Vinyl polymerization by metal complexes, 19. Formation of copper(II) chelates of vinylamine/vinyl alcohol copolymers

Chelate formation of vinylamine/vinyl alcohol copolymers with copper(II) was studied both by the spectrophotometric and by titrimetric methods. For comparison, polyvinylamine/poly(vinyl alcohol) mixtures were also taken up for measurements. In the case of the copolymer systems, copper(II) ions were found to be coordinated exclusively by nitrogen atoms of the copolymer ligand. The complexation constants of the chelates were determined by applying the modified Bjerrum method, in neglect of the acid dissociation of hydroxy groups in the copolymers. It was found that the copolymer/Cu(II) chelates tend to be unstable with decreasing contents of NH₂ groups in the copolymers. In the homopolymer mixture systems, copper(II) ions are not coordinated by the oxygen atoms of poly(vinyl alcohol), but only by the nitrogen atoms of polyvinylamine.     

Organometallic compound with lewis base, 3. Polymerization mechanism of vinyl compounds by aluminum alkyl-lewis base complex

Complexes of aluminum alkyl (AlR₃), formed with certain kinds of Lewis bases, induce anionic polymerization of polar vinyl compounds such as acrylonitrile (AN) or methyl methacrylate (MMA), whereas AlR₃ by itself cannot polymerize AN and MMA anionically. When the ligand Lewis base is bidentate, the resultant complex with a formal coordination number of five shows high catalytic activity for anionic polymerization even if the basicity of the ligand is small. On the other hand, when the ligand Lewis base is monodentate, the complex is four-coordinated and shows catalytic activity for the polymerization of AN and MMA only when the basicity of the ligand is sufficiently large. The initiation reaction for the polymerization of 1-substituted vinyl compounds such as MMA should be the conjugate addition of one alkyl group of the activated AlR₃ to the monomer. With 1-unsubstituted vinyl compounds such as AN or methyl acrylate (MA), a part of the initiation and the chain transfer reactions seem to take place through the abstraction of the 1-hydrogen of the vinyl monomer molecules.     

Alternating copolymerization of conjugated vinyl monomers with isobutylene,styrene, and vinyl acetate in the presence of ethylaluminum dichloride

Copolymerization of acrylonitrile (AN), methacrylonitrile (MAN), methyl vinyl ketone (MVK), methyl acrylate (MA), and methyl methacrylate (MMA), complexed by ethylaluminum dichloride, with isobutylene (IB), styrene (St), and vinyl acetate (VA) was studied. It was found to proceed spontaneously resulting alternating copolymers. The reactivity of the polar monomers complexed by EtAlCl₂ in their copolymerization with St and IB was investigated and found to decrease in the following order: AN > MAN > MA > MMA and AN > MVK > MA, respectively, (MAN and MMA do not give copolymers with IB). A correlation of the copolymerization yield with the e value for the uncomplexed monomers investigated was observed.     

Temperature and pH dependence of the catalytic activity of colloidal platinum nanoparticles stabilized by poly[(vinylamine)‐co‐(N‐vinylisobutyramide)

Colloidal platinum nanoparticles in the size range of 5–35 Å have been successfully prepared in water at room temperature by NaBH₄ reduction of ionic platinum in the presence of poly[(vinylamine)‐co‐(N‐vinylisobutyramide)] (PVAm‐co‐PNVIBA). To our knowledge, the temperature‐ and pH‐responsive copolymer was used for the first time as the stabilizer of colloidal metal particles. Three PVAm‐co‐PNVIBA copolymers with PVAm contents of 4.1, 8.3, and 19.8 mol‐% were examined. The particle size and morphology of the platinum colloids varied with the copolymer composition, as confirmed by TEM measurements. The polymer‐stabilized Pt nanoparticles precipitated on heating above their critical flocculation temperatures (CFTs), which were strongly dependent on the solution pH and the copolymer composition. The CFTs were 0.2–1.6°C lower than the lower critical solution temperatures (LCSTs) of the copolymers free in water and the differences increased with increasing PVAm content. The catalytic activity of the Pt nanoparticles was investigated in the aqueous hydrogenation of allyl alcohol. It was found that the activity was regulated through temperature‐ and pH‐induced phase separation. The PVAm content also strongly effected the catalytic activity and the morphology of phase separated catalysts. With a PVAm content of 4.1 mol‐%, the colloidal platinum sol reversibly changed its catalytic activity with changes in temperature.     

