Comparative study of the mechanical relaxation behavior of polymethacrylates containing different bulky side groups

The syntheses of poly(1,3-dioxan-5-yl methacrylate,), poly(cis-2-phenyl-1,3-dioxan-5-yl methacrylate), poly(trans-2-phenyl-1,3-dioxan-5-yl methacrylate), poly(cis-2-cyclohexyl-1,3-dioxan-5-yl methacrylate), and poly(trans-2-cyclohexyl-1,3-dioxan-5-yl methacrylate) are reported. The mechanical relaxation spectrum of the simplest polymer, poly(1,3-dioxan-5-yl methacrylate), exhibits a prominent beta relaxation centered at -98 degreesC, at 1 Hz, followed in increasing order of temperature by an ostensible glass-rubber relaxation process. In addition to the beta relaxation, the loss curves of poly(trans2-phenyl-1,3-dioxan-5-yl methacrylate) and poly(trans-2-cyclohexyl-1,3-dioxan-5-yl methacrylate) display in the glassy state a high activation energy relaxation, named the beta* process, that seems to be a precursor of the glass-rubber relaxation of these polymers. The mechanical spectra of poly(trans-2-cyclohexyl-1,3-dioxan-5-yl methacrylate) and poly(cis-2-cyclohexyl-1,3-dioxan-5-yl methacrylate) exhibit a low activation energy process in the low-temperature side of the spectra, which is absent in the other polymers. The molecular origin of the mechanical activity of these polymers in the glassy state is discussed in qualitative terms. (C) 2002 Wiley Periodicals, Inc.