Monomers dienic

The application of ultraviolet and visible spectroscopy to the identification and measurement of carbenium ions derived from aromatic and dienic monomer has already been discussed (see Sect. II-G-2). The use of this technique to monitor stable carbenium salts is also well known. We have finally stressed in a preceding section that the fate of certain anions could be followed spectrophotometrically during a cationic polymerisation. The limits of detection allowed by the values of the extinction coefficients of all these species and by the sensitivity of present-day instruments is 10 to 10 M. 

The only other dienic monomer studied in this context is sp/f )[2,4Ihepta-4,6-diene. Its polymerisation by various trityl salts was investi ted by Kunitake et al. in methylene chloride-toluene mixtures at —76°C. This study was entirely devoted to the alternative 1,2 and 1,4 propagation modes and no attention was given to the mechanism of initiation or other fundamental problems. 

It is very clear that if the initiator has hydroxyl groups, and if the termination takes place exclusively by recombination then a polymeric diol is obtained [2, 3], which is ideal for polyurethane. If the termination takes place by disproportionation, only monofunctional compounds are obtained, which cannot be used in PU. The vinylic and dienic monomers used in practice have various termination mechanisms. Some monomers give only recombination reactions, such as styrene, acrylates (methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethyl hexyl acrylate), acrylonitrile and butadiene. Other monomers give both mechanisms of termination, around 65-75% disproportionation and 25-35% recombination, such as methacrylates (methyl methacrylate, ethyl methacrylate, butyl methacrylate etc.), substituted styrenes and other monomers [2, 3, 4]. 

I 27 From Star-Like to Dendrimer-Uke Polymers For anionic polymerization of vinylic or dienic monomers... 

Unsaturated polymers, particularly of dienic monomers, undergo a number of interesting thermal rearrangements under non-pyrolytic conditions. Golub has studied these reactions in some detail and has recently reviewed the subject. In the past two years accounts of thermal rearrangements of l,2-poly(hexa-l,4-diene)s and l,2-poly(/ra 5-penta-l,3-diene) have appeared. The former polymers have a predominantly 1,8-diene structure and cyclize mainly by a [2 + 2] or type II mechanism accompanied by a small amount of a type III reaction (Scheme 24). The latter is more important in the trans-, A- than in the cir-1,4-isomer. The first unambiguous example of a type III reaction was provided by the polymer of penta-1,3-diene. Scheme 25 shows a macromolecular... 

We can also mention the production of polysulfide oligomers using dienic monomers as a raw material. The following reaction takes place [25] ... 

Unsaturated polymers,particularly of dienic monomers, undergo thermal rearrangements. Golub et distinguish three types of rearrangements. 

A comparison of the cationic polymerization of 2,3-dihydrofurans with that of furan and 2-alkylfurans shows that the complications of the latters two, arising from the dienic character of the monomers, obviously vanish when the monomer is a simple cyclic vinyl ether with just one reactive site, viz. the carbon-carbon double bond. However, it also points out that ring opening in the polymerization of furans by acidic catalysts in the absence of water is unlikely, because otherwise it would also occur to some degree in the polymerization of dihydrofurans. 

An alternate way to make block copolymers involving PDMS blocks 124,125) is to have these chains fitted with epoxide functions at chain end, and to react them with a vinylic or dienic polymer carrying terminal COOH functions. Sequential addition of monomers has also been used, the ring opening polymerization of the cyclic trimer (D3) being initiated by the anionic site of a living polymer126). 

The reactions of free radicals with furan and its derivatives can give both addition and substitution products depending on the specific system (11-13). With 2-substituted furans, the attack takes place predominantly at C5 and leads, by additon, to the corresponding furyl radicals which must be viewed as relatively stabilized interemediates because of the dienic-aromatic character of the furan heterocycle. These premises are essential to the understanding of the varied responses of furan monomers to free-radical activation. 

The first work was carried out by radiochemical polymerization of a mixture of dienic and acrylic monomers on a PVC latex. A parallel study by chemical means leads to equivalent products and the development of a reinforcing resin which satisfied the requirements listed above. At present a resin of this type is manufactured and sold by Pechiney-Saint Gobain under the name Lucovyl H 4010 (10). 

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