Study of temperature transitions in solid poly(oxymethylene) by thermal analysis methods

Poly(oxymethylene)s with different molecular mass and chemical structure were studied using DSC, dynamic mechanical relaxation, thermomechanical analysis, and thermogravimetry.Molecular mobilities of two types were found in the amorphous phase of poly(oxymethylene). Unconstrained chains of poly(oxymethylene) soften at –70°C and then amorphous chains with different restraints from the crystalline phase are successively activated in a wide temperature interval.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThis work has been supported by DuPont Company     

Brønsted酸性离子液体催化合成聚甲醛二甲醚的研究

合成并表征了两种Brønsted酸性离子液体N-甲基-2吡咯烷酮硫酸氢盐([Hnmp]HSO₄)和N-甲基-2吡咯烷酮对甲苯磺酸盐([Hnmp]PTSA),对两种离子液体在由甲缩醛和多聚甲醛缩合制备聚甲醛二甲醚(DMM_n,n > 1)反应中的催化性能进行了研究.结果显示,离子液体的催化活性与其酸性相关,离子液体[Hnmp]HSO₄具有较高的催化活性;当离子液体[Hnmp]HSO₄ 的用量为2.0%(质量分数)、m(甲缩醛)/m(多聚甲醛)= 2.00、反应温度110℃、反应时间6 h时,甲缩醛的转化率和DMM_3~8 的选择性分别为52.28%和49.18%.反应结束后,离子液体[Hnmp]HSO₄与产物自动分成两相,且该离子液体的稳定性好,重复使用五次后仍有较高的催化活性.     

Chirality Transfer in the Formation of Poly(oxymethylene) Helices by Anionic Polymerization

In this article, we present the synthesis of a series of oligo(oxymethylenes) capped with 1‐phenylethanol and MeOH. The anionic condition affords enantiomerically pure oligo(oxymethylene) oligomers, while the cationic oligomerization leads to a racemic mixture of the oligo(oxymethylene) chain.     

Photo-chemical reactions in commercial poly(oxymethylene)

Poly(oxymethylene) has been examined using infra-red, ultraviolet absorption and luminescence techniques. The first technique indicates that aldehydic carbonyl groups are present in the polymer whereas the latter two indicate the presence of α,β-unsaturated carbonyl groups. The behaviour of these impurity carbonyl species during irradiation under sunlight-simulated conditions has also been examined. Possible mechanisms for the participation of these chromophoric units in the photo-oxidation of the polymer are discussed.     

Replicated Banded Spherulite: Microscopic Lamellar-assembly of Poly(L-lactic acid) Crystals in the Poly(oxymethylene) Crystal Framework

The morphologies of poly(L-lactic acid) (PLLA) spherulites,when crystallized within the pre-existed poly(oxymethylene)(POM) crystal frameworks,have been investigated.PLLA/POM blend is a melt-miscible crystalline/crystalline blend system.Owing to the lower melting point but much faster crystallization rate than PLLA,POM crystallized first upon cooling from the melt state and then melted first during the subsequent heating process in this blend system.Lamellar assembly of PLLA crystals within the pre-existed POM spherulitic frameworks was directly observed with the polarized light microscopy by selectively melting the POM frameworks.The investigation indicated that PLLA crystals fully replicated the spherulitic morphology and optical birefringence of the POM crystal frameworks,which was independent of Tc.On the other hand,POM could also duplicate the pre-existed PLLA morphologies.The result obtained provides us a possibility to design the lamellar assembly and crystal structures of polymer crystals in miscible crystalline/crystalline polymer blends.     

