Crosslink/Crosslinking curve

A decline in catalytic activity with use was detected for reactions catalyzed by either species. Polymers 2 and 7 in the absence of cobalt both revealed excellent stability at 190 C (hydroformylation temperatures). This is illustrated by the TGA curves shown in Figure 4. Curve A shows an onset of decomposition for phosphinated polyphosphazene of 400 C, slightly better than that of phosphinated polystyrene (curve B, 20Z crosslinked curve C, 2Z crosslinked). Loss of phosphorus was observed over a period of 45 hours for a catalyst derived from 2 (2Z DVB crosslinked). The data depicted in Figure 5 reveal benzene, toluene, benzyl alcohol, diphenylphosphine and triphenyl phosphine as cleavage products. If one recalls the previously discussed homogeneous results it should be clear that the PPho is derived from a phosphide intermediate such as 8. ... 

Fig. 25 (a) Fluorescence SNOM image of a PMMA gel labeled with Pe and Eo dyes (b) Fluorescence decay curves of Pe observed for (curves A and B) PMMA gel at points A and B indicated in panel a, (curve C) PMMA bulk sample without crosslinker, (curve D) spin-cast PMMA film containing Pe dyes. Reprinted with permission of [26], copyright (2003) The Chemical Society of Japan... 

From the data of DTA and TGA analyses illustrated in Fig. 4, its evident that the visible exo-peaks in the range of 140-150°C appear in DTA curves (Fig. 4a), which can be taken as evidence of a crosslinking reaction of acylated macromolecules at the expense of side chain... 

Figure 4 (a) Polymerization time versus degree of swelling (in toluene) curves for styrene-PEG crosslinked copolymers initiated by macroinimers ( ) MAIM-200, ( ) MAIM-400, (O) MAIM-600, (A) MAIM-1000, and ( ) MAIM-1500. (b) Polymerization time versus degree of swelling (in water) curves for styrene-PEG crosslinked copolymers initiated by ( ) MAIM-1500 and ( ) MAIM-400. Source Ref. 50. 

The possibility of conformational changes in chains between chemical junctions for weakly crosslinked CP in ionization is confirmed also by the investigation of the kinetic mobility of elements of the reticular structure by polarized luminescence [32, 33]. Polarized luminescence is used for the study of relaxation properties of structural elements with covalently bonded luminescent labels [44,45]. For a microdisperse form of a macroreticular MA-EDMA (2.5 mol% EDMA) copolymer (Fig. 9 a, curves 1 and 2), as compared to linear PM A, the inner structure of chain parts is more stable and the conformational transition is more distinct. A similar kind of dependence is also observed for a weakly crosslinked AA-EDMA (2.5 mol%) copolymer (Fig. 9b, curves 4 and 5). 

Fig. 22. Relaxation time curves after temperature jump from 35 to 37 °C for trimer (A), dimer (B) and monomer (C) of crosslinked (Pro-Ala-Gly) (n = 12) (scale grand). Pants (O) denote the 0 values after 2 weeks at 5 °C. Solvent water concentration 2 mg/ml...

Yield strength as determined in tensile tests [53] at ambient temperature was plotted in Fig. 6.1 against M 1, the inverse molecular mass between crosslinks. All the samples of polymer A (the most crosslinked polymer) failed before the polymer started to yield. Therefore, load-extension-curves were extrapolated up to a hypothetical yield strain in this case. The extrapolated tensile is marked by brackets (Table 6.1). 

The anomalous increase of the water uptake observed in Fig. 10 when approaching equilibrium at 60 °C has been associated to the damage. The abrupt upturn of the sorption curve may be explained considering a possible crazing of the low crosslinked internodular matrix induced by the differential swelling stresses that can arise, at high water contents, between areas of different crosslinking density. 

Another transition appeared at about 130 °C on the rescanning after rapid cooling of the molten sample. It seems to be a glass transition point. The polyamide prepared in bulk at 70 °C also melted sharply at 250—260 °C. On the other hand, the crosslinked polymer, which was prepared in bulk at 100 °C in a high conversion, has nothing but a broad endothermic curve up to near 300 °C as shown in Fig. 9. 

