Study of solid-state polymerization by positron lifetime measurements

The positron lifetime measurement technique was applied to analyze the structural changes occurring in solid-state polymerization of acrylamide and trioxane. Positronium (Ps) parameters, τ₂ and I₂, which show a marked change as a function of the γ-ray irradiation dose, signaled the presence of three clearly defined stages in the polymerization process: initiation, propagation, and saturation. The initial increase in τ₂, may very well be the result of efficient trapping of Ps in vacancies created around the polymer nuclei. The complicated behavior of I₂ may be explained as a chemical reaction between Ps precursors and the radiolysis products of this polymerization process.     

Topotactic solid-state polymerization of 3-aminocrotonamide by radiation

Radiation-induced solid-state polymerization of 3-aminocrotonamide (3-amino-2-butenamide) was carried out at room temperature, in open air atmosphere and under vacuum condition. The polymer obtained was white powder, soluble in methanol, but insoluble in water. The nature of polymers were investigated by IR, UV, x-ray, DP-MS, and elemental analysis to elucidate the mechanism of the polymerization. The polymer was crystalline with melting point in the range of 245–255°C. The cell parameters and space group of monomer and polymers were determined from powder x-ray diffraction patterns. The similarity of crystal structures of monomer and polymer indicated a topotactic polymerization. It was shown by spectroscopic investigations and elemental analyses that the polymerization proceeds by condensation reaction with evolution of one mole ammonia per two combined moles of monomer through a free radical mechanism. © 1996 John Wiley & Sons, Inc.     

The thermal degradation of polyoxymethylene produced by solid-state polymerization

The thermal degradation of polyoxymethylene produced by the solid-state polymerization of trioxane crystals has been studied. Changes in small-angle and wide-angle x-ray patterns, weight loss, and density have been measured in specimens heated in air at 175°C, 185°C, and 195°C. The polyoxymethylene contained material in two different crystallographic orientations, which behaved differently. Material in the so-called “twin” orientation melted preferentially at 185°C and 195°C, and at 185°C resolidified on cooling in parallel to the main orientation, in a lamellar structure. At 195°C, randomly oriented material was produced on resolidification. At 175°C, there was no evidence of melting or the formation of a lamellar structure, but the twin material was preferentially degraded so that only material in the main orientation remained after a time of 1500 min. The more rapid loss by degradation of the twin material was attributed to its having a lower molecular weight than the material in the main orientation.     

Electric polarization generated by the solid-state polymerization of pTS

Single crystals of pTS (bis-p-toluene sulphonate of 2,4-hexadiyne-1,6-diol), when annealed at 350 K, generate an electrical signal peaking at a time corresponding to that of a maximum polymerization rate. It is shown that a steady-state polarization of the order of 10^?4 C/m² is built into the pTS samples during the polymerization. The effect is probably associated with a non-compensated dipolar species created on polymerizing pTS crystals, and possibly also accounts for the pyroelectricity of poly-pTS.     

On-line detection of emulsion polymerization by solid-state NMR spectroscopy

 The on-line detection of emulsion polymerization processes by means of solid-state NMR spectroscopy is demonstrated for the first time using poly(butyl acrylate) as a model system. Relatively short time intervals are accessible via ¹H detection while the use of ¹³C NMR spectroscopy results in an increased spectral resolution. Details of sample preparation and experimental techniques are given, while remaining artifacts of the preliminary results will be addressed in further investigations. Received: 7 November 1997 Accepted: 5 January 1998     

Synthesis of DNA conjugate by mechanochemical solid-state polymerization and its affinity separation of oligonucleotides having single-base difference by capillary electrophoresis

In this communication, we discuss the characterization of DNA conjugate synthesized by mechanochemical polymerization, Con-M, on the separation of model oligo-DNA and its single nucleotide polymorphisms (SNPs) by affinity capillary electrophoresis, compared with that prepared by radical-initiated solution polymerization, Con-RL. The average molecular weight of Con-M was similar to that of Con-RL, although the molecular weight distribution of Con-M was narrower than that of Con-RL. Capillary electrophoresis of oligo-DNA was performed using the capillary filled with DNA conjugate. The resolution of the capillary filled with Con-M was apparently higher than with Con-RL. It is considered that higher resolution using the capillary filled with Con-M could be ascribed not only to the narrow molecular weight distribution but also to the difference of copolymer structure.     

A model for x-ray-induced solid-state polymerization

A model for x-ray-induced solid-state polymerization based on experimental results obtained with the disubstituted diacetylene, 10,12-pentacosadiynoic acid, is presented.     

