Polymorphosis of poly(oxymethylene) crystals grown in a cationic polymerization system of 1,3,5-trioxane in solution

The morphology of poly(oxymethylene) appearing in the polymerization system of 1,3,5-trioxane in cyclohexane using BF₃ [or BF₃O(C₂H₅)₂] and water catalysis was studied in parallel with the kinetic behaviour of the reaction. Feather-shaped crystals, whose poor reproducibility was a problem, were found to be formed in a limited range of catalytic conditions. As a function of the mole ratio H₂O/BF₃, the change of morphology was ordered as follows: needle-like crystals (H₂O/BF₃<0,05), heterogeneous products (H₂O/BF₃=0,05 to 3), feather-shaped crystals (H₂O/BF₃=3 to 10). and amorphous products (H₂O/BF₃>10). A new type of single-crystal, tapered hexagonal rod, was found in the same catalytic region where feathershaped crystals were formed. The results of older preliminary work in a polar solvent, where a hexagonal, plate-like crystal had been obtained, are also briefly reconsidered in the discussion.     

Solution polymerization of 1,3,5-trioxane and 1,3,5,7-tetroxocane, 1. Rate of polymerization,characterization and melting behaviour of as-polymerized poly(oxymethylene)

A relationship between the rate of polymerization and the structure of the as-polymerized crystals is investigated in the cationic polymerization in solution of 1,3,5-trioxane and 1,3,5,7-tetroxocane. The monomer/solvent reaction systems chosen were: 1,3,5,7-tetroxocane/nitrobenzene (I); 1,3,5,7-tetroxocane/l,2-dichloroethane (II), 1,3,5-trioxane/chlorinated parafin (III), and 1,3,5,7-trioxane/normal paraffin (IV). The poly(oxymethylene), (POM), obtained in each case was characterized as to molecular weight, X-ray cristallinity and by differential scanning calorimetry (DSC). The data from the DSC curves indicated a folded chain structure for systems I and II, where the rate pf polymerization was very high. However in system II at high polymer conversion a fraction of POM appears with a melting behaviour characteristic of an extended chain structure. For systems III and IV, where the rate of polymerization was very low, the DSC curves indicated the presence of two crystal forms. One of these forms shows a clear response to overheating and annealing treatments, which indicates the presence of an extended chain structure. The second form shows ambiguous melting behaviour and by thermal data alone it is impossible to determine its structure.     

Solution polymerization of 1,3,5-trioxane and 1,3,5,7-tetroxocane, 2. Morphology of the as-polymerized poly(oxymethylene) crystals

The morphology of poly(oxymethylene), (POM), crystals obtained from different monomer/solvent polymerization systems was studied by means of electron microscope techniques. POM obtained from 1,3,5,7-tetroxocane in nitrobenzene had an irregular hexagonoidal shaped lamellar morphology, while rhombic POM crystals were obtained from the polymerization of 1,3,5,7-tetroxocane in 1,2-dichloroethane. Both types of crystals probably have a folded chain structure. POM obtained from 1,3,5-trioxane in normal (unbranched) paraffin represented the feather-like crystals with proliferating lateral growths. POM obtained from 1,3,5-trioxane in chlorinated paraffin presented numerous crystals of different morphologies. Two main groups could be discerned: one consisted of variations of the basic feather-like crystal, while the other comprised more geometrically triangular and orthorhombic morphologies. All these crystals presented lateral growths, and toward the end of the polymerization a fibrous morphology prevailed. Evidence points to their being crystals of an extended chain structure.     

Electroinitiated cationic polymerization by anodic dissolution

The polymerization of several monomers, such as styrene, α-methylstyrene, lactones, isobutyl vinyl ether, and hexamethylcyclotrisiloxane, was carried out in H-shaped cells equipped with sacrificial anodes. The solvents, dichloromethane or nitromethane, contained tetrabutylammonium perchlorate playing the role of supporting electrolyte. Among the different metals tested (Cu, Ag, Hg, Al, Pb, Sn), only mercury and aluminium anodes gave initiation. The conditions of the electrolysis, the nature of the monomers, and the results of special experiments carried out in the presence of a hindered pyridine demonstrate that the polymerization involves the electrophilic addition of the active species to the monomer followed by cationic chain growth.     

Polymerisation of 1,3,5-trioxane in presence of maleic anhydride, 2. An example of cationic living polymerisation

Evidence is presented for the possible existence of ‘living’ ends in the cationic polymerisation using ZnCl₂, BF₃ · OEt₂, and γ-rays as initiators of 1,3,5-trioxane to polyoxymethylene in presence of maleic anhydride (1 : 1 by mole), where this binary system exists as a melt.     

