Martin R. Tant

An Overview of the Viscous and Viscoelastic Behavior of Ionomers in Bulk and Solution

Abstract The subject of the viscous and viscoelastic behavior of ionomer systems is addressed from a general point of view. Following some introductory material concerning terminology and characteristics of ionomers that are pertinent for later discussion, the format will be to first briefly consider the glassy state followed with a more complete discussion of the rubbery and viscous flow (melt) states. The viscous and viscoelastic response of ionomer systems when in solution will then be discussed. We have also attempted to compare the so-called “random copolymer” ionomers to the telechelic systems. Emphasis is given to single component materials in contrast to blends or filled systems, but some brief remarks are made concerning the latter topics.

Effect of copolymer composition on free volume and gas permeability in poly(ethylene terephthalate)-poly(1,4 cyclohexylenedimethylene terephthalate) copolyesters

Abstract The gas permeability and free volume of a series of polyester copolymers were studied. The free volume was studied using the positron annihilation lifetime spectroscopy (PALS) technique to indicate the relative size and concentration of free volume cavities in the copolymers. The homopolymers were poly(ethylene terephthalate) (PET) and poly(1,4 cyclohexamethylene terephthalate) (PCT). The copolymers were prepared by reacting terephthalic acid with varying amounts of ethylene glycol and 1,4 cyclohexanedimethanol to produce a copolymer series containing 11.8, 30.8, 31.8, 60.9, 68.9, and 80.8 mol% PCT. The logarithm of the permeability to oxygen and carbon dioxide was found to increase linearly with vol% PCT. The mean free volume cavity size and relative concentration (as indicated by the PALS parameters τ 3 and I 3 , respectively) were found to increase approximately linearly with vol% PCT. The results are modelled using the Cohen-Turnbull theory for transport in polymers and discussed in terms of various methods of calculating, from PALS data, the free volume fraction that is important to transport properties.

A free volume approach to the mechanical behaviour of miscible polycarbonate blends

Composition-dependent mechanical properties and free volumes are compared for miscible, amorphous blends of bisphenol-A polycarbonate (PC) with (a) polyaryloxysiloxane (PAS), (b) a copolyester of 1,4-cyclohexanedimethanol and a mixture of isophthalic and terephthalic acids (EASTAR) and (c) an experimental polyester of 1,4-cyclohexane dicarboxylic acid and 1,4-cyclohexanedimethanol (CDACD). The free volumes were measured by the positron annihilation lifetime spectroscopy (PALS) technique. The strength of specific interactions, as indicated by data, is relatively weak in all of the blends. However, the fractional free volume quantity measured by PALS is less than additive in the polyester blends and is additive, or greater than additive, in the PC - PAS blends. The mechanical behaviour of the blends can be rationalized in terms of the free volume behaviour. The polyester blends which lose free volume (contract) on mixing exhibit higher than averaged yield strengths and brittle impact responses. The PC - PAS blends which retain or gain free volume on mixing exhibit averaged yield strengths and averaged ductile impact responses of the constituent polymers.

A diffusion model for water vapor transmission through microporous polyethylene/CaCo3 films

Abstract The stretching of mineral filled polymers can create an interconnected microporous structure due to debonding at the mineral/polymer interface. Such materials can allow for the transmission of gases (breathability) while retaining a liquid barrier. Stretched polyethylene/CaCO 3 films that allow for water vapor diffusion while providing a barrier to liquid water are used for the current work. A model for the diffusion of water vapor through these films is demonstrated. This model assumes Fickian behavior. The significance of the model is that it relates the pore microstructure to breathability. Analysis of the pore structure by density and surface area measurements is combined with the results of the Fickian diffusion model to gain insights into the effects of pore geometry on breathability.

Microstructure of the ionic aggregates in telechelic ionomers

Abstract Extended X-ray absorption fine structure (EXAFS) investigations of various types of zinc-neutralized telechelic ionomers have evidenced large differences in the degree of local order within the aggregates. Among the parameters influencing the microstructure, it is shown that the conditions of neutralization play an important role.

Sulfonated polyisobutylene telechelic ionomers

The gelation of polyisobutylene-based model ionomers with-S03−K+ terminal groups has been studied in hexane at 25°C. Both molecular architecture and molecular weight were found to significantly influence the concentration at which gelation occurs. Specifically, three-arm star trifunctional ionomers gel at lower concentrations than linear difunctional ionomers of similar molecular weight. In addition, the gelation concentration decreases with increasing molecular weight for the three-arm star trifunctional ionomer, but the results do not fit the relationship reported previously which relates gelation concentration and molecular weight for carboxylated linear telechelic polymers.