Characterization of vanadium-based olefin polymerization catalyst precursors by solid-state 51v-nmr

Several VOCL₃-based ethylene polymerization catalyst precursors were prepared on silica and studied by solid-state ⁵¹V-NMR. The structure of the vanadium species in these samples, as determined by ⁵¹V-NMR, did not have any significant effect on the resultant polyethylene MI or MWD. This result is significant since conventional wisdom says the attachment of the transition metal to the silica plays a key role in polymer properties. VOCl₃ reacted with hexamethyldisilazane-treated silica and with 250°C dried silica results in double attachment of the vanadium to the silica, yet the catalysts which formed had different reactivities and produced polyethylene with different HLMIs. On the other hand, VOCl₃ reacted with 600°C dried silica results in single attachment of the vanadium to the silica, yet this catalyst had a similar reactivity and produced polymer properties similar to the doubly attached vanadium on 250°C dried silica. Two theories are offered to explain the lack of correlation between catalyst precursor structure and catalyst performance. © 1995 John Wiley & Sons, Inc.     

Radiation-induced solid-state polymerization of methacrylic acid. II. In-source polymerization

The in-source polymerization of methacrylic acid in the solid state with γ-rays was studied. The conversion rates at various temperatures were obtained as well as the radical concentrations by the measurements of ESR spectrum. The rate of polymerization was found to be proportional to I^0.65 at 0°C. The results could be interpreted on the basis of the assumption that the rate of propagation is proportional to the concentration of the propagating radical, of the monomer, and of the polymer. The addition of water to the monomer seems to accelerate the polymerization reaction. The change of the line shape of the propagating radical during polymerization was interpreted in terms of the change of the matrix which surrounds the propagating radical.     

Low-temperature viscoelasticity of poly-oxymethylene by radiation-induced solid-state polymerization of trioxane single crystal

Summary The polymerizate is a porous, white cylinder of polyoxymethylene, whose direction of crystal axis is unique. The dynamic viscoelasticity was measured by the vibrating-reed-method at –180° +10 °C. The existence of the -dispersion is doubtful in this sample. Therefore we can conclude that (i) the amorphous part is negligibly small both on the surface and inside of this sample, and (ii) the vibration of molecular chains is prohibited even on the surface of a single crystal.

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Zusammenfassung Das Polymerisat ist ein poröser, weißer Zylinder von Polyoxymethylen mit einheitlich ausgerichteter Kristallachse. Die dynamische Viscoelastizität wurde zwischen –180° und +10 °C nach der Methode des vibrierenden Stäbchens bestimmt. Die Existenz des-Dispersionsgebiets ist bei dieser Probe zweifelhaft. Wir können daher folgern, daß 1. der amorphe Anteil vernachlässigbar klein — sowohl an der Oberfläche wie im Innern — ist und daß 2. die Schwingung der Molekülketten sogar auch in der Grenzfläche eines Einkristalls behindert, unterbunden ist.

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This work was presented at the 43rd Annual Meeting of Virginia Academy of Science, Richmond, Virginia, May 7, 1965.     

Molecular imprinting using monomers with solid-state polymerization

Molecular imprinting of two diolefinic compounds with solid-state photopolymerization, 2,5-distyrylpyrazine (DSP) and diethyl p-phenylenediacrylate (EPA), was demonstrated. Solid nanoscale particles of the monomer were produced and deposited onto the surface of a surface acoustic wave (SAW) transducer using the technique known as rapid expansion of supercritical solutions (RESS). The particles were polymerized by UV light in the presence of an alkane template vapor. Both imprinted and non-imprinted devices were tested upon exposure to a variety of alkane vapors in the gas phase. The results demonstrate an enhanced sensitivity to vapors at or below the size of the template. A size exclusion mechanism of recognition is proposed.     

Some features of the solid-state polymerization of diacetylenes

Simple models of the initial polymerization stage and the polymerization kinetics are considered on the example of the solid state topochemical polymerization of diacetylenes. These models take into account the reaction specifity of the solid state process and the nonlinear character of the monomer units interactions.     

Radiation-induced solid-state polymerization of trioxane under high pressure

The in-source polymerization of trioxane in the solid state was investigated over a wide range of temperature and pressure, i.e., from 30 to 140°C and up to 7000 kg/cm², respectively. In the polymerization that was carried out slightly below the melting point under pressure, the higher the pressure, the higher the rate of polymerization. It was confirmed that the maximum rate of solid-state polymerization of trioxane occurs near the melting points, even under elevated pressure. The rate of polymerization decreased with increasing pressure at constant temperature. The shape of the time–conversion curves may be classified into two types, i.e., one which is typical of high pressure and low temperature, and the other which is typical of low pressure and high temperature. Changes in the shape of the conversion—intrinsic viscosity curves occurred coincidentally. Thus, three regions for the different “polymerization characteristic” were determined as functions of polymerization temperature and pressure. Explanations are given for the above-mentioned polymerization characteristic.     