Kinetics and mechanism of the polymerization of cyclic acetals initiated by stable carbenium salts. II. Confirmation of the initiation mechanism for triphenylmethyl hexachloroantimonate in the polymerization of 1,3-dioxolan

The interaction of triphenylmethyl hexachloroantimonate (I) with 1,3-dioxolan (II) gives the corresponding dioxolenium salt IV which decomposes into β-chloroethyl formate (V) and antimon pentachloride (VI) (Eq. (2)) or acts as initiator by reacting with 1,3-dioxolan (Eq. (3)). Triphenylmethyl tetrachloroantimonate does not initiate polymerization of 1,3-dioxolan but forms exclusively β-chloroethyl formate. SbCl₅, formed according to Eq. (2), reacts with 1,3-dioxolan to produce again the dioxolenium salt IV together with HCl and non-initiating by-products: SbCl₃ and (CH₃OCH₂CH₂O)_n SbCl_5hyphen;n, in proportions depending on the reaction conditions. β-Chloroethyl formate has been found to be present in the polymerization mixture at concentrations close to those calculated on the assumption that the reaction between the original initiator (I, IV, VI, triethyloxonium hexachloroantimonate or triphenylmethyl tetrachloroantimonate) and 1,3-dioxolan as well as the further decomposition of IV go to completion. All the initiators (In) give the same polymerization rates which are proportional to [In]₀ in toluene solution and proportional to [In]²₀ in dichloromethane solution. Considering the competitive consumption of the initiator and the formation of the true initiating species these results can be rationalized by the analysis of the kinetics according to the reaction scheme. Polymerization has been found to be of first order in monomer and to proceed without an induction period. Thus, initiation is fast, in agreement with the previously measured rates of hydride transfer to the triphenylmethyl cation and the fast decomposition of the dioxolenium salt in the presence of 1,3-dioxolan.     

ESR measurements during γ-radiation induced solid-state polymerization of 1,3,5-trithiane

The time-dependences of ESR spectra were measured during the γ-radiation induced solid-state polymerization of 1,3,5-trithiane to polythiomethylene. The reaction was carried out at several temperatures, both under air and under N₂. The initial reaction kinetics are second order, but become of lower order at the highest temperatures under air. Mass spectrographic results indicate spontaneous degradation under these high temperature conditions. It is concluded that an observed peak in reaction rate with temperature derives from the onset of spontaneous chain termination.     

The electroinitiated polymerization of N-vinylcarbazole with zinc bromide,II. Kinetics of polymerization

The electroinitiated polymerization of N-vinylcarbazole (VCZ) in acetone solvent at 25°C with zinc bromide, as catalyst, and platinum electrodes was investigated in detail. The polymerization rate was found to be directly dependent on current strength, zinc bromide concentration and the initial water content of the solvent. The molecular weights of the formed polymers (1000–6000) are independent of current strength, zinc bromide concentration and degree of conversion of monomer to polymer, but are affected by water, monomer concentration, and by the type of electrodes used. The chemical composition of the polymer is invariant with current strength, zinc bromide concentration, degree of conversion, and electrode material but does vary slightly with the water content of acetone.     

The polymerization of acrylamide initiated with ceric ion

As part of an investigation of the graft copolymerization of acrylamide onto fibrous polymers, the homopolymerization of acrylamide initiated with relatively high concentrations of ammonium cerium (IV) nitrate was studied. The resulting polyacrylamide was purified by means of fractionation with Sephadex. The polymer contains one cerium atom per molecule, probably as an end group. Paper electrophoresis showed that the cerium atom is combined chemically to the polymer molecule. The IR spectrum of the polymer did not differ from that of polyacrylamide initiated by potassium persulfate, except the bands assigned to nitrate ion. The spectrum showed no band assigned to an unsaturated end group. A novel termination mechanism of the polymerization or formation of a complex compound between polymer and cerium is expected.     

Application of spin trapping technique to radical polymerization, 12 The polymerization of N-vinylcarbazole with benzoyl peroxide

To clarify the initiation and propagation mechanisms of the polymerization of N-vinylcarbazole ( 1 ) initiated by benzoyl peroxide ( 2 ), the spin trapping technique using 2-methyl-2-nitrosopropane ( 5 ) was applied. From the ESR spectrum observed from this system, the 1-(N-carbazolyl)-2-benzoyloxyethyl radical ( 6a ) was found to be trapped as its nitroxyl radical 6b , which was confirmed by a comparison with similar nitroxyl radicals ( 7b and 8b ) derived from the systems, di-tert-butyl peroxalate/ 1/5 and 2 /N-ethylcarbazole/ 5 , respectively. Therefore, it was concluded that the 1/2 system produces easily a primary propagating radical of 1 viz. 6a . Further, the monomer 1 was found to show a remarkable accelerating effect on the radical decomposition of 2 . From the copolymerization of 1 with styrene initiated by 2 , it was concluded that 6a propagates by ordinary successive ß-attack to the monomer 1 .     

