Head-to-head vinyl polymers. III. Preparation and characterization of head-to-head poly(acrylic acid) and its esters

Head-to-head (h-h) poly(acrylic acid) (PAA) and some h-h poly(alkyl acrylates) (PRA) with methyl, ethyl, n-propyl, n-butyl, isobutyl and 2-ethylhexyl substituents were prepared by hydrolysis or esterifications of the alternating copolymer of ethylene with maleic anhydride. In general, these esterification reactions became increasingly difficult as the carbon chain in the alcohols lengthened or branched. The softening, glass transition, and degradation temperatures of the h-h polymers obtained were somewhat higher than those of the corresponding head-to-tail (h-t) polymers. The main degradation products of both h-h and h-t PRA were identified by pyrolytic gas chromatography as the alcohol and monomer. In addition, the relative ratios of the amounts of alcohol to monomer were larger for h-h than for the corresponding h-t polymers.     

Head-to-head vinyl polymers. IV. Preparation and characterization of equimolar head-to-head copolymers of acrylic acid and its esters

The alternating copolymer of ethylene with maleic anhydride was esterified with a number of aliphatic alcohols to yield its monoesters, which correspond structurally to equimolar (1:1) head-to-head (h-h) copolymers of acrylic acid with alkyl acrylates. In addition, they were methylated with diazomethane to 1:1 h-h copolymers of methyl acrylate with alkyl acrylates. For comparison the 1:1 head-to-tail (h-t) copolymers of methyl acrylate with alkyl acrylates were prepared by radical copolymerizations. Some chemical, physical, and thermal properties of these 1:1 h-h and h-t copolymers were evaluated and compared. The softening and glass transition temperatures of the 1:1 h-h copolymers were somewhat higher than those of the corresponding 1:1 h-t copolymers, which indicated that the h-h replacements made the polymer chain stiffer and less flexible. The 1:1 h-h copolymers were also observed to degrade thermally at somewhat higher temperatures and with higher rates than the 1:1 h-t copolymers. The ratio of alcohol to monomer found in the pyrolysis products was higher for the 1:1 h-h than for its respective 1:1 h-t copolymer.     

Head-to-head vinyl polymers. VII. Hydrolysis of head-to-head poly(methyl acrylate)

Head-to-head (H–H) and head-to-tail (H–T) poly(methyl acrylate)s (PMAs) were hydrolyzed in a mixture of acetone and water (4:1 by volume) at 30°C by using various alkali hydroxides as catalysts. For comparison, the H–T copolymer with 26% H–H units, dimethyl succinate (DMS), dimethyl glutarate (DMG), and dimethyl adipate (DMA) as model compounds were also hydrolyzed. It was found that the hydrolyses of all PMAs proceeded autocatalytically; i.e., the rates increased as a function of the reaction time. Both the initial rate constant k₀ and the autoaccelerating effect observed markedly depended on the structures of polymer chains and they decreased with increasing of the H–H sequences. The molecular weights of either H—H or H—T PMA did not show remarkable changes in either k₀ value or accelerating effect. The k₀ values were almost independent of the kinds of bases and were calculated to be 0.06 and 0.18 L mol^?1 min^?1 for H–H and H–T PMA, respectively. On the other hand, the autoaccelerating effect decreased in the order NaOH ? KOH > LiOH > CsOH for H–H PMA and NaOH > LiOH > KOH > CsOH for H–T polymer. When the ratio of acetone to water increased, the k₀ value was found to decrease, whereas the accelerating effect increased. The results obtained are described and discussed.     

Head-to-head vinyl polymers. V. Preparation and characterization of alternating head-to-head copolymers of alkyl acrylates with alkyl methacrylates

Alternating head-to-head (h-h) copolymers of methyl or n-butyl acrylates with the corresponding methacrylates were synthesized by alternating copolymerization of ethylene with citraconic anhydride, followed by esterification and Characterization. The respective equimolar (1:) head-to-tail (h-t) copolymers were also prepared by conventional radical copolymerization as comparison. The alternating, relatively low molecular weight h-h copolymers obtained showed softening, glass transition, and degradation temperatures somewhat higher than those displayed by the 1:1 h-t copolymers. After pyrolysis the main decomposition products from both h-h and h-t copolymers were alcohols, acrylates, and methacrylates. Furthermore, the ratios of alcohols to acrylates were larger for the h-h than for the h-t copolymers and smaller for the methyl than for the n-butyl esters.     

