Oxymethylene and oxyethylene units

Polymerizations of this cyclic monomer yield polymers that consists of strictly alternating oxymethylene and oxyethylene units. The polymerization reaction can be induced by acidic catalysts, like sulfuric acid, boron trifluoride, p-toluenesulfonic acid, and phosphorous pen-tafluoride ... 

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 ... 

In particular the polymerization of 1.2.- and 1.3-epoxides (l)-(5) (18) (19) tetrahydrofurane (1)-(4) (6) (2o) Hioxolane (2177(22) and trioxane (11) (23)-X26) was thoroughly TnvestTgated. For reviews see (7T (8) (27) (28) (3o). It should be emphasized, that different oxacyclic monomers can also be copolymerized by cationic catalysts. Of great practical importance is e.g. the copolymerization of trioxane with ethylene oxide or dioxolane (31). Macromolecules with a statistic distribution of oxymethylene- and oxy-ethylene-units are formed in this way. On the other hand, however, the homopolymerization of dioxolane yields a polymer consisting of strictly alternating oxymethylene- and oxyethylene units (21) (32) therefore it can formally be considered as an alternating copolymer (eq.i). 

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. 

The many commercially attractive properties of acetal resins are due in large part to the inherent high crystallinity of the base polymers. Values reported for percentage crystallinity (x ray, density) range from 60 to 77%. The lower values are typical of copolymer. Poly oxymethylene most commonly crystallizes in a hexagonal unit cell (9) with the polymer chains in a 9/5 helix (10,11). An orthorhombic unit cell has also been reported (9). The oxyethylene units in copolymers of trioxane and ethylene oxide can be incorporated in the crystal lattice (12). The nominal value of the melting point of homopolymer is 175°C, that of the copolymer is 165°C. Other thermal properties, which depend substantially on the crystallization or melting of the polymer, are Hsted in Table 1. See also reference 13. 

Opitz,35>. Studying the NMR spectra of polymers and copolymers of TXN, DXL and 1,3,5-trioxocane, modeling the various distributions of oxymethylene (M) and oxyethylene (E) units in the resulting polymers, these authors were able to determine the concentrations of MMM, MME and EME triads. The respective chemical shifts are given in Table 7.14. Thus, the chemical shifts of M in triads is not constant, and depends on the neighbouring units. The difference, however, between MMM and EMM triads is only 0.05 ppm 6 for the same TXN-DXL copolymer, which is insufficient to distinguish between these triads with a lower resolution apparatus. 

Polyi v mylether)s °- o3-r 33 X Polyether is a polymer with oxygen atoms in the main or side chtiin. Among them, thermoresponsive poly(vinylether)s have oxymethylene and/or oxyethylene pendants in their side chains [30, 124,404-406] Phase separation temperature of vinyl ethers can be controlled by varying the number of the pendant oxyethylene units and/or the hydrophobicity of an co-alkyl group, R Tcp measurements typically reveal an abrupt reversible transition within AT = 1°C no hysteresis Homopolymers of ethyl vinylether and higher alkyl vinylethers are insoluble in water... 

In [320], jump-like creep was studied for two POM semi-crystaUine polymers. Analysis of their polarizing microscope images showed that homoPOM contained predominantly spherulites 1-5 pm in diameter, whereas poly(oxymethylene-co-oxyethylene) (95POM/5POE) sample contained both the same small spherulites and larger ones, up to 25 pm in diameter. It might be supposed that the size of these more dense structural units will be reflected in the character of variation of the creep rate and the values of deformation jumps L. Then the loosely packed inter-spherulite boundaries could be considered presumably as the most probable points for local shear displacements (micro-plasticity). 

The monomer is easily polymerizable by cationic catalysts in solution and in bulk. Colourless, waxlike polymers are obtained. At the polymerization of / /, either the bond between 01 and C2 or the bond between C2 and 03 can be cleaved. In both cases polymers with the same triad-sequence consisting of 2 oxymethylene and 1 oxyethylene-units (MME) would occur. 

Random copolymers are similar to PEO but when the regular helical structure of the chains is demolished, the crystallinity is also destroyed. One of the simplest and most successful amorphous host polymers is an oxyethylene- oxymethylene structure in which medium length but statistically variable EO units are interspersed with methylene oxide groups. First described in 1990 [37], aPEO has the general structure... 

Steady-state fluorescence spectra are obtained for dilute solutions of 16 aromatic polyesters with the repeating unit ABm. The chromophore, A, is isophthaloyl or phthaloyl, and the flexible spacer, B, Is methylene or oxymethylene. The number of methylene units Is 2 - 6, and the number of oxyethylene 1 - 4. Results obtained are interpreted within the frame of the RIS method. 

Other types of modifications tried include preparation of ethylene oxide-propylene oxide copolymers [129] as well as polymers containing regular sequences of oxyethylene and oxymethylene units [130]. 

Table 7.14. H-NMR chemical shifts of oxyethylene and oxymethylene units in polyacetals kj... 

The events occurring during the homogeneous period of the bulk copolymerization of trioxane with DXL have been recently reexamined in conditions as above but using the pairs of labeled comonomers, TOX-dg/DXL and TOX/DXL-In both cases, NMR allowed to track the pathways of the -(CH2-O)- oxymethylene (M) and -(CH2-CH2-O)- oxyethylene (E) units originating from the comonomers, and the fact that the -(CD2-O)- (M ) units were undetectable drastically improved the spectral resolution. Detailed analyses of the evolution of the complex sets of pentad sequences involving E, M, and M rmits confirmed the previous general observations of Lu et but the successive... 

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