Morphology and Properties of Poly(oxymethylene) Engineering Plastics

Comparative WAXD/SAXS/SEM/DSC structural studies of a series of semi-crystalline poly(oxymethylene) (POM) engineering plastics, including the commercial products, homopolymer Delrin^® and typical poly(oxymethylene-co-oxyethylene)s, and a few lab-made POM compositions, were performed. The latter differed in their content of functional additives (present in low concentrations) and POM molecular weight characteristics. In parallel, their densities, thermal behavior/laser-interferometric creep rate spectra (DSC/CRS) at 20-180 °C, as well as long-term creep resistance (LTCR) at 20 °C were studied. It has been found that introducing the nucleating agents and oxyethylene units resulted in formation of more fine spherulitic or practically non-spherulitic structure with close- or loose-packed lamellar stacks. The presence of both “thick” (5-10 nm) and “thin” (1.5-3 nm) lamellae in the weight ratio of ∼3:1 was shown in all cases. Close values of real POM crystallinities, not exceeding 50%, were obtained by WAXD and DSC. A predominant role of “straightened out” or slightly bent tie chains in disordered layers of isotropic POMs was presumed, resulting in segmental dynamics differently constrained by crystallites (DSC/CRS data). As a result, certain morphology - density - creep resistance correlations were found.     

Expected and unexpected etherification of 2-per(poly)fluoroethyl 4-substitutedphenol with β-haloethanol

Under different reaction conditions, the expected and unexpected reaction products (of which X-ray crystallographic structure was presented) of etherification of 2-per(poly)fluoroethyl 4-substituted phenol with β-haloethanol can be obtained respectively.     

Polymerization of β-carbomethoxypropionaldehyde

High molecular weight crystalline poly(carbomethoxyethyl)oxymethylene was prepared from β-carbomethoxypropionaldehyde with the use of organometallic compounds. The characterization, fractionation, x-ray analysis, and viscosity measurement were carried out. Degradation by hydrochloric acid gave a highly crystalline but soluble polymer of a lower molecular weight. It was interesting to note the high solubility character of the polymer in organic solvents in contrast to the poor solubility of the isomeric poly(acetoxyethyl)oxymethylene. From the relationship among the intrinsic viscosity, Huggins' constant, and the solubility parameter of solvent, the solubility parameter of the polymer was determined to be 9.3 (cal/ml)^1/2.     

Cationic grafting from carbon black. VII. Grafting of polyacetals by cationic ring-opening polymerization of trioxane and 1,3-dioxolane initiated by CO+ClO4− groups on carbon black

The cationic ring-opening polymerization of trioxane and 1,3-dioxolane was found to be initiated by CO⁺CIO₄^? groups on a carbon black surface, which were introduced by the reaction of COCI groups with AgCIO₄. The activation energy of the ring-opening polymerization of trioxane was estimated to be 15.5 kcal/mol. In the polymerization system, poly(oxymethylene) and poly(1,3-dioxolane) formed were effectively grafted onto carbon black depending upon the propagation of these polymers from the carbon black surface; for instance, the grafting ratio of poly(oxymethylene) onto carbon black increased with an increase in conversion and went up to about 180%. Although the grafted chain of poly(oxymethylene) was subject to stepwise thermal depolymerization from the chain ends, the thermal stability of poly(oxymethylene)-grafted carbon black was improved by acetylation of hemiformal end groups. The molecular weight of ungrafted poly(oxymethylene) formed in the polymerization was determined to be 1.8–2.0 × 10⁴. Furthermore, the copolymerization of trioxane with 1,3-dioxolane, styrene, and other comonomers initiated by CO⁺CIO₄^? groups and the thermal stability of these acetal copolymer-grafted carbon black were investigated.     