Microdomain control in graft copolymer and polymer blends by means of epitaxial growth

Poly(vinyl acetate) (PVAc) and poly(tert-butyl methacrylate) (PBMA) macromonomers with vinyl end-groups were synthesized by radical or anionic polymerizations. 4-Vinylpyridine (4VP)/vinyl acetate (VAc) and 4VP/tert-butyl methacrylate (BMA) graft copolymers were prepared by radical copolymerization of these macromonomers with 4VP as a comonomer. The 4VP/vinyl alcohol (VA) graft copolymer was derived from alkaline hydrolysis of 4VP/VAc graft copolymer. After having fixed the microdomains of 4VP/VA graft copolymer film, the solution of graft copolymer (or polymer blends) was cast on a support film of 4VP/VA graft copolymer. It was shown that the domain structure of the upper layer is governed by epitaxial growth of the microdomain pattern of the support film surface.     

Microdomain control of block copolymers by epitaxy in mesophases

Poly(vinyl alcohol(VA)-b-4-vinylpyridine(4VP))s were prepared by mechanochemical scission of PVA in the presence of 4VP monomer under ultrasonic irradiation. After establishing the morphology of a particular specimen of these block copolymers, a solution of well-defined poly(styrene(ST)-b-4VP), prepared by anionic living polymerization, was cast on the above mentioned specimen being used as a support membrane. It is shown that the microdomain structure of poly(ST-b-4VP) may be governed by epitaxial growth of the microdomain pattern of the support membrane surface.     

Graft copolymerization of methyl methacrylate by lithium diisopropylamide-treated poly(vinyl propionate)

The anionic grafting of methyl methacrylate (MMA) onto poly(vinyl propionate) (PVPr) was achieved after treatment of the latter with lithium diisopropylamide (LDA). The percentage of grafting of the polymer was between 120 and 730%, no homopolymers being obtained. The degree of lithiation was determined to be 26 mol-% with respect to monomer units by means of deuterolysis. The hydrolysis of the graft copolymers results in the side-chain polymers (PMMA) and poly(vinyl alcohol) (PVA). The average number of branches in the graft copolymer increases from 1 to 7 with increasing percentage of grafting. M?_w/M?_n of the side chain poymer is between 2,0 and 6,7. The low reactivity of the lithium sites may be caused by aggregation of enolates, leading of the broadening of the molecular weight distribution.     

Vertically-oriented charge mosaic microdomains by means of epitaxial growth

Vinyl alcohol (VA)/4-vinylpyridine (4VP) graft copolymers were prepared by the macromonomer method. After domain fixing of the PVA matrix of this graft copolymer, the water/1-propanol mixed solution of poly(sodium p-styrenesulfonate) (PSSS)/P4VP polymer blends was cast on the microheterophase surface of VA/4VP graft copolymer which served as a support membrane. The surface characterization of this composite membrane was carried out by means of transmission electron microscopy (TEM) and Electron Spectroscopy for Chemical Analysis (ESCA). The TEM observation indicated that charge mosaic microdomains formed by means of epitaxial growth are oriented perpendicularly to the film surface. The ESCA results clearly indicated that the two-phase composition of the surface (in sampling depths of ≈ 1 and ≈ 5 nm) is proportional to the overall bulk composition of the polymer blends.     

Der einfluß aromatischer azoverbindungen auf die polymerisation von vinylacetat,vinylchlorid und methylmethacrylat

The effect of aromatic azo compounds on the polymerization of vinyl acetate (VA), vinyl chloride (VC), and methyl methacrylate (MMA) was investigated with respect to initiation by di-(3-benzeneazobenzoyl)-peroxide (mABPO) as well as the effect of added aromatic azo compounds on the polymerization initiated by dibenzoylperoxide (BPO). With VA polymer formation occurred in neither case, so that aromatic azo compounds are considered to be inhibitors in the polymerization of this monomer. With VC and mABPO only negligible polymer yields were obtained in comparison to corresponding concentrations of BPO; addition of azobenzene to the BPO-initiated polymerization led to an extensive suppression of polymerization. With MMA only a weak retardation was found in similar experiments and the rates of polymerization obtained with mABPO were of the same order of magnitude as those with BPO-initiation. Owing to the low extent of side reactions occurring with aromatic azogroups during the polymerization of MMA the basic requirements for a “colorimetric” molecular weight determination are met to a high degree; the complicated character of chain termination, however, also in this case prevents a simple “integer number” relationship between degree of polymerization and the number of azo units incorporated in mABPO-prepared polymethylmethacrylates. Nevertheless the determination of azo endgroups in these polymers might be a valuable tool for the evaluation of further kinetic data.     