Head-to-head vinyl polymers. XI. Preparation and characterization of poly(methyl acrylate) and poly(methyl methacrylate) consisting of head-to-head and head-to-tail units through cyclopolymerization of acrylic and methacrylic anhydrides

Acrylic anhydride (AAn) and methacrylic anhydride (MAAn) were polymerized with radical initiator in polar solvents at high temperatures. The polymers obtained were found to consist of five-and six-membered ring structures by comparing IR spectra of the polymers with those of model compounds, succinic anhydride, and glutaric anhydride. Hydrolysis and methylation of the polymers gave new polymers composed of head-to-head (HH) and head-to-tail (HT) methyl acrylate (MA) or methyl methacrylate (MMA) units. The content of HH unit of these HH/HT polymers was determined by ¹H-NMR and ¹³C-NMR spectra. The softening, glass transition, and thermal degradation temperatures of the poly(MA) with HH and HT units were found to somewhat increase with increasing of the content of the HH units. On the other hand, the glass transition and thermal degradation temperatures of the poly(MMA) with HH and HT units increased similarly, but the softening temperature decreased as the content of the HH units increased.     

Preparation and characterization of iodinated poly(vinyl alcohol) microfibril

Iodination of poly(vinyl alcohol) (PVA) microfibril, which was obtained from saponification of poly(vinyl pivalate), was conducted before and after zone drawing at various conditions. The resulting PVA microfibrils were characterized by differential scanning calorimeter and scanning electron microscopy. Surface morphologies of these PVA microfibrils showed some differences between PVA microfibril iodinated after and before drawing. Crude shapes of PVA microfibrils iodinated after drawing indicated that iodine decreased the structural regularity severely. On the other hand, PVA microfibrils iodinated before drawing showed relatively ordered surfaces. This was ascribed to the enhanced molecular ordering of PVA microfibrils due on zone drawing. Iodinated PVA microfibrils showed a decrease in crystal melting temperature of about 100°C compared to the untreated sample. PVA microfibrils drawn after iodination showed relatively higher crystal melting temperature than those of microfibrils iodinated after drawing. These results were considered as the proofs of the changes in crystalline lattice of the PVA microfibrils. Effects, of drawing temperature on sublimation of iodine were also evaluated.     

Short branching in poly(vinyl alcohol). III. Some properties of model polymers of short-branched poly(vinyl alcohol)

Melting point, the iodine color reaction, and foam fractionation were studied on model poly(vinyl alcohol) (PVA) having short branches of one or two monomer units in length. An increase in the amount of short branching units caused a marked decrease in color intensity of the PVA–iodine reaction and in the melting point. These tendencies were more remarkable when the short branching was two monomer units in length than when it was one monomer unit. It was also found that foam fractionation of an aqueous PVA solution produced PVA fractions with different degree of short branching, the degree increasing with increase in the fraction number. The color intensity of the PVA–iodine reaction has been confirmed to decrease with increase in the fraction number, but this result cannot be explained solely in terms of the short branching. It is concluded that the phenomenon of foam fractionation of PVA and the iodine color reaction of the fraction appear to be governed by many factors such as molecular weight, stereoregularity, and short branching.     

Short branching in poly(vinyl alcohol). II. NMR spectroscopy of model polymers of short-branched poly(vinyl alcohol)

In order to develop a method of measuring the amounts of short branches in PVA, an NMR study was made of a model poly(vinyl alcohol) having short branches, one or two monomer units in length. Detection and estimation of the short branches were shown to be possible by using the ¹³C-NMR spectra of PVA and the ¹H-NMR of acetylated PVA. In the ¹⁹F-NMR spectra of trifluoroacetylated model PVA, the resonance peaks of primary and tertiary alcohols in the branching structure were not well resolved from that of secondary alcohol of the main chain.     

Preparation and characteristics of photocross-linkable poly(vinyl alcohol)

The reaction of poly(vinyl alcohol) with styrylpyridinium and quinolinium salts which contain formyl group produced water-soluble photosensitive polymers. The sensitivity was high, although the content of the styryl groups was extraordinarily low. Spectroscopical studies revealed that the high sensitivity is due to the aggregation of photofunctional group in the polymer matrix which leads to cyclodimerization on exposure to ultraviolet (UV) light.     

Head-to-head polymers—II. Dilute solution properties of head-to-head polypropylene

The behaviour in dilute solution of head-to-head (H-H) polypropylenes, covering the range $\text{M}{}_{\mathrm{n}}\text{= 0.22}$ to 4.19 × 10⁴, has been studied in cyclohexane as solvent at 303 K. The data could be represented by two distinct Mark-Houwink equations describing the low and the high molecular weight regions. The unperturbed dimensions of (H-H) polypropylenes were found to be less than those for conventional atactic polypropylene in agreement with theoretical predictions. The theta temperature for (H-H) polypropylene in isoamylacetate was found to be 316 K. At this temperature the characteristic ratio was estimated to be 4.5 compared with 6.4 for atactic and syndiotactic polypropylene. The conclusion is that (H-H) placements in polypropylene increase the flexibility of the chain.     