Synergistic effect of red phosphorus, novolac and melamine ternary combination on flame retardancy of poly(oxymethylene)

New flame retardant system for poly(oxymethylene) (POM) has been studied. The combination of red phosphorus with novolac and melamine was found to act as an effective flame retardant of POM. The base POM exhibited very low limiting oxygen index (LOI) value of 15.3, while the flame retarded POM gave remarkably high LOI value of 37.5 and UL94 V-1 ranking without dripping at 0.8 mm thickness. The results of cone calorimetry, thermogravimetry and FTIR analysis suggested that the flame retarding mechanism is the intumescent char formation in the condensed phase. Novolac having a phenolic hydroxyl group is miscible with POM, and in the flaming process, red phosphorus yields phosphine and its acidic product such as phosphoric acid due to hydrolysis and oxidation reactions. In addition, all of novolac, melamine and phosphine are able to readily react with formaldehyde generated from POM during burning to give the reinforced and cross-linked char network through the polyaddition and polycondensation reactions. Therefore, the red phosphorus/novolac/melamine ternary combination system could synergistically promote the high flame retardancy of POM without the flaming drips.     

Polymerization of β-cyanopropionaldehyde. II. Crystalline poly(cyanoethyl)oxymethylene

Additional investigation was made on the polymerization of β-cyanopropionaldehyde at ?78°C. with triethylaluminum and triethylaluminum—titanium tetrachloride complexes as initiators. The complexes give a higher polymer yield than triethylaluminum alone. The yield—Ti/Al plot also has a maximum at a Ti/Al mole ratio of about 0.2 at constant Al(C₂H₅)₃ concentration. The rate of polymerization seems to be increased in the following order: toluene < methylene chloride < tetrahydrofuran. This order is reversed with regard to the content of DMF-insoluble fraction mentioned below. The polymer obtained consists of two fractions: one is soluble in dimethylformamide (DMF) and the other is not. The former consists of an amorphous polymer and the latter of crystalline polymer. It was found that the infrared absorption bands at 790, 1258, and 1375 cm.^-1 were characteristic of crystalline polymer and were assigned to crystalline bands. Those at 1270 and 1345 cm.^-1 are characteristic of amorphous bands. The crystalline bands and C? O? C bands show very intense infrared dichroism, whereas the nitrile band does not. The crystal data obtained from the analysis of the x-ray diffraction pattern, including the fiber repeat distance of 4.95 A. and other unit cell dimensions in a triclinic system, were compared with those reported for various aldehyde polymers. The unit cell dimension a′ or the maximum interplanar distance is somewhat smaller, suggesting that the molecules are more tightly packed than poly(n-butyraldehyde), in which the side chain has the same carbon number as that of poly-(cyanoethyl)oxymethylene. Internal rotation angles and a radius of helix were calculated for an isotactic fourfold helical model of the polymer. Some other characterizations of the polymer were also made.     

Dependence of the conformation of nascent poly(oxymethylene) on the conditions of cationic polymerization of trioxane in solution

The conformational structure of nascent poly(oxymethylene) (POM) obtained by cationic polymerization of trioxane in nitrobenzene was investigated by i.r. spectroscopy. It was found that the conformational order of this POM depends considerably on the conditions of preparation. Under conditions of simultaneous polymerization and crystallization, “A” polymer, with long sequences of monomer units in regular G conformation, is obtained. Under conditions of successive polymerization and crystallization, the formation of conformational defects in the helical POM chains is favoured. Then, depending on the supersaturation, we obtained either (a) POM of “B” form with short sequences of monomer units in G conformation, or (b) POM of a mixed type, the i.r. spectrum being describable as a superposition of “A” and “B” spectra. The results indicate that, at comparatively high catalyst concentration, the thermodynamical approach for regulation of supermolecular structure of polymers can be applied successfully for regulation of the conformational order of nascent POM also. At lower concentration of active centres in the polymerizing system, kinetic factors affect considerably the conformational structure of nascent POM.     

