Behavior, glass transition

Because of their dual crosslinked nature, both networks exert a unique control over the size, shape, and composition of the phase domains in an IPN. The morphological detail strongly influences, in turn, the physical and mechanical behavior of the material. While Chapter 5 detailed several ways of synthesizing IPNs, little mention was made of how crosslink density, order of polymerization, overall composition, etc. affect the final product. The objective of this chapter will be to explore the interrelationships among synthesis, morphology, and glass transition behavior. Mechanical and engineering properties will be treated in Chapter 7. 

In an important way, this chapter also picks up where Chapter 2 left off. Chapter 2 described the morphology and mechanical behavior of several classes of polymer blends, grafts, and blocks. Like these materials, covalent bonding between the species encourages molecular mixing. Crosslinking plays a similar role. The nature of the interphase material requires special attention. It must be emphasized at the outset that all of these materials are interesting and useful because of their complex structure, certainly not in spite of this fact. 

The behavior of multicomponent polymer systems has been the subject of several recent reviews. Bucknall has examined polymer blends and grafts, with particular reference to the toughening of plastics. All aspects of block copolymers have been explored by Noshay and McGrath. Manson and Sperling reviewed the entire field of polymer blends and composites. 

Recent reviews in the field of IPNs have tended to emphasize the relationship between morphology and behavior, the subject of the present chapter. These reviews include materials by Lipatov and Sergeeva, Klempner, Sperling, and Frisch etal The edited two-volume work by Paul and Newman provides the most recent coverage of the entire field of multipolymer materials and includes a review of IPN materials 

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On the other hand, polymeric materials show universal aspects of glass transition behavior, just like other materials. For instance, the classical Vogel-Fulcher behavior... 

Table 10 summarizes the glass transition behavior of these polyimide blends and demonstrates that there is only one Tg for each blend. Similar results have been confirmed by Koros of the University of Texas [29], This data confirms that as long as the dianhydride is the same in the composition, the change of 6F diamine from 3,3 to 4,4 does not alter solubility significantly, and the pairs are miscible. The relationship between the Tg and the Fox equation is discussed by MacKnight et al. work [17]. 

Polynadimides. The exact structure of the network crosslink is somewhat controversial but it could resemble the structure shown in Fig. 10.6. These polymers cumulate all the problems encountered in other polymers Is it really pertinent to consider that we are in the presence of hexa-functional crosslinks In this case, how do we take into account their copolymer effect In fact, if the black junctions in Fig. 10.6 connect one crosslink directly to another, we are in the presence of crosslink lines rather than dispersed individual crosslinks. Does this feature modify the whole glass transition behavior There is, to our knowledge, no satisfactory answer to these questions, and the research field remains largely open in this domain. 

The aim of this section, therefore, is to correlate systematically the compatibilization of PPE/SAN 60/40 blends by SBM triblock terpolymers with the foaming behavior of the resulting blend. The reduction of the blend phase size, the improved phase adhesion, a potentially higher nucleation activity of the nanostructured interfaces, and the possibility to adjust the glass transitional behavior between PPE and SAN, they all promise to enhance the foam processing of PPE/SAN blends. 

Young, K. D., and LeBoeuf, E. J. (2000). Glass transition behavior in a peat humic acid and an aquatic fulvic acid. Environ. Sci. Technol. 34(21), 4549 1553. 

Based on the results of two amorphous compatible blend systems of 50/50 NC/PCL and 75/25 PVC/PCL, the following conclusion can be drawn. Compatible amorphous blend constituents show identical segmental orientation behavior, indicating good mixing at the molecular level. Thus, an amorphous compatible blend can exhibit the characteristics of a single homopolymer not only in its glass-transition behavior and mechanical properties but also in the uniform way in which the polymer chains orient. 

The most important results were observed in the glass transition behavior of the materials where increasing the epoxy prereaction time increased the glass transition of the epoxy-rich phase (Figure 8). At an epoxy prereaction time of about 1 hr, Tgl was 97 °C which was lower than the glass transition of the pure epoxy, 105°C. However when the epoxy prereaction time was increased, Tgl also increased. When the epoxy prereacted for 6 hr, the SINs Tgl was 105°C or nearly the same as that of the epoxy homopolymer. Surprisingly, for eleven hours prereaction time the SINs Tgl was 115°C or higher than that of the pure epoxy. The differences in T. i from 97° to 115°C could not readily be accounted for by experimental error. Replication of the center point showed that the experimental error was only about 2°C. 

Phase Composition and Simultaneous Polymerization. Theoretically the phase composition of the SIN s should not be determined by the true solubility of one polymer in the other. Even though the true solubility of one polymer in the other is low because the components of the SIN s are incompatible, simultaneous polymerization and gelation are expected to cause entrapment of one component in the other. The degree of entrapment presumably will be controlled by the relative rates of the two reactions and their degree of simultaneity. The phase composition is reflected in the glass transition behavior of the material. Thus a close look at the dynamic mechanical spectra of the SIN s is necessary to determine the effect of simultaneous polymerization on phase composition. 

Figures 7.20a-b show the physical/chemical states of soy globulins (7S and IIS soy globulins, respectively) as a function of moisture content and temperature. At low temperatures and at low moisture contents, the soy globulins are in the glassy state. Above the glass transition, a rubbery region is observed. Comparison of the glass transition behavior of 7S and 1 IS globulins shows that the transition of 1 IS globulin...

With the long term objective of treating the effects of moisture and other plasticizers on the mechanical properties of materials, a new scheme that yields a complete constitutive model of viscoelastic materials has been developed. The time-temperature principle is an integral part of this modeling with a quantitative description of the glass transition behavior of pol3nmers. 

Craig, D.Q.M. A review of thermal methods used for the analysis of the crystal form, solution thermodynamics and glass transition behavior of polyethylene glycols. Thermochim. Acta 1995, 248, 189-203. 

The implications of the drastic difference in the Tg vs. relation for the two types of polymers described here will be discussed more fully in Section II-D however, one can safely say that the difference between ionic and non-ionic polymers with regard to their glass transition behavior is quantitative rather than qualitative, provided that the number of ions per repeat unit is the same for the terminal groups as for the middle groups. The ions, most reasonably, act to increase the inter-molecular forces and thus raise the glass transition, just as hydrogen bonds or strong dipoles would be expected to do. 

The G" (or E") and tan 6 peaks occuring in the temperature range from -20 to -120 C are extremely broad and skewed in both vibrating reed and torsion pendulum experiments. These peaks are considered to be the sum of two overlapping peaks—the 8 and Y relations. The highest temperature a relaxation is seen around 5 to 20 C on the tan 6 curves the drastic drop in G (or E ) and the sharpness of the tan <5g peak are characteristic of typical glass transition behavior of a neutral amorphous polymer. 

Orford, P.D., Parker, R., Ring, S.G., and Smith, A.C. Effect of water as a diluent on the glass-transition behavior of malto-oligosaccharides, amylose and amylopectin, Int. J. Biol. Macromol., 11, 91,1989. 

Leprince, O. and Walters-Vertucci, C. A calorimetric study of the glass transition behaviors in axes of Phaseolus vulgaris L. seeds with relevance to storage stability. Plant Physiol, 109,1471, 1995. 

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