Effect of cross-linking temperature

FIGURE 2 Effect of cross-linking temperature on beads catalytic activity. 

Table 11.5 The effect of cross-linking temperature on the percentage of loading content and loading efficiency of BSA for grafted and mixed beads...

In this work, polyurethane (PU) and epoxy (EP) mixtures were selected for investigation because they are known to form partially miscible IPNs with broad glass transition temperatures. These were first prepared by Frisch et al(6) using a simultaneous polymerization technique in bulk. These materials showed the effects of cross-linking only one polymer component (pseudo-IPN) and intentional grafting between the component polymers. Klempner et al (2) also studied PU/EP IPNs for vibration attenuation. The polyurethanes in this work were chain extended and crosslinked with a 4 1 equivalent ratio of butanediol (BD) and trimethylol propane (TMP). 

Figure 2.32 Effect of cross-linking on the glass transition temperature of the system styrene with divinylbenzene. (From Ref. 34.)...

One can see in the figure that for both gel systems the temperature dependence of volume change is not continuous an abrupt change occurs when the temperature exceeds 30 °C. It is also seen that within the experimental accuracy no difference was observed between PNIPA and mPNIPA gel beads. The presence of magnetic nanoparticles influences neither the measure of volume change nor the collapse transition temperature (abbreviated as 7c). A careful analysis based on derivatives of the qr-T curves has shown that for both kinds of PNIPA beads, Tq was found to be 32 °C. We have also studied the effect of cross-linking density on the volume phase transition. Figure 39 shows these results. 

Yakushiji T, Sakai K, Kikuchi A, Aoyagi T, Sakurai Y, Okano T. Effects of cross-linked structure on temperature-responsive hydrophobic interaction of PIPAAm hydrogel modified surfaces with steroids. Anal Chem 1999 71(6) 1125-1130. 

An identical crosslink density does not necessarily lead to the same effect of cross-linking on properti. This is particularly evident in a case when crosslinks are formed between segments of polymer chains which are in the amorphous ase of semicrystalline polymer below the melting temperature of polymer crystallites. Ifcre, the effect of crosslinking on crystallinity is Icwer. 

At temperatures where the dominant phonon wavelengths of interchain modes are of the order of the cross-link distance, a pronounced effect of cross-linking on thermal conductivity and thermal expansion was found. Both quantities were strongly determined by anharmonic contributions of the binding potential. Elastic mechanical parameters or specific heat, which can be described in the harmonic approximations, showed no influence of cross-linking. The interpretation that the... 

In the field of water purification technology by membrane filtration, many researchers have studied the effect of cross-linking agents on membrane performance by varying the cross-linking conditions. The desired permeation and selectivity properties of the top thin layer vary with the concentration of polymer and cross-linking conditions like temperature and concentration of the cross-linker. Miao et al. [24] prepared... 

The effect of cross-linking on the course of relaxation at X is shown in Figure 6 for a series of networks prepared from Polymer C. For R > 0.5, the relaxation is slight and the stress approaches its equilibrium value even without raising the temperature toward the end of the experiment to increase molecular mobility. Similar observations were made for Polymer As R is decreased, the... 

Pig. 45. Schematic diagram showing the effects of cross-linking on modulus and damping (loss tangent) vs temperature behavior at Tg. 

Fig. 1-26 Effect of cross-linking on modulus-temperature behavior [36].

B.6.3.2 Effect of Cross-link Density on Tg The criterion of the second-order transition temperature is that the temperature-dependent conformational entropy, becomes zero. If So is the conformational entropy for the un-cross-linked system, and ASr is the change in conformational entropy due to adding cross-links (99),... 

Fig. 5.17 Typical variation of Young s modulus, E, with temperature for a polymer showing the effect of cross-linking upon E in the rubbery state.

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