Network physically crosslinked

Another approach of physically crosslinked SMP networks was demonstrated by the melt blending of an elastomeric ionomer based on the zinc salt of sulfonated poly[ethylene-ran-propylene-ran-(5-ethylidene-2-norbornene)] and low molecular mass fatty acids. In such a polymer network the nanophase separated ionomer provided the permanent network physically crosslinked by the zinc salt, while the fatty acids are located in nanophases, whose melting is triggering the shape recovery [61]. 

Possible morphologies of partially crystalline polymers are shown in Fig. 18. Figure 18a depicts the case of small crystallites that act as physical crosslinks between polymeric chains, thus connecting those chains into a 3-dimensional network. In the case depicted in Fig. 18b, the material forms ribbon-shaped or needle-shaped crystalline regions in which different segments of a large number of chains are incorporated. This could explain the low degree of crystallinity at the LST as detected for the iPP system [80]. 

Physical Crosslinking. A crosslinked network can also be achieved through physical aggregation of the hard segments of... 

Nanogels are nanometer-sized hydrogel nanoparticles (less than about 100 nm) with three-dimensional networks of physically crosslinked polymer chains. They have attracted growing interest over the last decade because of their potential for applications in biomedical fields, such as DDS and bioimaging [246-249]. 

To probe the 1/N dependence in the slope F, experiments were carried out on model end-linked networks with different precursor chain lengths (average molecular weight Mn varying from 3100 to 23000 g.mol 1) [55, 56]. As expected, the slope F decreases when N increases. However, it does not follow a 1/N variation F varies only by a factor of about 3 as N varies by a factor of 7. In an end-linked network, N should not be simply assimilated with the length of precursor chains, since trapped entanglements may play the role of effective crosslinks (often denoted as physical crosslinks), in addition to chemical... 

The monomer is completely soluble in water. We would predict that the homopolymer, too (sodium polyacrylate), would dissolve readily in water, because each repeating unit contains an ionic sodium carboxylate group. (Most sodium salts dissolve in water.) If we were to add, say, one gram to 400 to 600 mL of distilled water and stir, the result would be a gel, not the free-flowing solution that we expected. A gel is defined as a chemically or physically crosslinked polymer that is highly swollen by solvent. The solvent is held tightly by the polymer network and does not flow. If the solvent is water it is called a hydrogel. 

The modem theory of mbber-like elasticity theory suggests that there are two types of elastically active network chains which contribute to the overall equilibrium rubbery modulus, G (1) chains attached to the network by chemical crosslinks, G and (2) chains attached by physical crosslinks or entangelements, G . That is,... 

What is an IPN Operationally, an IPN is an intimate mixture of two (or more) network polymers in which at least one of the networks has been formed in the presence of the other (2) Ideally, bonding between the networks is absent, interpenetration of the network chains in the bulk mixture is complete on a molecular scale, and a single phase results. On the molecular level, chains of one network are threaded through those of the second network they are catenated. The total crosslink density of the composite material includes a contribution from the physical crosslinks as well as the chemical crosslinks created during polymerization. Such an ideal, albeit complex, system has seldom, if ever, been realized. 

Of particular interest is whether phase-separated domains of POSS are crystalline or glassy in nature. The POSS-rich-phase domains may serve as physical crosslinks, but there have been few investigations on the physical aging behavior in pseudo -network systems [ 181 ]. 

It should be stressed that the viscosity changes during formation of polyurethanes even from bifiinctional compounds can be correlated with gelation most likely they are connected with the formation of a physical network then crosslinks arise from sufficiently strong specific interactions like hydrogen bonds [50]. An example of such a process is the reaction of macro (diisocyanate) with 3,3 -dichloro-4,4 -diaminodiphenylmethane [43]. 

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