Study of photopolymers. XXXIV. Etherification and esterification reactions of polymers with (o,m, or p)-bromomethylnitrobenzene using the DBU method and the photochemical properties of the resulting polymers

Poly[4-(4-nitrobenzyloxy)styrene] was synthesized with a high degree of etherification by the reaction of poly(4-hydroxystyrene) (PHST) with p-bromomethylnitrobenzene (p-BMNB) using 1,8-diazabicyclo-[5,4,0]-7-undecene (DBU) in hexamethylphosphoramide (HMPA). Poly[4-(3-nitrobenzyloxy)styrene] and poly[4-(2-nitrobenzyloxy)styrene] were also prepared with a high degree of etherification by the corresponding reaction with m- or o-BMNBs. However, the degrees of etherification of PHST with these BMNBs were relatively low when the reactions were carried out in other aprotic polar solvents such as DMF, DMSO, and N-methyl-2-pyrrolidone. On the other hand, poly(4-introbenzyl methacrylate) (PPNBMA), poly(3-nitrobenzyl methacrylate) (PMNBMA), and poly(2-nitrobenzyl methacrylate) (PONBMA) were synthesized with a high degree of esterification by the reaction of poly(methacrylic acid) with the corresponding BMNBs using DBU in DMSO at 30°C. The photochemical properties of the resulting poly(nitrobenzyl methacrylate)s were examined, and it was found that the rates of photodecomposition of PPNBMA and PMNBMA were promoted by the addition of tributylamine and trifluoromethanesulfonic acid, respectively. However, the rate of photodecomposition of PONBMA was not affected by addition of the base or the acid.     

酸功能化离子液体催化合成聚缩醛二甲醚

对以酸功能化离子液体[Hnmp]HSO4、[Hnmp]H2PO4、[Hnmp]PTSA和[PyN(CH2)3SO3H]HSO4催化三聚甲醛和甲醇缩合制备聚缩醛二甲醚(PODEn,n1)的反应进行了研究,考察了催化剂用量、物料配比、温度和时间等对反应活性的影响。结果表明,离子液体的催化活性与其酸性相关。[PyN(CH2)3SO3H]HSO4具有较高的催化活性;当[PyN(CH2)3SO3H]HSO4的用量为2.0%、甲醇和三聚甲醛的物质的量比为2.0、反应温度110℃、反应压力2.0 MPa、反应时间6 h时,三聚甲醛的转化率和PODE3~8的选择性分别为97.69%和32.54%。反应结束后,[PyN(CH2)3SO3H]HSO4与产物可自动分成两相。     

Effect of miscible polymer diluents on the development of lamellar morphology in poly(oxymethylene) blends

The development of lamellar morphology in poly(oxymethylene) (POM) and its miscible blends was studied by synchrotron time-resolved small-angle X-ray scattering (SAXS), during primary and secondary crystallization at temperatures near 150°C. The blends contained two different diluents: poly(vinyl 4-hydroxy styrene) [common name poly(vinyl phenol), (PVP)], which had a high glass temperature (T_g = 150°C), and styrene-co-hydroxy styrene oligomer (PhSO), which had a low glass temperature (T_g = −37°C). The SAXS data were analyzed by correlation function analysis to extract several lamellar parameters: long period (L), lamellar crystalline thickness (lc), amorphous layer thickness (la), and invariant (Q). The variation in Q defined the region where spherulites quickly grew and filled the entire space, and was referred to as the primary crystallization dominant regime. A rapid drop in L and lc was observed at early times, and this can be explained by defective lamellar stacks filling in space between primary stacks, as secondary crystals form during the nominal primary crystallization dominant regime. Lamellar thickening with time in the long-time secondary crystallization region was observed in neat POM and the blend with 10 % low T_g diluent, while this process was inhibited with the high T_g diluent due to the higher T_g of the interlamellar species. A decrease in la at long times confirmed the lamellar thickening. We refer to the lamellar thickening process as a type of secondary crystallization. Interlamellar inclusion or trapping was detected to different degrees with the high T_g diluent, while exclusion was found for the low T_g diluent. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3115–3122, 1999     

Quantitative NMR spectroscopy of binary liquid mixtures (aldehyde + alcohol). Part III: (1-decanal or 3-phenylpropanal or 2-chlorobenzaldehyde) + (methanol or ethanol or 1-propanol)

