Poly free volume polymers

Because the so-called ultrahigh free volume polymers aroused much interest during the last 10 years, they will be briefly described in this introductory chapter. The publication of the physical properties of poly(l-trimethylsilyl-l-propyne) (PTMSP) in 1983 [281] aroused much interest in the field of membrane research. Up to this time it had been believed that the rubbery poly(dimethyl si-loxane) has by far the highest gas permeability of aU known polymers. Very surprisingly, the glassy PTMSP showed gas permeabilities more than 10 times higher than PDMS. This could be attributed to its very high excess-free volume and the interconnectivity of the free volume elements. Since then a number of... 

This work offers a contribution to the understanding of some fundamental aspects of sorption and diffusion in glassy polymers. The research focuses on an extensive experimental study of sorption and mass transport in a specific polymeric matrix. A high free volume polymer, (poly l-trimethylsilyl-l-propyne) [PTMSP], has been used here in order to emphasise aspects of sorption and transport which are peculiar to polymer/penetrant mixtures below the glass transition temperature. The discussion of the experimental data presented in this work permits a clarification of concepts which are of general validity for the interpretation of thermodynamic and mass transport properties in glassy systems. 

Fig. 15. Oxygen permeability versus 1/specific free volume at 25 °C (30). 1. Polybutadiene 2. polyethylene (density 0.922) 3. polycarbonate 4. polystyrene 5. styrene-acrylonitrile 6. poly(ethylene terephthalate) 7. acrylonitrile barrier polymer 8. poly(methyl methacrylate) 9. poly(vinyl chloride) 10. acrylonitrile barrier polymer 11. vinyUdene chloride copolymer 12. polymethacrylonitrile and 13. polyacrylonitrile. See Table 1 for unit conversions.

Fluorinated poly(arylene edier)s are of special interest because of their low surface energy, remarkably low water absorption, and low dielectric constants. The bulk—CF3 group also serves to increase the free volume of the polymer, thereby improving various properties of polymers, including gas permeabilities and electrical insulating properties. The 6F group in the polymer backbone enhances polymer solubility (commonly referred to as the fluorine effect ) without forfeiture of die thermal stability. It also increases die glass transition temperature with concomitant decrease of crystallinity. 

The method is based on the fact that the rate of conformational change required for excimer formation depends on the free volume induced by the segmental motions of the polymer occurring above the glass transition. DIPHANT (compound 3 in Figure 8.3) was used as an excimer-forming probe of three polymer samples consisting of polybutadiene, polyisoprene and poly(dimethylsiloxane).a)... 

In this system the a relaxation can be analyzed by the symmetric equation of Fuoss-Kikwood and a new model which is similar to Havriliak- Negami equation used in the analysis of dielectric spectroscopy. According to the Tg values calculated for these systems, the free volume can be appropriately described by the free volume theory. The analysis of these families of poly(methacrylate)s allow to understand in a good way the effect of the structure and nature of the side chain on the viscoleastic behavior of polymers [33],... 

The affect of polymer stereoregularity in the chains on the PAL data has also been studied. Hamielec et al [56] found what appears to be an increased lifetime (hole size) with increased randomness of the chain configuration in a series of polyvinlychloride (PVC) polymers, despite the large degree of scatter in the sample (probably due to the fact that a series of commercially available products were used.). They however found little correlation with tacticity in polypropylene. More recently a PAL study on a series of very well characterized polystyrene and poly(p-methlystyrene) samples of differing tacticity [57] was performed. In addition to finding that the polystyrene samples have smaller free volume holes than the poly(p-methylstyrene) samples, they found that the syndiotactic samples had broader hole distributions than the attactic samples. 

The diffusion of gases through a polymer matrix is determined by the mobility of gas molecules through the matrix. The diffusion coefficient is therefore, at least partially determined by the free volume size of the polymer. It has been shown, for example, that there is a correlation between the free volume measured by PAL and the diffusivity of carbon dioxide in a seriers of polycarbonates [58], In a study of poly (trimethylsilyl propyne) (PTMSP), which has an extremely high gas permeability and diffusion coefficients, it was found that the lifetime data could be resolved into four components [59]. The longest lifetime component (T4) had a lifetime of... 

Nicolau, Y.F., Moser, P. (1993) Study of free volume and crystallinity in polybithiophene and poly(3-methylthiophene) . J. Poly. Sci. B Polymer Physics. 31,1529. 

Uedono, A., Sadamonto, R., Kaqano, T., Tanigawa, S., Uryu, T. (1995) "Free volumes in liquid-crystalline main-chain polymer probed by positron annihilation . J. Poly. Sci. B Poly. Phys. 33, 891. 

---