Dioxolane monomers, copolymers

In the copolymerization of trioxane with dioxolane, reactivity ratios of dissolved copolymer cations are quite different from those of active centers in the crystalline phase. The former strongly prefer addition of dioxolane. The difference in reactivity ratios between dissolved and precipitated active centers is attributed to the fact that in the solid phase, polymerization and crystallization of the copolymer are simultaneous. The cationic chain ends are assumed to be directly on the crystal surface. Determination of the equilibrium concentrations of formaldehyde confirms this conclusion dissolved copolymer has a higher tendency to cleave formaldehyde than crystalline polyoxymethylene. In the latter stages of copolymerization the soluble copolymer is degraded gradually to the dioxolane monomer which is incorporated into the crystalline copolymer in an almost random distribution. 

Dioxolane was also formed in the absence of trioxane when the soluble copolymer was simply dissolved in a 0.03M solution of SnCl4 in methylene dichloride at 30°C. (conditions similar to those of the copolymerization in Figure 3). Within one hour half of the soluble copolymer was depolymerized under formation of dioxolane monomer and formaldehyde. 

In the copolymerization of trioxane with dioxolane, however, depolymerization and regeneration of dioxolane monomer is a faster and more effective way of converting soluble into crystalline copolymer with random distribution. A similar mechanism may hold true for trioxane polymerization with similar comonomers such as 1,3-dioxane, 1,3-dioxacyclo-heptane and in part even for copolymerization of trioxane with ethylene oxide which also involves formation of some dioxolane and soluble copolymer. 

The physical properties of perfluorodioxolane polymers are modified by copolymerizing the dioxolane monomers. The refractive indices and 7g depend on the copolymer compositions [16,18,23], The copolymers can be prepared in solution and in bulk. For example, the copolymerization reactivity ratios of monomers A and C (Figure 16.6)... 

The typical results of these copolymers are shown in Table 16.7. The content of monomer F in the copolymer produced is considerably higher than that in the feed. It indicates that the reactivity of the vinyl monomers is much lower than that of the perfluorinated dioxolane monomers. The reactivity ratios of CTFE and monomer F are = 0-74 and rp = 3.64, respectively. 

Perfluoro-2-methylene-l,3-dioxolane monomers can be copolymerized with each other to modify the physical properties of the polymers. The refractive index and Tg depend on the copolymer composition. The copolymers are readily prepared in solution and in bulk. For example, the copolymerization reactivity ratios of monomers A and C (Figure 4.10) are = 0.97 and - 0.85 [35]. The data show that this copolymerization yields nearly ideal random copolymers. Figure 4.11 shows the change in Tg as a function of the copolymer composition. The copolymers have only one T, which increases from 110 to 165 C as the mole fraction of monomer A increases. The copolymer films prepared by casting are flexible and tough and have a high optical transparency. 

The remarkably high molecular weights of copolymers of dioxolan and styrene, which were achieved by Yamashita, are also easily intelligible in terms of the insertion mechanisms shown in schemes (D) and (E) the fact that cationically produced polystyrenes have low molecular weights is mainly due to proton transfer to monomer from the P-carbon at the growing end of a chain. If there is no growing end but a cyclic oxonium ion, this reaction cannot occur, and thus the principal chainbreaking reaction is frustrated. 

Finally, it should be mentioned that there exist two other routes for the synthesis of copolymers. First the partial chemical conversion of homopolymers (see Sect. 5.1), for example, the partial hydrolysis of poly(vinyl acetate). Secondly, by homopolymerization of correspondingly built monomers. An example for these macromolecular compounds, sometimes called pseudo-copolymers, is the alternating copolymer of formaldehyde and ethylene oxide synthesized by ringopening polymerization of 1,3-dioxolane. 

On the other hand copolymer with a trioxane unit at the cationic chain end (Pi+) may be converted intp P2+ by cleavage of several formaldehyde units. These side reactions change the nature of the active chain ends without participation of the actual monomers trioxane and dioxo-lane. Such reactions are not provided for in the kinetic scheme of Mayo and Lewis. In their conventional scheme, conversion of Pi+ to P2+ is assumed to take place exclusively by addition of monomer M2. Polymerization of trioxane with dioxolane actually is a ternary copolymerization after the induction period one of the three monomers—formaldehyde— is present in its equilibrium concentration. Being the most reactive monomer it still exerts a strong influence on the course of copolymerization (9). This makes it impossible to apply the conventional copolymerization equation and complicates the process considerably. 

To investigate the copolymerization of trioxane with dioxolane and to determine r1 by the excess method, a molar ratio of trioxane to dioxolane of 100 1.8 was used. All polymerizations were run in methylene dichloride at 30°C. with SnCl as initiator. To reduce the influence of formaldehyde production at the beginning of copolymerization, dioxolane was added to the solution of trioxane and initiator only at the end of the induction period—i.e., at the appearance of the first insoluble polyoxy-methylene. After various reaction times polymerizations were terminated by adding tributylamine. Monomer conversions were determined by gas chromatography, the liquid phase being injected directly. When conversions were small, isolation and analysis of the copolymer yielded more accurate results. 