The thermodynamic properties of binary liquid mixtures of (aldehyde + alcohol) are strongly influenced by chemical reactions in particular around and below ambient temperature. In two previous publications the chemical reaction equilibrium was investigated by ¹³C – Fourier transform NMR-spectroscopy at temperatures between 255 K and 295 K for a series of aldehydes (acetaldehyde, 1-propanal, 1-butanal, 1-heptanal) with three alcohols (methanol, ethanol, 1-propanol). Here these investigations are extended to three more aldehydes (1-decanal, 3-phenylpropanal and 2-chlorobenzaldehyde, respectively). The results for the binary systems with decanal or 3-phenylpropanal as the aldehyde in the binary mixture (aldehyde + alcohol) confirm the expectations from the first parts of this series, i.e., that the majority of the constituents of the mixture is present as hemiacetal and the first two poly(oxymethylene) – hemiacetals. The numerical results for the chemical reaction equilibrium constants from the previous investigations can be used to predict quantitatively the speciation in binary systems of ((either 1-decanal or 3-phenylpropanal) + (either methanol or ethanol or 1-propanol)). However the experimental results with 2-chlorobenzaldehyde reveal a different behaviour. In all investigated systems (2-chlorobenzaldehyde + alcohol) the most important reaction product was the corresponding acetal whereas the amounts of hemiacetal were very small. While the amounts of hemiacteal could still be quantified, it was not possible to quantify the amount of any poly(oxymethylene) – hemiacetal.     

Transitions and the relaxation spectrograph: Poly(oxymethylene)

In place of directly assaying the relative rebound height of a ball from a polymeric sample, the passage time of the ball between fixed points is used in a much more precise version of the poor man's relaxation spectrograph. Poly(oxymethylene) has a sharp transition at — 74.8°C which progressively becomes broader and moves to — 39.0°C as the polymer is pretreated at 70°C and exposed to 330 nm light for times up to 1038 ksec. A second transition, broad and shallow, is seen in the range 104 to 124°C and is unaffected by the pretreatment. This is attended by a slight decrease in density, proportional to the time held at 70°C, at the rate of ?3.54 × 10^?9 g/cm³ sec.     

Synthesis and mesomorphic properties of some novel chiral fluorinated liquid crystals containing a flexible oxymethylene linkage in the core

Four series of tolane-based chiral liquid crystals that incorporate a tetrafluorophenyl moiety and a flexible oxymethylene linkage into the core have been synthesized. The mesomorphic properties have been studied by thermal polarizing microscopy. The relationship between the properties and chemical structures of all these target compounds, especially the influence of flexible oxymethylene linkage in core on the formation of mesophases, is also discussed in detail.     

The synthesis of a mesogenic poly(azine-ether) by polyetherification via cesium diphenoxides and α,ω-dibromoalkanes

The synthesis of a poly(azine–ether) via Williamson etherification using the cesium salt of 4–hydroxyacetophenone azine and 1,10–dibromodecane was carried out in N-methyl–2–pyrrolidone. The heterogeneous reaction proceeded readily at temperatures from ambient to 150°C. Polymers of varying molecular weight with essentially alkyl bromide end groups were produced either by changing the polymerization temperature or by using an excess of the organic substrate. The thermal stability of the polymers was molecular weight dependent and those with the highest DP_n exhibited monotropic nematic mesomorphism.     

Poly-Sugar: Modification of Poly(vinyl Alcohol)

This paper describes the attachment of sugar (sucrose) onto low molecular weight poly(vinyl alcohols) (etherification) to produce a new class of synthetic sweetener. Because of its regulated molecular weight, the new sweetener would pass through the digestive tract and be excreted in its original molecular form. We have termed the new class of sweeteners poly-sugar. The etherification of sucrose with poly(vinyl alcohol) can be carried out either in dimethyl sulfoxide or water. We have prepared poly-sugars with varying degrees of etherification (3.4–5.4). Highly etherified products were bitter, but a poly-sugar with a 4.23 degree of etherification was sweet without any bitter aftertaste.