Polystyrene, deuterated

Our measured B value for i-PS/l%PEC is generally more exothermic than the estimate obtained by Macon-nachie, et al. (39) from neutron scattering in diluted atactic polystyrene/deuterated PPO systems. They obtain an equation. 

Fig. 15.4. Representation of experimental results of neutron scattering by blends of atactic polystyrenes, deuterated and non-deuterated. (From Tangari et al.9.)...

Benoit and coworkers [9] have furnished experimental support for the affine deformation of rubber networks. They carried out neutron scattering experiments on polystyrene/deuterated polystyrene polymers. Their analysis of the neutron scattering data showed that network structures do deform affinely. More recently, Han, Yu and coworkers... 

For a polymer pair that would undergo phase separation at high relative molecular masses, such as an isotopic polymer mixture like polystyrene/ deuterated polystyrene, this criterion means that one would have to approach closer to the critical point than about 0.05 °C for these fluctuation effects to be important. Even for much more strongly immiscible pairs, that undergo phase separation at much lower relative molecular masses, the non-classical region will be within only a few degrees of the critical point (Schwahn et al. 1987, Bates et al. 1990). This is in sharp contrast to the situation for small-molecule liquids, for which fluctuations must always be taken into account in order to predict the phase behaviour. Mean-field theories - neglecting bulk concentration fluctuations - often can be expected to work quite well for polymers. 

So far, the tacticity effect on polymer mixtures has been investigated mainly for the special systems where hydrogen bonding interaction is dominant, such as poly (vinyl chloride)/poly(methyl metacrylate) (PVC/PMMA) [1] or poly-styrene/poly(vinyl methyl ether) (PS/PVME) [2] mixtures. However, recently, there has been an interest in the effect of tacticity on polymer mixtures without specific interaction such as polyolefin/polyolefin [3] or polystyrene/ deuterated polystyrene mixtures [4,5]. 

Fig. XI-7. Volume fraction profile of 280,000-molecular-weight poly(ethylene oxide) adsorbed onto deuterated polystyrene latex at a surface density of 1.21 mg/m and suspended in D2O, from Ref. 70.

Figures (a) Scattering geometry for ERS (b) ERS spectrum from 200-A partially deuterated polystyrene on Si, E h 3.0 MeV (adapted from ref. 101 and (cl schematic ERS depth profile spectrum.

The main experimental techniques used to study the failure processes at the scale of a chain have involved the use of deuterated polymers, particularly copolymers, at the interface and the measurement of the amounts of the deuterated copolymers at each of the fracture surfaces. The presence and quantity of the deuterated copolymer has typically been measured using forward recoil ion scattering (FRES) or secondary ion mass spectroscopy (SIMS). The technique was originally used in a study of the effects of placing polystyrene-polymethyl methacrylate (PS-PMMA) block copolymers of total molecular weight of 200,000 Da at an interface between polyphenylene ether (PPE or PPO) and PMMA copolymers [1]. The PS block is miscible in the PPE. The use of copolymers where just the PS block was deuterated and copolymers where just the PMMA block was deuterated showed that, when the interface was fractured, the copolymer molecules all broke close to their junction points The basic idea of this technique is shown in Fig, I. 

We present here a simple experiment, conceived to test both the reptation model and the minor chain model, by Welp et al. [50] and Agrawal et al. [51-53]. Consider the HDH/DHD interface formed with two layers of polystyrene with chain architectures shown in Fig. 5. In one of the layers, the central 50% of the chain is deuterated. This constitutes a triblock copolymer of labeled and normal polystyrene, which is, denoted HDH. In the second layer, the labeling has been reversed so that the two end fractions of the chain are deuterated, denoted by DHD. At temperatures above the glass transition temperature of the polystyrene ( 100°C), the polymer chains begin to interdiffuse across the... 

