Tetrahydrofuran polymerisation

Initiation of tetrahydrofuran polymerisation by Ph C SbClg has been studied speetrophotometrieally by Ledwith and co-workers (20). Decay of the characteristic triphenylmethyl cation absorption, in methylene chloride was represented by the expression... 

Polyether Polyols. Polyether polyols are addition products derived from cyclic ethers (Table 4). The alkylene oxide polymerisation is usually initiated by alkah hydroxides, especially potassium hydroxide. In the base-catalysed polymerisation of propylene oxide, some rearrangement occurs to give aHyl alcohol. Further reaction of aHyl alcohol with propylene oxide produces a monofunctional alcohol. Therefore, polyether polyols derived from propylene oxide are not truly diftmctional. By using sine hexacyano cobaltate as catalyst, a more diftmctional polyol is obtained (20). Olin has introduced the diftmctional polyether polyols under the trade name POLY-L. Trichlorobutylene oxide-derived polyether polyols are useful as reactive fire retardants. Poly(tetramethylene glycol) (PTMG) is produced in the acid-catalysed homopolymerisation of tetrahydrofuran. Copolymers derived from tetrahydrofuran and ethylene oxide are also produced. 

High molecular weight polymers are produced by an adiabatic bulk polymerisation process ° using di-tert-butyl peroxide (0.02%) and 2,2 -azo-bisdi-isobutyronitrile (0.01%) as initiators and pressurised with N2. Heating to 80-90°C causes an onset of polymerisation and a rapid increase in temperature. After the maximum temperature has been reached the mass is allowed to cool under pressure. A typical current commercial material (Luvican M.170) has a A -value of about 70 (as assessed in a 1% tetrahydrofuran solution). 

Some alkali metal complexes are also capable of initiating anionic polymerisation. For example, sodium and naphthalene in tetrahydrofuran is a homogeneous solution initiates polymerisation as follows ... 

Some polar monomers such as vinyl chloride, vinyl-acetate and acrylonitrile may be polymerised by this method using an active solvent such as tetrahydrofuran. 

The initiation reaction in the polymerization of vinyl ethers by BF3R20 (R20 = various dialkyl ethers and tetrahydrofuran) was shown by Eley to involve an alkyl ion from the dialkyl ether, which therefore acts as a (necessary) co-catalyst [35, 67]. This initiation by an alkyl ion from a BF3-ether complex means that the alkyl vinyl ethers are so much more basic than the mono-olefins, that they can abstract alkylium ions from the boron fluoride etherate. This difference in basicity is also illustrated by the observations that triethoxonium fluoroborate, Et30+BF4", will not polymerise isobutene [68] but polymerises w-butyl vinyl ether instantaneously [69]. It was also shown [67] that in an extremely dry system boron fluoride will not catalyse the polymerization of alkyl vinyl ethers in hydrocarbons thus, an earlier suggestion that an alkyl vinyl ether might act as its own co-catalyst [30] was shown to be invalid, at least under these conditions. 

The short-stop method of measuring [Pn ] was developed to produce an easily determinable end-group in systems in which the natural end-groups are unsuitable for accurate, quantitative determination. It was first used by Jaacks et al., (1968) to determine the concentration of tertiary oxonium ions during the polymerisation of 1,3-dioxolan, and by Saegusa et al., (1968) for similar studies on tetrahydrofuran. For the polymerisation of alkenes it has only been used on two occasions. 

Jaacks and co-workers [17], however, maintain that in these polymerisations the propagating species is a tertiary oxonium ion (VII), and they consider the propagation to be essentially the same as in the polymerisation of tetrahydrofuran, as is shown in Reaction (C). 

Amine initiated polymerisation is achieved by stirring the NCA with an appropriate amount of initiator in a suitable solvent, such as tetrahydrofuran. Over a period of time, the polymer precipitates and can be isolated by filtration. 

The chemical removal of water can be done in several ways. For anionic polymerisations it is customary to rinse all the glassware repeatedly with a solution of sodium naphthalide which reacts with water to form naphthalene and NaOH, both of which are adequately soluble in the usual solvent tetrahydrofuran (THF) at the low concentrations used. This method, however, requires that the whole reactor assembly be detachable from the vacuum line so that it can be tilted around for the sodium naphtalide solution to reach all parts of the system. Care If much water is to be removed and the volume of the purging solution is too small, some NaOH may be precipitated ). 