Formation of crosslinked PTFE by radiation-induced solid-state polymerization of tetrafluoroethylene at low temperatures

Tetrafluoroethylene monomer (TFE) was polymerized with gamma rays at various temperatures. The thermal properties of product were measured by using a differential scanning calorimeter (DSC) and the structure was analyzed by means of ¹⁹F high speed magic angle spinning nuclear magnetic resonance (¹⁹F NMR). It was found that, the PTFE obtained by the solid-state polymerization has been made clear to be crosslinked.     

Emitting stability of poly（9,9-dialkylfluorene-co-N-butylcarbazole） by solid-state oxidative coupling polymerization

Dihexylfluorene and N-butylcarbazole were copolymerized by solid-state oxidative coupling polymerization in the presence of anhydrous FeCl_3 at room temperature.The solid-state films of the copolymers emitted blue light after heating at 150℃in air for 24 h,no red-shifted emission was observed by fluorescence spectroscopy.     

Synthesis of degradable copolymers by ring-opening polymerization

Hydrolysable copolymers made from different cyclic monomers have been studied. The monomers involved are 1,5-dioxepan-2-one (DXO), L-dilactide, 1,3-dioxan-2-one (TMC), oxepan-2,7-dione (AA) and oxepan-2-one (ϵ-CL). The hydrolysis of the DXO/L-dilactide copolymer showed great differences in degradation rate depending on composition. A statistical copolymer made from TMC and ϵ-CL was amorphous with a glass transition temperature of −48°C. TMC and AA could form a blockcopolymer with n-BuLi as initiator in toluene, 0°C.     

Synthesis of ultra-high-molecular-weight polyacrylonitrile by anionic polymerization

The anionic polymerization of acrylonitrile in DMF initiated by lithium 1,2-bis(diethylamino)-2-oxoethanolate in the range ?60 to 0°C has been studied. The initiator efficiency at low temperatures (?60 to ?40°C) is 2–6%; it remains nearly invariable with conversion owing to the associated state of the initiator. The low concentration of growing active centers is constant throughout the process; as a result, polymers with M > 3 × 10⁵ are produced. The polymers are characterized by a narrow molecular-mass distribution, M _w/M _n = 1.3–1.6, and contain insignificant amounts of low-molecular-mass fractions. It has been shown that controlled polymerization processes can be carried outat moderately low temperatures (?30 to 0°C), and experimental conditions for freezing of polymerization and its recommencement have been ascertained. Optimum conditions for the synthesis of a high-molecular-mass polyacrylonitrile with M > 3 × 10⁵ have been established, and the method for preparing polymers with M = (6.50–8.5) × 10⁵ on an enlarged scale using high concentrations of the monomer has been developed.     

Raman spectral changes during the solid-state polymerization of diacetylenes

Raman spectral changes resulting from the solid-state 1,4-addition polymerization of conjugated diacetylenes are reported. The monomers show an intense C?C stretching frequency near 2260 cm^?1, where as the polymers showed two strong bands, a C?C vibration near 2100 cm^?1 and a C?C vibration near 1500 cm^?1. The presence of both double and triple bonds in the polymers suggests the backbone structure (?C? C?C? C?)_n. The alternate mesomeric structure (? C?C?C?C? )_n can be eliminated as a possibility by the presence of the strong C?C vibration in the polymer. Sequential Raman spectra obtained during radiation-induced polymerization revealed intermediate spectral states between the initial monomer and final polymer. Intermediate-state vibrations first increase and then decrease in intensity as polymerization proceeds. However, the observed vibtrational frequencies of intermediate states were not dependent upon the extent of polymerization. Whether polymerization occurred thermally or as a result of radiation did not appear to influence the spectrum of the final polymer, but the observed number of intermediate states differed. Polymerization mechanisms, required molecular motions, and resulting structural changes are discussed.     

Crystal structure and radiation-induced solid-state polymerization of 1,3,5,7,9,11-hexoxecane

One of the cyclic oligomers of formaldehyde, 1,3,5,7,9,11-hexoxecane, was found to undergo polymerization in the solid state to form polyoxymethylene both during and subsequent to x- or γ-irradiation. The polymer yield increases with polymerization temperature but decreases drastically near the melting point of the hexoxecane crystal. In order to clarify the specificity of the solid-state polymerization, the crystal structure of hexoxecane was first analyzed; hexoxecane forms a trigonal crystal with cell dimensions of a = b = 7.917 Å, c = 11.345 Å, space group R3 –C_3i², three molecules of 3 symmetry per unit cell. The polyoxymethylene as polymerized from a single crystal of hexoxecane is highly crystalline and the crystallites are definitely oriented with respect to the original crystal. There are three kinds of oriented trigonal polyoxymethylene: i.e., with the polymer chains oriented along the 〈100〉, 〈001〉, and 〈210〉 axes of the hexoxecane crystal. The relative yields of these crystallites depend upon the polymerization temperature. In addition to the ordinary trigonal polyoxymethylene, oriented orthorhombic polyoxymethylene was also found in the case of polymerization during treatment with x-rays.