Showing papers in "Journal of Polymer Science Part A in 1987"

Polyanhydrides. I: Preparation of high molecular weight polyanhydrides

Abstract: Polycondensation a l'etat fondu d'anhydrides mixtes de diacides carboxyliques et d'acide acetique. Etude de la reaction catalysee et non catalysee

Living carbocationic polymerization. IV. Living polymerization of isobutylene

Abstract: Truly living polymerization of isobutylene (IB) has been achieved for the first time by the use of new initiating systems comprising organic acetate-BCl3 complexes under conventional laboratory conditions in various solvents from −10 to −50°C. The overall rates of polymerization are very high, which necessitated the development of the incremental monomer addition (IMA) technique to demonstrate living systems. The living nature of the polymerizations was demonstrated by linear Mn versus grams polyisobutylene (PIB) formed plots starting at the origin and horizontal number of polymer molecules formed versus amount of polymer formed plots. DPn obeys [IB]/[CH3COORt · BCl3]. Molecular weight distributions (MWD) are very narrow in homogeneous systems (Mw/Mn = 1.2–1.3) whereas somewhat broader values are obtained when the polymer precipitates out of solution (Mw/Mn = 1.4–3.0). The MWDs tend to narrow with increasing molecular weights, i.e., with the accumulation of precipitated polymer in the reactor. Traces of moisture do not affect the outcome of living polymerizations. In the presence of monomer both first and second order chain transfer to monomer are avoided even at −10°C. The diagnosis of first and second order chain transfer has been accomplished, and the first order process seems to dominate. Forced termination can be effected either by thermally decomposing the propagating complexes or by nucleophiles. In either case the end groups will be tertiary chlorides. The living polymerization of isobutylene initiated by ester. BCl3 complexes most likely proceeds by a two-component group transfer polymerization.

Ethylene homopolymerization with P, O‐chelated nickel catalysts

Abstract: ion of phosphine from the nickel(II) P, O-chelated complexes, Ni[Ph2PCHC(Ph)O] (Ph)(PPh3), and related species converts them from olefin oligomerization to olefin polymerization catalysts. Phosphine acceptors such as Rh(acetylacetonate)(C2H4)2 or Ni(1,5-cyclooctadiene)2 are most effective. Alternatively, nickel complexes in which the phosphine ligand is replaced with weakly coordinated pyridine can be prepared. These active, homogeneous catalysts can be tuned to give either low or high molecular weight, linear low or high density polyethylene. Depending on the diluent, the same catalytic complex can be used as heterogeneous or homogeneous catalyst. They are tolerant of oxygenated, hydroxylic, or polar molecules that would poison normal early transition metal-based Ziegler-Natta catalysts. In fact, the polymerizations can be run in solvents such as ethanol or acetone, but hydrocarbon solvents are preferred.

Curing studies of a polyimide precursor

Abstract: Complexes between diphenylcarbamido-dicarboxybenzene and 1-methyl-2-pyrrolidinone, 1/4 and 1/2 M, are obtained by reacting pyromellitic dianhydride with aniline in the solvent 1-methyl-2-pyrrolidinone Decomplexation and imidization of this diamic acid are studied by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectrometry, polarizing microscopy, and gas chromatography/mass spectrometry Side reactions competing with the imide formation are discussed The presence of solvent is found to markedly influence imidization

The effect of temperature and initiator levels on the dispersion polymerization of polystyrene

Abstract: Considerable interest has been generated recently by the preparation of large monodisperse polymer latices by a multistage swelling process. Dispersion polymerization in organic media has been shown to be an alternative route to the preparation of large monodisperse polymer colloids. The size of the resulting particles is known to be dependent on the polarity of the reaction medium. Several other factors are also extremely important in determining both the size and size distribution of the resulting particles. These include the temperature of the reaction and the level of initiator. The temperature affects both the rate of free radical formation and the thermodynamic properties of the polymerization system. It is shown that monodispersity can be achieved over a considerable range of temperatures provided that a particular level of initiator is used at a given temperature. It is also shown that higher levels of initiator at a particular temperature actually produced larger particles. Interestingly, the level of initiator was not found to significantly change the overall rate of polymerization.

