Degradation Of Polymer Chains Research Articles

A study on the kinetics of thermal decomposition of polyaniline

The kinetic analysis of the thermogravimetric curves for the thermal decomposition processes of polyaniline in undoped and doped state (udpan and dpan) was performed. Various forms of non-isothermal methods of analysis for determining the kinetic parameters were used. The results show that the apparent activation energies for both udpan and dpan in static air are 126.5 and 78.5 kJ mol −1, and those in N 2 are 45.2 and 36.6 kJ mol −1, respectively. The mean reaction orders obtained from integral method for udpan and dpan in static air are 2.1 and 2.0, and those in N 2 are 1.9 and 2.1, respectively. Therefore the reaction function f( α) = (1 − α) 2 for the thermal decomposition of both udpan and dpan is reasonable. The thermal decomposition processes for udpan and dpan in N 2 may be a random degradation of polymer chain, whereas in air it should be an oxidation degradation involving the participation of oxygen. Thus the maximum of reaction rate in nitrogen is only 20–26% of those in air and the apparent activation energies for them are only 1/2–1/3 of those in air. But the temperatures corresponding to the maximum reaction rate are higher by about 230–320 K than those in air.

Biodegradation of PVA‐based formulations

AbstractInvestigation of the biodegradability of water soluble poly(vinyl alcohol) (PVA) based blown films was carried out under different lab‐scale environmental conditions. In particular respirometric tests were utilized in order to evaluate the biodegradability of PVA films in composting, in modified Sturm test and in soil burial simulation tests. Several microbial inocula present in river water, mature compost, forest and farm soils as well as sewage sludge from municipal and paper mill wastewater treatments plants were utilized for the relevant tests. A mixed PVA‐degrading microbial culture was obtained by a common enrichment procedure by using sewage sludge from paper mill as inoculum; this culture was tentatively utilized for the isolation of single PVA‐degrading microorganisms. As a first result we can stress that significant biodegradation extent in fairly low incubation time can be obtained only in the presence of acclimated microbial populations such as those deriving from paper mill sewage sludge, in liquid cultures. Nevertheless separation of single degrading microbial species was impossible most likely due to the establishment of symbiotic or commensal interactions between the single components of the PVA‐degrading mixed cultures. On the other hand, limited mineralization rates were recorded in solid cultures in the presence of soil or compost. Finally, a mechanism of degradation of polymer chains unlike random or unzipping was suggested in the presence of either PVA‐degrading mixed culture and its filtrate by means of viscometric determinations of molecular weight within the time.

Influence of Waste Polymer Inclusion on the Performance of Oriented Polypropylene Geotextile Tapes

Part I of this series demonstrated the effects of recycled polymer inclusion on the tensile properties of oriented polypropylene tapes. Part II describes the effects of re cycled waste on structure and morphology. Under constant conditions of tape extrusion and drawing, the IR crystallinity of orientated tape shows a U-shaped relationship with waste concentration. There is a sudden drop of crystallinity at low waste concentration, which passes through a minimum with increasing waste content, and then gradually rises to the lower crystallinity value of the tape containing 100% waste. Sonic modulus and birefringence values decrease with increasing waste concentration. These changes in tape crystallinity and orientation, along with decreasing molecular weight, explain the loss of tape tenacity owing to the introduction of waste polymer during extrusion. Improved molecular orientation is evident in the presence of additional antioxidant stabilizer, because polymer chain degradation during processing is reduced.

Influence of nitrogen implantation on the properties of polymer films deposited in benzene glow discharges

Investigations of the structural, optical and electrical properties of plasma-polymerized benzene films were carried out as a function of the ion fluence. The films were obtained from rf (40 MHz, 70 W) plasmas of benzene and afterwards implanted with 170 keV molecular nitrogen ions (N 2 +) with fluences Φ ranging from 10 17 to 10 21 m −2. Infrared (IR) and ultraviolet–visible (UV–VIS) spectroscopy were used to analyze the chemical and the electronic structure of the films, respectively. Further structural informations were obtained from etching experiments using an oxygen plasma. Electrical resistivity measurements were performed by the two-point probe technique. With rising ion fluence, the IR spectra of the implanted films reveal an increasing loss of hydrogen, the formation of new single and condensed aromatic structures and oxygen-containing functional groups. The latter are formed from reactions between the free radicals created upon ion implantation and oxygen from ambient air. The optical gap E G, calculated from the UV–VIS spectra of the films, showed a decrease from 1.6 to 0.9 eV as Φ increased from 0 to 10 19 m −2. The electrical resistivity ρ of the films decreases significantly with the fluence. The decreases in E G and ρ are attributed to an increase in the overlap of the π-orbitals. The plasma etching experiments show that at low ion fluences, polymer chain degradation prevails. The highly chemically resistant polymer surface developed under high fluences suggests a strongly cross-linked structure.

