Copolymerization above ceiling temperature

An interesting feature of the styrene-S02 system, —which indeed is true of all SO2 copolymerizations with comonomers capable of homopolymerizing—, is the existence of a ceiling temperature above which the formation of alternating units, SMS, is forbidden. The number fraction of M sequences of length n is... 

Aldehyde Copolymer Self Developing Electron-beam Resists. The ceiling temperature for the copolymerization of aliphatic aldehydes is usually below 0°C and the copolymers are easily depolymerized into monomeric aldehydes above 150°C under vacuum. This depolymerization into monomers also occurs on electron-beam or X-ray exposure as evidenced by combined gas-liquid partition chromatography-mass spectrometry. As a result, the copolymers of aldehydes behaved as self-developing positive resists and almost complete development was accomplished without any solvent treatment. Electron-beam exposure characteristics of the aliphatic aldehyde copolymers studied here are... 

A typical example showing that we are able to build macromolecules at will is given by C. P. Pinazzi and co-workers in the first chapter of the second section, Chapter 27. They report how model polyenes can be built and how they react. In Chapter 28 K. F. O Driscoll illustrates the limitations in polymerization. For every vinyl monomer, a ceiling temperature exists, above which depropagation exceeds polymerization. If two vinyl monomers are copolymerized at a temperature at which one depropa-gates, the polymer formed will have an unusual composition and sequence distribution. 

For every vinyl monomer there exists a ceiling temperature above which it is thermodynamically impossible to convert monomer into high polymer because of the depropagation reaction. If two vinyl monomers are copolymerized under conditions such that one or both may depropagate, the resultant polymer will have an unusual composition and sequence distribution. Existing theoretical and experimental works are reviewed which treat of copolymer composition, rate of copolymerization, and degree of copolymerization. 

Copolymerization is characterized by a ceiling temperature of 64°C. above which no polymerization takes place. 

Melt copolymerization requires high temperatures (T > 200 °C). In spite of the six-membered ring it has the extrapolated ceiling temperature T = 1800 °K, well above the decomposition temperature 43). Polyglycolide (mp = 224-226 °C) is converted into multifilament yam by usual melt-spinning and -drawing procedures giving products with tenacities (5-10 g/den) close to polyethyleneterephtalate fibres. 

The copolymerization of BCMO with THF above its ceiling temperature will be examined. The more reactive THF forms alternating copolymer only above 60 mol % content of THF in the mixture. At lower THF concentrations BCMO-BCMO dyads are also formed 33). 

In a similar manner vinyl f-butyl carbonate copolymerizes with SO2 [61b]. Vinyl f-butyl carbonate and vinyl acetate have the same ceiling temperature ( —20°C), as was observed in the VAc/SOa copolymerization. No polymer is obtained above this temperature and the yield of polymers increases as the temperature is lowered to — 80°C (85% yield). 

Figure 22-2. Free radical copolymerization of Ma (methyl methacrylate or methyl acrylate) with Mb (a>methoxystyrene) at 60 C. Since the copolymerization is carried out above the ceiling temperature of a-methoxy styrene, no di-, tri-, etc. sequences of this monomeric unit can be formed because of the rapid depolymerization. The copolymerization parameter rs is then equal to zero, and the resit is a simple alternating copolymerization. (After data by H. Liissi.)...

Chloral, CChCHO, can be anionically or cationically polymerized. The polymerization is initiated above the ceiling temperature of 58° C and then allowed to proceed well below the ceiling temperature. Phosphines and lithium /-butoxide are especially suitable as anionic polymerization initiators, whereas tertiary amines only produce poly (chlorals) of low thermal stability. Anionic copolymerization of chloral with excess isocyanates produces alternating polymers, as is also the case for the cationic copolymerization of chloral with trioxan. 

Bates and Alfrey prepared SAMS copolymer by using AMS itself as the solvent at temperatures above 60°C, the ceiling temperature of poly(AMS). The normally slow AMS copolymerization was accelerated by the large excess of AMS. At the same time, long sequences of AMS could not enter the copol-... 

Equilibrium Copolymerization of Tetrahydrofuran Above Its Ceiling Temperature with Oxetanes 65... 

Assuming the above statements are correct, any two p-xylylene species should be capable of copolymerization in any desired ratio. This is somewhat of a simplification since it has been observed that for each substituted p-xylylene there is a definite ceiling condensation temperature above which it will not condense and polymerize at any appreciable rate. Thus, if the monomer does not condense, it is not available for copolymerization. This was demonstrated in the studies described earlier of the pyrolysis of acetyl-di-p-xylylene and separation of the monomers VI and VII on the basis of widely differing Tc s. 

---