Networks around free chains

Building a network around free chains might classically (Flory-Huggins) predict to lead to phase separation for the following reasons first, the entropy of mixing of the free chains maybe insufficient to balance the elasticity of the network. Second, if the chains... 

More often than not, molecular imprinting in polymers has involved the synthesis of a crosslinked polymeric network around a template molecule [27,28]. Generally an appropriate template molecule, T, is identified or synthesised in order to complex with suitable polymerisable binding sites in a solvent (Fig. 8). A crosslinking comonomer and a free radical initiator are added, and a radical chain polymerisation initiated thermally. 

The Phantom Model. In this model polymer chains are allowed to move freely through one another and the network junctions fluctuate around their mean positions [3,91-93], The conformation of each chain depends only on the position of its ends and is independent of the conformations of the surrounding chains with which they share the same region of space. The junctions in the network are free to fluctuate around their mean positions and the magnitude of the fluctuations is strain invariant. The positions of the junctions and of the domains of fluctuations deform affinely with macroscopic strain. The result is that the deformation of the mean positions of the end-to-end vectors is not affine in the strain. This is because it is the convolution of the distribution of the mean positions (which is affine) with the distribution of the fluctuations (which is strain invariant, i.e., nonaffine). The elastic free energy of deformation is given by... 

In the phantom network model, chains may move freely through one another and junctions fluctuate around their mean positions due to Brownian motion and are independent of deformation. The instantaneous distribution of chain vectors r is not affine in the strain because it is the convolution of the distribution of mean vectors r, which is affine, with the distribution of fluctuations Ar, which is independent of the strain. The elastic free energy of such a network is... 

Phantom Networks. In this idealized model, chains may move freely through one another (135). Junctions fluctuate around their mean positions because of Brownian motion, and these fluctuations are independent of deformation. The mean square fluctuations Ar of the end-to-end distance r are related to the mean square of the end-to-end separation of the free unperturbed chains r2(102,136,137) by... 

A new and elegant solvent-free approach to main chain LCEs was found by Yang et al. [39] who, based on the work on linear LC polymers by Lub et al. [40 2], made use of the photo-induced addition of thiols and olefins (click-chemistry) to synthesize nematic polymer networks. Starting from a mixture of the mesogen, a tetrafunctional crosslinker and a photo-initiator networks with a around 170 °C were obtained by UV crossUnking (Scheme 8). 

Some properties of polydimethylsiloxane (PDMS) polymer networks, which have been put into evidence by use of Deuterium Nuclear Magnetic Resonance ( H NMR), will be described in this paper. The anisotropy of molecular motions (in the time range 10 to 10" s) may be investigated with this technique, It has been already shown that deuteriated probes(solvent or free PDMS chains)dissolved in uniaxially deformed networks, acquire a uniaxial orientational order, which means that their motions, in the range 10" s, become uniaxial around the applied force direction This property and... 

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