Polymer networks, macromolecular

Defize, T., Riva, R., Raquez, J.M., Dubois, P, Jerome, C., Alexandre, M., 2011. Thermorev-ersibly crossfinked poly(E-caprolactone) as recyclable shape-memory polymer network. Macromolecular Rapid Communications 32, 1264—1269. 

Hem Ndez, R., Mijangos, C., 2009. In situ synthesis of magnetic iron oxide nanoparticles in thermally responsive alginate-poly(iV-isopropylacrylamide) semi-interpenetrating polymer networks. Macromolecular Rapid Coimnunications 30, 176—181. 

Although the basic concept of macromolecular networks and entropic elasticity [18] were expressed more then 50 years ago, work on the physics of rubber elasticity [8, 19, 20, 21] is still active. Moreover, the molecular theories of rubber elasticity are advancing to give increasingly realistic models for polymer networks [7, 22]. 

The concept of silicates as inorganic polymers was implicit in the ideas developed by W. H. Zacheriasen in the early 1930s. He conceived of silicates as consisting of macromolecular structures held together by covalent bonds but including network-dwelling cations. These cations were not assumed to have a structural role but merely to be present in order to balance the charges on the anionic polymer network. 

Covalent polymer networks or (Class II) crosslinked macromolecular architecture polymers rank among the largest molecules known. Their molecular weight is given by the macroscopic size of the object for instance, a car tire made of vulcanized rubber or a crosslinked layer of protective coating can be considered one crosslinked molecule. Such networks are usually called macronetworks. On the other hand, micronetworks have dimensions of several nanometers to several micrometers (e.g. siloxane cages or microgels). 

The Commission on Macromolecular Nomenclature is currently working on the extension of macromolecular nomenclature to branched and cyclic macromolecules, micronetworks and polymer networks, and to assemblies held together by non-covalent bonds or forces, such as polymer blends, interpenetrating networks and polymer complexes. 

The polymer networks based on silicon are very suitable for the study of cross-linked systems because of the possibility to synthesize smaller model molecules and macromolecular networks of well defined structure. An additional advantage of silicon polymers is that the resonances arising for different structural units are usually well... 

It is not an easy task to define inhomogeneities in the structure of a polymer network. Every system will exhibit the presence of defects and fluctuations of composition in space when the scale of observation becomes smaller and smaller. A hierarchy of structures exists, from atomic dimensions to the macroscopic material. A scheme of different scale levels used to describe linear and crosslinked polymer structures is shown in Fig. 7.2. Inhomogeneities described in the literature for polymer networks are ascribed to permanent fluctuations of crosslink density and composition, with sizes varying from 10 nm up to 200 nm. This means that their size lies in the range of the macromolecular scale. 

Important theoretical and experimental considerations of the use of macromolecular theories for the description of coal network structures have been recently analyzed (1). Relevant equations describing the equilibrium swelling behavior of networks using theories of modified Gaussian distribution of macromolecular chains have been developed by Kovac (2 ) and by Peppas and Lucht (3) and applied to various coal systems in an effort to model the relatively compact coal network structures (1 4). As reported before (1), Gaussian-chain macromolecular models usually employed in the description of polymer networks (such as the Flory... 

Macromolecules with nonlinear structure form a special group that includes branched, graft, comb, star, cyclic and network type macromolecules. Also, macromolecular assemblies are known, such as polymer blends, interpenetrating polymers, polymer networks, polymer-polymer complexes. The names of these types of macromolecules can be made using qualifiers such as -branch-, -blend-, -i- indicating crosslinked, etc. 

The versatility associated with nitroxide-mediated polymerizations, in terms of both monomer choice and initiator structure, also permits a wide variety of other complex macromolecular structures to be prepared. Sherrington201 and Fukuda202 have examined the preparation of branched and cross-linked structures by nitroxide-mediated processes, significantly the living nature of the polymerization permits subtlety different structures to be obtained when compared to traditional free radical processes. In addition, a versatile approach to cyclic polymers has been developed by Hemery203 that relies on the synthesis of nonsymmetrical telechelic macromolecules followed by cyclization of the mutually reactive chain ends. In a similar approach, Chaumont has prepared well-defined polymer networks by the cross-linking of telechelic macromolecules prepared by nitroxide-mediated processes with bifunctional small molecules.204... 

Erisch, H.L., 1993. Macromolecular topology. Metastable isomers from pseudo interpenetrating polymer networks. New J. Chem. 17 697-701. 

Data on the fractal forms of macromolecules, the existence of which is predetermined by thermodynamic nonequilibrium and by the presence of deterministic order, are considered. The limitations of the concept of polymer fractal (macromolecular coil), of the Vilgis concept and of the possibility of modelling in terms of the percolation theory and diffusion-limited irreversible aggregation are discussed. It is noted that not only macromolecular coils but also the segments of macromolecules between topological fixing points (crosslinks, entanglements) are stochastic fractals this is confirmed by the model of structure formation in a network polymer. 

The structure of lignin consists of phenylpropane units forming a three dimensional polymer network which have not an ordered and regular super-macromolecular structure. The X-ray dififractometry and differential scanning calorimetry (DSC) indicated that the isolated lignins in the solid state are amorphous polymers. 

Inclusion complexation has developed to becoming another widely exploited supramolecular interaction for the formation of supramolecular polymer networks, mostly in water [197, 198]. Several classes of macrocycles have been developed, including crown ethers [199, 200], porphyrins [201, 202], cyclophanes [203], catenanes [204], cavitands [205, 206], cryptophanes [207], calix[n]arenes [208], and carcerands [209]. Macrocyclic-based supramolecular gels can either be formed from low molecular weight precursors or from macromolecular building blocks. The following discussion focuses on the latter. 

More recently, the importance of introducing supramolecular interactions between macromolecular chains has become evident, and many new options have been introduced. The final step in this development would be to develop polymers based on reversible, noncovalent interactions. Rather than linking the monomers in the desired arrangement via a series of polymerization reactions, the monomers could be designed in such a way that they self-assemble autonomously into the desired stracture. As with covalent polymers, a variety of structures of these so-called supramolecular polymers are possible, with block-copolymers or graft copolymers - as well as polymer networks - being created in this way. 

Li et al. (2008a) introduced solvent-resistant multifunctional PV membranes based on segmented polymer networks (SPNs). Hydrophilic (acrylate)-terminated poly(ethylene oxide) was used as a macromolecular cross-linker of different hydro-phobic polyacrylates for the synthesis of amphiphilic SPNs. Multifunctional canposite membranes with thin SPN top layers were prepared by in situ polymerization. The support consisted of hydrolyzed PAN. These membranes were tested for dehydration of EtOH and isopropyl alcohol. The selectivity of the membranes greatly depended on the composition or the ratio of the hydrophilic and hydrophobic phases of the SPN. 

Schmidt, A.M. (2006), Electromagnetic activation of shape memory polymer networks containing magnetic nanoparticles , Macromolecular Rapid Communications,Vo. 27,No. 14,pp. 1168-1172. 

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