Styrene in cyclohexane

V, is the molar volume of polymer or solvent, as appropriate, and the concentration is in mass per unit volume. It can be seen from Equation (2.42) that the interaction term changes with the square of the polymer concentration but more importantly for our discussion is the implications of the value of x- When x = 0.5 we are left with the van t Hoff expression which describes the osmotic pressure of an ideal polymer solution. A sol vent/temperature condition that yields this result is known as the 0-condition. For example, the 0-temperature for poly(styrene) in cyclohexane is 311.5 K. At this temperature, the poly(styrene) molecule is at its closest to a random coil configuration because its conformation is unperturbed by specific solvent effects. If x is greater than 0.5 we have a poor solvent for our polymer and the coil will collapse. At x values less than 0.5 we have the polymer in a good solvent and the conformation will be expanded in order to pack as many solvent molecules around each chain segment as possible. A 0-condition is often used when determining the molecular weight of a polymer by measurement of the concentration dependence of viscosity, for example, but solution polymers are invariably used in better than 0-conditions. 

Figure 15. Effect of segregation on polymerization of styrene in cyclohexane solution. Standard CSTR with h baffles and a 6-blade turbine, V = 670 cm, T = 75 °C. Dispersion Index DI vs. space time. Influence of agitation speed. Curves S (segregated flow) and M (well-micromixed flow) calculated from batch experiments. Initiator PERKAD0X l6, A = 0.033 mol L - -, kd = 5 x 10 5 s-1, f = 0.85 Mq = 6.65 mol L l, SQ = 2.22 mol IT1.

The formation of a styrene and a-methylstyrene anion, absorbing at about 390 m/x, was shown by Schneider and Swallow (23, 24, 25), even for conventionally purified monomers which had not been treated to remove traces of water. The nature and reactions of this transient were studied in more detail in dilute solutions of styrene in different solvents. A solution (10 3M) of styrene in cyclohexane showed, immediately after the pulse, a spectrum with a distinct absorption band at 390 m/x (Figure 1), similar to that observed by Keene et al. (14). However, the intensity of the absorption was irreproducible during a series of experiments, probably because of the varying moisture content of the air and of the... 

Figure 1. Absorption spectrum of a deaerated 10 3M solution of styrene in cyclohexane, taken immediately after a 2-fisec. pulse of —5000 rads...

Figure 2. Influence of small amounts (10 SM) of additives on the absorption spectrum of a 10 SM solution of styrene in cyclohexane dose rate —5000 rads/pulse...

The styrene anion was extremely short lived when cyclohexane and hexane were used as solvents, but contrary to the findings of Katayama et ah and of Metz et ah, Schneider and Swallow stated that the decay of the anion followed second-order kinetics with a first half-life of about 3—4 fisec. for styrene (10-3M) in cyclohexane and hexane. Evaluation of the decay curves at 390 m/x, led to values for k/e 7 X 106 cm. sec.-1 for styrene in the pure state and fc/c = 3.8 0.6 X 107 cm. sec.-1 for a 10-3A/ solution of styrene in cyclohexane. The decay kinetics were not influenced by varying the dose rate of the pulse by a factor of about 6, thus confirming that the decay is second order. If a G value of 0.2 is assumed for the formation of free ions in hydrocarbons, an extinction coefficient... 

For the last block, a styrene-in-cyclohexane solution is prepared and purged similar to the starting solution, and the proper amount is added by syringe directly into the polymerization bottle at 50°C. This portion of the polymerization is allowed to proceed for an additional 3 hours and is terminated by the addition of a few milliliters of methanol. The polymers are precipitated in methanol in a Waring Blendor, stabilized with 1% N-phenyl-/ -naphthylamine and dried in a vacuum oven. If the product is hydrogenated, the quench with methanol is not done and the cyclohexane solution of the polymer is used directly. 