When 1,3-dioxolane was added to the solution of living (nontermi-nated) poly(l,3-dioxepane) or vice versa, further polymerization ensued and the increase of molecular weight indicated that polymerization of added monomer proceeded exclusively on living active species of the former monomer. The isolated copolymer was analyzed by l3C NMR spectroscopy and it was found that, instead of a block copolymer, the copolymer with nearly statistical distribution of DXL and DXP units was formed practically from the beginning of the process. This is a clear indication that chain transfer to polymer leads to branched oxonium ions, which participate in further reactions with a rate comparable to the rate of propagation. 

Thus, in sequential polymerization of two different cyclic acetals, 1,3-dioxolane and 1,3-dioxepane, the sequential polymerization (i.e., polymerization of added second monomer initiated by active species of the first monomer polymerization) may be easily achieved as evidenced by increase of molecular weight [130]. The isolated polymer is not a block copolymer, however, having nearly statistical distribution of both types... 

Some heterocyclic monomers may undergo random copolymerization with vinyl monomers. This is a case of cyclic acetals (e.g., 1,3-dioxolane) which forms the random copolymers with styrene [308,309] or isoprene [310], Apparently, the oxycarbenium ions, being in equilibrium with tertiary oxonium ions (cf., Section II.B.6.b), are reactive enough to add styrene ... 

At low trioxane concentrations, i.e., at Mtr.dis < Mtr.cp.dis> the copolymer composition does not depend on the composition of the monomer mixture. The average length of dioxolane blocks is also constant and differs markedly from the length expected in a random distribution of dioxolane units in the copolymer. 

Morphological studies of copolymers have shown that, in the first case, they have a globular structure, while in the second, lamellar hexahedral copolymer monocrystals are formed. All these investigations show that, regardless of the ratio between the monomers in the mixture, only the quite definite, and most probably regular, polymer obtained is the most favorable from a thermodynamic point of view. The internal portion of the copolymer monocrystal can be expected to consist of trioxane units, with the dioxolane units located on the lower and upper surfaces of the monocrystal and forming a fold in the chain. 

Block Copolymers. Several methods have already been used for the synthesis of block copolymers. The most conventional method, that is, the addition of a second monomer to a living polymer, does not produce the same spectacular results as in anionic polymerization. Chain transfer to polymer limits the utility of this method. A recent example was afforded by Penczek et al. (136). The addition of the 1,3-dioxolane to the living bifunctional poly(l,3-dioxepane) leads to the formation of a block copolymer, but before the second monomer polymerizes completely, the transacetalization process (transfer to polymer) leads to the conversion of the internal homoblock to a more or less (depending on time) statistical copolymer. Thus, competition of homopropagation and transacetalization is not in favor of formation of the block copolymers with pure homoblocks, at least when the second block, being built on the already existing homoblock, is formed more slowly than the parent homoblock that is reshuffled by transacetalization. 

The radical ring-opening elimination polymerization of 4-methylene-l,3-dioxolane stimulated us to construct a novel template polymerization (3). The concept is that polymers bear polymers. Polymer-supported monomer, which had a structure of 2,2-dipheny 1-4-methylene-1,3-dioxolane, reacted with radical species to afford polyketone and copolymer of styrene with vinylbenzophenone as newborn polymer and template, respectively (Figure 12). These polymers were easily separated by fractional precipitation without any particular chemical treatment after polymerization. On the other hand, common template polymerization requires annoying procedures for the separation of obtained polymers form template. On this point, our novel template polymerization system differs from conventional template polymerization. 

Polymers with pendant cyclic carbonate functionality were synthesized via the free radical copolymerization of vinyl ethylene carbonate (4-ethenyl-l,3-dioxolane-2-one, VEC) with other imsaturated monomers. Both solution and emulsion free radical processes were used. In solution copolymerizations, it was found that VEC copolymerizes completely with vinyl ester monomers over a wide compositional range. Conversions of monomer to polymer are quantitative with complete incorporation of VEC into the copolymers. Cyclic carbonate functional latex polymers were prepared by the emulsion copolymerization of VEC with vinyl acetate and butyl acrylate. VEC incorporation was quantitative and did not affect the stability of the latex. When copolymerized with acrylic monomers, however, VEC is not completely incorporated into the copolymer. Sufficient levels can be incorporated to provide adequate cyclic carbonate functionality for subsequent reaction and crosslinking. The unincorporated VEC can be removed using a thin film evaporator. The Tg of VEC copolymers can be modeled over the compositional range studied using either linear or Fox models with extrapolated values of the Tg of VEC homopolymer. 

Copolymers from a single monomer can be obtained by copolymerization of a preformed unit or by partial isomerization before or during polymerization. Polymerization of preformed units can occur with a ringopening polymerization or with a cyclopolymerization. For example, the ring-opening polymerization of 1,3-dioxolan leads to a copolymer of alternating oxymethylene and oxyethylene units ... 

The Celanese route for the production of polyacetal yields a more stable copolymer product via the reaction of trioxane, a cyclic trimer of formaldehyde, and a cyclic ether, such as ethylene oxide or 1,3 dioxolane. The structures of these monomers are shown in Figure 3.25. The polymer structure is represented in Figure 3.26. 

Saponifying and deketalizing a copolymer of vinyl ester monomer and 2,2-dialkyl-4-vinyl-l,3-dioxolane, or... 

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