Studies in some new initiator systems for vinyl polymerization. Part I. Molecular halogens or halates as one component

Several new initiating systems involving a molecular halogen, halates, or perhalate as one of the components and a reducing metal salt, ammonia, an amine or an organic compound as the other component, have been introduced for the aqueous (and in a few cases the non-aqueous) polymerization of methyl methacrylate. Some of the resulting polymers have been subjected to endgroup analysis by the application of the ultrasensitive dye techniques recently developed in our laboratory. Reducing metal salt—halogen-initiated polymers are found to incorporate hydroxyl and halogen endgroups, while polymers initiated by amine—halogen systems incorporate hydroxyl and halogen as well as amino endgroups. However, in the ammonia—halogen system polymers incorporate only halogen endgroups. On the basis of the results of the endgroup analysis of the polymers an attempt has been made to explain the probable initiation mechanism with regard to the nature and identity of the initiating species involved in such processes.     

Mechanistic studies of thiol-dimethylsulfoxide initiated polymerization of methylmethacrylate from endgroup analysis

Summary Endgroup analysis of polymethylmethacrylate obtained by initiation with thiol-dimethyl sulfoxide systems has been carried out using dye-techniques developed in our laboratory. Thiols used are 2-mercaptoethylamine hydrochloride, 2-mercaptoethanol, thioglycolic acid and n-butane thiol. The first three thiols incorporated amine, hydroxyl and carboxyl endgroup respectively to the extent of about one per macromolecule, while the last one as expected produced none of the above functional endgroups in the polymer. In the light of endgroup results initiation through thiyl radicals has been suggested. Probable termination mechanism has also been discussed.

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Zusammenfassung Die Endgruppenanalyse von Polymethylmethacrylat, das durch Initiierung mit Thioldimethylsulfoxid-Systemen hergestellt war, wurde unter Anwendung unserer in unserem Labor entwickelten Färbungstechnik durchgeführt. Die verwendeten Thiole waren 2-Mercaptoäthylaminhydrochlorid, 2-Mercaptoäthanol, Thioglykolsäure und N-Butandiol. Die ersten drei Thiole fügten Amin-Hydroxyl- und Carboxyl-Endgruppen respektiv bis zum Betrag von etwa einer pro Makromolekül ein, während das letztere wie erwartet keine der oben genannten funktionalen Endgruppen im Polymer erzeugte. Aufgrund dieser EndgruppenResultate wird auf eine Initiierung durch Thiylradikale geschlossen. Der wahrscheinliche Abbruchmechanismus wird ebenfalls diskutiert.

     

Studies in some new initiator systems for vinyl polymerization. III. Amine–halogen systems as redox initiators

Amine–halogen redox systems are very efficient initiators of polymerization of a number of vinyl monomers in benzene media and are rather inefficient initiators in aqueous media. A large number of aliphatic amines and a few aromatic amines have been used. Among the halogens, chlorine and bromine are very effective. Iodine initiates with a few amines only. Endgroups incorporated are halogen and amine totalling an average of nearly one per chain in the case of polymerization in benzene media and 0.5–0.7 per chain in polymerization in aqueous media. In the light of endgroup results, a mechanism of initiation through halogen and amine radicals has been suggested.     

Detection and incorporation of amino endgroups in free-radical polymerization of methyl methacrylate

Amino endgroups have been incorporated in poly(methyl methacrylate) by two methods: (a) initiation with systems producing amine radicals and (b) chain transfer with amines. A new dye-partition technique with the use of disulfine blue was developed for qualitative and in some cases quantitative estimation of amino endgroups in the polymer.     

Haloaldehyde Polymers. XIV. Endgroups in Polychloral

Chloral polymers prepared by anionic polymerization have alkoxide endgroups as terminal ends at the end of this polymerization. The initiating anion has, as expected, no influence on the type of terminal group formed. Polychloral with terminal alkoxide ends degrades easily thermally to monomeric chloral. Alkoxide endgroups in polychloral do not readily react with alkylating or acylating agents, although partial stabilization has been observed when alkoxide-terminated polymers were allowed to stand for periods of time; the endgroups seem to react either with impurities or with excess chloral in side reactions. With protic acids, alkoxide-terminated polychloral is transformed into hydroxyl-terminated polymer of higher thermal stability. Studies of the initiation step of the chloral polymerization revealed that above the ceiling temperature of polymerization, strong nucleophiles, such as soluble tertiary butoxide, initiate quantitatively, but polymerization does not proceed until the mixture is cooled. When chloral is initiated with weaker nucleophiles such as chloride or carboxylates, the initiation equilibrium is not on the side of the initiated species, although it shifts effectively as polymerization proceeds; with carboxylates as initiators the ester group has been found incorporated as the initial endgroup in polychloral. With sufficient amounts of lithium tertiary butoxide as anionic initiator, polychloral of low molecular weight was prepared. This polymer does not react with end-capping reagents (other than PCl₅) as does high molecular weight polychloral; in spite of considerable effort it was not possible to prepare low molecular weight soluble polychloral or oligomeric polychloral. Polychloral prepared with cationic initiators is thermally more stable than unstabilized anionically initiated polychloral but is generally crumbly and incoherent. The end-groups of such polymers are usually hydroxyl endgroups. Identification of endgroups of the polymers has been done where possible by IR spectroscopy, for the initiation reaction by NMR spectroscopy, but for high molecular weight insoluble polymers almost exclusively by comparative thermal polymer degradation.     

