Probing the cooperative and local modes of a poly(methyl acrylate) sample via ESR spectroscopy

Length Scales and Dynamics in the Reorientational Relaxation of Tracers in Molecular and Polymeric Glass Formers via Electron Spin Resonance Spectroscopy

“…18 We found a very similar behavior, with the same probe, in several other polymers such as PMA, 63 PnBA, 28 PEA, 26 and some liquid crystalline polymethacrilates, 79 where the crossover was already ascribed to the onset of cooperativity. In ref 79 by an extension of the Vrentas-Duda 80 phenomenological approach, an estimation of the number of cooperative units was also achieved.…”

Heterogeneity and Dynamics in Azobenzene Methacrylate Random and Block Copolymers: A Nanometer–Nanosecond Study by Electron Spin Resonance Spectroscopy

“…7,23 A further main finding in ESR studies of paramagnetic molecular tracers in polymers is the sensitivity to cooperative dynamics of the polymer matrix associated with signatures and dynamic anomalies in the temperature dependence of the times of the molecular reorientation. [19][20][21][22]24 The present work reports on an ESR investigation, complemented by rheology and calorimetry studies, into the dynamics and matrix heterogeneity of MA4-MMA random and diblock copolymers (Figure 1). We highlight how the different architecture results in very different dynamic responses and matrix heterogeneities.…”

“…The cholestane rotational dynamics is described in terms of the diffusion model under cylindrical symmetry. 20,35,36 Accordingly, a spinning diffusion coefficient D∥ characterizes the rotation along the symmetry axis of the molecule and a tumbling diffusion coefficient D⊥ accounts for the rotation of the axis itself. 37 The ratio D||/D⊥ resulted to be close to 15 for cholestane in all the investigated samples.…”

On the Dynamics of the Cholestane Spin Probe in a Nematic Azobenzene Side Group Oligomer

“…The values of the fit parameters are reported in Table 4. The Arrhenius behavior exhibited below 290 K, in the temperature region around the glass transition temperature (onset of the glass transition at 288 K), presents DE a % 10 kJ=mol, to be compared with 31-35 kJ=mol for PMA4 homopolymers and copolymers [12] and various poly(alkyl acrylate)s at temperatures below T g [23,24]. In molecular glass formers activation energies of 14-15 kJ=mol are found.…”

“…In fact, it is known that the parameter c g 1 ¼ T b =ðT g À T 0 Þ Â ln 10 is almost molar mass independent in series of homologous monodisperse polymers [17]. Moreover, for monodisperse samples of poly(meth)acrylates (PMMA [22], poly(alkyl acrylate)s of different molar masses [17] and side-chain lengths [23,24]) a value of ca. 12 was found for c g 1 , which might imply for the oligomer PMA4 a T b % ð1300 AE 200Þ K. Thus, average values of T b % ð1150 AE 150Þ K and T 0 ¼ 244 K in the following were assumed as VF parameters for the temperature dependence of g of the oligomer.…”