Vinyl polymerization by metal complexes, 12. Initiation by poly(vinyl alcohol)-copper(II) chelates

The polymerizations of acrylonitrile, methyl methacrylate and styrene initiated by copper(II) chelates were studied in the presence of carbon tetrachloride. Polymeric and dimeric compounds of vinyl alcohol, that is poly(vinyl alcohol) and 1,3-propanediol were chosen as ligands. It was found that these systems could initiate the polymerization of methyl methacrylate and styrene effectively. The activity of the polymer chelate was estimated by varying the metal/ligand mole ratio of the initiator system, the pH values and the polymerization temperature. From the results, the mechanism of the free-radical formation was discussed.     

Thermal decomposition of acrylonitrile copolymers investigated by direct pyrolysis in the mass spectrometer

The thermal behaviour of copolymers of acrylonitrile containing up to 15 wt.-% of methyl acrylate (MA), methyl methacrylate (MMA), vinyl acetate (VA), and vinyl bromide (VB) units, was investigated by gradually increasing the temperature of a polymer sample placed in the ion source of a mass spectrometer (MS). The resulting pyrolytic processes (time-temperature resolved) were analyzed by detecting the volatile decomposition products formed. Several decomposition processes were ascertained. Bromine derivatives evolution from the VB copolymer chain occurs already at 160–200°C. The thermal decomposition of the pendant ester groups in the MA and MMA copolymers occurs in the temperature range of 200–260 °C. Typical polyacrylonitrile (PAN) decomposition fragments were detected in the 240–300 °C range in all the copolymers investigated. Acetic acid units are evolved from the VA copolymer simultaneously to the PAN thermal fragments. Heterocyclic compounds originated from the ladder structures appear beyond 300°C.     

Synthesis of poly(vinyl alcohol) having a thiol group at one end and new block copolymers containing poly(vinyl alchohol) as one constitent

Poly(vinyl alcohol) (PVA) and poly(vinyl acetate) having a thiol group at one end were synthesized by free-radical polymerization of vinyl acetate in presence of thioacetic acid as a chain transfer agent followed by treating with sodium hydroxide/methanol and ammonia, respectively. It was found that block copolymers containing the PVA sequence as one constituent were obtained by the redox-initiated polymerization of some vinyl monomers, for example, acrylic acid (AA) and acrylamide (AAm), using PVA having a thiol end group as reductant and an oxidant such as potassium bromate and potassium persulfate.     

Metal compounds in free radical processes, 4. polymerization of vinyl monomers initiated by the system nickel(II) chloride/N,N-dimethylaniline

The system nickel(II) chloride (NiCl₂)/N,N-dimethylaniline (DMA) initiates the polymerization of methyl methacrylate and acrylonitrile. The thermal polymerization of styrene is not affected. From the polymerization and copolymerization studies as well as from spectral measurements in the UV and visible region it is concluded that this polymerization exhibits free radical character. Neither NiCl₂ nor DMA used separately initiate the polymerization. The initiating species are assumed to be formed as a result of interaction between the vinyl monomer/NiCl₂ complex {e.g. in the case of MMA, [Ni(CH₃OH)_6–x(MMA)_x]²⁺2Cl^?, ( 2 )} and DMA. Possible causes for the different initiating efficiency of the system NiCl₂/DMA for various vinyl monomers are also discussed.     

Regulation in free-radical polymerization of vinyl acetate and synthesis of end-group modified poly(vinyl alcohol)s

A kinetical investigation on the consumption of a chain transfer agent in the free-radical polymerization of vinyl acetate (VAc) was carried out. A new method to control the degree of polymerization of poly(vinyl acetate) (PVAc) or poly(vinyl alcohol) (PVA) as well as the end group content by continuous addition of a chain transfer agent, whose chain transfer constant is much larger than unity such as thiol compounds, during the course of VAc polymerization was proposed. The method using 2-mercaptoethanol was applied to the preparation of lowmolecular-weight PVAc and PVA with M?_w/M?_n ≈ 2.     

