Degradation Of Polymer Chains Research Articles

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.

Poly(?-malic acid) : a new polymeric drug-carrier

Poly(β-malic acid) is a new synthetic functional polyester of the poly(β-hydroxy-acid)-type whose properties are investigated in regard to possible uses as bioresorbable polyvalent drug-carrier. Degradation of polymer chains in 0.15 N phosphate buffer at pH=7.5 is monitored by aqueous GPC on SEPHADEX gels and by enzymatic titration of ultimate degradation products. It is shown that the rate of degradation obeys first order kinetics at the begining and that poly(β-malic acid) degrades to malic acid at last.

Photo-induced polymerization of diethylene glycol diacrylate in the presence of poly(methyl methacrylate): 1—Polymerization without any photoinitiator

With a view to the manufacture of printing plates, films consisting of diethylene glycol diacrylate and poly(methyl methacrylate) acting as a binding agent were irradiated with UV light. The monomer absorbs UV radiation below 300 nm, whereas the resulting polymer as well as the poly(methyl methacrylate) only weakly contribute to total absorption. On irradiation, UV light of wavelengths below 300 nm initiates polymerization of the monomer also in the absence of any photo-initiator and induces degradation of polymer chains: the poly(methyl methacrylate) depolymerizes to the monomer methyl methacrylate, whereas poly(diethylene glycol diacrylate) does not decompose to degradation products with CC double bonds. No degradation occurs when the films are irradiated with UV radiation of wavelength above 300 nm, but polymerization of diethylene glycol diacrylate is initiated to some extent under these conditions. Annealing at 60°C of films irradiated at room temperature to maximum conversion results by thermal polymerization in a loss of pendant double bonds of diacrylate monomer units which are incorporated into the network only by polymerization via one double bond.

Statistics of Degradation and Cross-Linking of Polymer Chains with the Use of the Theory of Branching Processes

Statistics of Degradation and Cross-Linking of Polymer Chains with the Use of the Theory of Branching Processes

PHOTOCHEMISTRY OF cis‐POLYISOPRENE AND ITS SINGLET OXYGEN ADDUCT

Abstract— Reaction of singlet oxygen (1Δg, 1O2) with cis‐polyisoprene yields an allylic hydroperoxide with an olefinic double bond shifted in the polymer chain. The photochemical decomposition of the resultant hydro‐peroxide and the subsequent polymer chain scission kinetics have been studied in the absence of oxygen. Quantum yields of hydroperoxide decomposition range from 3.1 to 8.4 in cyclohexane, depending on the initial amount of hydroperoxide in the polymer. On the other hand, the quantum yields for polymer chain scission are low, and vary with the frequency of the incident light. The ratio for number of polymer scissions per number of hydroperoxy groups decomposed is of the order of 10‐2. The polymer chain degradation is sensitized by the addition of ketones. Based on these data, a reaction mechanism for the overall photodegradation of the cis‐polyisoprene initiated by singlet oxygen is proposed.

Kinetics for unidirectional endwise chain depolymerizations. Experiments with amylose in aqueous alkaline solutions

A kinetic model for the unidirectional endwise chain-propagated depolymerization of a linear polymer is described in terms of three pseudo-first-order rate constants: k1 for the unzipping itself; k2 for termination through the formation of stable endgroups; and k3 for termination through complete degradation of polymer chains. It is shown that the calculated zip length, ν = k1/(k2 + k3), will decrease as the initial substrate D.P. is reduced. For the dimer, a maximum value of ν = 1 is expected. During the anaerobic degradation of potato amylose in aqueous alkaline solutions, k1 decreases and k2 increases in value as the initial amylose concentration is raised. As a result, quantitative depolymerization occurs at low substrate concentrations, while at raised starch levels an alkali-stable residue is formed. It is proposed that intermolecular association between polymer chains causes these kinetic differences. For amylose, the constants k1, k2, and k3 are approximately related by the ratio 1000:1:1 or 1000:0:1; and for the homologous disaccharide, the ratio is 10:1:10. The relevance of these findings to the kinetics of cellulose decomposition in aqueous alkali is discussed.

