Permanent chains

Even if completely homogeneous and disordered in the relaxed state, a real network differs from the ideal network, defined in Chapter I. Three types of network defects are commonly considered to be present in polymer networks unreacted functionalities, closed loops, and permanent chain entanglements. Within each group there are several possibilities dependent on the arrangement of chains the effect of defects on the elastic properties of the network is thus by no means simple, as has been stressed e.g. by Case (28). Several possible arrangements are shown in Fig. 1, where only nearest neighbour defect structures have been drawn. 

Conversely, permanent chain entanglements25 act as additional, but not fixed, crosslinks, which are more likely to form when the functionality of the crosslinks is rather high, as it will be seen in a later section of this review. 

Now, let us discuss why those chains with a high content of hydrophobic MACA form smaller aggregates. Picarra and Martinho [143] showed that in the phase separation of a thin-layer dilute homopolymer solution on the surface, the collision would not be effective as long as the collision (or contact) time (rc) is shorter than the time (re) needed to establish a permanent chain entanglement between two approaching aggregates. Quantitatively, Tanaka [144] showed that rc and re could be roughly characterized as... 

This is not necessarily the case at the molecular level where the efficiency of permanent chain extension can be influenced by factors like chain relaxation, topological restraints, chain size and distribution, dissipation of frictional heat, chain repeating structure, and chain slippage. An expression that accounts for chain slippage and provides a measure of true molecular extension has been proposed by Porter et al. ... 

Figure 9.2 Main elements constituting the structure of a polymer network (1) crosslink point, (2) elastically active chain, (3) dangling chain, (4) loop or cycle, (5) multiple connection between two crosslink points, and (6) permanent chain entanglements between two adjacent crosshnks.

Considering the competition between intrachain contraction and interchain association, we have to discuss an overlooked viscoelastic effect in the formation of stable mesoglobules in dilute solutions. Otherwise, it would be difficult to understand why copolymer chains with a high content of hydrophobic comonomers could form smaller interchain aggregates. In the micro-phase separation, copolymer chains in solutions contract and associate. The collision between contracted and associated chains would not be effective if the collision (or contact) time (tc) is much shorter than the time (te) needed to establish a permanent chain entanglement between two ap-... 

Sterilisation by high-energy beams, e.g. y rays or fast electrons beams, is very efficient, as these beams are usually not stopped by materials. However, some covalent bonds of the polymeric network can be broken easily by such a high energy. Depending on the type of polymer and the dose and dose rate of the radiation, permanent chain scission or cross-linking can result from this process, modifying the polymeric structure and properties of the material. 

When the chain-forming particles aggregate in the primary minimum, the filaments or at least parts of them will remain assembled even in the absence of the magnetic field. In this section, we study the three-dimensional structure of the magnetic filaments formed by means of aggregation. The deformation and magnetorheological properties of these permanent chains have been the subject of... 

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