Tetrahydrofuran cationic polymerization

Cationic polymerization of tetrahydrofuran with the or bis(3,5-di-bromomethyl) benzoyl peroxide and AgPp6 pairs of 4,4 -bromomethyl benzoyl peroxide and AgPp6 yield active poly-THP having peroxide group in the main... 

With respect to the initiation of cationic chain polymerizations, the reaction of chlorine-terminated azo compounds with various silver salts has been thoroughly studied. ACPC, a compound often used in condensation type reactions discussed previously, was reacted with Ag X , X, being BF4 [10,61] or SbFa [11,62]. This reaction resulted in two oxocarbenium cations, being very suitable initiating sites for cationic polymerization. Thus, poly(tetrahydrofuran) with Mn between 3 x 10 and 4 x lO containing exactly one central azo group per molecule was synthesized [62a]. Furthermore, N-... 

Cationic polymerization of ethylene oxide is accompanied by depolymerization and oligomerization. It has been reported that ethylene oxide polymerized cation-ically with the living dication of tetrahydrofuran and a surface active material was obtained290. ... 

It has been shown for many metal halides and monomers that binary mixtures of these can be prepared (usually in a solvent) without any polymerization taking place. Such a quiescent mixture can be made to react by the addition of a suitable third compound, which is called the co-catalyst. This term is preferable to the word promoter , because in certain contexts a substance is called promoter which enhances the rate or yield of a reaction that will also go in the absence of the promoter herein lies the true distinction between promoter and co-catalyst [28]. (For example, small quantities of epoxides or epichlorohydrin act as promoters in the cationic polymerization of tetrahydrofuran.) I will take it that in the above quotation the word promoter was inadvertently used in place of co-catalyst , for only thus does it become really meaningful. 

On the other hand, in cyclic ethers (alkene oxides, oxetans, tetrahydrofuran) and formals the reaction site is a carbon-oxygen bond, the oxygen atom is the most basic point, and, hence, cationic polymerization is possible. The same considerations apply to the polymerization of lactones Cherdron, Ohse and Korte showed that with very pure monomers polyesters of high molecular weight could be obtained with various cationic catalysts and syncatalysts, and proposed a very reasonable mechanism involving acyl fission of the ring [89]. 

In this section, it should be mentioned that star poly(tetrahydrofuran) has been prepared by coupling cationically polymerized THF with multifunctional diethylenetriamine [92] in the presence of 2,2 6,6 tetramethylpiperidine as a proton trap. When the MW of poly(THF) is 1600 seven chains are added to the triamine, when the MW is 8000 a five-arm star has been obtained. 

Fig. 4. Rate of cationic polymerization of tetrahydrofuran to polyether at 0° C as function of monomer concentration. Reproduced, with permission, from Vofsi and Tobolsky J. Polymer ScL 3 A, 3261 (1965).

In the patent literature, there are several reports of the cationic polymerization of tetrahydrofuran (THF) with Nafion-H. In most cases, small amounts of acetic anhydride were added so the initial polymer had a terminal acetate group that could be hydrolyzed to the free hydroxyl. THF has also been homopolymerized936 938 and copolymerized with ethylene oxide and propylene oxide in the presence of Nafion-... 

The use of a precision digital density meter as supplied by Mettler Instruments (Anton Paar, Ag.) appeared attractive. Few references on using density measurements to follow polymerization or other reactions appear in the literature. Poehlein and Dougherty (2) mentioned, without elaboration, the occasional use of y-ray density meters to measure conversion for control purposes in continuous emulsion polymerization. Braun and Disselhoff (3) utilized an instrument by Anton Paar, Ag. but only in a very limited fashion. More recently Rentsch and Schultz(4) also utilized an instrument by Anton Paar, Ag. for the continuous density measurement of the cationic polymerization of 1,3,6,9-tetraoxacycloundecane. Ray(5) has used a newer model Paar digital density meter to monitor emulsion polymerization in a continuous stirred tank reactor train. Trathnigg(6, 7) quite recently considered the solution polymerization of styrene in tetrahydrofuran and discusses the effect of mixing on the reliability of the conversion data calculated. Two other references by Russian authors(8,9) are known citing kinetic measurements by the density method but their procedures do not fulfill the above stated requirements. 

