A study of low-energy processes in polymethyl methacrylate and its short-chain oligomers by terahertz IR and Raman spectroscopies

Based on the data of low-frequency (terahertz) IR and Raman spectroscopies, it is established that low-energy vibrational excitations in PMMA and its oligomers with a degree of polymerization $n$ = 2, 7, 9, and 50 are due to correlated small-angle torsional–vibrational dynamics, which prepares the relaxational mobility of macromolecules. The minimum size of the chain segment (“torsional–vibrational segment”), the spectrum of which is identical to the spectrum of the high-molecular polymer, is determined.