Molecular design of biodegradable functional polymers, 5. Enzymatic degradation of polycarboxylates containing vinyl alcohol blocks as biodegradable segment

Poly(sodium carboxylate)s containing vinyl alcohol blocks were prepared, and their microbial degradability and the poly(vinyl alcohol) (PVA) dehydrogenase activity as a function of vinyl alcohol block length in the polymer chain were analyzed. A clear relationship between the biochemical oxygen demand (BOD) biodegradability using the activated sludge and the relative activity of PVA dehydrogenase of a PVA-assimilating strain, Alcaligenes faecalis KK314, was observed. A vinyl alcohol block length of about 7 monomer units corresponds to the minimum chain length of the vinyl alcohol block length which acts as a biodegradable segment in the poly[(disodium fumarate)-co-(vinyl alcohol)]. The enzymatic cleavability of polycarboxylates containing vinyl alcohol blocks was estimated using the cell-free extracts of a PVA-assimilating microbial strain, A. faecalis KK314, as the PVA-cleaving enzyme source for both PVA dehydrogenase and hydrolase. The molecular weight of the polycarboxylates was reduced depending on the vinyl alcohol block length, and a similar molecular weight reduction tendency was observed with respect to the BOD values and PVA dehydrogenase activities.     

Étude de l'état solide des copolymères du chlorure de vinylidène avec le chlorure de vinyle,l'acrylonitrile et le méthacrylate de méthyle, 1. Structure des copolymères,modélisation mathématique en relation avec la structure chimique des chaînes

The properties of a random copolymer are not only determined by composition, but also by the repartition of the monomeric units along the chain. In order to explain the properties of such a copolymer it is necessary to know the sequence distribution or microstructure, each sequence by itself showing structural characteristics: length, relative position, etc. It is thus necessary to conduct a precise synthesis process, and to know the kinetic parameters of the polymerization reaction. Knowledge of the kinetic invariants and monomer feed composition gives access to the theoretical sequence distribution. By different physicochemical methods (NMR, IR and UV spectroscopy), the results obtained by calculation are confirmed. Specifically the effect of microstructure and composition on the properties of some vinylidene chloride (VDC) copolymers with acrylonitrile (AN), vinyl chloride (VC) and methyl methacrylate (MMA) is studied. VDC leads to a very cristalline polymer, whereas PVC generally shows very poor cristallinity, and PAN shows particular structural characteristics. VDC copolymers can easily crystallize when they are rich in VDC. Generally the polymers are semi-crystalline with an amorphous phase. A theoretical model accounting for the lamellar structure and crystallinity of VDC copolymers is described. It utilizes the microstructural data, obtained by a kinetic study and some simple hypotheses, among them the possibility for molecules to slide along each other. This sliding brings together the material which is crystallizable in determined areas. It is thus possible to explain the presence of crystallinity peaks, or at least of paracrystallinity, up to a relatively high amount of comonomer MMA, AN and especially VC in the diffractograms of VDC copolymers with MMA, AN and VC. The paracrystalline domains are defined as areas which can present some degree of order at great distance, with a relatively high amount of comonomer defects.     

Free-radical polymerization of acrylates and vinyl acetates initiated by transition metal/hydrosilane two-component initiation systems

