Subglass relaxation processes: dielectric relaxation in methyl acrylate/ethylene copolymers

Buerger, D. E.; Boyd, R. H.

doi:10.1021/ma00196a028

Cited by 21 publications

(21 citation statements)

References 6 publications

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“…The amorphous material below the glass–rubber transition temperature is subjected to subglass relaxations,40, 41 which can be related to the local motions of carbon atoms belonging to both main chains and side groups. Minor changes in the spectrum of amorphous starch at different temperatures (Table II) and moisture contents ‐ for example, minor changes in peak area (Figure 3) and increasing width of the peaks (Figure 2) may be related to these local changes in the mobility of the molecules.…”

Section: Discussionmentioning

confidence: 99%

The effect of water content on the ordered/disordered structures in starches

2001

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13C cross‐polarization magic angle spinning NMR has been used to study the ordered and disordered structures of starches with different water contents. The amorphous regions of starch have been shown to produce NMR patterns only if they are in a glassy state, the widths, positions, and areas of the peaks to some extent being dependent on the temperature and the water content of the starch. In the amorphous region, the peaks were all Gaussian in shape, while the peaks in the ordered regions had Lorentz profiles. Water contents in the range 10–50% did not influence the proportion of double helices in the starch. Decreasing the water content to 1–3%, however, resulted in a significant decrease in the proportion of double helices, the effect being greater in B‐ than in A‐type starches. It is suggested that short‐range order structures in starches (double helices) are stabilized by becoming part of long‐range order structures (crystallites). © 2001 John Wiley & Sons, Inc. Biopolymers 58: 247–259, 2001

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Section: Discussionmentioning

confidence: 99%

The effect of water content on the ordered/disordered structures in starches

2001

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“…For example, chair-inverse-chair conformational transitions of cyclohexyl in poly(cyclohexyl methacrylate) produce an ostensible secondary  relaxation that causes a significant decrease of the real relaxation modulus of the polymer in the glassy state [10][11][12]. Since to date, while no quantitative theory that describe the glass-rubber relaxation and the secondary relaxations in terms of the chemical structure has been formulated, (i) the theory of the total dielectric relaxation strength for the -process is wellestablished in terms of molecular dipole moments [4][5][6][13][14][15][16][17][18][19][20][21][22] and (ii) much success has been achieved in understanding the characteristic behavior of the dielectric  relaxation through computer "molecular dynamics" simulations [23][24][25][26][27][28][29]. In this sense, actually the design of polymers with specific physical properties relies on empirical rules based on experimental studies of the relaxation properties of polymers with different chemical structures.…”

Section: Introductionmentioning

confidence: 99%

Effect of slight crosslinking on the mechanical relaxation behavior of poly(2-ethoxyethyl methacrylate) chains

Carsí

Sanchı́s

Díaz‐Calleja

et al. 2013

European Polymer Journal

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Elsevier Carsí Rosique, M.; Sanchis Sánchez, MJ.; Díaz Calleja, R.; Riande, E.; Nugent, MJD. (2013). Effect of slight crosslinking on the mechanical relaxation behavior of poly(2-ethoxyethyl methacrylate) chains. Abstract The synthesis, thermal and mechanical characterizations of uncrosslinked and lightly crosslinked poly(2-ethoxyethyl methacrylate) are reported. The uncrosslinked poly(2-ethoxyethyl methacrylate) exhibits in the glassy state two relaxations called in increasing order of temperature, the gamma and beta processes respectively. These are followed by a prominent glass-rubber or alpha relaxation. By decreasing the chains mobility by a small amount of crosslinking, the beta relaxation disappears and the peak maximum associated with the alpha relaxation is shifted from 268 K to 278 K, at 1 Hz. An investigation of the storage relaxation modulus of the crosslinked polymer indicates two inflexion points that presumably are related to segmental motions of dangling chains of the crosslinked networks and to cooperative motions of the chains between crosslinking points. Nanodomains formed by side-groups flanked by the backbone give rise to a Maxwell-Wagner-Sillars relaxation in the dielectric spectra that have no incidence in the mechanical relaxation spectra. 2

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“…It can be modeled by molecular mechanics and appears to lead to welcome significant differences in experimental behavior depending on its chemical environment and the direction of attachment to the chain. A study of the pendant methyl ester group in methyl acrylate/ethylene copolymers has been completed.1 Here the results of a O (1) study of the chemically isomeric but differently attached pendant acetate group in vinyl acetate/ethylene copolymers are reported. It is already known that the homopolymers poly(methyl acrylate) (PMA) and poly(vinyl acetate) (PVAc) differ significantly in their subglass relaxation behavior.…”

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confidence: 99%