Oxetane copolymerization

Many copolymerization studies have been made. A detailed discussion and critique of the results has been pubHshed (1) and the breadth of the comonomers studied has been summarized (6). Among the comonomers used are oxiranes, oxetanes, 1,3-dioxolane, substituted tetrahydrofurans. 

Bis(3-nitrofurazanoxymethyl)oxetane 221 was synthesized in 52% yield by base-promoted ring closure of the corresponding 3-hydroxy-l-propyl triflate, 219, which is readily available from the diol and triflic anhydride. Oxetane 221 can also be prepared in 74% yield by treatment of the trifurazanyl ether 220 with DBU. Polymerization and copolymerization reactions of oxetane 220 have also been investigated (97MI7) (Scheme 148). 

BAMO is also copolymerized with nitratomethyl methyl oxetane (NIMO) to formulate the energetic liquid polymer BAMO-NIMO. Since NIMO is a nitrate ester containing an -O-NO2 bond in its molecular structure, BAMO-NIMO copolymer is more energetic than BAMO-THF copolymer. The chemical structures of BAMO and NIMO are both based on the oxetane structure, and the structure of the BAMO-NIMO copolymer is shown in Fig. 4.10. 

Keywords Carbon dioxide Copolymerization Oxetanes Polycarbonates Schiff-base ligands... 

Kinetic measurements of the ring-opening polymerization of trimethylene carbonate (TMC) versus the enchainment of oxetane and CO2 to provide poly (TMC) reveal that these processes in the presence of (salen)CrCl and an ammonium salt have similar free energies of activation (AG ) at 110°C. This similarity in reactivity coupled with the observation that in situ infrared studies of the copolymerization of oxetane and CO2 showed the presence of TMC during the early stages of the reaction has led to the overall mechanism for copolymer production shown in... 

Scheme 8 Mechanistic pathways for the copolymerization of oxetane and carbon dioxide...

Some monomers with no tendency toward homopolymerization are found to have some (not high) activity in copolymerization. This behavior is found in cationic copolymerizations of tetrahydropyran, 1,3-dioxane, and 1,4-dioxane with 3,3-bis(chloromethyl)oxetane [Dreyfuss and Dreyfuss, 1969]. These monomers are formally similar in their unusual copolymerization behavior to the radical copolymerization behavior of sterically hindered monomers such as maleic anhydride, stilbene, and diethyl fumarate (Sec. 6-3b-3), but not for the same reason. The copolymerizability of these otherwise unreactive monomers is probably a consequence of the unstable nature of their propagating centers. Consider the copolymerization in which M2 is the cyclic monomer with no tendency to homopolymerize. In homopolymerization, the propagation-depropagation equilibrium for M2 is completely toward... 

Oxetanes can be copolymerized very successfully with a wide range of other monomers and even carbon dioxide, to give plastic compositions with a wide variety of properties. Naturally, this area has been the subject of a great deal of research, and many patents have appeared which are beyond the scope of this survey. 

Polymers of these compounds are in widespread use. Poly-BCMO is a very tough, durable plastic, which is estimated to have an average lifetime of 70 years in water. As most oxetanes and /3-lactones can be polymerized and copolymerized to form a variety of useful solid compositions, this application will probably grow. One unusual application mentioned is the preparation and polymerization of 3,3-bis(azidomethyl)oxetane, which could be an explosive polymer (81MI51302). 

Cross-linked, insoluble PEG can be prepared by copolymerizing PEG with epi-chlorohydrin [107,160] or with the tosylate of 3-methyl-3-(hydroxymethyl)oxetane [161,162], These supports are highly permeable and hydrophilic, and enable the use of... 

THF copolymerizes readily with other cyclic ethers such as oxides and oxetanes. The comonomers used include ethylene oxide (67), propylene oxide (99,100), epichlorohydrin (ECH) (101,102), phenyl glycidyl ether (102), 3.3-bis(chloromethyl) oxetane (BCMO) (25, 98, 101, 103) and 3-methyl-3-chloromethyl oxetane (103). Just as in THF homo-polymerization, a large variety of catalysts have veen used. In many cases the kinetics of copolymerization have been studied. Table 22 summarizes the monomer reactivity ratios, rx (THF), and r2 (comonomer) which have... 

An alternative source of polycarbonate derived from C02 involves the alternating copolymerization of oxetane and C02 (Equation 8.1). 

The ring-strain energy of oxetane is less than that of PO (106.7k] mol 1 versus llTZkJmoT1) hence, its copolymerization with C02 is less favored thermodynamically [3], Nevertheless, the copolymerization of oxetane and C02 occurs readily under similar catalytic conditions, producing poly(trimethylene carbonate),... 

Figure 8.13 General structure of the metal (111) salen catalysts employed in the copolymerization of oxetanes and C02.

The proposed mechanism for the copolymerization of oxetane and C02 is summarized in Scheme 8.9. Following the initial ring-opening and C02 insertion into the resulting chromium-oxygen bond, two pathways are open for the intermediate ... 

The field of metal-catalyzed copolymerization of oxetanes and C02 will continue to flourish, due not only to the versatility of the reaction but also to the aliphatic polycarbonate products being important components of thermoplastic elastomers that, in turn, have huge potential in medical applications such as sutures, drug-delivery systems, body, and dental implants, and tissue engineering. The exploration of other oxetane monomers (Figure 8.17) such as 3,3-dimethyloxetane and 3-methoxymethyl-3-methyloxetane, will surely provide a multitude of applications... 

Scheme 8.9 Mechanistic aspects of the copolymerization of oxetane and C02 catalyzed by (salen)CrN3/PPNN3.

---