Proton magnetic resonance of some α‐methyl group‐containing polymers and their monomers

Proton magnetic resonance spectra of poly(methyl methacrylate) (PMMA), poly(methacrylic acid), poly(sodium methacrylate), poly(α‐methylstyrene), and the four corresponding monomers have been obtained from 77°K. At 77°K. all four polymers and α‐methylstyrene exhibit complex derivative line shapes. Coincidental with the loss of the broad component of the derivative shape, marked second‐moment changes in all four polymers occur in the 100–250°K region and are attributed to the onset of hindered α‐methyl group rotation. α‐Methylstyrene shows a corresponding second moment change in the 77–140°K. region which is 90–140° below that found for the polymer. At 77°K. considerable motion, presumably hindered methyl group rotation, is occurring in the methacrylate monomer crystals. At temperatures above 300°K. the NMR line narrowing is found for PMMA, poly(methacrylic acid), and poly‐(α‐methylstyrene) and is believed to be due to reorientation motions associated with the glass transition. The line narrowing process for highly isotactic PMMA and highly syndiotactic PMMA occurs rear 360 and 420°K., respectively, while for commercial samples it takes place near 410°K.—behavior in agreement with the different Tg values reported for these materials. Correlation frequencies have been calculated for the low‐temperature transition region for the four polymers and α‐methylstyrene, and are compared with theoretically derived curves.