Thermal degradation of polyacrylamide and poly(acrylamide‐co‐acrylate)

Abstract: The thermal degradation behavior of polyacrylamide and poly(acrylamide-co-acrylate) was studied by differential scanning calorimetry, thermogravimetric analysis, gas chromatography/mass spectrometry, and carbon-13 solid state nuclear magnetic resonance. The degradation products over the temperature range of 115–450°C were characterized. Mechanisms are proposed for the degradation processes involved.

Curing studies of a polyimide precursor. II. Polyamic acid

Abstract: The cure of pyromellitic dianhydride–oxydianiline polyamic acid is compared with that of a model compound, diphenylcarbamido–dicarboxy–benzene, both having been synthesized in 1-methyl-2-pyrrolidinone (NMP). Laser interferometry and thermogravimetric analysis showed that, analog to the diamic acid model compound, the polyamic acid forms complexes with NMP (repeat unit/NMP: 1/4 and 1/2). Thermal stability of these complexes was found to be similar to the ones of the diamic acid model compound as revealed by comparison of decomplexation temperature–heating rate curves. Activation energies of the decomplexation processes for the diamic acid are given. Anhydride formation, a reaction found in the cure of the model compound to compete with imidization, takes place also during the polyamic acid cure at fairly low temperatures. The molecular weight drop due to chain scission resulting from anhydride formation was followed by viscometry.

Relationship between distribution of substituents and water solubility of O‐methyl cellulose

Abstract: The solubility behavior of O-methyl cellulose (MC) in water was investigated in terms of the distribution of substituents along the cellulose chain as well as in the anhydroglucose (AHG) units. For this purpose, three different types of MC samples were prepared by respective homogeneous reaction, i.e.. (i) methylation of cellulose acetate (CA) prepared from cellulose triacetate (CTA), followed by deacetylation, (ii) methylation of CA prepared by direct acetylation of cellulose in a 10% LiCl–dimethylacetamide (DMAc) solution, followed by deacetylation, and (iii) methylation of cellulose with dimethyl sulfate in a 10% LiCl–DMAc solution. Their water solubility was compared with that of MC samples prepared by the alkali cellulose process, i.e., by the heterogeneous reaction, including commercial products. It was found that water-soluble MC samples prepared by the alkali cellulose process exhibit a thermally-reversible sol-gel transition in aqueous solution, but all of the MC samples preapred homogeneous reactions show a normal phase separation in aqueous solution. This result gives a direct support for the consideration that the highly substituted glucose sequences present in the commercial MC act as “crosslinking loci” on warming. The distribution of substituents in the AHG units was estimated by 13C-NMR method. The results on the water solubility of MC were also discussed in terms of the distribution of substituents in the AHG units.

Polyimides containing carbonyl and ether connecting groups

Abstract: New polyimides have been prepared from the reaction of aromatic dianhydrides with novel aromatic diamines containing carbonyl and ether connecting groups between the aromatic rings. Several of these polyimides were shown to be semi-crystalline as evidenced by wide angle x-ray diffraction and differential scanning calorimetry. Most of the semi-crystalline polyimides form tough solvent resistant films with high tensile properties. One of these materials exhibits very high fracture toughness and can be thermally processed.

Preparation of plastic optical fibers for near‐IR region transmission

Abstract: Loss factors of PMMA and PS core plastic optical fibers (POFs) were analyzed, and it was revealed that the vibrational absorption owing to CH vibration plays the most significant role in reducing the near-IR region attenuation loss. Conversion of the hydrogen of the CH bond in the core polymer to deuterium gives rise to a large reduction of the attenuation loss not only in the visible wavelength region but also in the near-IR region. The deuteration of styrene is not so effective as that of methyl methacrylate because of PS core POFs higher loss owing to imperfections in the wave guide structure and Rayleigh scattering. Using a perdeuterated PMMA as a POF core, a loss of 20 dB/km was attained in the 650–680 nm wavelength region. The loss limits of these deuterated polymer core POFs were also estimated.

Plasma fluorination of polyolefins

Abstract: ESCA and contact angle measurements were used to characterize the surfaces of Polyethylene and polypropylene films exposed to SF6, CF4, and C2F6 plasmas. None of these gases polymerized in the plasma. However, all plasma treatments grafted fluorinated functionalities directly to the polymer surfaces. SF6 plasmas graft fluorine atoms to a polyolefin surface. CF4 plasmas also react by a mechanism dominated by fluorine atoms, but with some contribution from CFx-radical reactions. Although C2F6 does not polymerize, the mechanism of grafting is still dominated by the reactions of CFx radicals. For all gases studied, the lack of polymerization is attributed to competitive ablation and polymerization reactions occurring under conditions of ion bombardment.

