Polymerization of liquid sulfur

Finally, the data published by Gee (30) permit one to evaluate the sharpness of a transition involving floor temperature. Gee studied the temperature dependence of the viscosity of liquid sulfur and observed its sudden, steep increase at a critical temperature followed by its decrease at still higher temperatures. He developed the first, relatively complete theory of equilibrium polymerization of liquid sulfur (30) from which he estimated the chain length of the polymeric sulfur at various temperatures. His results have been recently confirmed by experimental measurements of magnetic susceptibility of the liquid sulphur (50) and its electron spin resonance (57). 

Three different kinds of experiments can be used to study the polymerization of liquid sulfur and selenium. First, those which lead to direct results without any parameter adaptation are represented in 15.2.2.3 and 15.2.2.5, Figs. 1 and 2. Second are those where the measured quantity is linearly dependent on the ring-chain composition of the liquid, but where the value of the quantity for a pure polymer is not known. Here the difference of this quantity between eight-membered rings and chains must be adapted. This means that for a quantity Aj, measured as a function of T, we use ... 

Similar p-T relationships exist also in the liquid state in sulfur, selenium, and tellurium. Gee (37) has studied the polymerization of liquid sulfur extensively. At high temperatures at atmospheric pressure all three elements show a thermally induced dissociation of the liquid chain structure with a gradual change toward a lower resistance liquid (38,39, 40,41,42), In the liquid state p-T reaction boundaries have been observed in sulfur (18, 43) and tellurium (31, 44). For sulfur these are consistent with the high temperature atmospheric-pressure data (39,40). For tellurium, however, the low pressure extrapolation of the liquid boundaries must be nonlinear to achieve consistency. The p—T reaction boundaries in the liquid for sulfur are plotted in Figure 1. 

Using the first-principles molecular-dynamics simulation, Munejiri, Shimojo and Hoshino studied the structure of liquid sulfur at 400 K, below the polymerization temperature [79]. They found that some of the Ss ring molecules homolytically open up on excitation of one electron from the HOMO to the LUMO. The chain-like diradicals S " thus generated partly recombine intramolecularly with formation of a branched Sy=S species rather than cyclo-Ss- Furthermore, the authors showed that photo-induced polymerization occurs in liquid sulfur when the Ss chains or Sy=S species are close to each other at their end. The mechanism of polymerization of sulfur remains a challenging problem for further theoretical work. 

Abstract Molecular spectroscopy is one of the most important means to characterize the various species in solid, hquid and gaseous elemental sulfur. In this chapter the vibrational, UV-Vis and mass spectra of sulfur molecules with between 2 and 20 atoms are critically reviewed together with the spectra of liquid sulfur and of solid allotropes including polymeric and high-pressure phases. In particular, low temperature Raman spectroscopy is a suitable technique to identify single species in mixtures. In mass spectra cluster cations with up to 56 atoms have been observed but fragmentation processes cause serious difficulties. The UV-Vis spectra of S4 are reassigned. The modern XANES spectroscopy has just started to be applied to sulfur allotropes and other sulfur compounds. 

Fig. 8. Equilibrium composition (weight-%) of liquid sulfur in the temperature region 115-350 °C according to spectroscopic investigations after rapid quenching to —196 °C. S, represents the fraction of rings soluble in CSj and with x > 8 is the insoluble, polymeric fraction. Two scales have been used on the ordinate...

The melting point of /3-Ss (120 °C) is reversible only if the freshly produced melt is cooled down immediately before the last crystal has disappeared. If the melt is kept for some hours at temperatures above 120 the freezing point is observed at a constant temperature of 115 °C (triple point). This phenomenon is explained by the formation of novel low molecular weight molecules S with n 8. In the older literature these molecules have been termed collectively as r-sulfur or (in contrast to Ss which was termed A-sulfur [17]). In addition, polymeric sulfur Soo is a component of liquid sulfur at all temperatures. After isolation from the melt the polymer is usually called //-sulfur [17] or S. In the following sections we will show how the molecular nature of r-sulfur has been found out and how the physical properties of hquid sulfur can be understood on the basis of the rather complex but very interesting molecular composition. 

