Poly thiol

Additional polythiocarbonate poly thiol derivatives of the current invention were prepared by the authors (1) and are described. 

The reported synthesis and properties of poly(thiol esters) of the A-B and A-A/B-B types are reviewed for these classes of compounds 2 poly(a-mercapto acids), 7 poly(/3-mercapto acids), 4 poly (e-mercapto acids) and 44 A-A/B-B type poly(thiol esters). The melting points of poly(thiol esters) are generally lower than those of the corresponding polyamides and higher than those of the polyesters. They are readily hydrolyzed by alkali, which seems to be the main reason for the lack of commercial interest in these materials. 

In terms of their properties, poly (thiol esters) lie between polyesters and polyamides. In polyesters, oxygen atoms can be replaced formally by sulfur in three different ways to give poly (thiol esters) (I), poly (thion esters) (II), and poly (dithio esters) (III). 

Poly (thiol esters) have been prepared by various methods, often analogous to preparation of polyesters, as is shown here. 

As with polyamides, it is useful to distinguish between poly (thiol esters) of the A-B type and the A-A/B-B type. Typical examples are poly(e-thiocaprolactone) (IV) and poly(hexamethylene dithiol tereph-thalate) (V). 

Thiolactones and substituted thiolactones with four to seven ring atoms have been prepared. Except for y-thiolactones, they have been polymerized. Other general procedures for making A-B type poly (thiol esters) are the internal addition reaction of w-unsaturated thio acids (VII),... 

The polymerization with strong bases yielded high-molecular-weight poly (thiol esters), which could be extruded to films and fibers. Some poly (thiol ester-coesters) are also described in the patent. 

Poly(8-mercapto acids). 8-Thiovalerolactone was polymerized in 21% yield to a linear poly(thiol ester)—UJ chci. = 14.7 ml/gram, m.p. 117°-118°C (17). The molecular weight of the polymer seems to be controlled by the monomer-polymer equilibrium. The same product (XXII) was obtained by distilling thiol-4-pentenoic acid (XXI) (19), giving the thiolactone (XXIII) as a by-product. 

The methods by which these poly (thiol esters) have been synthesized are summarized in Table V. Three other types of reactions exist that could also yield poly (thiol esters) ... 

Table VI gives the poly (thiol esters) made by the reactions mentioned in Table V. In several cases, information given about polymer...

Poly (thiol esters) from Dibasic Acids and Dimercaptans (Reaction A/M). By this procedure (26), only low molecular weights were obtained because of side reactions. The reaction has therefore not found wider application, compared with the synthesis of polyesters. 

This is the most widely used reaction to produce poly (thiol esters) of the A-A/B-B type (27, 28, 29, 32, 33, 34). The polymerization process can be carried out three different ways ... 

A number of poly (thiol esters) have been synthesized by method BC (29). The reaction temperature was increased from room temperature to above 200°C. The products were often colored because of side reactions (replacement of hydroxyl with chlorine, formation of ketene structures, and ester pyrolysis are known side reactions in polyester formation). 

Some all-aromatic poly (thiol esters) have also been prepared by this method (34). There is also a continuous process for interfacial condensation polymerization by which poly (thiol esters) with high inherent viscosities have been produced (27). 

The molecular weights of the poly (thiol esters) increased with decreasing water solubility of the dithiolcarboxylic acid. Initiation with hydrogen peroxide gave higher molecular weights than did initiation... 

High-molecular-weight poly (thiol esters) show fiber-forming properties. This section covers the available data concerning melting points, crystallinity, solubility, and stability of this class of esters, and compares them with polyesters and polyamides. Information about spectra is also reviewed. 

The melting points of poly (thiol esters) lie between those polyesters and polyamides (Figures 1-4). They melt 30° to 70°C higher than do the corresponding polyesters, the shape of the curves being very similar. This behavior is most likely because of a decreased flexibility O O... 

The melting points of aliphatic poly (thiol esters) (Figures 2 and 3) lie below that of polyethylene (143°C) and tend to increase with... 

The introduction of alicyclic parts into the poly (thiol ester) chain increases conformational rigidity and, consequently, the melting point. This can be seen from the melting points of poly(hexamethylene... 

All-aromatic poly (thiol esters), such as poly (4,4 -biphenylene dithiolterephthalate)(XXXII) have very high melting points (34). 

From these results, it is evident that a number of aromatic or alicyclic poly (thiol esters) have melting points suitable for making fibers. 

Crystallinity. Most poly (thiol esters) are quite crystalline. Crystallinity can be lowered by using nonlinear monomers—for example, HSCH2(C2H5)CH-(CH2)4SH (31)—or by copolymerization (29). The x-ray pattern of a uniaxially oriented poly( -thiocaprolactone) (17) indicates that this polymer adopts a planar structure with extended chains. 

Solubility. The sparse data available show no marked difference between polyesters and poly (thiol esters) in their behavior toward organic solvents. Good solvents for many poly (thiol esters) are chlorinated hydrocarbons, phenol, and organic acids such as dichloroacetic acid. With the exception of poly(thioglycolide) (4) and poly(thiolac-tide) (II), the problem of degradation by organic solvent action was not studied systematically. Solubility is increased in poly (thiol ester coesters) (34). 

Applying results from low-molecular-weight thiolesters and esters to the corresponding polymers should give slightly slower acid hydrolysis, equally fast alkaline hydrolysis, and a much faster aminolysis of poly-(thiol esters) compared with polyesters (24, 35, 36). 

No data are available concerning the thermal stability of poly (thiol esters). 

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