Cyclopolymerization of divinyl esters of dibasic acids and structure of poly(vinyl alcohol) derived from the polymers

Divinyl esters of dibasic acids, CH₂?CHOCO(CH₂)_n?2COOCH?CH₂, n = 2–10, were synthesized and polymerized with a radical initiator, and the structure of poly(vinyl alcohol)(PVA) derived from the polymers were studied. The cyclopolymerizability of these monomers was nearly equal to or less than that of divinyl carbonate which was previously reported, and the extent of cyclization was 15–65%. All the monomers yielded gelled polymers. The monomers which are to yield even-membered rings tend to cyclopolymerize more easily than those of odd-membered rings. PVA derived from these polymers showed a similar structure with respect to 1,2-glycol content and stereoregularity to that from poly(vinyl acetate).     

Preparation and characterization of antibacterial cobalt-exchanged natural zeolite/poly(vinyl alcohol) hydrogels

In the present study, potential application of the local clinoptilolite-rich natural zeolite in formulation of antibacterial hydrogels was investigated. The zeolite powder exchanged with cobalt(II) ions was used in preparation of the zeolite/poly(vinyl alcohol) hydrogel films in different amounts. The films were physically crosslinked by the freezing-thawing method and characterized for their crystallinity, surface and cross sectional morphology, chemical composition, thermal behaviour, mechanical properties, swelling and dissolution behaviours, and antibacterial activities against a Gram-negative bacteria. The films with 0.48 wt% and higher cobalt-exchanged zeolite contents showed antibacterial activity. Addition of the zeolite powder in the formulations did not cause significant changes in the other properties of the films.     

Head-to-head vinyl polymers. X. Cyclopolymerization of o-dimethacryloyloxybenzene

To clarify the possibility of preparing a polymer that contained head-to-head (h–h) methyl methacrylate (MMA) unit radical cyclopolymerization of o-dimethacryloyloxybenzene (o-DMB) was investigated. p-Dimethacryloyloxybenzene (p-DMB) was also used in comparison. When the polymerizations were carried out with higher monomer concentrations than ca. 0.5 mol/L, benzene-insoluble polymer was produced. The extent of cyclization (f_c) in benzene-soluble polymer increased with a decrease in the monomer concentration and an increase in the polymerization temperature. The ¹H-NMR and ¹³C-NMR spectra of poly(MMA) derived from poly(o-DMB) by hydrolysis and methylation were in fairly good agreement with those of ordinary head-to-tail (h–t) poly(MMA). Therefore, it was concluded that the intramolecular propagation in cyclopolymerization of o-DMB was mainly performed by a h–t mechanism. However, the initial and maximum degradation temperatures of the poly(MMA) were observed to be somewhat higher than those of the ordinary poly(MMA), which suggests that a minor amount of the h–h unit was formed.     

Synthesis and characterization of poly(phosphon acetal) derivatives of poly(vinyl alcohol)

Preparation of poly(phosphonoacetals) (PPA) by transacetalation of poly(vinyl alcohol) with diethyl-phosphonoacetal is described. PPA with a degree of substitution of 60% is an alcoholsoluble polymer with a glass transition temperature (T_g) of 67°C. High resolution ¹H and ¹³C NMR spectra reveal the presence of hemiacetals alongside the six-membered acetal ring with an approximate ratio of 2:8 of these substituents. A possible correlation between the microtacticity of the parent PVA and the structure of PPA is indicated; the syndiotactic and isotactic sequences on the parent polymer controls the relationship between the two pendant groups.     

Head-to-head polymers. XXIV. Synthesis of head-to-head polyisobutylene by Grignard coupling reaction

Head-to-head polyisobutylene of molecular weight 3000 to 10,000 was prepared in about 30% yield by Grignard coupling polymerization of 2,2,3,3-tetramethyl-1,4-dibromobutane with copper(I) tris(triphenylphosphino)bromide as the catalyst. Head-to-head polyisobutylene is crystalline, with a T_m of 187°C and a T_g of 87°C and still has bromine end groups left. The polymers have been characterized by their infrared, ¹H-, and ¹³C-NMR spectra and compared to the corresponding head-to-tail polymers of similar molecular weight. A substantial portion of the reaction product of the Grignard coupling polymerization is not polymeric but was identified as cyclized product, 1,1,2,2-tetramethylcyclobutane.