Polystyrene relaxation

We assume that the basic relaxation strengths in the polystyrene relaxation spectrum as described by Ferry and others [5], based on a Rouse-Bueche [6] model, are maintained in the ionomer. A normal wedge-box distribution is assumed. The ions are in multiplets below 6 mole % ionic groups [2]. If a segment... 

The data points and the minimized curves based on Equation 1 for the six styrene/MAA-Na copolymers with ionic mole fractions ranging from. 006 to 0.055 are given in Figures la and lb. A polystyrene relaxation curve is also shown. The values of the parameters used are listed in Table 1, together with the Tg s of the copolymers and the standard error of the fit. 

As we did in the case of relaxation, we now compare the behavior predicted by the Voigt model—and, for that matter, the Maxwell model—with the behavior of actual polymer samples in a creep experiment. Figure 3.12 shows plots of such experiments for two polymers. The graph is on log-log coordinates and should therefore be compared with Fig. 3.11b. The polymers are polystyrene of molecular weight 6.0 X 10 at a reduced temperature of 100°C and cis-poly-isoprene of molecular weight 6.2 X 10 at a reduced temperature of -30°C. 

The isothermal curves of mechanical properties in Chap. 3 are actually master curves constructed on the basis of the principles described here. Note that the manipulations are formally similar to the superpositioning of isotherms for crystallization in Fig. 4.8b, except that the objective here is to connect rather than superimpose the segments. Figure 4.17 shows a set of stress relaxation moduli measured on polystyrene of molecular weight 1.83 X 10 . These moduli were measured over a relatively narrow range of readily accessible times and over the range of temperatures shown in Fig. 4.17. We shall leave as an assignment the construction of a master curve from these data (Problem 10). 

Figure 4.17 Experimental stress relaxation moduli of polystyrene measured over about two orders of magnitude in time at the temperatures indicated. [Reprinted with permission from H. Fujita and K. Ninomiya, J. Polym. Sci. 24 233 (1957).]...

Example consider polystyrene with M = 245,000 and welded to itself at 118°C, the characteristic relaxation times are te 10 s, tro 21 min and Ty 1860 min [15], At these relaxation times, the respective average monomer interdiffusion distance is as follows [1 j ... 

Molecular Motion in amorphous atactic polystyrene (PS) is more complicated and a number of relaxation processes, a through 5 have been detected by various techniques as reviewed recently by Sillescu74). Of course, motions above and below the glass transition temperature Tg have to be treated separately, as well as chain and side group mobility, respectively. Motion well above Tg as well as phenyl motion in the glassy state, involving rapid 180° jumps around their axes to the backbone has been discussed in detail in Ref.17). Here we will concentrate on chain mobility in the vicinity of the glass transition. 

Fe(6-Mepy)2(py)tren] (004)2 Doped in PSS. Magnetic susceptibilities measured for a microcrystalline sample of the complex produce a magnetic moment value = 0.36 pg at 10 K and 0.61 pg at 150 K, followed by a gradual increase to Peff = 2.80 pe at 311 K [138]. Thus 26% of the complexes are in the HS state at 300 K if a magnetic moment of 5.1 Pe is assumed for the pure HS compound. On the other hand, the complex doped into a polystyrene sulfonate (PSS) film does not provide any evidence for a thermal population of the HS state up to 340 K as demonstrated by variable-temperature UV-VIS and Mossbauer spectra. In fact, all the complexes doped into the PSS film are in the LS state at temperatures below 340 K. However, if irradiated by a single pulse of a Q-switched Nd/YAG laser (532 mp), the complex is excited from the LS ground state to the HS J2 states via an intermediate MLCT state and the metal states. The subsequent back relaxation from the excited T2 state to the... 

The mechanical properties of two-phase polymeric systems, such as block and graft polymers and polyblends, are discussed in detail in Chapter 7. However, the creep and stress-relaxation behavior of these materials will be examined at this point. Most of the systems of practical interest consist of a combination of a rubbery phase and a rigid phase. In many cases the rigid phase is polystyrene since such materials are tough, yet low in price. 

Several attempts have been made to superimpose creep and stress-relaxation data obtained at different temperatures on styrcne-butadiene-styrene block polymers. Shen and Kaelble (258) found that Williams-Landel-Ferry (WLF) (27) shift factors held around each of the glass transition temperatures of the polystyrene and the poly butadiene, but at intermediate temperatures a different type of shift factor had to be used to make a master curve. However, on very similar block polymers, Lim et ai. (25 )) found that a WLF shift factor held only below 15°C in the region between the glass transitions, and at higher temperatures an Arrhenius type of shift factor held. The reason for this difference in the shift factors is not known. Master curves have been made from creep and stress-relaxation data on partially miscible graft polymers of poly(ethyl acrylate) and poly(mcthyl methacrylate) (260). WLF shift factors held approximately, but the master curves covered 20 to 25 decades of time rather than the 10 to 15 decades for normal one-phase polymers. 

Structural relaxation in glass-forming polymers has been studied for many years using chemically realistic simulations. Most of the early work that examined incoherent, as well as coherent scattering functions, is more of a qualitative nature because of the unsatisfactory quality of the force fields employed and the severe limitations on the length of the MD simulations performed. Roe studied the slowdown of structural relaxation in a PE-like model140,141 as well as for polystyrene.142 More recently Okada et al.143,144... 

The relaxation function has been calculated and is compared with experimental data in Figure 5.16. The agreement between the model and the data is reasonable. The storage and loss moduli for a polystyrene latex have also been measured and compared to the model for the relaxation spectra. The data was gathered for a dispersion in 10 2M sodium chloride at a volume fraction of 0.35 is shown in Figure 5.20. 

To the best of our knowledge, the supercoil conformation of the monoden-dron jacketed polystyrene is one of the first observations of a defined tertiary structure in synthetic polymers. The plectoneme conformation could be caused by underwinding or overwinding of a backbone from its equilibrium state [168]. Quick evaporation of the solvent certainly can cause a residual torsion in the molecule as it contracted in itself. Unlike macroconformations of biomolecules, where the tertiary structures are often stabilized by specific interactions between side groups, the supercoil of the monodendron jacketed polymers is metastable. Eventually, annealing offered a path for the stress relaxation and allowed the structural defects to heal [86]. 

The simplest motional description is isotropic tumbling characterized by a single exponential correlation time ( ). This model has been successfully employed to interpret carbon-13 relaxation in a few cases, notably the methylene carbons in polyisobutylene among the well studied systems ( ). However, this model is unable to account for relaxation in many macromolecular systems, for instance polystyrene (6) and poly(phenylene oxide)(7,... 

COMPARISONS OF INTERPRETATIONS OF METTHINE CARBON RELAXATION IN DISSOLVED POLYSTYRENE... 

The solvent mobility in atactic polystyrene-toluene solutions has been studied as a function of temperature using NMR. The local reorientation of the solvent was studied using deuterium NMR relaxation times on the deuterated solvent. Longer range motions were also probed using the pulsed-gradient spin-echo NMR method for the measurement of diffusion coefficients on the protonated solvent. The measurements were taken above and below the gel transition temperatures reported by Tan et al. (Macromolecules, 1983. 16, 28). It was found that both the relaxation time measurements and the diffusion coefficients of the solvent varied smoothly through the reported transition temperature. Consequently, it appears that in this system, the solvent dynamics are unaffected by gel formation. This result is similar to that found in other chemically crossed-linked systems. 

---