1,3-Dioxepane copolymerization

Ring-opening polymerization of 2-methylene-l,3-dioxepane (Fig. 6) represents the single example of a free radical polymerization route to PCL (51). Initiation with AIBN at SO C afforded PCL with a of 42,000 in 59% yield. While this monomer is not commercially available, the advantage of this method is that it may be used to obtain otherwise inaccessible copolymers. As an example, copolymerization with vinyl monomers has afforded copolymers of e-caprolactone with styrene, 4-vinylanisole, methyl methacrylate, and vinyl acetate. 

These representative aliphatic polyesters are often used in copolymerized form in various combinations, for example, poly(lactide-co-glycolide) (PLGA) [66-68] and poly(lactide-co-caprolactone) [69-73], to improve degradation rates, mechanical properties, processability, and solubility by reducing crystallinity. Other monomers such as 1,4-dioxepan-5-one (DXO) [74—76], 1,4-dioxane-2-one [77], and trimethylene carbonate (TMC) [28] (Fig. 2) have also been used as comonomers to improve the hydrophobicity of the aliphatic polyesters as well as their degradability and mechanical properties. 

The structure of copolymers obtained by ATRP copolymerization of 5,6-benzo-2-methylene-l,3-dioxepane (BMDO) with H-butyl acrylate ( BA) using ethyl 2-bromoisobutyrate and iV,iV,iV, iV ,iV -pentamethyldiethylenetri-amine/copper(l) bromide, as the initiator and catalyst, respectively, was studied by ID and 2D NMR techniques, which revealed a quantitative ring opening of BMDO in the copolymerization <2005PLM11698>. For a similar study of copolymers of BMDO and styrene, see <2003MM6152>, and with methyl methacrylate, <2003MM2397>. 

Random copolymers of e-CL with l,5-dioxepan-2-one (DXO) have been investigated [52,138,139]. The copolymers were crystalline up to a DXO content of 40%, and it was concluded that the DXO units were incorporated into the po-ly(e-CL) crystals. The block copolymerization has also been investigated and the resulting material was shown to exhibit thermoplastic elastomeric properties [63]. 

Up to now we have not found reaction conditions permitting exclusive production of insoluble copolymer, which is the desired product in commercial copolymerization of trioxane. Conversion of a large portion of the dioxolane into soluble copolymer could not even be avoided by slow and gradual addition of the comonomer to a homopolymerization run of trioxane in methylene dichloride (9). The same result was obtained in solution copolymerization of trioxane with 8 mole % of 1,3-dioxacycloheptane (dioxepane), and even 1,3-dioxane—which is not homopolymerizable and is a very sluggish comonomer—formed a soluble copolymer in the initial phase of copolymerization (trioxane 2.5M 1,3-dioxane 0.31M SnCb 0.025M in methylene dichloride at 30°C.). 

It has been shown, however, that in the copolymerization much more reactive 1,3-dioxolane polymerizes first and is practically completely consumed at still low conversion of 1,3,5-trioxane [139]. Thus, by polymerization alone, it would not be possible to achieve the random distribution of 1,3-dioxolane units along the chain. Both analysis of the microstructure of the chain [140], as well as thermal behavior of the copolymer [141], indicate, however, that nearly random distribution of comonomer units is indeed attained by scrambling process similar to that described earlier for sequential polymerization of 1,3-dioxolane and 1,3-dioxepane. 

In many instances in cationic ring-opening polymerization, all the reaction steps, however, are reversible. The final composition of copolymer (in equilibrium) is governed then by thermodynamics. Thermodynamic approaches have been developed [305] and recently reviewed [306]. Such thermodynamic approach has been used to analyze the copolymerization of pairs of cyclic acetals (1,3-dioxolane with 1,3-dioxepane and... 

Table I. Copolymerization of Ethylene with 2-Methylene-l,3-dioxepane (I)... 