The collagen shield, fabricated from procine scleral tissue, is a spherical contact lens-shaped film whose thickness can be made to vary from 0.027 to 0,071 mm. It has a diameter of 14.5 mm and a base curve of 9 mm. Once the shield is hydrated by tear fluid and begins to dissolve, it softens and conforms to the corneal surface. Dissolution rates can be varied from 2 to as long as 72 hr by exposing the shields to ultraviolet radiation in order to achieve varying degrees of crosslinking. 

When this resin was exposed as a thin film to the UV radiation of a medium pressure mercury lamp (80 W aiH), the crosslinking polymerization was found to develop extensively within a fraction of a second (18). The kinetics of this ultra-fast reaction can be followed quantitatively by monitoring the decrease of the IR absorption at 810 an-1 of the acrylic double bond (CHCH twisting). Figure 8 shows a typical kinetic curve obtained for a 20 pm thick film coated onto a NaCl disk and exposed in the presence of air to the UV radiation at a fluence rate of 1.5 x 10 6 einstein s-1 cm 2. 

Figure 1. Swelling titration curves for 5 mol% crosslinked polyacids.

When the five mol percent crosslinked poly(acrylic acid) release curve was compared (Figure 5) to that for a very lightly crosslinked (less than one percent)... 

Recent work has focused on a variety of thermoplastic elastomers and modified thermoplastic polyimides based on the aminopropyl end functionality present in suitably equilibrated polydimethylsiloxanes. Characteristic of these are the urea linked materials described in references 22-25. The chemistry is summarized in Scheme 7. A characteristic stress-strain curve and dynamic mechanical behavior for the urea linked systems in provided in Figures 3 and 4. It was of interest to note that the ultimate properties of the soluble, processible, urea linked copolymers were equivalent to some of the best silica reinforced, chemically crosslinked, silicone rubber... 

Figure 31 compares the dynamic structure factors obtained from the crosslinks and the chain ends for two different Q-values. Without any analysis a strong reduction of the cross-link mobility compared to that of the chain end is obvious. A closer inspection also shows that the line-shape of both curves differs. While S(Q,t)/S(Q, 0) from the chain end decays continuously, S(Q,t) from the cross-links appears to decay faster at shorter than at longer times. This difference in line shape is quantified via the line shape parameter p. For the end-labelled chains, p is in close agreement with the p = 1/2 prediction of the... 

Figure 2 shows a typical evolution of G(t, p) near the LST of a crosslinking polymer. The x axis shows the time of crosslinking reaction which corresponds to an extent of reaction, p. For each of the curves in Fig. 2, p is kept constant. The crosslinking reaction was stopped at discrete values of p, which increased from sample to sample. 

In samples with early stages of crosslinking (lower curves in Fig. 2), stress can relax quickly. As more and more chemical bonds are added, the relaxation process lasts longer and longer, i.e. G(t) stretches out further and further. The downward curvature becomes less and less pronounced until a straight line ( power law ) is reached at the critical point. 

Fig. 12. Dynamic moduli master curves of PBD 44 precursor (p = 0) and PBD 44 critical gel [60]. The entanglement and glass transition regime is hardly affected by the crosslinking. Open symbols correspond to G, filled ones to G"...

Fig. 20. Dynamic moduli, G (open symbols) and G" (filled symbols), for five partially crosslinked PDMS samples at different extents of reactions (same data as Fig. 2). Gr curves downward for the liquid and curves to the left for the solid. The straight lines belong to the sample which is very close to the gel point, t — tc is given in minutes...

Fig. 26. Tan 3 of a crosslinking PBD (Mw = 18 000) as a function of reaction time [31]. Parameter is the frequency co. The polymer is vulcanized at the pendant vinyl units with a bifunctional silane crosslinker using a platinum compound as catalyst. The curves intersect at the gel point resulting in...

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