Studies in some new initiator systems for vinyl polymerization. IV. Amino acids as the reducing component

Amino acids have been found to form good redox initiator systems with halogens (Cl₂ and Br₂), KBrO₃, KMnO₄, and Fe(NH₄)(SO₄)₂. The three systems, viz., glycine–Cl₂, taurine–Cl₂, and sulfamic acid–Cl₂ incorporate amine, carboxy (or sulfoxy), chlorine, and hydroxy endgroups in the resulting polymers, the monomer investigated being mainly methyl methacrylate. On the basis of endgroup results it is suggested that initiation through amino acid radical, chlorine radical and also through some hydroxyl radicals takes place. The probable termination mechanism is discussed.     

Endgroup-based separation and quantitation of polyamide-6,6 by means of critical chromatography

Polyamide-6,6 is a polycondensation product from the two monomers adipic acid and 1,6-hexamethylenediamine. Depending on the reacted amount of these monomers, different ratios of amine and carboxylic acid endgroups can be formed. Besides linear chains, cyclic polyamides will also be formed. Using critical chromatography, polyamide-6,6 can be separated independently of molar mass. Retention is based solely on endgroup functionality. It is demonstrated that high-molecular-mass polyamide-6,6 (Mw approximately 20,000-30,000) can be separated using this approach. The separation was optimized by using different parameters, such as percentage modifier, temperature and pressure. The concentration of phosphoric acid was used for selective retention of the different endgroup functionalities. Using this property, a new method called critical gradient chromatography was performed where the mobile phase changes from a weak to a strong solvent with respect to the endgroup functionality, while retaining the critical conditions of the backbone unit. Quantification using UV detection is discussed.     

Studies in some new initiator systems for vinyl polymerization. II. Ammonia–halogen system as the redox initiator

The ammonia–halogen redox system has proved a promising initiator for polymerizing a number of vinyl monomers in aqueous media. Chlorine and bromine are most efficient, whereas iodine fails to initiate polymerization, probably due to its inhibitive tendency. Endgroups are halogen and amine and total about 0.5 per chain. On the basis of results of endgroup analysis, a mechanism of initiation through halogen and amine radicals, mainly through hydrogen atoms, is suggested. Consistent with the proposed mechanism the endgroup profile changes significantly with changes in pH.     

Novel route for synthesizing hyperbranched polyamine

A novel route for the synthesis of hyperbranched polyamine containing imidazolidine rings was developed, proceeding by the step‐growth polymerization of acrolein with ethylene diamine. The reaction kinetics and polymerization mechanism were studied with NMR and ultraviolet–visible spectroscopy. The influence of the reaction temperature and the concentration and feed ratio of the reactants on the structural characteristics of the obtained products was investigated. To obtain stable hyperbranched polyamines as analogues of hyperbranched poly(ethylene imine) or dendrimeric poly(propylene imine), sodium borohydride was used to reduce the synthesized hyperbranched polyamines to open the imidazolidine rings. The molecular weights, degrees of branching, and glass‐transition temperatures of the hyperbranched polyamines before and after reduction were compared. The polymerization behaviors of acrolein with other amines such as ethanol amine, propylene diamine, and 1,6‐hexane diamine were also investigated. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 699–708, 2007     

Redox-initiated vinyl polymerization with thiourea as the reductant

A few redox systems containing thiourea as reductant have been found to be quite effective in initiating vinyl polymerization in aqueous media and polymers obtained in the process have all been found to contain amino endgroups to various extents by the application of dye techniques. Quite a few oxidants have so far been utilized for this purpose; among them are ferric chloride (Fe³⁺), ethylene dibiguanide complex salts of tripositive silver (Ag³⁺), hydrogen peroxide (H₂O₂), persulfate (S₂O₈^2?), bromate (BrO₃^?) + hydrochloric acid (HCl). In case of oxidants Fe³⁺ and Ag³⁺, amino endgroups are mainly incorporated in polymers; but in case of oxidants H₂O₂ and S₂O₈^2?, fragments of oxidants are also incorporated as hydroxyl and sulfate endgroups. BrO₃^?, however, forms a very efficient redox-initiating system with thiourea, as is evidenced by its capability of polymerizing even hydroquinone-stabilized water-soluble vinyl monomers at very low temperature (～0°C.) and at a quite rapid rate. Besides amino endgroups, sulfonate endgroups have also been detected in polymers in this case, and the relative extents of these two types of endgroups depend generally on the acid concentration of the system. Evidences so far collected indicate the generation of S? C(?NH)NH₂ radicals in the system by oxidation of isothiourea, HS? C(?NH)NH₂, and these are incorporated in polymers as endgroups. Sulfonate endgroups may be generated by oxidation of these amino-bearing endgroups. Suitable initiation mechanisms have been suggested in each case.     

