Interpenetrating cyclics

Figure 5. Preparation of a chain mail or Olympic network consisting entirely of interlooped cyclic molecules, without any cross-links [193]. Linear chains passing through the cyclics are difunctionally end-linked at the regions shown by the rectangles. The result is a series of interpenetrating cyclics, which would function as an elastomeric network.

Preparation of a chain-mail or Olympic network, which has no cross links at all. Linear chains (light lines) passing through the cyclics (heavy lines) in part a are di-functionally end linked to form a series of interpenetrating cyclics in part b. 

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. 

As their structures define, polyrotaxanes are polymeric composites. Their ultimate properties are related both to the chemical compositions of the cyclic and backbone and to their relative proportions. However, because of its different topology relative to simple mixtures, the interpenetrated structure introduces new outcomes in terms of properties. Because the applications of materials rely on their properties, these aspects are incorporated into this section. 

If a bulky hydrophobic group is introduced at the 5-position of isophthalic acid, a cyclic hexamer (rosette) is generated. In the crystal structure of trimesic acid, the voids are filled through interpenetration of two honeycomb... 

It is important to appreciate that these ditopic macrocycles contain a polyether moiety on one side and present a diamido motif on the other. Addition of a charged pyridinium cation to the substrate-free form of these macrocycles then generates a highly efficient receptor for chloride, presumably as the result of both template-induced organization and electrostatic effects. The further incorporation of hydro-quinone groups and polyether functionalities into the cyclic framework presumably contributes to the stabilization of the cationic pyridinium component within the final interpenetrated structure. Interestingly, while titration of the pyridinium cation building block alone revealed a preference for oxoanions, the final receptor-anion... 

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. 

Another Py-GC/MS experiment was performed on polyacrylic /nfer-net-polysiloxane, a copolymer used as impact properties modifier. This is a polymer of butyl acrylate with low levels of allyl, methyl, and 3-(dimethoxymethylsilyl)propyl methacrylates interpenetrated with cyclic dimethylsiloxane. The copolymer has CAS 143106-82-5. The pyrolysis was done at 600 C in He similar to other experiments previously discussed. The pyrogram is shown in Figure 6.7.14 and peak identification is given in Table 6.7.10. 

Table 6.7.10. Compounds identified in the a copolymer of butyl acrylate with low levels ofallyl, methyl, and 3-(dimethoxymethylsilyl)propyl methacrylates interpenetrated with cyclic dimethylsiloxane as shown in Figure 6.7.14.

An interesting case of cyclic bottleneck-connected channels that are interpenetrated by cleavage planes in two directions is found for the disulfide 51 (Fig. 2.1.38). This sponge-like solid may be solid-state reactive, even though it contains intractably mobile molecules of tetrahydrofuran, dichloromethane, or other solvents, depending on the crystallization. 

Figure 2.1.38 Crystal packing of 51 (C2/c) [83] (a) along [001] showing bottlenecked cyclic channels (b) interpenetrating cleavage planes along [100] these crystals contain intractably mobile molecules of solvents, for example tetrahydrofuran.

Polymers are normally classified into four main architectural types linear (which includes rigid rod, flexible coil, cyclic, and polyrotaxane structures) branched (including random, regular comb-like, and star shaped) cross-linked (which includes the interpenetrating networks (IPNs)) and fairly recently the dendritic or hyperbranched polymers. I shall cover in some detail the first three types, but as we went to press very little DM work has been performed yet on the hyperbranched ones, which show some interesting properties. (Compared to linear polymers, solutions show a much lower viscosity and appear to be Newtonian rather than shear thinning [134].) Johansson [135] compares DM properties of some hyperbranched acrylates, alkyds. and unsaturated polyesters and notes that the properties of his cured resins so far are rather similar to conventional polyester systems. 

More recently, iodonium salts have been widely used as photoinitiators in the polymerization studies of various monomeric precursors, such as copolymerization of butyl vinyl ether and methyl methacrylate by combination of radical and radical promoted cationic mechanisms [22], thermal and photopolymerization of divinyl ethers [23], photopolymerization of vinyl ether networks using an iodonium initiator [24,25], dual photo- and thermally-initiated cationic polymerization of epoxy monomers [26], preparation and properties of elastomers based on a cycloaliphatic diepoxide and poly(tetrahydrofuran) [27], photoinduced crosslinking of divinyl ethers [28], cationic photopolymerization of l,2-epoxy-6-(9-carbazolyl)-4-oxahexane [29], preparation of interpenetrating polymer network hydrogels based on 2-hydroxyethyl methacrylate and N-vinyl-2-pyrrolidone [30], photopolymerization of unsaturated cyclic ethers [31] and many other works. 

Figure 3. Schematic of the electrostatically driven layer-by-layer adsorption process. It describes the case of the adsorption of a polyanion to a positively charged substrate (A), followed by washing (B), the adsorption of a polycation (C) and another washing step (D). Multilayer films are prepared by repeating steps (A) through (D) in a cyclic fashion. More complicated film architectures are obtained by using additional adsofption/washing steps and applying more than two polyelectrolytes. Note that the drawing is oversimplified with respect to polyion conformation and interpenetration of adjacent layers. Furthermore, any counterions that might be present in the films were omitted for reasons of clarity.

Formation of a network of low molecular weight polymers will manifest itself through a loss in mechanical properties. Conversely, a network of unsaturated, cyclic, low molecular weight polymers will have the potential of improving the mechanical properties of the material in a composite structure such as a tire. This is due in part to their participation in vulcanization. The high macrocyclic ring structure of poly-octenamers improves heat stability at elevated temperatures, owing to the interpenetration of linear polymer chains and cyclic macromolecules. 

Molecular-sieving effects based on size/shape exclusion are common in rigid zeolites and molecular sieves. One famous example is the separation of normal paraffins from branched-chain and cyclic hydrocarbons by using a 5-A molecular sieve. Similar selective adsorption effects have been observed in several porous MOFs. Kim and coworkers reported that Mn(HCOO)2 has a robust 3D framework structure with ID channels interconnected by small win-do ws/apertures. This material can selectively adsorb H2 over N2 and Ar at 78 K, and CO2 over CH4 at 195 K, as indicated by the gas adsorption isotherms. In both cases, the uptake of the excluded gases N2, Ar, and CH4 was negligible. Thus, the selectivity was attributed to the small aperture of the channels. An interpenetrated MOF, PCN-17, contains nanoscopic cages with a window size of 3.5A and displays selective adsorption of H2 and O2 over N2 and CO. ° MIL-96 " and Zn2(cnc)2(dpt) were also found to selectively adsorb CO2 over CH4 based on size/shape... 

Non-linear polymers comprise branched, graft, star, cyclic, and network macromolecules. Polymer blends, interpenetrating networks, and polymer-polymer complexes are summarized as macromolecular assemblies. Their skeletal structure should be reflected in the name by using an italicized connective as a prefix to the source-based name of the polymer component or components to which the prefix applies. Table 5.10.1 lists aU classifications for non-Unear macromolecules and macromolecular assemblies with their corresponding prefixes [971UP2]. Examples for nomenclature are given in Table 5.10.2 (non-linear macromolecules) and Table 5.10.3 (macromolecular assemblies). 

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