Copolymerization of Ethylene with 2-Methylene-l,3-dioxepane (I)— Typical copolymerizations were carried out as follows To a 10.125 X 1.5-inch steel pressure vessel (300-ml capacity) was added 50 ml of a solution of 1.1 g (1.0 mol- ) of di-tert-butylperoxide and 5.0 g (0.043 mol) of 2-methylene-l,3-dioxepane, bp 49-50 C (20 mm), in purified cyclohexane to give 50 ml of the reaction mixture. The sealed vessel was flushed twice with ethylene gas (99.9 pure) and finally filled with ethylene to an equilibrium pressure of 1000 psi. If one neglects the amount of ethylene that dissolves in the organic layer, the amount of ethylene gas with a volume of 250 ml at 1000 psi was calculated to be 21 g (0.75 mole). The copolymerization was allowed to proceed to low conversions (less than 2%) at 120 C for 30 minutes. After the reaction vessel was quickly cooled in Dry Ice, it was opened and methanol was added to it to facilitate the removal of the product as a white precipitate. After the solid was collected by filtration with suction and washed with methanol, the polymer was purified further by dissolution in hot chloroform and addition of the resulting solution into the nonsolvent methanol. The polymer was collected by filtration and dried in vacuo at 40 C for 24 hours to give a white powder. 

The free radical polymerizations of cyclic ketene acetals have recently evoked a lot of interest (10-13). TTie oly(e-caprolactone) (PCL) can be synthesized by free radical ring opening polymerization (10). The copolymerization of its monomer, 2-methylene-l,3-dioxepane (MDO), with some vinyl monomers resulted in an aliphatic ester backbone, as well as the pendant functional groups from the vinyl monomers (10). By free radical polymerization of MDO and the vinyl monomers vinylphosphonic acid (VPA), dimethylvinylphosphonate (VPE) and acrylic acid (AA), we synthesized a series of biodegradable copolymers including PCL... 

Examples given in this volume are the papers by Yang (on the cationic copolymerization of trioxane and 1,3-dioxepane) (58) and by Luther (on labelled polyphosphazenes) (71). Poly(ethylene oxide) is also included in the HPLC-NMR studies by Hiller and Pasch (66). 

An NMR Study on the Bulk Cationic Copolymerization of Trioxane with 1,3-Dioxepane... 

The cyclic acetal 1,3-dioxepane (DOP) can be copolymerized with TOX to form copolymers having properties comparable to other acetal resins ... 

Yuan, J.Y. and Pan, C.Y. (2002) Block copolymerization of 5,6-benzo-2-methylene-13 dioxepane with conventional vinyl monomers by AXRP method. Eur. Pdym. J, 38, 1565. 

Roberts, G.E., Coote, ML., Heuts, J.P.A., Morris, L.M., and Davis, X.P. (1999) Radical ring-opening copolymerization of 2-methylene 1,3-dioxepane and methyl methacrylate experiments originally designed to probe the origin of the penultimate unit effect. Macromolecules,... 

Agarwal, S. (2007) Radical ring opening and vinyl copolymerization of 2,3,4,5,6 pentafluorostyrene with 5,6-benzo-2-methylene-13-dioxepane synthesis and structural characterization using ID and 2D NMR techniques. / Polym. Res., 13 (5), 403. 

Undin, J., Hime-Wistrand, A., and Albertsson, A.C. (2013) Copolymerization of 2 methylene-l,3-dioxepane and glycidyl methacrylate, a well-defined and efficient process for achieving functionalized polyesters for covalent binding of bioactive molecules. Biomacromolecules, 14, 2095. 

Telechelic polystyrene and polyethylene containing a hydroxyl and a carboxylic end group are obtained by copolymerizing a small quantity of 2-methylene-1,3-dioxepane with a large quantity of st5Tene or ethylene, and then hydrolyzing the resulting polymers (reactions 10 and 11). 

The stereocopolymers of lactic acid, prepared by the polymerization of various stereoisomers, are discussed in a subsequent section in this book and will not be discussed here. Typical comonomers that have been used for lactic acid or lactide copolymerization are glycolic acid or glycolide (GA) [11-17], poly (ethylene glycol) (PEG) or poly(ethylene oxide) (PEG) [15 3], poly(propylene oxide) (PPO) [16-18], (7 )- 3-butyrolactone (BL), 6-valerolactone (VL) [44-46], E-caprolactone (CL) [47-54], 1,5-dioxepan-2-one (DXO) [55-60], trimethylene carbonate (TMC) [61],... 

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