The effect of the tetraethylammonium ion on the delayed currents of frog skeletal muscle

1. A method which permitted control of the membrane potential near the end of a muscle fibre and measurement of an approximation of the membrane current was used to investigate the effects of the tetraethylammonium (TEA) ion on the delayed outward potassium current obtained on depolarizing.2. Assuming R(i) to be 250 Omega cm and a fibre diameter of 80 mu, the mean value for the maximum potassium conductance (g(K)) was 23.2 +/- 3.2 mmho.cm(-2).3. 58 mM-TEA, in two series of experiments, reduced g(K) by about 90%. A concentration-effect relation for TEA in its action on the delayed rectifier could be fitted by a curve for a drug-receptor complex assuming one molecule of TEA to combine reversibly with one receptor, and a dissociation constant of 8 x 10(-3)M.4. TEA tended to shift the threshold for delayed rectification to slightly more negative membrane potentials. TEA caused a similar shift in the relation between n(infinity) and membrane potential, but did not much alter the form of the relation.5. The relation between n(infinity) and membrane potential and between tau(n) (-1) and membrane potential were well fitted by the model of Adrian, Chandler & Hodgkin (1970a) assuming that the Q(10) was 2.5.6. TEA slowed the rate of onset of the delayed potassium currents, decreasing tau(n) (-1) (the reciprocal of the time constant of the fourth power function which described the current's development) by about 80%.7. The inactivation of the delayed current with time was shown to follow a complex time course. A fast phase decays with a time constant of 270 msec and a slow phase with a time constant of 2.3 sec at a membrane potential of + 10 mV.8. The fast phase of the delayed current is much more susceptible to the action of TEA than the slow phase, and these are interpreted in terms of different potassium channels. TEA has little effect on the time constant with which either the fast current or the slow current inactivates.     

The anionic polymerization of methyl methacrylate with a bifunctional initiator

Using a bifunctional initiator such as the tetrameric dianion of α-methylstyrene for the anionic polymerization of methyl methacrylate the rate constant is found to increase with conversion approaching that observed with a monofunctional initiator while the tacticity of the polymers obtained changes from that of an almost ideally atactic to a highly syndiotactic polymer. The results are explained by the assumption of an intramolecular association of the two terminal ion pairs yielding a new active species and gradually dissociating with increasing degree of polymerization of the chain. Using a polymeric dianion of α-methylstyrene as an initiator the association phenomenon is not observed.     

Rapid interaction of tetraethylammonium with delayed K+ channel in mammalian brain neuron.

In order to study the rapidity of interaction between tetraethylammonium (TEA) and the delayed K+ channel of the mammalian brain neuron, TEA was applied to isolated rat hippocampal pyramidal neurons in a time-controlled sequence with a voltage step using a concentration clamp technique. TEA at a concentration of 30 mM, externally applied, started to decrease the delayed K+ current (IKD) without any detectable delay after the onset of the drug application. The inhibitory action of TEA reached a steady state within 10 ms while the full recovery from the inhibition required 20-30 ms after removing TEA from the external solution. Ba2+ at a concentration of 30 mM also reduced the IKD without any detectable delay. However, it took 40-60 s to reach the steady state of inhibition. Full recovery from the inhibition by Ba2+ was obtained around 60 s after removal of Ba2+ from the external solution. It is suggested that the interaction of TEA with the delayed K+ channel is much faster than that of Ba2+.     

Secretion of tetraethylammonium by proximal tubules of rabbit kidneys

The secretory transport of tetraethylammonium (TEA) was investigated in perfused and nonperfused isolated S1, S2, and S3 segments of proximal tubules from rabbit kidneys. In the perfused tubules the transepithelial net secretory flux and in nonperfused tubules the TEA cellular uptake were saturable (Km = 67 microM, Vmax = 2,480 fmol X min-1 X mm-1 in perfused S2 segments), energy dependent, and inhibited by mepiperphenidol. The net secretory flux of TEA (J b leads to j TEA) at a bath TEA concentration of 40 microM differed for the three segments and decreased in the order S1 greater than S2 greater than S3. The concentration of TEA in the perfusate leaving the tubule was approximately twice as great and the intracellular TEA concentration approximately 40 times as great as that in the bath. In nonperfused segments (40 microM TEA in the incubation medium) the TEA tissue water-to-medium ratio reached 100. In the three segments the ability to accumulate TEA across the peritubular membrane, thus, was similar, but the transepithelial secretory flux differed significantly. The differences in secretory rate between the three segments presumably result from differences in the luminal membrane permeability.