Fig. 6. The ripple experiment at the interface between a bilayer of HDH- and DHD-labeled polystyrene, showing the interdifussion behavior of matching chains. The protonated sections of the chain are marked by filled circles. The D concentration profiles are shown on the right. Top the initial interface at / = 0. The D concentration profile is flat, since there is 50% deuteration on each side of the interface. Middle the interface after the chain ends have diffused across (x < / g). The deuterated chains from Que side enrich the deuterated centers on the other side, vice ver.sa for the protonated sections, and the ripple in the depth profile of D results. A ripple of opposite sign occurs for the H profile. Bottom the interface when the molecules have fully diffused across. The D profile becomes flat [20,56].

Fig. 5. Hydrogen depth profile of a deuterated polystyrene PS(D) film deposited on a protonated polystyrene PS(H) film on top of a silicon wafer as obtained by l5N-nuclear reaction analysis ( 5N-NRA). The small hydrogen peak at the surface is due to contamination (probably water) of the surface. The sharp interface between PS(D) and PS(H) is smeared by the experimental resolution (approx. 10 nm at a depth of 80 nm) [57], The solid line is a guide for the eye...

The resolution of infra-red densitometry (IR-D) is on the other hand more in the region of some micrometers even with the use of IR-microscopes. The interface is also viewed from the side (Fig. 4d) and the density profile is obtained mostly between deuterated and protonated polymers. The strength of specific IR-bands is monitored during a scan across the interface to yield a concentration profile of species. While in the initial experiments on polyethylene diffusion the resolution was of the order of 60 pm [69] it has been improved e.g. in polystyrene diffusion experiments [70] to 10 pm by the application of a Fourier transform-IR-microscope. This technique is nicely suited to measure profiles on a micrometer scale as well as interdiffusion coefficients of polymers but it is far from reaching molecular resolution. 

Bruder and Brenn (1992) studied the spinodal decomposition in thin films of a blend of deuterated polystyrene (dPS) and poly(styrene-co-4-bromostyrene) (PBrxS) by TOF-ERDA. They examined the effect of different substrates on the decomposition process. In one series of experiments, a solution of the polymers in toluene was spread on a silicon wafer to form a film of thickness 550 nm which was then heated in vacuum at 180°C for various times. 

Zink et al. used a blend of polystyrene (hPS) and its deuterated counterpart (dPS), both of molecular weight 1.95 x 106 (abbreviated 1.95 M). The average volume fraction (4>dPS) of deuterated polystyrene was 30%. The polymers were dissolved in toluene and spin cast on thin silicon wafers (about 10 x 10 mm), the resulting film thickness being about 300 nm. The samples were annealed at 245°C for 8 days, and the measurement of the resulting depth profiles was conducted by NRA using a monoenergetic 700 keV 3He beam. The nuclear reaction employed can be written ... 

Rouse behavior observed on PI homopolymer melts has to be modified if the labelled (protonated) PI species are replaced by diblock copolymers of proto-nated PI and deuterated polystyrene (PS) [46]. The characteristic frequency Q(Q) is slowed down considerably due to the presence of the non-vanishing X-parameter. Thus, the reduction is stronger at smaller Q-values or at larger length scales than in the opposite case. In addition, as a minor effect, Q(Q) becomes dependent on both friction coefficients per mean square monomer length, //2, valid for PI and for PS. 

Fig. 53. Small-angle neutron scattering data from the 12-arm polystyrene star PS120A (Mw = 1.49 x 105) where the 11 deuterated arms were matched by the solvent THF. In order to demonstrate the asymptotic Q behavior, the data are plotted in a generalized Kratky representation (Iq01 vs. Q with a = 1.5 and 5/3). The solid line marks the high Q-plateau. (Reprinted with permission from [149]. Copyright 1989 American Chemical Society, Washington)...

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. 

The method of microstructure analysis with the a-deuterated derivative was successfully applied to poly-tertiarybutylethylene oxide-a-d ((53), but could not be applied to polystyrene oxide due to overlapping of absorption bands (64). 

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