Surface modification by plasma techniques. I. The interactions of a hydrogen plasma with fluoropolymer surfaces

Abstract: The rapid defluorination of fluoropolymer surfaces by their exposure to a hydrogen plasma excited by an inductively coupled RF field has been studied using ESCA. The results are interpreted in terms of a reaction/depth profile; the reaction is not uniform with depth leading to the formation of an approximately 20 A thick boundary layer of defluorinated material.

Soluble alkyl substituted polygermanes: Thermochromic behavior

Abstract: : We have prepared a number of high molecular weight, soluble, symmetrical dialkyl substituted germanium homopolymers and germanium-silicon copolymers. In solution, the absorption of the homopolymers was approx. 20 nm red shifted from the corresponding silicon derivatives. That was somewhat unexpected based on theoretical predictions and has been rationalized on the basis of conformational arguments. In the solid state, samples of poly(di-n-hexylgermane) and poly(di-n-octylgermane) are strongly thermochromic. The effect is attributed to the conformational locking of the backbone which is caused by the crystallization of the side groups. In this regard, the germanium derivatives behave similarly to the corresponding silicon polymers and the convergence of the long wavelength absorptions for both types of polymers is consistent with theoretical predictions. The germanium-silicon copolymers are also strongly thermochromic, but the long wavelength absorption is somewhat blue shifted (8 nm) from the respective homopolymers. As expected, the new germanium homo and copolymers are quite sensitive to light and readily undergo chain scission to produce lower molecular weight materials.

Kinetics and mechanism of urethane reactions: Phenyl isocyanate–alcohol systems

Abstract: Urethane reactions of phenyl isocyanate alcohol systems with toluene as solvent and various aprotic polar solvents (including tertiary amines) as additives were carried out at constant temperature of 10–40°C. Analysis of the variation of the second order rate constants of these systems and those available in the literature indicates that formation of the hydrogen bonding complexes (alcohol with phenyl isocyanate and with aprotic solvent) and electron donor number (DN) of the aprotic solvent are the two factors allowing satisfactory explanation of the catalysis and inhibition effects of the wide range of aprotic solvents (including amines, amides, etc.). Based on these considerations, an ion-pair mechanism and the resulting kinetic equation for the urethane reaction are proposed. Verification on the kinetic equation with experimental results for the systems of phenyl isocyanate with alcohol in toluene (for the self catalysis of the alcohol), with dimethyl formamide and dimethyl sulfoxide in toluene (for the catalysis of the aprotic solvents), and with triethylamine in toluene (for the catalysis of the tertiary amines) shows satisfactory. In the mechanism, the aprotic solvent is considered to solvate the complex of phenyl isocyanate/alcohol at the active hydrogen to form an ion-pair which can undergo the urethane reaction more easily.

Polymerization of surface‐active monomers. II. Polymerization of quarternary alkyl salts of dimethylaminoethyl methacrylate with a different alkyl chain length

Abstract: The cationic monomers (CNBr), obtained by quarternization of dimethylaminoethyl methacrylate with n-alkyl bromide containing varying carbon number (N = 4, 8, 12, 14, and 16) were polymerized with radical initiators in water and various organic solvents. The degree of polymerization of the resulting polymers was determined by GPC measurements on poly(methyl methacrylate) samples derived from them. The rate of polymerization of the micelle-forming monomers (N = 8, 12, 14, and 16) in water increases with increasing a chain length of alkyl group, whereas it is little dependent on N in isotropic solution in dimethylformamide. The data on the degree of polymerization for the polymers of C4Br, C8Br, and C12Br show that the polymerization of C12Br with azo initiators in water and benzene gives polymers with a very high degree of polymerization. The results obtained here suggest that highly developed or relatively rigid, aggregated structures of monomers in solution are responsible for the formation of the polymers with a very high degree of polymerization, in addition to an enhanced rate of polymerization. Also considered are the relation of the molecular weight of poly(C12Br) to the viscosity data in chloroform and methanol.

