Oligomer backbone chain

We know two major competing directions of tribodestruction of heterocyclic polymers i) decomposition of a heterocycle (quinoxaline, imide, oxa-diazole or others) as a result of the destruction of weak links of the backbone chain leading to a drop in the polymer molecular mass until the formation of low-molecular products and ii) the reactions resulting in formation of a branched and cross-linked polymer structure [97, 104-106]. Low-molecular products of macromolecular destruction (both gaseous and oligomer) may serve as tribochemical lubricants that reduce the friction coefficient and function as wear inhibitors. 

Oxidation of lovastatin in aerated ethylene dichloride solution at 35°, containing a free radical initiator, has been monitored kinetically using HPLC (34). The degradates formed in this complex solution system, different from those in the solid state, are primarily oligomers, with peroxide groups within the backbone chain and hydroperoxide end groups. Also, some monomeric epoxides are formed. 

Long-chain branched polyethylenes can be also obtained by copolymerization of ethene with ethene oligomers by tandem polymerization in one step [100] or with ethene/propene oligomers in two steps [101]. In the latter case, polymers are obtained with crystalline polyethylene backbone chains and amorphic ethene/ propene copolymer side chains [102]. 

We present below our original estimates of the value of a vibrational segment of the backbone chain based on the FIR spectra of polymer and oligomer samples with various degree of polymerization (n). Experiments were performed for oligomers of PMC with m = 4, 7, 10, 14 and 2 x 10 MMA oligomers with n = 2,7,9 and 50 and oligocarbonates with n = 2,3,4,6,7 and 1.3 X 10. ... 

Let us assume that the absorption at the intersKdiate frequencies Vi, both of cross-linked polymers and oligomers is due to the torsion vibrations in the short (with N backbone chain parts. The potential barrier of this motion can be evaluated from the frequency of the skeletal torsional vibrations in the corresponding polymers and the frequency trf the intermediate absorption according to the relation [73, 135] ... 

PIA bands appear in the near IR at around < 0.8 eV which shift to the red on increasing the chain length. The near IR absorption at around 0.8 eV and the shoulder at 1.5 eV (especially visible in six membered and seven membered oligothiophene 6T and 7T, Figure 8.35) are the charged photoexcitations on the oligomer backbone. 

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