Poly bimodal

Recently, particular interest has focused on bimodal poly(dimethylsiloxane) (PDMS) networks (9-17) containing large mol fractions of very short chains as well as chains of the... 

Calorimetric measurements on bimodal poly(ethylene oxide) networks indicate that the short chains decrease crystallinity in the unstretched state.This is an intriguing result since short chains increase the extent of crystallization in the stretched state. 

Viers, B. D. Mark, J. E., Large-Scale Structures in Bimodal Poly(dimethylsiloxane) Elastomers. J. Inorg. Organomet. Polym. 2006,15, 477-483. 

Galiatsatos, V. Clarson, S. J., An Investigation of the Properties of Bimodal Poly(dimethylsiloxane) Elastomers Upon Swelling with a Linear Oligomeric Polymethylsiloxane. Polym. Comm. 1986, 27, 260-261. 

Curro, J. G. Mark, J. E., A Non-Gaussian Theory of Rubberlike Elasticity Based on Rotational Isomeric State Simulations of Network Chain Configurations. II. Bimodal Poly(dimethylsiloxane) Networks. J. Chem. Phys. 1984, 80, 4521-4525. 

Chen, C. C. Borden, M. A., Ligand Conjugation to Bimodal Poly(ethylene glycol) Brush Layers on Microbubbles. Langmuir 2010,26,13183-13194. 

Scherer, C. Utech, S. Scholz, S. Noskov, S. Kindervater, P. Graf, R. Thun-emann, A. F. Maskos, M., Synthesis, Characterization and Fine-Tuning of Bimodal Poly(organosiloxane) Nanoparticles. Polymer 2010,51,5432-5439. 

The freezing points of solvents absorbed into bimodal networks are also of interest since solvent molecules constrained to small volumes form only relatively small crystallites upon crystallization, and therefore exhibit lower crystallization temperatures. " Differential scanning calorimetry measurements on solvent molecules constrained in the pores of PDMS elastomers gave evidence for several crystallization temperatures, which could be indicative of an unusual distribution of pore sizes. Calorimetric measmements on bimodal poly(ethylene oxide) networks indicated that the short chains seemed to decrease the amount of crystallinity in the unstretched state. This is an intriguing result since they inaease the extent of crystallization in the stretched state. A similar study on poly (tetrahydrofuran) did not show any decrease, however. ... 

Figure 11.12 Stress-strain behavior of bimodal poly(dimethyl siloxane) networks. Each curve is labeled with the mol% of the short chains. The area under each curve represents the energy required for rupture (22).

Strain-induced crystallization would presumably further improve the ultimate properties of a bimodal network. It would therefore obviously be of considerable importance to study the effect of chain length distribution on the ultimate properties of bimodal networks prepared from chains having melting points well above the very low value characteristic of PDMS. Studies of this type are being carried out on bimodal networks of polyethylene oxide) (55), poly(caprolactone) (55), and polyisobutylene (56). 

Figure 7 Examples of the bimodal DPD curves for poly(2-chloroethyl vinyl ether) obtained with (4-ClC6H4)3C+ PF6 (curve a, experiment 24) and with 4-ClC6H4CO+...

Microcellular foaming, bimodal cell size distributions, and high open-celled contents of molecular composites of HT-polymers were reported by Sun et al. [33], investigating blends of a rod-like polymer polybenzimidazole with an aminated PSU and poly(phenyl sulfone) by using carbon dioxide as a blowing agent. The complex foaming behavior was related to phase separation within the otherwise... 

By foaming an immiscible blend system of a poly(ethylene glycol)PEG/ polystyrene (PEG/PS), Taki et al. detected a similar foaming behavior as well as a bimodal cell size distribution [78], While smaller cells formed in the more... 

For strong scatterers an average diameter can be obtained within +/- 5 every 10 or 20 seconds. To get this precision with the poly-dispersity takes 2 or 3 minutes. To distinguish between a broad unimodal and a bimodal distribution may take several minutes. Finally, as already mentioned, it may take hours to obtain representative widths. 

The advantage of the swelling method is that it is not limited by the crosslinking reactions of each phase so any interference from these will be limited. A good representative example is the synthesis developed by Hamurcu and Baysal [75]. They synthesized a bimodal PDMS (15 000 gmoD1)/ PDMS (75 000 g mol ) IPN with the same condensation curing system. First, the 75 000 g mol 1 PDMS network was formed from the corresponding a, tw-dihydroxypolydimethylsiloxane and tetraethylorthosilicate catalyzed by stannous 2-ethylhexanoate. It was then swollen in a 15 000 g mol 1 a,a>-dihydroxy-poly(dimethylsiloxane) monomer. The second monomer was then crosslinked via the same condensation cure. The sequential full IPN structure... 

Chen [4] prepared a bimodal terpolymer poly(ethylene-co-n-butylacrylate-co-methacrylic acid) that was converted into a sodium salt and used as a component in gold balls. 

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