FT–IR spectroscopic study on the thermal and thermal oxidative degradation of nylons

Abstract: The effects of heat and oxygen on nylon films were studied by FT–IR spectroscopy. Nylons 6, 66 and nylons containing carbonyl groups in either the diamine or the diacid moiety were prepared. Nylon films cast on aluminum were studied in an environmental chamber under controlled conditions. The progress of chemical and physical changes was monitored by FT–IR spectroscopy. Thermal energy caused largely an increase in crystallinity due to annealing and also an increase of nonhydrogen-bonded amide groups, which seemed to entail mainly amide groups from the amorphous region. The intensities of IR absorption bands related to the folded structure reduced as soon as heating began. The IR spectra of the carbonyl groups formed by thermal oxidation showed band shapes that indicated that the formed carbonyl groups were of many different origins. The presence of keto groups purposely inserted into the backbone chains increased the rate of oxidation. Pyrolysis of the nylons was also studied to supplement data obtained at lower temperatures.

Phthalonitrile‐based conductive polymer

Abstract: An aromatic, diether-linked phthalonitrile resin, prepared from 4,4′-bis(3,4-dicyanophenoxy)biphenyl, can be converted into an environmentally stable, highly conductive material by thermal means. The conductivity of the pyrolyzed polymer can be varied and controlled as a function of both the pyrolytic temperature and annealing time. This allows the generation of a range of electrical behavior from an insulator to semiconductor and approaching metallic regions.

Polymerization in nonuniform latex particles: Distribution of free radicals

Abstract: Previous kinetic studies in emulsion polymerization have almost always involved an assumption of uniform distribution of free radicals in the latex particle. Such an assumption is not likely to reflect reality in many systems that employ water-soluble initiators because the hydrophilic end-group of the oligomeric free radical will preferentially stay in the surface layer of the particle. This constrained end-group location would result in nonuniform distribution of free radicals in the polymerizing latex particles. A Monte Carlo simulation of the growth of a single polymer chain within the latex particle supports this hypothesis. Such a nonuniform distribution of free radicals in the latex particle is expected to have an influence on reaction kinetics and product properties. The mechanism for transport of free radicals out of polymerizing latex particles is reexamined based on the proposed concept, and a modified expression for the desorption rate constant is presented.

Functional polymers and sequential copolymers by phase transfer catalysis. 24. The influence of molecular weight on the thermotropic properties of a random copolyether based on 1,5‐dibromopentane, 1,7‐dibromoheptane, and 4,4′‐dihydroxy‐α‐methylstilbene

Abstract: The influence of molecular weight on thermal transitions and on their thermodynamic parameters is discussed for a random thermotropic liquid crystalline copolyether based on the reaction of a 1:1 molar mixture of 1,5-dibromopentane and 1,7-dibromoheptane with 4,4′-dihydroxy-α-methylstilbene. Optimum phase transfer catalyzed polyetherification reaction conditions were established for the synthesis of polymers containing bromoalkane chain ends only over a wide variety of molecular weights. All these copolyethers present a crystalline and an enantiotropic nematic mesophase over the entire range of molecular weights studied. Both the thermal transitions and their thermodynamic parameters are strongly molecular weight-dependent up to Mn = 10,000–12,000, after which they remain constant. The enthalpies and entropies of isotropization of the copolyethers are higher than those of melting. This is in contrast to the same thermodynamic parameters of the corresponding homopolyethers. The enthalpies and entropies of isotropization of both homopolymers and copolymers present similar values, suggesting that copolymerization does decrease the degree of order in the crystalline phase but does not significantly change the alignment degree of the mesogenic units in the nematic mesophase.

The Synthesis of Biodegradable Polymers with Functional Side Chains

Abstract: Trifunctional hydroxy-terminated oligomeric polyesters, Mn 500, 1000, and 2000, were prepared by initiating ring-opening copolymerization of δ-valerolactone and e-caprolactone with glycerol. The prepolymers were converted to crosslinked polyester-urethanes by their reaction with hexane-1,6-diisocyanate in proportions corresponding to 70, 80, 90, and 100% of the hydroxyl content. The moduli of the resulting elastomers varied between 0.12 MPa and 3.83 MPa, and the elongation at break between 60 and 2000%. The residual hydroxyl groups were derivatized by heterogeneous reaction with chloroacetic anhydride or excess hexane-1,6-diisocyanate, and these and further transformations of the functional groups were verified by infrared spectroscopy and electron probe x-ray microanalysis. A second series of hydroxy-substituted elastomers was synthesized by copolymerization of δ-valerolactone, e-caprolactone, and 4-(t-butyldimethylsilyloxy)-e-caprolactone, using different amounts of 2,2-bis(caprolacton-4-yl)propane as the crosslinking agent; removal of the t-butyldimethylsilyl group to liberate pendant hydroxyl groups was achieved with acetic acid but not fluoride ion. The hydroxylated polyester (but not the polyesterurethanes) was shown to undergo enzymatic surface erosion in rabbit. The biodegradation data were compared with results previously obtained with low-modulus elastomeric polyesters.

