Cyclic acetal copolymerization

R. Reed, Moldable Ethylene/Vinyl Acetate Copolymer , USP 4090894 (1978) CA 39, 148908 (1978) [Vinyl acetate copolymerized with ethylene is used as a desensitizer and binder for moldable expl compns of cyclic nitramines such as RDX. From 82 to 98 wt % of binder is used, and various ratios of ethylene to vinyl acetate moieties in the resin are utilized to modify molding and extrusion properties. Prepn of typical compns consists of dissolving the copolymer in benz and addition with stirring to an RDX/w slurry, which is stirred until mixt is complete, followed by filtration and drying. Table 1 presents properties of sample compns with and without the ethylene/vinyl acetate copolymer (EVA). The inventor also states that the EVA, unlike other polymeric binders, endothermically breaks down at high temps and acts as a heat sink for the expl content]... 

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... 

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 ... 

Problem 8.18 (a) Consider the cationic polymerizability of vinyl ethers, cyclic ethers (like tetrahydrofuran), cyclic acetals (like trioxane), and N-vinyl car-bazole. (b) Why do these monomers not copolymerize cationically with olefins like styrene or isobutene ... 

Several papers57"59 were devoted to investigating a complex process such as the cationic copolymerization of monomeric formaldehyde with dioxolane in the gas, liquid, and gas-liquid phases. It is known that polyacetal resins are industrially produced by copolymerizing cyclic acetals (trioxane, 1,3,5,7-tetraoxane), or by anionic homopolymerization of monomeric formaldehyde with subsequent modification of end groups. 

More recently cyclic acetal-styrene systems were reinvestigated by the GPC technique 154,155). Using double detection (UV and RI), Yamashita et al. showed that products of copolymerization of styrene with tri- and tetraethylene glycol formals have a unimodal molecular weight distribution, and that the maxima of both RI and UV traces coincide indicating that the products are true copolymers. 

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

In this investigation two classes of monomers were synthesized, nonvinyl cyclic acetals and vinyl cyclic acetals (NVCA and VGA, respectively (Figure 2)). All monomers w evaluated for their ability to homo- and copolymerize under free radical conditions. The monomers that displayed sufficient reactivity to warrant further study were then incorporated into dental composite resin systems. The diametral tensile strength (DTS) of several experimental composites were determined and compared with various controls. 

Of the cationically-polymerizable cyclic acetals, 1-3-dioxolan has received the most attention. By means of an ion-trapping technique, quantitative measurements of the concentration of active centres have been made and correlated with initiator incorporation to confirm the living characteristics of the linear polymers under certain conditions. The oxycarbenium ion nature of these propagating centres has been verified by C-n.m.r. spectroscopy. Methyl substitution alters the polymerizability of the homologous 1,3-dioxepanes significantly and steric hindrance in the initiator can influence both the homopolymerization and copolymerization of cyclic acetals. ... 

It is not formed by a normal copolymerization starting from 2 different monomers, but since the monomer itself already contains both units in the ratio of 1 to 1. We wanted to investigate, whether it would be possible to prepare copolymers with other sequences from analogous monomers by homopolymerization. For this purpose one needs cyclic acetals, which contain the oxymethylene- and oxyethylene-units in the desired molar ratio. Of course during the polymerization of these monomers no elimination of formaldehyde or rearrangement may occur, since otherwise the regular sequence in the polymer is disturbed. 

Both linear and cyclic acetals with vinyl residues copolymerize in an alternating fashion with MA. Two good examples are the copolymers prepared from the O-vinyl acetals of formaldehyde or acetaldehyde and 2-vinyl-l,3-dioxalane. The monomer 4-methylene-2-(trichloromethyl)-l,3-dioxolane also copolymerizes in a 1 1 fashion with MA, regardless of the initial monomer feed ratio in the reaction mixture, duration of reaction time, and monomer conversion. l,3-Dioxep-5-enes are also cyclic acetals. The copolymerization of these monomers with was discussed in... 

Polyacetals containing functional groups were prepared by cationic copolymerization of cyclic acetals with methyl 2-oxopropanoate (methylglyoxylate (GM)) (Scheme 33). 

Scheme 33 Copolymerization of cyclic acetal with methyl-2-oxopropanoate.

As noted earlier in this chapter, poly(oxymethylene) (POM) is thermally unstable and tends to depolymerize starting at the unstable hemiacetal hydroxy group releasing formaldehyde (methanal) by an unzipping mechanism. The early strategy to prevent this depolymerization, used for the homopolymers prepared anionically, consisted in stabilizing the polymer chain ends by a suitable capping method. Industrially, a widely developed alternative way to obtain thermally stable POMs is to copolymerize cationically TOX with a few percent of EO or cyclic acetals (DXL, DXP). 

The bulk and solution copolymerizations of TOX were extensively studied with EO and DXL but paradoxically not that much with DXP even though the copolymers issued from this last comonomer are also of major industrial importance. The higher basicities (by 3-4 orders of magnitude)of the usual comonomers (EO, cyclic acetals) with respect to TOX lead essentially to protonation of the comonomer and to subsequent initiation of copolymerization consuming this comonomer more rapidly until its concentration becomes... 

Copolymerizations of the five-membered cyclic acetal (X = Y = phenyl) bearing exo-methylene group and vinyl monomers have also been reported. This cyclic monomer can undergo the copolymerizations with vinyl pyrrolidone, styrene, vinyl acetate, and MMA to afford the corresponding... 

Related work had shown that the nitrogen analogs of the cyclic ketene acetals were readily synthesized and would polymerize with essentially 100% ring opening. For this reason their copolymerization with a variety of monomers was undertaken (6). 

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