CONCERNING THE ORIGIN OF CHARGE AT THE POLYSTYRENE PARTICLE/WATER INTERFACE

The electrophoretic mobility behavior of well-characterized polystyrene latex particles, carrying one type of surface functional endgroups, has been studied as a function of pH. At low pH, the interaction of protons with the functional endgroups increased in the order: Hydroxyl > carboxyl > sulfate; at high pH the order of interaction was reversed; and at intermediate pH no interactions were observed. The particles of the polystyrene latexes in their different forms at the intermediate pH range, dispersed in deionized water, all exhibited the same mobility irrespective of the functional endgroup. The origin of charge in these systems is explained as being the result of either the preferential adsorption of hydroxyl ions or an electron - injection mechanism due to the overlap of local intrinsic molecular - ion states in polystyrene and water. At low concentrations of functional endgroups, the surface properties of the polystyrene latexes are largely dependent upon the hydrophobic nature of the surface.     

Mechanistic studies on ceric-thiourea-initiated polymerization of methyl methacrylate in acid-aqueous media from end group analysis

The mechanism of the redox polymerization of methyl methacrylate in acid-aqueous medium was studied for ceric-thiourea initiator system by analysis of polymer end groups using the dye partition method. Polymerization at room temperature and at pH 2.30 with this initiator system incorporates mostly amino end groups in the polymers to the extent of 1.18-1.31 and a small amount of hydroxyl end group not exceeding 0.08 per polymer molecule. Under the same pH condition, a higher polymerization temperature increases the amine end group content to 2.17-2.30 and hydroxyl end group content to 0.14-0.18 per polymer molecule. A lower polymerization temperature (5°C), or a lower pH (ca. 1) of the reaction medium, produces polymers with exclusively amine end groups, hydroxyl end groups being totally absent. At pHs greater than 3, amine end group incorporation decreases significantly, with simultaneous increase in hydroxyl incorporation. On the basis of end group results the initiating radical has been identified and the mechanism of initiation has been suggested. The possible mode of termination has also been discussed.     

Oligomerisation anionique de l'ethylene—VII. Application a la synthese d'acides a longue chaine

Living oligomers of ethylene obtained with nBuLi complexed by tertiary amines, such as tetramethylethylene diamine (TMEDA), tetraethylethylenediamine (TEEDA) and pentamethyldiethylenetriamine (PMDT), have been deactivated by gaseous carbon dioxide or dry ice. The nuclear magnetic resonance study of the product has allowed study of the influence of the tertiary amine and the nature of the deactivation agent toward the functionalization. Two products have been characterized:

By increasing the ratio [tertiary amine]/[nBuLi] and using gaseous carbon dioxide instead of dry ice, one obtains a decrease of the functionalization.     

Use of Some Organic Acids and Amines as Photoinitiators of Vinyl Polymerization in the Absence and in the Presence of Benzophenone Photosensitizer

Preliminary studies on the suitability of some organic acids and amines, separately and in combination with each other, as photo-initiators for the polymerization of methyl methacrylate were made. Combinations of maleic acid or phthalic acid with any of the tertiary amines–triethyl amine, demethyl aniline, and diethylaniline-proved to be interesting photoinitiator systems in view of the fact that the initiator components in each combination were ineffective as initiators when used separately. The rate of photopolymerization in each of the above acid-amine combination system was much enhanced and the respective inhibition period largely reduced when benzophenone was used as the photoinitiator. Aliphatic diamine or polyamines such as ethylene diamine, diethylene triamine, and tri-ethylene tetramine, were ineffective as photoinitiators when used alone or in combination with maleic acid, but became effective     

粉状白钨酸的研究(Ⅻ)——某些聚钨酸有机铵盐的合成和性质

以粉状白钨酸和三种有机铵--乙二胺、乙醇胺和异丙胺为原料,分别合成了偏钨酸盐和仲钨酸盐。通过紫外,红外光谱、核磁共振谱以及极谱测定,研究了三种不同类型有机胺聚钨酸盐的组成与性质,发现乙醇胺和异丙胺的偏钨酸盐具有光敏性。     

Haloaldehyde Polymers. XIX. Degradation Behavior of Chloral Polymers

Thermal stability of samples of polychloral prepared with different initiators and treated with various endcapping agents was studied using differential thermogravimetric analysis (DTG). Four temperature regions at which maxima of DTG curves occur were identified. On the basis of the known mechanism of initiation and the possible mechanism of termination, the structures of both initial and terminal endgroups of individual polychloral samples were elucidated which enabled the identification of the specific temperature region of thermal degradation of polychloral molecules having a specific type of endgroup. These results were confirmed by studies of the DTG curves of chloral-isocyanate copolymers containing stable terminal fragments with a high content of urethane linkages.     