Molecular factors affecting solubility in rigid-rod polyamides

Abstract: The solubility of a series of para-linked, substituted phenyl, biphenyl, terphenyl, and quaterphenyl polyamides is reported. Most of these polymers are soluble in amide solvents without lithium chloride, and several are soluble in ethers and/or ketones. The results indicate that solubility in this class of polymers is affected by the position, polarizability and size of the substituents, enantiomeric purity, and the number of non-coplanar biphenyl rings per repeat unit.

Chemiluminescence of hydrocarbon polymers

Abstract: The thermal oxidation of some hydrecarbon polymers differing by their degree of branching was studied simultaneously by chemiluminescence and infrared spectrophotometry. In the case of isotactic polypropylene, measurements were made at various temperatures ranging from 140 to 180°C. The other polymers—ethylene–propylene copolymer, low and high density polyethylene—were studied only at 160°C. In all cases, the induction times of chemiluminescence coincide with those of carbonyl growth. The previously proposed mechanisms of light emission are not consistent with the kinetic data or with the structure effects on luminescence, which seems directly related with the presence of tertiary hydrogens. A hypothetical mechanism based on the β scission of tertiary alkoxyls is proposed.

Synthesis and characterization of deuterated poly(arylene ether sulfones)

Abstract: Preparation des monomeres et des polymeres deuteres par reaction de Friedel-Crafts. Caracterisation par chromatographie couche mince, RMN, IR-FT et analyse thermique (DSC)

Kinetics of polyesterification III: Solid-state polymerization of polyethylene terephthalate

Abstract: Experimental studies on the solid-state polymerization (SSP) of polyethylene terephthalate (PET) for the particle sizes of 14–16 mesh at 170–200°C and for the particle sizes of 14–18 mesh at 210–240°C are carried out under a vacuum of about 60 mtorr. Analysis of the data of the concentrations of hydroxyl and carboxyl groups and the number average molecular weight during the SSP allows determinations of the rates of esterification and ester interchange separately. It is found that at the temperature 170–200°C and the particle size 80–100 mesh the SSP is end-group diffusion limiting, and that at the temperature 210–240°C and the particle size 14–16 mesh the ester interchange is ethylene glycol diffusion limiting and the esterification is predominantely end-group diffusion limiting due to higher diffusion rate of water. These phenomena are explored by an assistance of the proposed rate expressions for the end-group diffusion limited reactions and diffusion models for the by-products, water, and ethylene glycol.

Electrophilic substitution of organosilicon compounds. II: Synthesis of allyl-terminated polyisobutylenes by quantitative allylation of tert-chloro-polyisobutylenes with allyltrimethylsilane

Abstract: Essentially quantitative allylation of linear and three-arm star tert-chloro capped polyisobutylenes [tCl–PIB–Clt and PIB(Clt)3] has been achieved by the use of allyltrimethylsilane (AllylSiMe3) and Friedel–Crafts acids. Quantitative allylation occurs under suitable conditions, e.g., slight molar excess of TiCl4 and AllySiMe3 polar media, −70°C. These conditions have been developed from quantitative model allylation experiments using 2,4,4-trimethyl-2-chloropentane. Essentially quantitative allylation occurs with long-chain or “once fired” tert-chloro-end groups. Complete allylation can also be effected in a “one-pot two-step” synthesis, i.e., by first preparing the tert-chloro-ended PIB by the inifer method and without isolating the product, completing the synthesis by allylation in the same reactor. Extensive but not quantitative allylation can also be obtained in situ, i. e., during polymerization, by the use of the AllylSiMe3/cumyl chloride/BCI3/isobutylene combination. While allylation proceeds with great ease under the mildest conditions, e.g., −70°C, vinylation with vinyltrimethylsilane could not be achieved even under more forcing conditions.