the dimensions of loopholes in the network, the more significant are the changes in the polymer I operties. The elasticity of a polymer is also enhanced by i iyskally entangled chains, whose number increases with the number of crosslinks, the character of the crosslinks being interrdated with the character of the physical aitan ements [27]. This may be illustrated by experiments with two crosslinked samples prepared from low density polyethylene. The first sample was crosslinked via the silane pathway, the second by... 

Two examples are shown in 28 and 29. The polymeric ligands form 1 1 complexes with ZnClj linked to the pyridyl group. Although the polymer ligands are liquid at room temperature, the melting point of the complexes has been observed to be 140 °C. The polymeric complexes are thermoelastic and exhibit elastic properties. 

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