Copolymers ceiling temperatures

An inportant feature of olefin-S02 polymerizations is their relatively low ceiling temperatures the reverse reaction becomes evident at quite low temperatures. In fact, it is while studying such copolymers that Dainton and Ivin in 1948 ( ) first clearly recognized the existence of ceiling temperatures in vinyl polymers. The reversibility of the propagation has important effects on the composition of the chains, which, as we shall see, exhibits a very... 

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... 

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. 

Poly(2-methyl-1-pentene sulfone) (PMPS) is an alternating copolymer of 2-methyl-l-pentene (2MP) and sulfur dioxide. The formation of PMPS occurs only by a free radical polymerization mechanism and is complicated to a degree by ceiling temperature considerations. For all exothermic addition polymerization reactions there is a critical temperature called the ceiling temperature (Tc) above which no reaction occurs. The precise Tc depends upon the monomer concentration according to the expression (i)... 

H5P, an a-methylstyrene derivative, seems to have a low ceiling temperature and consequently did not homopolymerize but underwent copolymerization with styrene, methyl methacrylate, and n-butyl acrylate. Based on the homopolymerization attempts, it appears that 2H5P is present as isolated monomer units in these copolymers. The co-polymerization parameters of 2H5V and 2H5P with styrene, methyl methacrylate, and n-butyl acrylate have also been determined. The results are shown in Figure 3 The copolymerization experiments were done to 5 conversions. 

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). 

The use of poly(olefin sulfones) in resist applications was first demonstrated by Bowden and Thompson at Bell lahoratories. They prepared them hy radical copolymerization of (liquid) SO2 with a whole range of olefins, at reaction temperatures deliberately kept low because of the low ceiling temperatures of poly(afk-ene sulfones). For poly(butene sulfone), Tc 64°C. The resulting copolymers possess a regular 1 1 alternating composition. 

Matthews and Strange [42] reported a similar reaction of isoprene with sulfur dioxide in the presence of hydrogen chloride. Seyer and King [Id] reported that 1,3-cyclohexadiene reacted with sulfur dioxide to give a white amorphous compound, as earlier reported by Hofmann and Damm [43]. 2-Methyl- and 4-methyl-1,3-pentadiene were reported by Morris and Van Winkle [44] to react with sulfur dioxide to yield a cyclic sulfone and some hydrocarbon polymer. Starkweather [45] in 1945 reported that chloroprene (2-chloro-l,3-butadiene) reacted with sulfur dioxide in an emulsion system to give a copolymer. Poly-sulfone is the major product when radical initiators are used. Cyclic products predominate when radical inhibitors (hydroquinone) or temperatures in excess of the ceiling temperature are used. For example ... 

The depolymerization can be prevented by incorporating monomeric units with higher thermodynamic ceiling temperatures into the polymer. Thus, a-methyl styrene/methyl methacrylate copolymers have achieved a certain commercial importance as heat-stable, transparent polymers for special applications. 

The copolymer compositions versus the monomer concentration in a CSTR for SAN (styrene acrylonitrile) and AMS-AN (alphamethyl-styrene-acrylonitrile) copolymers are shown in Figure 10.2. The copolymer composition equation changes for AMS-AN copolymers, as explained in detail in Chapter 12, due to the lack of AMS-AMS propagation reactions. The azeotropic compositions for SAN and AMS-AN copolymers with and without the ceiling temperature effects are shown... 

Entropy, enthalpy, and free energy of reversible polymerization Arrhenius relationship for rate constants Subcritical damped oscillations during thermal polymerization Polyrate of terpolymerization of AMS-AN-Sty Enthalpy of random copolymers Effect of chain sequence distribution Entropy and free energy of copolymerization Copolymer composition with and without ceiling temperature effect... 

FIGURE 12.3 The copolymer composition as a function of monomer composition with one monomer with lower ceiling temperature. 

The ceiling temperature of the copolymer can be derived in the same manner as for homopolymers as given by Equation (12.43). The conversions of the comonomer when the free energy expression becomes negative are the conditions when the reactions become favorable for occurrence. The stability of the reactions can be calculated from the spinodal condition that... 

Three types of copolymerization can be expected (1) both monomers have high ceiling temperatures (2) one monomer has a low ceiling temperature (3) both monomers have low ceiling temperatures. The copolymer composition equation was modified for a system where reversible reactions are pronounced. 

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