Iridium-catalyzed, substrate-directed C-H borylation reactions of benzylic amines

The iridium-catalyzed arene C-H borylation reaction of benzylic amines has been developed, which inverts the typical steric-controlled product distribution to provide ortho-substituted boronate esters. Picolylamine was found to be an ideal ligand to replace 4,4'-di-tert-butylbipyridine to induce the directing effect. Preliminary experiments are consistent with a mechanism involving dissociation of one amine of the hemilabile diamine ligand.     

Hydrogen bonding by alcohols and amines

The pure base calorimetric method has been used to determine the enthalpies of hydrogen bond complex formation between aliphatic amines and alcohols. The enthalpies of complexation for the series methanol-n-butanol bonding with triethylamine increase with decreasing alkyl chain length in accordance with the electron donating properties of alkyl groups. Unexpectedly, the enthalpies for the complexes of n-butanol with tributylamine, tripropylamine, and triethylamine increase with decreasing alkyl chain length.Primary and secondary amines form hydrogen bonded complexes with n-butanol in which the amine protons form an NH···O bond with the alcohol and the alcohol hydroxyl proton donates a proton to the amine nitrogen. The difference in enthalpy of complex formation between tertiary amines and secondary amines is largely accounted for by the involvement of the amine proton of the secondary amine. Primary amines, like secondary amines, donate only one proton to the complex with n-butanol but have a larger complex enthalpy than secondary amines probably because of steric hindrance and differences in basicity.     

Mode of termination in the copolymerization of vinyl acetate–isobutyl methacrylate and methyl methacrylate–methyl acrylate at 60°C

The mode of termination in the vinyl acetate–isobutyl methacrylate (VA–IBMA) and methyl methacrylate–methyl acrylate (MMA–MA) copolymerization systems has been investigated at 60°C. by using the dye-interaction technique for functional endgroup estimation. The results show that pairs of poly(vinyl acetate) radicals interact almost exclusively through a disproportionation mechanism. In the homopolymerization of methyl methacrylate and methyl acrylate, about 1.16 and 1.22 carboxyl-containing endgroups per polymer molecule have been estimated, which shows the predominance of disproportionation over combination in these termination reactions. In poly(isobutyl methacrylate) about 1.55 tagged initiator fragments per chain indicate that 29% of the total radicals terminate through the disproportionation mechanism. Cross termination in the (VA–IBMA) copolymerization system occurs almost entirely through combination for monomer feeds richer in isobutyl methacrylate content while for the MMA–MA system, combination is more important at intermediate monomer feed ratios. These results have been discussed in the light of different explanations for the reaction mechanism.     

Conformational behavior of dodecyldiamine inside the confined space of montmorillonites

We have investigated the change of the intercalated amount and conformational behavior of dodecyldiamine (C(12)H(28)N(2), di-C(12)amine) inside the confined space of the montmorillonite (MMT) intergallery at different pHs of the intercalation solution (H(2)O/ethanol/Na(+)-MMT/di-C(12)amine), and these results were compared with those of dodecylmonoamine (C(12)H(27)N, mono-C(12)amine). The mono-C(12)amine with one end-functional amine (-NH(2)) has a constant intercalated amount independent of the pH of the intercalation solution, confirming the tail conformation in the MMT intergallery. On the other hand, the intercalated amount of di-C(12)amines remains quite low at low pH due to the long-range Coulombic repulsion among protonated amines. The di-C(12)amines dominantly take the bridge conformation inside the MMT intergallery up to pH 9.5 and adopt a fraction of the tail conformation at pH 11.5, which is verified by Fourier transform infrared spectra with an abrupt frequency shift of the CH(2) stretching band and the emergence of a new NH(2) scissoring band at 1598 cm(-)(1) related to unanchored free amines. The d-spacing and the square of the half-width at half-maximum of the MMT based on X-ray diffraction measurements are also constant up to pH 9.5, while these two variables are suddenly increased at pH 11.5. The bridge conformation of di-C(12)amines in the confined space of the MMT intergallery prevents poly(ethylene oxide) chains from intercalation into the MMT intergallery, called the gluing effect.