Dielectric relaxation of polystyrene with side-chain- and chain-end-labels

Mansour, Ahmed S.; Happ, E.; Wolf, Thomas F.; Stoll, B.

doi:10.1007/bf00658887

Cited by 8 publications

(15 citation statements)

References 13 publications

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“…It can be also observed in Figure 1 that the high frequency tail of the glass process is slightly broadened than that observed normally in thermally polymerized PS [17]. This can be attributed to the fact that in the present work the PS chains are terminated by the hydroxyl groups, which possess a strong dipole moment that can relax cooperatively within the spectrum of the glass process [20,21]. In a previous work, the effect of side and end groups on the glass relaxation spectrum has been thoroughly studied [20,21].…”

Section: Resultssupporting

confidence: 49%

“…This can be attributed to the fact that in the present work the PS chains are terminated by the hydroxyl groups, which possess a strong dipole moment that can relax cooperatively within the spectrum of the glass process [20,21]. In a previous work, the effect of side and end groups on the glass relaxation spectrum has been thoroughly studied [20,21]. The results showed that flexible end groups relax at the high frequency tail of the glass process, while stiff groups relax with the same relaxation frequency of the glass process or even slower depending on the length of the side or end groups [20,21].…”

Section: Resultsmentioning

confidence: 94%

“…In a previous work, the effect of side and end groups on the glass relaxation spectrum has been thoroughly studied [20,21]. The results showed that flexible end groups relax at the high frequency tail of the glass process, while stiff groups relax with the same relaxation frequency of the glass process or even slower depending on the length of the side or end groups [20,21]. The glass process of polycarbonate, PC, appears in the temperature Figure 2 shows that CSC block copolymer exhibits two glass processes, one appearing at temperatures lower than 125 C, while the other appears at higher temperatures.…”

Section: Resultsmentioning

confidence: 99%

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Effect of Block Position on the Dynamics of the Glass Processes in Carbonate/Styrene Triblock Copolymers, CSC and SCS

Mansour¹,

Mohamed

Minko

2003

Journal of Elastomers & Plastics

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Molecular dynamics of specially prepared triblock copolymers of polystyrene and polycarbonate were studied by dielectric spectroscopy over wide ranges of frequency; 10 À1 À 10 5 Hz and temperature; 50-200 C. Two block copolymers are used in the current investigation; carbonate-styrene-carbonate, CSC and styrene-carbonate-styrene, SCS, which have blocks with the same molecular weights but with different positions. The dielectric relaxation spectra and d.s.c scans showed that these block copolymers CSC and SCS exhibit two relaxation processes corresponding to the glass transitions of the two microseparated PS-and PC-phases. It is surprising to find that the molecular dynamics of either PS-or PC-blocks are different in CSC and SCS and also differ from the dynamics of the corresponding homopolymers with same molecular weight, i.e. the molecular dynamics of the blocks depends on their position within the chain. The results are assessed and discussed in terms of the different Downloaded from factors that could affect the glass transition and its dynamics for different blocks; namely: the number of free end groups per block and the morphological confinement that influence the size of the cooperative regions responsible for the glass transition.

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Section: Resultssupporting

confidence: 49%

Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

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Effect of Block Position on the Dynamics of the Glass Processes in Carbonate/Styrene Triblock Copolymers, CSC and SCS

Mansour¹,

Mohamed

Minko

2003

Journal of Elastomers & Plastics

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“…This result is in good agreement with the DS works on end-functionalized PS. 10,11,13,14 We consider that taking into account the size of the CRR and/or the strength in intersegmental couplings around T g is important to understand quantitatively this result. The length scale of the CRR for bulk glass formers around T g has been determined by various methods.…”

