Network trimodal networks

Because of the improvements in properties exhibited by elastomers having bimodal distributions [5], there have been attempts to prepare and characterize "trimodal" networks [56]. The calculations suggest that adding a small amount of very high molecular weight end-linkable polymer could further improve mechanical properties. 

Because of the improvements in properties exhibited by elastomers having bimodal distributions,82 there have been attempts to prepare and characterize trimodal networks.283 Although experiments have been carried out to evaluate the mechanical properties of trimodal elastomers, this has not been done in any organized manner. The basic problem is the large number of variables involved, specifically, three molecular weights and two independent composition variables (mol fractions) this makes it practically impossible to do an exhaustive series of relevant experiments. For this reason, the only mechanical property experiments that have been carried out have involved arbitrarily chosen molecular weights and compositions.284 286 Perhaps not surprisingly, only modest improvements have been obtained over the bimodal materials. 

Some recent computational studies,287 however, indicate that it is possible to do simulations to identify those molecular weights and compositions that should maximize further improvements in mechanical properties. Results to date283 suggest that a trimodal network prepared by incorporating small numbers of very long chains into a bimodal network of long and short chains could have significantly improved ultimate properties. 

Differential scanning calorimetry measurements exist on solvent molecules constrained in the pores of a variety of PDMS elastomers. Some results on trimodal networks have been reported. The several... 

G enesky, G. Cohen, C., Toughness and Fracture Energy of PDMS Bimodal and Trimodal Networks with Widely Separated Precursor Molar Masses. Polymer 2010,51, 4152-4159. 

Most bimodal networks synthesized to date have been prepared from PDMS [88], One reason for this choice is the fact that the polymer is readily available with either hydroxyl or vinyl end groups, and the reactions these groups participate in are relatively free of complicating side reactions. These ideas can obviously be extended to higher modalities (trimodal, etc., eventually approaching an extremely broad, effectively-unimodal distribution) [102-104],... 

Madkour, T. Mark, J. E., Some Evidence on Pore Sizes in Poly(dimethylsiloxane) Elastomers Having Unimodal, Bimodal, or Trimodal Distributions of Network Chain Lengths. Polym. Bull. 1993, 31, 615-621. 

There has been some NMR work on trimodal PDMS elastomers, with regard to thermal degradation and the presence of network heterogeneities. The idea of employing trimodality has also been employed in some triblock copolymers. - ... 

E. Bowen, D. Stephens, T., Investigation of Network Heterogeneities in Filled, Trimodal, Highly Functional PDMS Networks by H Multiple Quantum NMR. Macromolecules 2007,40,4953-4962. 

Erman, B. Mark, J. E., Calculations on Trimodal Elastomeric Networks. Effects of Chain Length and Composition on Ultimate Properties. Macromol-ectdes 1998,31, 3099-3103. 

Poly(N,N-dimethylacrylamide) (PDMA) star polymers with 2, 3, and 4 arms and with dodecyl chains as hydrophobic end-caps were obtained in high yield with narrow polydis-persities by means of the RAFT technique. At sufficiently high concentration they form interconnected hydrophobic domains, i.e., a transient network. SANS experiments show that these hydrophobic domains contain about 20 dodecyl chains and they interact repulsively due to the PDMA chains that separate them. While the static structure is only very little affected by the number of arms this applies not at all to the dynamic properties as observed by DLS and rheology. Here one observes in DLS a complex, trimodal relaxation process, where the slower modes become more pronounced with increasing munber of arms. The fast mode corresponds to the diffusion of the hydrophobic domains while the second mode shows no q-dependence and corresponds in its values to the time deduced from the cross-over of G and G" in the oscillatory rheological experiments. Finally the slowest motion shows a rather pronounced q-dependence and is pre-stunably linked to a more complex relaxation mechanism of... 

We cannot judge at this point whether the importance of small mesoporosity for charge transport is really general or specific to the investigated film, but the authors have clearly demonstrated that films with bimodal and trimodal pore-size distributions are useful for electrochemists, because such combinations may at times alter the obtained electrochemical response in unexpected ways. We anticipate that multimodal pore-size distribution film-modified electrodes and mem-branes (i.e., hierarchical networks) will become widespread in electrochemical sensing, catalysis, and energy storage applications. 

Erman B, Mark JE. Calculations on trimodal elastomeric networks. Effects of chain length and composition on ultimate properties. Macromolecules 1998 31 3099-103. 

Fleury (2002) proposed a trimodal pore-size model for carbonates with three pore populations (micro, meso, macro). The electrical network comprises a series of mesopores and macropores micropores are in parallel. 

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