The polymerization of vinyl acetate (VA), methyl methacrylate (MMA), and methyl acrylate (MA) in ethyl acetate and tetrahydrofuran solution was initiated by the two-component initiating systems Fe(III) 2-ethylhexanoate or Co(II) acetylacetonate and pentamethyldisiloxane as co-initiator. Whereas Fe(III) 2-ethylhexanoate initiated the polymerization of all three monomers also in the absence of the siloxane, with an activity increasing from VA to MA, Co(II) acetylacetonate was completely inactive under these conditions. Addition of the siloxane co-initiator raised the monomer conversions with both transition metal initiators, particularly pronounced for MMA and MA. Number-average degrees of polymerization for poly(vinyl acetate) and poly(methyl acrylate) amounted to some hundred or less, but increased to several thousand for poly(methyl methacrylate). Electron spin resonance (ESR) spin trap experiments with N-tert-butyl-α-phenylnitrone (PBN) revealed that the transition metal compounds and the siloxane undergo a reaction in which free radicals are produced by oxidative cleavage of the co-initiator to generate hydrogen atoms which initiate the polymerization. With Fe(III) 2-ethylhexanoate PBN adducts of carbon-centered radicals are observed in the absence and in the presence of the monomers. By way of contrast, with Co(II) acetylacetonate only the hydrogen atom adduct to PBN is observed in the absence of the monomers. Co(acac)₂ is likely to form a new complex with the co-initiator and the spin-trap molecules. The co-ordinated PBN competes with the two parent ligands of the complex for the liberated hydrogen atoms, however, due to favorable reaction rate the PBN-H adduct is formed preferably. The PBN adducts of carbon-centered radicals replace the PBN-H adduct when the monomers are added to the initiator solution, i.e. the H atoms are now preferably trapped by the monomer molecules.     

Phase separation in random copolymers from high conversion free radical copolymerization, 1

The phase separation of random copolymers during free radical copolymerization to high conversion was studied. In order to prepare in situ high impact thermoplastics during the copolymerization process, the attention was focussed on systems in which the more reactive comonomers form thermoplastics, whereas the less reactive components form elastomeric homopolymers. The studied systems (A, B) were (AN, EA), (AN, VA), (CHMA, MA) and (S, BA) (AN: acrylonitrile, EA: ethyl acrylate, VA: vinyl acetate, CHMA: cyclohexyl methacrylate, MA: methyl acrylate, S: styrene, BA: butyl acrylate). These copolymers display varying compositional heterogeneity depending on the different radical reactivity ratios and the feed composition used. Curves of instantaneous copolymer composition versus fractional conversion and the distribution functions of chemical composition were calculated for the various systems. In addition, miscibility diagrams of corresponding low conversion copolymers A_xB_1−x and A_yB_1−y, derived from the same monomer pair (A, B) but differing in composition, were recorded at high temperatures. Phase separation was detected by light microscopy and differential scanning calorimetry (DSC) using cast films. The onset of phase separation depending on the actual stage of copolymerization was recorded. The composition of the copolymers at the onset of phase separation was compared with the miscibility of low conversion copolymer blends. A satisfactory prediction of the start of phase separation during copolymerization is presented.     

Functional metal-porphyrazine derivatives and their polymers, 6. Free radical polymerization initiated by Fe(III)-phthalocyanine-2,9,16,23-tetracarboxylic acid

The polymerization of various vinyl compounds initiated by the Mt-phthalocyanine-2,9,16,23-tetracarboxylic acid (Mt-taPc, Mt = Fe(III), Co(II), Ni(II), and Cu(II)) was studied in aprotic polar solvents in the presence and absence of molecular oxygen. Fe(III)-taPc only was found to initiate smoothly the polymerization of methyl methacrylate (MMA) in the presence of air in aprotic polar solvents by a free radical mechanism. The kinetics of the polymerization of MMA initiated by Fe(III)-taPc were studied under air in dimethylformamide at 60°C. The rate of polymerization, R_p, can be expressed as R_p = k[Fe(III)-taPc]^0,5[MMA]^1,5. From the data of electronic and ESR spectra of this polymerization system, the polymerization mechanism is discussed.     

Random Poly(methyl methacrylate‐co‐styrene) Brushes by ATRP to Create Neutral Surfaces for Block Copolymer Self‐Assembly

Random copolymer brushes of styrene and methyl methacrylate (MMA) on silicon wafers by atom transfer radical polymerization (ATRP) are synthesized using CuCl/CuCl₂/HMTETA. It is found that with increasing amount of styrene the thickness of the brush layer could no longer be well controlled by the amount of free (sacrificial) initiator in the reaction. At constant concentration of free initiator a constant thickness is obtained for various ratios of MMA to styrene. Within 30–70% MMA in the monomer feed the composition of the free polymer corresponds well to the monomer feed ratio, displaying a water contact angle in agreement with the theoretical value for a random copolymer. These copolymers are shown to create a neutral surface directing spin‐coated poly(styrene‐b‐MMA) into a perpendicular lamellae orientation.