Reversible network

Reversible network structure is the single most important characteristic of a thermoplastic elastomer. This novel property generally arises from the presence of a phase-separated morphology in the bulk material which in turn is dictated by the molecular structure, often of a block copolymer nature. A wide variety of synthetic methods can, in principle, produce endless varieties of thermoplastic elastomers this fact coupled with the advantageous processing characteristics of these materials suggest that the use of thermoplastic elastomers will continue to grow in the 1980 s. 

Note The junction points in a reversible network are usually small erystallites or glassy domains sueh as those formed within block copolymers. 

Reversible network that forms or breaks up as the temperature is changed. 

Leibler L, Rubinstein M, Colby RH. Dynamics of reversible networks. Macromolecules 1991 24 4701-4707. 

Having discussed self-assembly strategies toward noncovalently functionalized side chain supramolecular polymers as well as studies toward the orthogonahty of using multiple noncovalent interactions in the same system, this section presents some of the potential applications of these systems as reported in the literature. The apphcations based on these systems can be broadly classified into two areas 1) self-assembled functional materials and 2) functionalized reversible network formation. 

Ni YP, Becquart F, Chen JD, Taha M (2013) Polyurea-nrethane supramolecular thermo-reversible networks. Macromolecules 46(3) 1066-1074... 

The ease with which bimolecular reactions between mononuclear species were occurring in the mechanisms [M = M, m, M — M ]cber+uni leads to some concern about potential for partial product formation reversibility. Therefore, a triply labelled cyclopentane carboxaldehyde was prepared (C5H8D) CDO. This triply labelled product was then injected under hydroformylation conditions where H2 and natural abundance CO were used. There was no indication whatsoever over the circa 4 h reaction that any (CsHgDj CDO was incorporated into the mechanism [M = M, M, M — M ]cber+uni and then converted back to product either as (CsHgDj CDO or (CsHgD) CHO or (CgHgDj CHO by a partially reversible network. 

A reversible crosslinked system forms a transient network that when placed under a macrodeformation shear rate exhibited shear flow. The properties depended on disruption and recombination of the reversible network. The linear response to oscillatory deformations has been determined for the reversible network with uniform chains with reversible crosslinking at end groups. Where molar mass (M) was less than the critical M for entanglements the dynamic moduli were related to temperature, M and crosslink bond... 

To describe such reversible network formation in associating mixtures, we start from the conventional lattice theoretical picture of polymer solutions described in Section 2.3 and references [7-11], with an attempt to include association [16-18] in the form of reaction equilibrium by taking the simplest theoretical viewpoint described in Section 3.2. 

The firs t systematic study of the reversible networks was the transient network theory developed by Green and Tobolsky [ 11 ], in which stress relaxation in rubber-Uke polymer networks was treated by the kinetic theory of rubber elasticity suitably extended so as to allow the creation and annihilation of junctions during the network deformation. 

In the first part of this chapter, we aim to introduce and discuss complementary functional groups that have beeu developed to allow for reversible network formation in bulk materials. The second part of the chapter deals mainly with polymer matrices in the gel state. In both parts of the chapter, we highlight how material properties at the meso-and macroscopic scales are governed by noncovalent forces on the molecular level, and how supramolecular interactions can offer opportunities in the development of stimuli-responsive materials. Lead examples and applications are highlighted throughout. 

Networks have also been assembled from trifunctionalized copolymer 45 (Figure 25). Solution viscosity studies, including capping studies, indicated that a reversible network formed in chloroform [87], Likewise, the polymer had interesting bulk mechanical properties — for example, a higher plateau modulus in dynamic mechanical analysis than a covalent network polymer — as a result of the formation of reversible, hydrogen-bonded cross-links, and, thus a thermodynamically stable network. 

This copolymerization is initiated by radicals in bulk, solution, or suspension. Emulsion polymerized copolymers of styrene and acrylic esters are important basic materials for coating resins. Copolymerization of styrene with acrylic acid salts (Zn, Co, Ni ", and Cu " ) in methanol as solvent yields copolymers that form ionomers with properties of reversible networks [135]. 

The advantage of this addition vulcanization is that no revision occurs because no byproducts are formed which might interfere with the network in terms of a reversible network degradation. Furthermore, although this vulcanization reaction is considerably accelerated at elevated temperatures. For a given receipe, the curing characteristics at different temperatures are shown in Table 4. 

In this chapter, we will focus on the design of polymers that exhibit photo-triggered self-healing properties. In addition to systems based on reversible network structures, the original strategies developed to heal un-cross-linked polymers with light will also be presented. 

Figure 4.10 Schematic representation of reversible network formed by a mixt di-ethylenetriamine, followed by reaction with urea to produce a mixture of oli...

---