Not all monomers are anionically polymerizable. Nevertheless, one can take advantage of the activity of the living ends to introduce reactive end groups at the extremity of homopolymers and then use such end groups to initiate the polymerization of anionically non polymerizable monomers. This method has been applied to the synthesis of copolymers with polyvinyl and polylactone blocks19 and of copolymers with polyvinyl and polypeptide blocks20-2S). One can at last use both anionic and cationic polymerization to prepare block copolymers of tetrahydrofuran with styrene or methylstyrene2. ... 

Use of triphenylmethyl and cycloheptatrienyl cations as initiators for cationic polymerization provides a convenient method for estimating the absolute reactivity of free ions and ion pairs as propagating intermediates. Mechanisms for the polymerization of vinyl alkyl ethers, N-vinylcarbazole, and tetrahydrofuran, initiated by these reagents, are discussed in detail. Free ions are shown to be much more reactive than ion pairs in most cases, but for hydride abstraction from THF, triphenylmethyl cation is less reactive than its ion pair with hexachlorantimonate ion. Propagation rate coefficients (kP/) for free ion polymerization of isobutyl vinyl ether and N-vinylcarbazole have been determined in CH2Cl2, and for the latter monomer the value of kp is 10s times greater than that for the corresponding free radical polymerization. 

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). 

Cationic polymerization of 2-methylpropene at temperatures about 170 K may be almost flash-like the transformation of tetrahydrofuran to an equilibrium polymer-monomer mixture may last tens to hundreds of hours at 260 K. Evidently the overall polymerization rate is a function of many factors which may be interconnected or may act separately. The aim of kinetic measurements is to describe the polymerization, and to find conditions under which it would proceed in the desired manner. This is usually only possible after the various factors and their consequences have been isolated and investigated. The rate of monomer consumption during polymerization mostly depends on the generation rate of active centres, and on their concentration and reactivity. 

Figure 17 MWDs of poly(isobutyl vinyl ether) to illustrate the three general methods for living cationic polymerizations at -15° C [M]0 = 0.38 Af [HCI]0 = [ZnCl2]0 = rSnCL(]0 = 5.0 mA/ conversion = ca.100%. Initiating systems and reaction conditions (a) HCl/ZnCl2, in toluene without additive (b) HCl/SnCU, in toluene without additive (c) HCl/SnCLt, in toluene with added tetrahydrofuran (100 mM) (d) HCl/SnCU, in CH2C12 without additive (e) HCl/SnCU, in CH2C12 with added Bu4NCl (2.0 mM). (From Refs. 73 and 105.)...

There are several reports in recent literature on the application of silicon-containing compounds as the initiators of cationic ring-opening polymerization. This apparently is related to the attempts to prepare block copolymers containing polysiloxane or polysilane segments. (CfL SiCFAgClCL system was used to initiate cationic polymerization of tetrahydrofuran... 

Cationic polymerization of tetrahydrofuran is one of the few systems in cationic ring polymerization in which chain transfer to polymer may be practically avoided. The reasons for that are of purely kinetic nature. 

The polymerization of tetrahydrofuran in the presence of methylenemalonitrile has already been described. Co-ordination of aluminium trichloride to the cyano groups would make methylenemalononitrile an even more effective initiator of cationic polymerization. 

Other monomers that are suitable for cationic polymerization include cyclic ethers (like tetrahydrofuran), cyclic acetals (like irioxane), vinyl ethers, and N-vinyl carbazole. In these cases the hetero atom is bonded directly to the electron deficient carbon atom, and the respective carboxonium ion (9-13) and immonium ion (9-14) arc more stable than the corresponding carbocalions. 

In this paper we analyze the cationic polymerizations of cydic monomers udng mostly results of living systems like tetrahydrofuran (THE) which is at present the only comprehensively studied monomer Other systems are also reviewed and reasons for transfer and termination procreses accompanying propaption are analyzed. 

The monomers most comprehensively studied in cationic polymerization are the non-planar tetrahydrofuran and 1,3-dioxolane. HowevCT, 5-membered rings do not assume such favorable conformations like the chair conformation of 6-membered rings. Consequently, the energetic barrier (pseudorotation barrier) between the con-... 

Tetrahydrofuran, just as other cyclic ethers, can be submitted to a cationic polymerization. It leads to polytetrahydrofuran (PTHF). Schematically, this can be expressed as follows ... 

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