Tetrahydrofuran polymerization behaviors

The oxolane (tetrahydrofuran) ring system can be incorporated into polymers either by polymerization of the suitably substituted heterocycle itself or by addition polymerization of a dihydrofuran derivative. A prime example of the former case is found in the utilization, as a component of adhesives and coatings for example, of the acrylate (38) and methacrylate (39) esters of tetrahydrofurfuryl alcohol. Although the bulk of the investigations concerning these monomers is recorded in the patent literature, a detailed study of the polymerization behavior of ester (39) has appeared (74MI11101) that indicates it is a fairly typical methacrylate monomer. 

Epoxides readily undergo anionic copolymerization with lactones and cyclic anhydrides because the propagating centers are similar—alkoxide and carboxylate [Aida et al., 1985 Cherdron and Ohse, 1966 Inoue and Aida, 1989 Luston and Vass, 1984]. Most of the polymerizations show alternating behavior, with the formation of polyester, but the mechanism for alternation is unclear. There are few reports of cationic copolymerizations of lactones and cyclic ethers other than the copolymerizations of [5-propiolactone with tetrahydrofuran and... 

Saegusa, T., S. Matsumoto, T. Ueshima, and H. Imai Preprint of paper Polymerization of tetrahydrofuran by AlEt3—H20-promotor system, behavior of promotor given at International Symposium on Macromolecular Chemistry, Japan, 1966. 

Pseudoliquid-phase catalysis (bulk type I catalysis) was reported in 1979, and bulk type II behavior in 1983. In the 1980s, several new large-scale industrial processes started in Japan based on applications of heteropoly catalysts that had been described before (5, 6, 72) namely, oxidation of methacro-lein (1982), hydration of isobutylene (1984), hydration of n-butene (1985), and polymerization of tetrahydrofuran (1987). In addition, there are a few small- to medium-scale processes (9, 10). Thus the level of research activity in heteropoly catalysis is very high and growing rapidly. 

The influence of tetrahydrofuran on the propagation and association behavior of poly(isoprenyl)Iithiura in n-hexane has been examined47. As for the case of poly(styryl)lithium156), the rate of polymerization was found to first increase followed then by a decrease as the THF/active center ratio increased. This decrease ultimately reached the polymerization rate found in pure tetrahydrofuran at a THF active center ratio of ca. 2 x 103. This was for the case where the active center concentration was held constant and the tetrahydrofuran concentration varied. The maximum rate of polymerization was found to occur at a THF active center ratio of about 500 a value at which the viscometric measurements demonstrated 47 the virtual absence of poly(isoprenyl)lithium self-aggregation. As noted before in this review, the equilibrium constant for the process shown in Eq. (12) has the relatively small value of about 0.5 LM-1, which is in sharp contrast with the value of about 160 LM 1 found for the THF-poly(styryl)lithium system. The possibility of complexation of THF directly with the poly(isoprenyl)lithium aggregates, Eq. (13), was not considered by Morton and Fetters47. ... 

Initiation with Triphenylmethyl Cation. When tetrahydrofuran (THF) is used to dissolve triphenylmethyl hexachlorantimonate at room temperature, there is almost immediate decomposition of the triphenylmethyl cation (6). On the other hand, solutions of the trityl salt in THF can be prepared and stored as deep yellow solutions if maintained at temperatures around — 80°C. At room temperature the initial decoloration of the catalyst is followed rapidly by polymerization of the monomer to poly(tetramethylene oxide), and the actual percentage conversion depends markedly on the temperature. This behavior is typical of systems exhibiting monomer-polymer equilibria (28), and Table III shows values for the equilibrium conversion of monomeric THF to polymeric THF obtained with a variety of catalysts. As for vinyl ether polymerization, it is most convenient to use the trityl hexachlorantimonate salt however, recourse to Table III shows clearly that above room temperature this anion yields less than the expected equilibrium conversion monomer... 

The propagating species in the cationic polymerization can be examined from the copolymerization behavior (21). Cyclic ethers such as tetrahydrofuran (THF) or 3,3-bischloromethyloxetane (BCMO), and cyclic esters such as 0-propiolactone (/3-PL) or -caprolactone (c-CL) are classified as oxonium ion type monomers. Copolymerizations between these monomers are observed easily as in the case of BCMO-THF (12, 13), BCMO-/3-PL (14, 15), BCMO-c-CL (16), and THF- -CL (21). 

Because Reaction (24) is reversible, eventually all the carbenium salt is consumed in irreversible Reaction (25). Similar behavior was observed for polymerization of tetrahydrofuran initiated with trityl salts. In this case, however, hydride transfer from tetrahydrofuran molecule is followed by proton expulsion to form 2,3-dihydrofuran, which complicates the initiation mechanism [27,28] ... 

Viscosities of the polymeric materials were obtained in tetrahydrofuran with an Ubbelohde-type viscometer at 30.00 0.02 C. The infrared absorption spectra in the region of 400-4000/cm were measured for the sample by Hitachi Model EPI-G3 infrared spectrophotometer. The samples were prepared by the KBr pellet technique. The thermal behavior of the specimens was observed with a Rigakudenki DSC-TGA apparatus. The X-ray diffraction pattern of the powdered polymer was taken in the region of 3-37 by a Rigakudenki Model 3D-F X-ray diffractometer with the use of Ni-filtered copper K radiation. 

Currently known initiation methods for ring opening pol)rmerization are reviewed in a systematic way with special emphasis on their influence on the properties of the resulting polymer. The importance of the chemical elements that comprise each group of initiators is demonstrated and it is shown that the behavior of the initiators is related to the position of these chemical elements in the Periodic Chart of the Elements. The ring opening polymerization of tetrahydrofuran is used as a model for the review. 

Small angle neutron scattering (SANS) measurements were performed on poly(isoprene) networks at different uniaxial strains, i.e., 1,0 < X (extension ratio) <2.1. The networks were prepared from anionically polymerized, a, oo-dihydroxy-poly(isoprene) precursors (H-chains) and the corresponding poly(isoprene-dg) isotopic counterparts (D-chains), crosslinked in concentrated tetrahydrofuran solutions by trifunctional crosslinkers, tri-isocyanates. The two components of the radius of gyration of elastic strands, parallel and perpendicular to the strain axis, were determined from the vSANS data of the networks with 8% and 15% D-chains. Two molecular weights of D-chains, 26,000 and 64,000, crosslinked with approximately the same molecular weight H-chains (29,000 and 68,000 respectively) were examined for the deformation behaviors. 

---