Properties of nylon 6 anionically obtained with NaAl(Lac)4 catalyst and polymerization of ϵ‐caprolactam with NaAl(Lac)3(OEt) catalyst

AbstractThe m‐cresol‐insoluble polymer of ϵ‐caprolactam obtained with NaAl(Lac)4 catalyst is converted to a soluble polymer on treatment with dilute (0.1 wt‐%) aqueous hydrochloric acid without any accompanying degradation of polymer chain. Aluminum contained in the polymer was not removed completely by extensive extraction with methanol, regardless of the solubilities of the polymers. This fact suggests the existence of two forms of aluminum in the polymer: one contributes to insolubility of the polymer and the other does not. The polymerization behavior in the case of NaAl(Lac)3(OEt) was somewhat different from that of NaAl(Lac)4 and of NaAl(Lac)3(NHBu). These results are considered to reflect a difference in the stability of the Al‐O, Al‐(Lac), and Al‐N bonds in the catalyst.

Effects of ultraviolet radiation on aqueous polyelectrolyte solutions

AbstractThe effects of ultraviolet radiation on dilute aqueous solutions of poly(acrylic acid) and of other polyelectrolytes were studied by viscosity measurements in connection with the effects of ionizing radiation. It was found that ultraviolet light of wavelength below about 2300 Å brought about degradation of polymer chains mainly by indirect action via water, while light of wavelength above 2300 Å caused degradation by direct action in some polymers. It was deduced from the experiments that the protective effect of NaCl could be largely attributed to a decrease in the indirect action. It was also found that a low concentration of methanol was effective in preventing degradation by direct action, although methanol promoted degradation when present in high concentration. Since the promotive effect was not observed when light of wavelength below 3700 Å was eliminated by a filter, this effect was attributed to active products of the irradiation of methanol.

Nitration of Polystyrene Part-I Effect of Molecular Weight of Polymer on Nitration

Polystyrene in the molecular weight range, 3.67*10/Sup4 to 47.86*10/Sup10 has been nitrated in fuming nitric acid at 50 Degree C and degree of substitution of nitro group per monomeric unit in the polymer chains varying from 1.03 to 1.11 has been obtained. Molecular weight of the initial polymers have been found no appreciable effect on the degree of substitution. Degradation of the polymer chain is, however, found to be more pronounced in high molecular weight polymers.

Thermal degradation of plastics. I. The kinetics of polymer chain degradation

AbstractKinetic equations were derived for polymer chain degradation. The usual type of initiation‐depropagation‐termination mechanism was postulated. Chain transfer was ignored. Random and terminal initiation were considered as well as unimolecular, bimolecular, and no‐termination (complete unzipping). It was assumed that a steady state of radicals was achieved, and that monomer product rapidly diffused out of the polymer bulk as soon as it formed. Only average molecular weights were considered. Polymer and radical molecule concentrations were employed in the kinetic equations, while in all the previous work, polymer and radical molecule numbers were used. The same kinetic equations resulted for unimolecular termination and complete unzipping for both treatments, but for bimolecular termination, the results were different. Where the use of number units predicted that the rate of loss of polymer weight should be half‐order in polymer weight, concentration units gave a first‐order relationship. The equations that were derived in this work were found to be similar to those that were previously derived in treatments where number units were employed together with the assumption of exponential molecular weight distribution. A comparison of the various treatments showed that the similarities were not necessarily due to the use of the distribution assumption, but may have been a consequence of the forms of the basic kinetic equations that were utilized in the earlier work.

Reactions of Free Radicals in Solution. V. Destruction of Polymeric Molecules by Free Radicals

Abstract 1. It was established that free radicals produce degradation of polymer chains. 2. Ideas were put forward on the possible mechanism of the reaction leading to the breaking of a carbon-carbon bond in polymer molecules.