Section: Resultsmentioning

confidence: 99%

Glass Transition Temperature and β Relaxation Temperature around Chain End of Polystyrene Determined by Site Specific Spin Labeling

et al. 2012

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A glass transition temperature, T(g), and a β relaxation temperature, T(β), of spin-labeled polystyrene (PS) having a number average molecular weight (M(n)) of ca. 25 kDa were determined by the microwave power saturation (MPS) method of electron spin resonance (ESR). Spin labeling was selectively carried out at chain ends or midchain segments. This method allowed us to determine the local T(g) and the local T(β) around the spin-labeled sites, selectively. The T(g) determined by the ESR, T(g,ESR), was in good agreement with that determined by differential scanning calorimetry, T(g,DSC); the T(g,ESR) decreased with decreasing M(n) with blending oligomers as well as the T(g,DSC). The T(g,ESR) for the end-labeled PS (PS-E) was equal to that for the midchain-labeled PS (PS-M) irrespective of the M(n). However, we previously reported that the PS-E showed distinctly higher segmental mobility than the PS-M in the temperature range 423-463 K (above T(g)). Therefore, we conclude that the chain ends intrinsically have higher segmental mobility than midchain segments due to the discontinuity of repeat units; however, the mobilities of chain ends and midchain segments are averaged out in the vicinity of T(g) due to the cooperativities with neighboring numerous chain segments. Concerning the β relaxation, the T(β) determined by the MPS was in good agreement with those determined by dielectric and dynamic mechanical spectroscopies and dilatometry. The T(β) of the PS-E was the same with that of the PS-M within experimental uncertainties; the T(β) was insensitive to the M(n) in contrast to the T(g). Therefore, we conclude that the effect of chain end is little on the β relaxation of PS due to its local character. In addition, the effect of annealing at 353 K was found to be the same for the T(β)s of the PS-E and PS-M.

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“…This process was associated by the authors to librational motion of phenyl rings coupled with main-chain motion near T g . Strong coupling of the side groups and backbone relaxation was found by Mansour et al, 9,10 who studied dielectric relaxation of different chemical groups (p-cyanobenzyl, p-cyanobiphenyl) chemically fixed at the end of the PS chain or attached as side groups.…”

Section: Introductionmentioning

confidence: 88%

Correlated Segmental Dynamics in Amorphous Atactic Polystyrene: A Molecular Dynamics Simulation Study

2002

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Molecular dynamics simulations of bulk atactic polystyrene have been performed in a temperature range from 100 to 650 K at atmospheric pressure. Local translational mobility has been investigated by measuring the mean square translational displacements of monomers. The long-time asymptotic slope of these dependencies is 0.54 at T > Tg, showing Rouse behavior. Crossover from motion in the cage to Rouse-like dynamics has been studied at T > Tg with a characteristic crossover time follows a power law behavior as a function of T, as predicted by mode-coupling theory (MCT). We studied the coherent intermediate scattering function and show the agreement with scaling predictions of MCT. Local orientational mobility has been studied via the orientational autocorrelation functions, ACFs (Legendre polynomials of the first and second order), of both the main-chain and side-group bonds. The ACF relaxation times analysis shows strong coupling between the phenyl groups and the backbone relaxation. The relaxation times of the orientational R-relaxation follow the same power law (γ ∼ 2.9) as the characteristic translational diffusion time and the intermediate scattering function. Below Tg, both types of dynamics are described by the same activated law. The ACFs time-distribution functions reveal the existence of activated local rearrangements already above T g.

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Dielectric relaxation of polystyrene with side-chain- and chain-end-labels

Cited by 8 publications

References 13 publications

Effect of Block Position on the Dynamics of the Glass Processes in Carbonate/Styrene Triblock Copolymers, CSC and SCS

Effect of Block Position on the Dynamics of the Glass Processes in Carbonate/Styrene Triblock Copolymers, CSC and SCS

Glass Transition Temperature and β Relaxation Temperature around Chain End of Polystyrene Determined by Site Specific Spin Labeling

Correlated Segmental Dynamics in Amorphous Atactic Polystyrene: A Molecular Dynamics Simulation Study

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