Biodegradable drug carriers based on poly(ethylene glycol) block copolymers

AbstractThe synthesis of a model water‐soluble drug carrier system based on poly(ethylene glycol) (PEG) block copolymers is described. In the system, two blocks of PEG are connected via a biodegradable oligopeptide or amino acid linkage incorporating at least one glutamic acid residue. A drug model (4‐nitroaniline) is attached to the γ‐carboxyl group of glutamic acid of the polymer carrier via an enzymatically degradable oligopeptide spacer. All oligopeptides were prepared as potential substrates for cathepsin B, a representative of lysosomal enzymes. The relationship between the structure of oligopeptides forming the linkage between two PEG molecules and the rate of cathepsin B‐catalyzed polymer chain degradation is evaluated. The relationship between the structure of the spacer and kinetics of drug model release from the carrier after incubation in cathepsin B solution is also discussed in detail. The results show that, by altering the structure of oligopeptides in the polymer construct, marked changes in the rate of both polymer degradation and the drug model release can be achieved.

Studies on ?-radiation treatment of poly(tetrafluoroethylene) powder

γ-Irradiation of poly(tetrafluoroethylene) (PTFE) in the presence of air results in degradation of polymer chains by insertion of oxygen. At first, in the low-dose range below 400 kGy, a rise in crystallinity can be observed due to main chain scission in the amorphous part of the macromolecules. Dose increase up to approximately 1000 kGy causes progressive degradation of molecular weight as well as a growing degree of carboxylation of PTFE and increased concentration of trifluoromethyl groups in near-surface regions. At constant irradiation temperature, the properties of irradiated PTFE hardly depend on dose rate and starting material. The degree of carboxylation of the irradiated unsintered PTFE is appreciably lower in comparison with electron-irradiated PTFE under comparable conditions. © 1996 John Wiley & Sons, Inc.

The influence of modification by nitric acid or chlorine on the regiospecific structure of poly(3-alkylthiophenes) (P3ATs)

The nitric and chloro derivatives of chemically synthesized poly(3-alkylthiophenes) (P3ATs) were obtained by chemical modification using chlorine (Cl 2) or nitric acid (HNO 3). On the basis of spectral analyses (UV-Vis, IR, 1H NMR), elemental analysis and gel permeation chromatography (GPC), it was observed that the nitric group (−NO 2) was substituted in the 4- or 5-position of the thiophene ring of P3ATs. The −NO 2 group substitution in the 4- or 5-position of the thiophene ring depends on the regiospecific structure of the P3AT polymer chains. The substitution in the 4-position takes place in the head-to-tail sequence diad in polymer chains. The substitution of −NO 2 in the 5-position occurs in the head-to-head diad sequences and causes the degradation of the polymer chains. The modification of P3ATs by Cl 2 causes the substitution of the chlorine atom in the 4-position of the thiophene ring and in the β-position of the alkyl group. The chlorine substitution in the 4-position of the thiophene ring does not depend on the regiospecific structure of the polymer; however, the chlorine substitution in the β-position of the alkyl group takes place in the head-to-head diad sequences. Moreover, the modification of P3ATs using chlorine does not cause the polymer chain degradation.

Synthesis of Poly(ethylene glycol) Block Copolymers as Potential Water-Soluble Drug Carriers

The synthesis of a model water-soluble drug carrier based on poly(ethylene glycol) (PEG) block copolymers is described. In the copolymers, two blocks of PEG are linked by a biodegradable oligopeptide or amino acid linkage containing the glutamic acid residue. 4-Nitroaniline as a drug model is attached to the γ-carboxyl group of glutamic acid of the polymer carrier via an enzymatically degradable oligopeptide spacer. The oligopeptides used were potential substrates for chymotrypsin. The relationship between the structure of oligopeptides linking two PEG blocks and the rate of chymotrypsin-catalyzed polymer chain degradation as well as the relationship between the structure of the spacer and kinetics of drug model release from the carrier after incubation in chymotrypsin solution is discussed in detail. The results showed that by modifying the structure of oligopeptides in the polymer construct, changes in the rates of both polymer degradation and the drug model release can be achieved in a very broad range.

Rheological Changes in the Processing of Rubber-Carbon Black Compounds

This work shows that the apparent viscosity and the effective relaxation time of rubber-carbon black compounds can be used to evaluate the quality of mixing along the mixing-milling-extrusion process. These rheo metric functions allow one to estimate the degree of carbon black dispersion in relation to mechanical degradation of polymer chains along the production line. It is found that the Occluded Rubber Model is consistent with experimen tal results, which are obtained through capillary rheometry.