Sulphonated polyisobutylene telechelic ionomers: 12. Solid-state mechanical properties

Abstract The solid-state mechanical properties of well defined sulphonated polyisobutylene telechelic ionomers are presented. Specifically, the effect of (1) molecular architecture, (2) molecular weight, (3) type of cation used for neutralization and (4) excess neutralizing agent has been investigated. In addition, the effect of moisture and ionic plasticizer on the stress-strain behaviour has also been studied. These ionomers do not display the characteristic small-angle X-ray scattering (SAXS) peak, which is indicative of the presence of clusters, above a number-average molecular weight of about 10 000. However, below this molecular weight a weak shoulder is sometimes observed on the SAXS curve. The tri-arm species form a network structure at ambient temperatures which results in materials with good mechanical properties. The mechanical properties of the linear difunctional species are inferior to those of the three-arm star trifunctional species due to a less well developed network structure. The monofunctional species are very tacky at ambient temperatures and cannot be handled as solid materials. However, by their incorporation into the trifunctional systems they do serve as a model for ‘dangling ends’. As expected, these blends display significantly different properties than those possessed with the pure trifunctional species. Addition of excess neutralizing agent significantly increases the high deformation properties with little effect on Youngs modulus. A simple morphological model has been postulated in which it is suggested that the excess neutralizing agent resides at the ionic sites rather than being uniformly distributed throughout the matrix. Zinc-neutralized ionomers show stress-strain behaviour which is comparable to the potassium- and calcium-neutralized materials at ambient conditions, but the softening temperature is lower for the zinc neutralized material. Water absorption in these materials is relatively low. Addition of zinc stearate, an ionic plasticizer, facilitates melt processing by lowering the viscosity at high temperatures yet at ambient temperatures it crystallizes and acts as a reinforcing filler thus increasing Youngs modulus.

Structure and properties of carboxylato-telechelic polyisoprene

Abstract The effects of molecular weight, type of neutralizing cation and excess neutralizing agent on the structure and properties of carboxylato-telechelic polyisoprene have been studied. In particular, the effects of cation valence and cation size were studied for group IA and IIA elements, for which the bonding to the carboxylate anion is primarily ionic. It was found that increasing cation valence and decreasing cation size have the general effect of increasing the electrostatic association of the ion pairs, resulting in a more elastic stress-strain response. Neutralization with zinc( ii ) and nickel( ii ), elements of the first transition series that form less ionic, more coordinative complexes with the carboxylate ion, resulted in materials with quite different mechanical properties. The zinc-neutralized material displayed rather poor mechanical properties, while the nickel-neutralized material was much stronger. Materials neutralized with aluminium ( iii ) or titanium ( iv ) were observed to display a wide range of properties depending upon the amount of cation incorporated. It was determined that at least four times the stoichiometric amount of titanium ( iv ) is necessary to crosslink the material effectively. Materials of higher number-average molecular weight (33 000 vs. 15 000) displayed higher stresses and higher ultimate elongations owing to the development of a more extensive entanglement network. Finally, small-angle X-ray scattering studies of the M n = 15 000 and 33 000 materials indicate that an ionic peak is observed for the M n = 15 000 materials but is generally not observed for the M n = 33 000 materials even with 100% excess neutralizing agent. The position of this peak is essentially unaffected by the type of neutralizing agent used. Analysis of the tail region of the scattering curves indicates that the interface between the ionic and non-ionic regions is sharp.

Viscoelastic Behavior of Ionomers in Bulk and Solution

An overview is given of the viscoelastic behavior of ionomers in both the bulk and solution. For bulk materials, the various regions of the viscoelastic spectrum, i.e. glassy, glass transition, rubbery, and melt flow, are addressed separately. The effects of system variables (molecular weight, molecular architecture, ion content, ion type, neutralizing ion type, excess neutralizing ion, etc.) upon the morphological structure of the ionic regions and the resulting effects on viscoelastic behavior are discussed in some detail. For ionomer solutions, in addition to the effects of the same variables, the effect of solvent environment on the viscoelastic behavior is explored. Finally, some ideas regarding potential fruitful areas for future research on ionomers are presented.

Mechanical properties of carboxylato-telechelic polyisoprene

Abstract The mechanical properties of carboxylato-telechelic polyisoprenes neutralized with barium, aluminium and zirconium have been studied. In addition to the variable of neutralizing cation valence, the effect of molecular weight was also investigated. It was found that, for those cations studied, increasing cation valence at an approximately constant molecular weight results in increased stresses during a stress-strain experiment. For the barium-neutralized materials, both modulus and observed stresses increase with molecular weight due to entanglement effects. For the zirconium-neutralized materials, this trend is reversed due to the formation of a more well developed network induced by different chemistry.