Styrene and a-Methylstyrene in Organic Solvents. Pulse radiolysis studies have been made on styrene and a-methylstyrene dissolved in methanol, benzene, carbon tetrachloride, dioxane, tetrahydrofuran, hexane, and cyclohexane (9, 24, 29, 30, 31). The results are easiest to understand for the aliphatic hydrocarbons and especially for the styrene in cyclohexane, which has been studied the most (31). For such solutions, two absorption bands were seen after the pulse by Keene, Land, and Swallow (24) and Schneider and Swallow (30) with peaks at 320 and 390 m/. The absorption at 320 m/u disappeared slowly by complex kinetics, and the 390-m/x absorption was very short lived, decaying by second-order kinetics with k/c = 4-7 X 10 cm. sec.-1. The relative intensities of the two peaks were quite variable. Chambers et al. saw the long lived absorption at 320 m/, but did not see a separate peak at 390 m/a, although it was observed that the absorption at 375 mfi decayed rapidly with k/e = 2.6 X 106 cm. sec.-1. 

Table 4 Photophysical parameters of some styrenes in cyclohexane 41...

Effects of Structure and Temperature. Both the structure of a polymer and temperature conditions affect the formation and decay of exclmer emission In the polymers discussed above, and these observations can be rationalized by a consideration of the conformational requirements for exclmer formation In these polymers and model compounds. Table 3 reveals that exclmer formation Is favored In Isotactic poly(styrene) compared with the atactic polymer, although these results are In conflict with an earlier qualitative observation and Interpretation (50), or the 80% syndlotactlc polymer In cyclohexane. In Isotactlc poly(styrene) in cyclohexane, the preferred structure Is reported to be a 3/1 helix (61), which corresponds to the ground-state... 

From these data determine the second virial coefficient and the theta temperature of poly(a-methyl styrene) in cyclohexane, knowing that K = K hl AhlAcf, where K = 18.17 mol cm , the refractive index increment (d /dc) is 0.199 ml gr, and the temperature dependence of the refractive index is expressed by = -0.0005327 x T (°C) + 1.446. Static light-scattering measurements were carried out by Zimm (1948b) on polystyrene in butanone at 340 K at two concentrations. 

Figure 6-4. Dependence of the Flory-Huggins interaction parameter, x, on volume fraction, 2, of the polymer for poly(styrene) in cyclohexane and chloroform and for m-l,4-poly(isoprene) in benzene as well as for cellulose nitrate in acetone.

Figure 6-18. Determination of the theta temperature of poly(styrene) in cyclohexane from the critical temperature dependence on the degree of polymerization (after A. R. Schultz).

Fig. 14 Flow microreactor system for anionic polymerization of styrene in cyclohexane at 80°C initiated by s-BuLi. M T-shaped micromixer R microtube reactor...

Figure 16-1. Dependence of the monomer concentration at polymerization equilibrium on the temperature for a-methyl styrene in cyclohexane (from data from F. S. Dainton and K. J. Ivin) and thioacetone, TA (from data from V. C. E. Burnop and K. G. Latham). The temperature at which the molar concentration, [A/]b, of the pure monomer is reached is the thermodynamic transition temperature Tc...

The intrinsic viscosity [r ] of a polymer increases with rising solvent quality (see Solvent in Chap. 5) due to the increased solvating envelope of the polymer chain. An increased effective volume of the chain leads to an expansion of the polymer coil and therefore to an increased intrinsic viscosity (see Fig. 5.2). The solvent quality can also be seen in the exponent a of the [q]-M-relationship. In the case that the interactions of the solvent molecules with the chain are so small that the coil is not contracted or expanded, theta-conditions are reached and the coil has its unperturbed dimensions in solution. A theta solvent is referred to as a thermodynamically poor solvent. In this solution state a theoretical value for the exponent a=0.5 can be derived (the required Eqs. 8.22 and 8.33 are discussed in detail in A deeper insight into in Chap. 8). This value of a=0.5 is also experimentally observed as shown in Fig. 6.7 for the theta system poIy(styrene) in cyclohexane (T=34.5 C). 