Nonlinear dynamics and the problem of polymer fracture

AbstractThe results of the experimental and molecular‐dynamics study of the process of mechanical degradation of polymer chain, testifying to the essential role of nonthermal channels of dissipation of elastic energy accumulated during deformation, have been discussed. High‐energy molecular products of mechanical degradation, which are able to induce a chain branching process leading to “explosive” formation of submicrocrackes, have been discovered. It has been noted that a considerable part of polymer chain energy is concentrated in localized excitations of a soliton type, which play the determining role at all the stages of mechanical degradation under consideration.

The influence of curing systems on the properties of bromobutyl rubber: Part 2—Effect of concentration of curing resin on the dynamic mechanical properties

Measurements of isochronal dynamic mechanical properties of cured, uncured and thermally aged rubber vulcanizates have been carried out using a Rheovibron DDV-III-EP elasticoviscosity meter as a function of temperature between −150°C and +250°C. The effects of curing resin (phenol/formaldehyde[resole] resin; SP-1045) concentration and time of heat ageing on different relaxation transition characteristics and dynamic mechanical properties have been discussed. It has been observed that the molecular mobility is not affected, but only the sensitivity of E (in-phase modulus) in the dispersion region is affected by resin content and time of ageing. With increase in resin content in the vulcanizate, on ageing, the crosslinking reaction becomes more predominant over degradation of polymer chains and scission of crosslinks.

An analytical investigation of the thermal degradation of a cation-exchange resin — part 2

In part 1 of this study the thermal degradation of an ion-exchange resin was followed by laser microprobe mass analysis (LAMMA), which revealed the processes of desulphonation and polymer chain degradation. Also, an initial gas chromatography/mass spectrometry (GC/MS) analysis identified 1,3-diphenylpropane as being a major degradation product. Unsaturated organic degradation products were not particularly evident. In this article the identification by GC/MS analysis of the organic thermal degradation products of the same ion-exchange resin are presented, permitting the LAMMA technique to be used alone in order to follow the resin's degradation processes. All the information obtained has led to the proposal of an approximate thermal degradation mechanism for this resin, which is presented here. The resin is a sulphonated copolymer of polystyrene and divinylbenzene. The organic degradation products are formed from pyrolysis at 300 °C over 24 h. During pyrolysis the resin is in an aqueous environment.

Formation of the gel fraction in low pressure polyethylene compositions of decreased combustibility

The formation of a crosslinked fraction at various temperatures of heating and different fire retardant contents is studied using various low density polyethylene compositions containing chloroparaffin and antimony oxide as examples. Crosslinking starts at temperatures above 250°C and attains a maximum at 325–350°C. The chloroparaffin acts as a crosslinking initiator, and at these temperatures reacts with the polymer to form a hydrogen halide and low density polyethylene microradicals, which initiate polymer chain degradation and crosslinking. These reactions promote an increase in hydrogen halide formation, change the course of polymer and halogen-containing compound degradation, and decrease carbon formation on heating and combustion of the compositions.

Application of a modified polytetrafluoroethylene powder in diaphragms for alkali chloride electrolysis

AbstractA shape retaining asbestos diaphragm which is well suited for alkali chloride solution electrolysis can be obtained from sintering of a mixture of asbestos and a modified polytetrafluoroethylene powder. The usual different polymers of tetrafluoroethylene are not suitable as additives to asbestos diaphragms, whereas an irradiation process permits the production of a modified polytetrafluoroethylene powder which has proved its worth as a component in the diaphragm composition. With reactants present during the irradiation process, functional groups which reduce the water repellency of the polytetrafluoroethylene are incorporated into the polymer. The parallel process of partial polymer chain degradation simultaneously provides an intense reduction of the melt viscosity of the polytetrafluoroethylene so that a composite structure with asbestos can be formed by sintering.

A mechanistic kinetic model for the initiated anionic polymerization ofϵ‐caprolactam

AbstractThe preparation of Nylon‐6 via the initiated anionic polymerization of EE‐caprolactam is characterized by rapid reaction rates displaying marked auto‐acceleration. A mechanistic approach has been taken to analyze the kinetics of this system and has resulted in the postulation that the auto‐acceleration is directly linked to a polymer chain degradation reaction. This reaction is significant even in the early stages of the polymerization and in many cases becomes the dominant mechanism for the production of reactive end groups, thereby controlling the overall reaction rate. A kinetic model is presented which is capable of differentiating between polymerizations carried out with different levels and ratios of catalyst and initiator, and contains but two rate constants—one for the propagation reaction and one for the degradation reaction. Predictions of the model are compared to experimental rate data derived from using both mono‐and difunctional initiators and close agreement is found.