Table 1 Polymerization temperature of liquid sulfur as a function of the heating rate start-...

Dilution of liquid sulfur with an inert organic solvent shifts the polymerization temperature to higher values. 

Ludwig et al. have tried to model the composition of liquid sulfur by quantum-chemical calculations [97] which is not accurately possible since the polymeric molecules—a major component above 159 °C—cannot be calculated. Therefore, the results are of little use and no novel insights were achieved. 

From measurements of the dielectric constant of liquid sulfur in the temperature range 134-206 °C [15] it was concluded that the molar polarization increases from 134-159 °C which was explained by the assumption of a temperature dependent equilibrium between Ss(crown) and Ss(chair) molecules, the latter possessing a permanent dipole moment owing to their low symmetry (Cs). However, the most natural rationalization of the findings is that certain components of r-sulfur like Sy and Sg—molecules of low symmetry possessing a dipole moment—contribute to the molar polarization. Since their concentration increases with temperature up to the polymerization transition it is to be expected that the molar polarization changes accordingly. Above 159 °C the molar polarization is proportional to the polymer content of the melt. 

Numerous authors have tried to model the equilibrium composition and the related physical properties of liquid sulfur theoretically assuming certain reversible reactions and adjusting the thermodynamic functions AH° and AS° in such a way that the polymerization behavior, that is the polymer content of the melt at various temperatures as known at the particular time, could be simulated or explained . In almost all cases, however, the melt was considered to consist entirely of Ss rings (Ss ) and polymeric chain-like diradicals (Sx ). The other small and/or medium sized rings were neglected despite the fact that at the time there was already experimental evidence available for the presence of such species in liquid sulfur. Nevertheless, we will discuss some of these theories or models here to illustrate the complexity of the problem. 

The very first reported PHOST that is transparent in the DUV was prepared by thermolysis or acidolysis of PBOCST, which is in turn prepared via radical polymerization of the BOCST monomer by 2,2-azobis(butyronitrile) (AIBN), benzoyl peroxide (BPO), or other radical initiators. The BOCST monomer can be prepared by the Wittig reaction on a protected 4-hydroxybenzaldehyde with a rather high yield due to the good stability of the t-BOC group toward a base cata-lyst. " The PBOCST polymer thus obtained is readily converted to PHOST by heating the polymer to 200°C or by treating the polymer with an acid such as acetic acid or HCl in solution. And PBOCST can be synthesized via cationic polymerization in liquid sulfur dioxide. ... 

PBOCST is readily synthesized from the polymerization of r-hutoxycarhonyl oxystyrene via radical or cationic polymerization in liquid sulfur dioxide or alternatively by reacting poly(hydroxystyrene) with di-tert-h xty dicarbonate in the presence of a base PBOCST polymers with narrow dispersity have been prepared by living anionic polymerization of 5-tert-butyl(dimethyl)silyloxystyr-ene), followed by desilylation with HCl to form PHOST and protection with di-tert-butyl carbonate PBOCST is very transparent around the 250-nm region of the spectrum (absorbance <0.1/ p,m), thus making it an ideal candidate for DUV 248-nm lithography. 

To an 8.0 ounce pressure polymerization bottle or Hoke cylinder are added 160 ml of water, 1.0 gm sodium lauryl sulfate, 0.25 gm ammonium nitrate, and 50 gm (0.78 mole) of liquid sulfur dioxide. The temperature is lowered to... 

Radical Co- and Terpolymerization of Norbornenes with SO2. A typical polymerization procedure is described below. The fluoroalcohol monomer la (2.74 g, 0.01 mol) was placed in 25 mL of liquid sulfur dioxide at -60 to which were added... 

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