Polymer unsaturated bonds

The low unsaturation requires powerful curing systems whilst the hydrocarbon nature of the polymer causes bonding problems. To overcome these problems chlorinated and brominated butyl rubbers (CIIR and BUR) have been introduced and have found use in the tyre industry. 

The second type of polymer, unsaturated polyanhydrides of the structure [-(OOC-CH=CH-CO)x-(OOC-R-CO)y-]n, have the advantage of being able to undergo a secondary polymerization of the double bonds to create a crosslinked matrix. This is important for polymers requiring great strength, for instance. These polymers were prepared from the corresponding diacids polymerized either by... 

Another example where antioxidant performance can be improved dramatically lies in the mechanochemlcally initiated addition of reactive antioxidants on rubbers (5.10) or unsaturated thermoplastics such as ABS (12). For example, using thiol antioxidants 2 and 3 as the reactive antioxidants, Kharasch-type addition of the thiol function to the polymer double bond takes place during melt processing to give bound antioxidant adduct (see Equation 1) the polymer becomes much more substantive under aggressive environments. 

It is known that aromatic azides are photodecomposed to give active nitrenes as the transient species, which react with the environmental binder polymers to crosslink them. However, the mechanism of these photocrosslinking polymers has not been studied in detail. L.S.Efros et al. have proposed that the rubber polymer is crosslinkes in such a way that the aromatic nitrene inserts into an unsaturated bond of the polymer to give an aziridine ring. The experimental evidence for this, however, has not been given (8). 

Maleic anhydride is a cyclic anhydride with one double bond in the ring and two double-bonded oxygens hanging off the ring. The resulting reactivity leads to maleics use in making polymers, unsaturated polyesters, alkyd resins, plasticizers, and dicarboxylic acids. 

Polymeric hydrocarbon elastomers, such as natural rubber, are cross-linked or vulcanized by the use of sulfur, which reacts with the carbon of the unsaturated bonds in polymer molecules to form a bridge between two molecules so that one polymer molecule is covalently bonded to a second polymer molecule (6). 

Radicals add to unsaturated bonds to form new radicals, which then undergo addition to other unsaturated bonds to generate further radicals. This reaction sequence, when it occurs iteratively, ultimately leads to the production of polymers. Yet the typical radical polymerization sequence also features the essence of radical-induced multicomponent assembling reactions, assuming, of course, that the individual steps occur in a controlled manner with respect to the sequence and the number of components. The key question then becomes how does one control radical addition reactions such that they can be useful multicomponent reactions Among the possibilities are kinetics, radical polar effects, quenching of the radicals by a one-electron transfer and an efficient radical chain system based on the judicious choice of a radical mediator. This chapter presents a variety of different answers to the question. Each example supports the view that a multicomponent coupling reaction is preferable to uncontrolled radical polymerization reactions, which can decrease the overall efficiency of the process. 

Firstly, Aharoni et al. [128] described a process of ozonization of polymers or copolymers containing unsaturations in a mixture of two solvents. One of them is inert to ozone and the other one is less reactive than polymer double bonds but more reactive than the single C-C bonds of this polymer. A typical solvent mixture is composed of toluene and 1,1,2,2,-tetra-chloroethane, or xylene and decaline. This mixture permits one to control the attack of polymer only onto unsaturations and not to produce unstable sites in the polymer backbone (as peroxides or hydroperoxides coming from single bond C-C attack) which could decompose in a second step producing undesirable by-products. In this way, only unsaturations are reacted and... 

There are many different types of PHA, distinctly characterised by chain length, type of functional group and degree of unsaturated bonds. A higher degree of unsaturation increases the rubber qualities of a polymer, and different functional groups change the physical and chemical properties of a polymer. 

Hydrocarbon Based Polymers. The substitution of one hydrogen atom in the -CH2-CH2- unit by some short carbon chains induces subtle modifications in the electronic structure (molecular orbitals) of the polymers. Though these modifications cannot be easily evidenced on the XPS carbon Is core level spectra, it appears that the XPS valence band structures are much more sensitive to these substitutions and that they become unique and readable fingerprints of the polymers (1, 22). We will not speak here of the Cls shake-up data that were revealed useful to distinguish between saturated and unsaturated bonds (this field with various applications was recently reviewed (23)). 

De Sarlo et al.55) suggest that the stereochemical course of the polymerization leading exclusively to cyclic polymers with methyl groups in anti-positions is in agreement with the usual trans-addition to unsaturated bonds. The nucleophilic centre binds to the... 

As EPR and EPDM elastomers, the vulcanization process is carried out using organic peroxides because the polymer chains do not contain unsaturated bonds. If the polydimethylsiloxane chains are modified by introducing a small quantity of vinyl groups, the vulcanization is carried out using cumyl peroxide. 

In membrane separation of the olefin/paraffin mixture, the predominant selective separation of the olefin is evident. First, the olefin molecule is smaller in size compared to the respective paraffin. Specifically, C—C distance in paraffins is 0.1534 nm, whereas the C=C distance in olefins is 0.1337 nm. Atoms of carbon in paraffins feature sp hybridization and free rotation around C—C bonds. Atoms of olefins feature sp hybridization. The rigid C=C bond impedes internal rotation in the olefin molecule and makes it flat. It is therefore clear why olefin molecules are smaller in size compared to paraffin and why the diffusion coefficients of olefins in polymers would be higher than those of paraffins. Second, the presence of unsaturated bonds in olefin molecules makes them capable of specific interactions with the membrane matrix. Efforts to take advantage of these capabilities resulted in the development of an important field of research facilitated transport. 

Thus, it follows from the above data that glassy polymers are promising materials for selective separation of olefins from their mixtures with paraffins. The main contribution to the high values of permselectivity is made by the diffusion component ao- However, unsaturated bonds in olefin molecules make them capable of specific interactions with ir-conjugated polar... 

Addition polymerization In addition polymerization, all of the atoms present in the monomers are retained in the polymer product. When the monomer is ethene, an addition polymerization results in the polymer polyethylene, as shown in Table 23-3. Unsaturated bonds are broken in addition polymerization just as they are in addition reactions. The difference is that... 

Nitroxy radicals may also reac unsaturated bonds in polymers according to the reactions ... 

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