耐食ＦＲＰ用樹脂の腐食挙動に及ぼす化学構造と温度の影響

Corrosion behavior of four kinds of thermosetts as a matrix of corrosion resistant FRP was studied with special attention to their chemical structures. Immersion tests were carried out at various temperatures in 10 wt% NaOH solution up to 3, 000 hr. As a result of testing, corrosion behavior and also mechanism by hydrolysis were found to be affected greatly by the structure of the resin. In iso-phthalic unsaturated polyester resin, degradation of main polymer chain takes place, while crosslinked polymer chain remains unaffected. Thus elastic soft corroded surface layer is formed. In novolack type vinyl ester resin, only at the ester bonds between main and crosslinked chains are attacked from the viewpoint of the structure. However, dense and tight corroded layer in an appearance is formed with longer immersion time which seems to be an incubation period, and severe lowering of strength occured. As for epoxy resins, the one cured by MDA shows no sign of corrosion because of no ester bonding, while the one cured by MTHPA both main and crosslinked chains are dissolved easily as low molecular weight corrosion products, therefore the specimen thickness decreases uniformly.

Kinetics of milling of polymers

Parameters pertaining to polymer chain degradation have been defined and related to energy provided to the material by external mechanical means such as milling. The ratio R of the number of bonds broken to the number of bonds originally present is an experimentally accessible quantity in terms of changes of the number-average molecular weight M as a fraction of the degradation time t. A relation between R and t has been derived. The equation has been tested against the accurate experimental data of van der Hoff and Chopra for cold milling of polyisobutylene at several shear rates, and was found to give very good results in all cases. Some puzzling aspects of earlier interpretation of these data have now been explained.

The kinetics of cluster fragmentation and depolymerisation

The equation that describes fragmentation kinetics, such as that which occurs in cluster breakup and polymer chain degradation (depolymerisation), is solved for models where the rate of breakup depends upon the size of the object breaking up. The resulting dynamic scaling behaviour is investigated. Both discrete and continuous models are considered.

Reactions of vinilydene fluoride-hexafluoropropene copolymers

The alkaline dehydrofluorination of Vinylidene Fluoride (VDF) -Hexafluoropropene (HFP) copolymers in dimethylacetamide has been reported by Schmiegel [1]. Basing on the reduction of 19F NMR signals related to HFP-VDF-HFP sequences and the apprearance of small low-field resonances attributed to allilic CF 3, he suggested that the reaction takes place at HFP-VDF-HFP sequences, to give conjugated dienes and α, β unsaturated ketones deriving from OH − addition to dienes. This communication presents a study of the dehydrofluorination of VDF-HFP copolymers in THF, by alcoholic KOH. The reaction has been followed by analysis of the fluoride ion in solution. The intrisinc viscosity of the polymer did not change after elimination of up to 7.9 x 10 −4 moles F − per g polymer. Higher reaction extents resulted in a decrease of intrinsic viscosity, suggesting polymer chain degradation. The reation products exhibit IR absorptions at 1720, 1684 and 1638 cm −1, that can be attributed to isolated double bonds and/or carbonil groups. No IR bands indicate conjugation that is also not evidenced by UV spectra. 19F NMR spectra are similar to those reported by Schmiegel, but show a larger variety of new CF 3 signals, both in the low-field and the usual CF 3 regions. The Tg of the unsaturated polymers and the reation of these products with phenate anions have also been studied.

Effects of various factors on the formation of high molecular weight polyamic acid

AbstractThe reaction of pyromellitic dianhydride (PMDA) and aromatic diamine in an aprotic solvent such as dimethylacetamide (DMAc) gives a solution of poly(amic acid). The effects of certain variables on the polymerization and some additives on the stability and imidization of the poly(amic acid)s were studied. It was found that the addition of PMDA portionwise to the solution of diamine always keeps the excess diamine in solution and enables one to obtain the highest molecular weight of poly(amic acid). When the addition process was reversed, either by the change or dehydration of solvent, a high molecular weight was not attained. The inevitable water in the solvent or the reaction medium is the major factor, and the more the water content in the solvent or the reaction medium, the larger is the probability of destruction of PMDA during the reaction and hence low molecular weight is obtained. If very pure monomers were used in the polymerization, the 1:1 of molar ratio is the optimum value. Excess diamine or dianhydride results in the exchange reaction with poly(amic acid) and causes a rapid degradation of polymer chain. This exchange reaction was proved by NMR measurements. The presence of electrophilic agents or the nucleophilic agents containing active protons in the poly(amic acid) solution promotes the decomposition of polymer and causes the brittleness of polyimide film in the curing process. Using acetic anhydride (A) to convert the poly(amic acid) to polyimide, pyridine (P) can protect the polymer chain from the nucleophilic attack by the anhydride. The mixture with proper ratio of A/P (1/1–15/1) can be used as good dehydrating agents.Meanwhile, according to the results to the results of experiments, we suggested the probable reaction mechanisms about how the water, amine, and anhydride destroy the polyamic acid chains.