Glassy polymers introduction

This amorphous glassy polymer has the permeability coefficients P(02) in the range 800-1000Barrer (for different samples) [12,13]. Such behaviour is in line with well-documented effects of the introduction of bulky Si(CH3)3 group into various main chains however, the effect here, bearing in mind very rigid stmcture of the backbone chain, is much larger (Table 3.1). 

The strategy for the development of mixed-matrix membranes is to combine the advanced features of polymer membrane and inorganic membrane into one composite membrane. As discussed in the previous section, this is done by incorporating dispersed fillers into continuous polymer matrices. As noted in the introduction, there are three main types of mixed-matrix membranes reported in the literature solid-polymer, liquid-polymer, and solid-liquid-polymer mixed-matrix membranes. The polymer matrices providing low cost and easy processability are selected from either glassy polymers (e.g., polyimide, polysulfone, polyethersulfone, or cellulose acetate) or rubbery polymers (e.g., silicone rubber). The dispersed fillers include solid, liquid, or both solid and liquid. 

Donald, A. M., and E. J. Kramer, The Competition Between Shear Deformation and Crazing in Glassy Polymers, Cornell Materials Science Center Report 4568, 1981. Ward, I. M., and D. W. Hadley, An Introduction to the Mechanical Properties of Solid Polymers, Wiley, Chichester, 1993. 

Figure 1.67 Specific volume as a function of temperature on cooling from the melt for a polymer that tends to crystallize. Region A is liquid, B liquid with elastic response, C supercooled liquid, D glass, E crystallites in a supercooled liquid matrix, F crystallites in a glassy matrix, and G completely crystalline. Paths ABCD, ABEF, and ABG represent fast, intermediate, and very slow cooling rates, respectively. From K. M. Ralls, T. H. Courtney, and J. Wulff, Introduction to Materials Science and Engineering. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

Based on their thermal properties, polymeric and glassy molecular PR materials can be classified as high-7 and low-7), materials. The Tg values of polymer composites can be lowered by doping small molecules as plasticizer. Introduction of a long alkyl side chain can effectively reduce the Tg of fully functionalized polymers. The glassy molecular materials usually possess low Tg if they are amorphous. For the high-7 and low-7), materials, the figures of merit of the NLO chromophores are defined by Eqs. (35) and (40), respectively. The latter are obviously enhanced by contributions from the polarizability anisotropy of the NLO chromophore. 

A polymer is in the glassy state at room temperature if the Tg is above room temperature, and it behaves as an elastomer if the Tg is considerably below room temperature. The T of a polymer depends on the freedom of rotation available about bonds in the polymer chain. Flexible polymers are made by the introduction of groups about which rotation is facile, like -0-, -Si-O-Si-, CHg-S-, = CH-CH2 . Discussions of different adhesive systems provide a number of examples of such groups being introduced in otherwise intractable polymers to make them flexible and tough. Plasticizers are also employed to make rigid polymers pliable. Plasticizer molecules, by their interaction with polymer chains, reduce interchain interactions and consequently, their rigidity. 

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