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DFT calculations , with VWN exchange correlation functional and double numeric basis set , were used to evaluate the energies required for the scission reactions taking place in the initial stage of the thermal degradation of Poly ( methyl methacrylate ) ( PMMA ) in the presence of a carbon nanotube ( CNT ) .
 Poly ( methyl methacrylate ), PMMA, carbon
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Poly ( methyl methacrylate ), PMMA, carbon