The effects of lithium alkoxides on the rates of alkyllithium-initiation reactions depend on the solvent, the monomer, the alkoxide structure, the alkyllithium initiator, and the ratio of [RLi]/[LiOR l (49,50). For n-butyllithium initiation of styrene in cyclohexane, the rate of initiation is increased at low relative concentrations of added lithium alkoxide [ -C4H90Li]/[C4H9Li]< 0.5). At a ratio of 1/1, the rate is essentially the same as the control without alkoxide beyond this ratio, the rate decreases continuously with increasing relative concentration of lithium alkoxide. In aromatic solvents, the initiation rate decreases with increasing relative concentrations of lithium alkoxide. Lithium alkoxides generally accelerate the rate of initiation by alkyllithiums (n-butyllithium and sec-butyllithium) for isoprene in hexane. 

Figure 3.15. Hydrodynamic radius 1 h of different molecular weights of a polymer, a Polystyrene in 2-fluorotoluene at 42.6°C (good solvent). (From Ref. 30.) b Poly(a-methyl styrene) in cyclohexane at 30.5°C (theta solvent). (From Ref. 31.)...

C (good solvent), and panel b was obtained for poly(a-methyl styrene) in cyclohexane at 30.5°C (theta condition). In the two panels of the figure, the plots are on a straight fine, in agreement with the predicted power relationship, oc N. The exponents v obtained in the fitting are 0.567 and 0.484, shghtly smaller than the values predicted for the two enviromnents. 

In the addition reactions of P-NH2-C6H4-S and p-(Me)2N-C6H4-S with styrene and a-methylstyrene in various solvents, large solvent effects are observed on the forward and backward rate constants and the equilibrium constants [15]. The ka value for the reaction of /7-NH2-C6H4-S with styrene in cyclohexane is 2.2x 10 M s, which decreases to 3x lO M" s" in dimethyl sulfoxide (Table 9). 

A significant step forward was accomplished with the heteroleptic fluorenyl-benzylcalcium complex 11 (Fig. 3), which was obtained by reaction of the homoleptic benzylcalcium compound 9 with 9-Me3Si-fluorene. Compound 11 indeed allowed the syndioselective polymerization of styrene [31]. The PS obtained with the heteroleptic benzylcalcium initiator 11 under standard polymerization conditifMis (10 % of styrene in cyclohexane at 50 °C) was only slightly emiched in syndiotactic sequences. However, the syndiotacticity of the materials could be increased considerably by increasing the monomer concentration in fact, polymerization in neat styrene yielded PS with 85 % r-diads and 76 % rr-triads. 

For a listing of values see Table III of reference 43. A value of 2.5 x 10 for poly(a-methyl-styrene) in cyclohexane is derived from the combined data of Cowie JMG, Bywater S, Worsfold DJ (1967) Polymer 8 105 and Lindner JS, Hadjichristidis N, Mays JW (1989) Polym Commun 30 174. This is larger than the value for the same system reported in reference 43. Very recently d> = 2.4 X 10" has been measured for poly(a-methylstyrene) in cyclohexane (Li J, Mays JW, to be published)... 

Figure 2.6 Sedimentation in Theta polymer solvent systems from top to bottom, 950 (T), 390 ( ), and 110 (x) kDa polystyrene cyclopentane(16), 2.2 MDa (A) and 213 kDa ( ) branched polystyrene cyclohexane(15), 1.8 MDa (A) and 390 kDa (O) polystyrene cyclohexane( 15), 6.6 (A) and 1.0 ( ) MDa and 234 ( ) kDa polyCa-metiiyl styrene) in cyclohexane(17X with stretched-exponential fits. Arbitrary vertical shifts for clarity (hence, arbitrary units) were already supplied by Ref. (15).

X10" M seo-butyllithium with 8.67 x 10 M styrene in cyclohexane solution at40°C. From Bywater, S. Worsfold, D. J.d Organometal. Chem. 1967, tO, 1 reprinted by permission of Elsevier Science Technology Journals. 

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