Drijvers and Goethals 52) have reported that excess sulphide functions (monomer and polymer) and diethyl ether have no detectable effect on the dissociation of two sulphonium tetrafluoroborate salts in methylene chloride and nitrobenzene, when present in similar proportions to those in corresponding polymerisation reactions. In contrast to this, however, Jones and Plesch 51) have shown that the dissociation constant of triethyloxonium hexafluorophos-phate in methylene chloride at 0°C increases by a factor of - 2 when small quantities of tetrahydrofuran are added. The latter molecule has a lower dielectric constant than methylene chloride and might therefore be expected to reduce dissociation. These workers have interpreted their results in terms of specific solvation of the cation by ether molecules, with subsequent reduction in the effective charge density of the positive ion and hence in the coulombic force favouring ion pairing, e.g. 

The bimolecular termination reaction can be neglected at low conversions since no linear sulphide residues are present initially, enabling a simpler interpretation of initial conversion/time curves to be made. In the earlier work the concentration of active centres was equated with the initial catalyst salt concentration, but later an XH NMR method of analysis was employed (137). As in the polymerisation of tetrahydrofuran it was anticipated that both free ions and ion pairs were likely to contribute to the propagation reaction and the calculated rate constant kP.pp e t, was described by... 

Wenger, F. Polymerisation of methyl methacrylate with sodium naphthalene and organo lithium compounds in tetrahydrofuran. Chem. and Ind., p. 1094. 

Explain why tetrahydrofuran can be concatenated into the polymer chain in copolymerisation systems with coordination catalysts. Give examples of copolymers and terpolymers, obtained by coordination polymerisation, that contain oxytetramethylene units in the main chain. 

Polyether polyols are usually produced by the polymerisation of ethylene or propylene oxide in the presence of a polyfunctional alcohol or amine as an initiator. Copolymers are also produced from mixtures of ethylene oxide and propylene oxide with di and tri -OH functionality. Polytetramethylene ether glycols (PTMEG) from tetrahydrofurans are also found. 

The use of ethers as cocatalysts for the cationic polymerisation of alkenyl monomers induced by Lewis acids has received little systematic attention and the mechanism through which these compounds operate is not well understood. The complex diethyl-ether-boron fluoride has been extensively used as a very convenient cationic initiator, but mostly for preparative purposes. As in the case of alcohols and water, ethers are known to act as inhibitors or retarders in the cationic polymerisation of olefins, if used obove cocatalytic levels, because they are more nucleophilic than most rr-donor monomers. Imoto and Aoki showed that diethyl ether, tetrahydrofuran, -chloro-diethyl ether and diethyl thioether are inhibitors for the polymerisation of styrene-by the complex BF3 EtjO in benzene at 30 °C, at a concentration lower than that of the catalyst, but high enough (0.5 x 10 M) to quench the active species formation for a time. Their action was temporary in that the quenching reaction consumed them, and therefore induction periods were observed, but the DP s of the polystyrenes were independent of the presence of such compounds, as expected from a classical temporary inhibition. 

Acylium hexafluoroantimonates have been successfully used as initiators in the polymerisation of tetrahydrofuran but little work has been undertaken to our knowledge to test their effectiveness for the polymerisation of olefins. Hesch and Padc discovered recently that some of these salts can induce the polymerisation of isobutene. This area of research diould provide much useful and fundamental information. 

Ledwith has recently speculated about the possibility of initiating cationic polymerisation using common free radical sources coupled with oxidising cations. This idea has already been put into practice in his laboratory and the successful polymerisation of vinyl ethers and tetrahydrofuran has been achieved with two systems ... 

AlkyIbismabenzenes have been prepared and although 4--methylbismabenzene (6) is more stable towards polymerisation than bismabenzene (3) it is still in mobile egulibrium in tetrahydrofuran with its head to head Diels-Alder dimer (7). 

Unfortunately, DMC catalysts are not efficient for EO polymerisation, and it is practically impossible to obtain PO-EO block copolymers with this catalyst. Acidic catalysts are not used on an industrial scale for alkylene oxide polymerisation due to the formation of substantial amounts of cyclic ethers as side products. Acidic catalysts are used industrially only for the synthesis of polytetrahydrofuran polyols or, to a lesser extent, for tetrahydrofuran - alkylene oxide copolyether polyol fabrication (see Sections 7.1, 7.2 and 7.3) Other catalysts have a minor importance for large scale polyether polyol production. 

Polytetrahydrofuran (PTHF) is a polyether obtained by cationic ring opening polymerisation of tetrahydrofuran (THF), a five membered cyclic ether ... 

Tetrahydrofuran (THF), the cyclic monomer used for the synthesis of polytetramethyleneglycols (see Chapters 7.1-7.3) by cationic ring opening polymerisation, was produced in the earlier stages of this technology from furfurol. Furfurol results from the acid hydrolysis of pentosanes existing in many agricultural wastes (corn on the cob, straw and so on). 

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