Molecular-weight changes in the degradation of long-chain polymers

1954 ◽  
Vol 224 (1156) ◽  
pp. 120-128 ◽  
Keyword(s):  
Molecular Weight ◽  
Main Chain ◽  
High Energy ◽  
Initial Distribution ◽  
Weight Changes ◽  
Chain Polymer ◽  
High Energy Radiation ◽  
Molecular Weights ◽  
Random Fracture ◽  
Long Chain

The changes in molecular weight of a long-chain polymer (initially of arbitrary molecular-weight distribution) are studied when the main chain is subjected to random fracture, such as occurs when certain polymers are exposed to high-energy radiation. For several distributions studied, all trace of the initial distribution curve is lost after an average of some 3 to 8 main-chain fractures per molecule. For lower degrees of degradation the shape of the curve of weight average against degradation can provide information as to the initial weight average, z average, z + 1 average molecular weights. The initial number-average can be obtained by a method of extrapolation.

The degradation of solid polymethylmethacrylate by ionizing radiation

1954 ◽  
Vol 223 (1154) ◽  
pp. 392-404 ◽  
Keyword(s):  
Molecular Weight ◽  
Main Chain ◽  
High Energy ◽  
Side Chain ◽  
Radiation Doses ◽  
Cage Effect ◽  
Γ Radiation ◽  
High Energy Radiation ◽  
Direct Dissociation ◽  
Solid Form

When polymethylmethacrylate in the solid form is irradiated in the atomic pile, or with γ-radiation, two reactions predominate: breakdown of the main chain, and decomposition of the side chain with evolution of gases. The former was followed by changes in viscosity, the molecular weight of the irradiated polymer being inversely proportional to the radiation dose (plus a small quantity of R 0 which depends on the initial molecular weight). The degradation is thought to proceed by random rupture of main-chain C— C bonds by rearrangement of the excited polymer, and 61 eV are absorbed per fractured bond. For each main-chain rupture approximately one ester side chain is also decomposed. The cage effect is thought to prevent direct dissociation, and reaction occurs by rearrangement of the molecule to give relatively stable entities. Added substances reduce the amount of degradation, possibly by transfer of energy from the excited polymer molecule. This is only possible if the excited molecules have an appreciable life before decomposition. Viscosity measurements on irradiated polymethylmethacrylate in the solid form offer a possible means of measuring high-energy radiation doses in the range of about 1 million röntgens and upwards.

Gel formation by main-chain fracture of long-chain polymers

1955 ◽  
Vol 231 (1187) ◽  
pp. 521-534 ◽  
Keyword(s):  
Molecular Weight ◽  
Random Distribution ◽  
Main Chain ◽  
Average Molecular Weight ◽  
Gel Formation ◽  
Fracture Density ◽  
Chain Polymer ◽  
Infinite Extent ◽  
Limiting Value ◽  
Long Chain

The conditions are examined under which the fracture of main-chain bonds in a long-chain polymer, which would normally result in a decrease in average molecular weight, can nevertheless result in formation of a network of infinite extent (gel). It is assumed that the two end-groups produced at a fractured site can attack neighbouring molecules, and link them ­ selves to them. For an initially random distribution it is shown that gel formation will first occur when one molecule in three is thus fractured. The sol fraction is found to equal ( i /3 r ) 2 , where r/i is the average number of fractures per molecule; with increasing fracture density the sol therefore tends to zero. Where only a proportion of the fractures result in linking, the sol fraction decreases to a limiting value. Expressions are derived for many of the parameters of the sol and gel fractions and for the swelling. The results obtained are compared with those for crosslinking of polymers with a similar molecular weight distribution. To distinguish the process considered in this paper from that usually referred to as crosslinking, the term endlinking is proposed.

Radiation Crosslinking of Rubber. III. Chain Fracture

1960 ◽  
Vol 33 (4) ◽  
pp. 1072-1082
Author(s):  
L. Mullins ◽  
D. T. Turner
Keyword(s):  
Main Chain ◽  
High Energy ◽  
Elastic Behavior ◽  
Experimental Conditions ◽  
High Energy Radiation ◽  
Polymer Molecules ◽  
Molecular Weights ◽  
Relaxation Measurements ◽  
Crosslinked Networks ◽  
Hydrocarbon Polymer

Abstract Exposure of hydrocarbon polymer molecules to high energy radiation results either in a decrease in their molecular weight or else in an increase with the eventual formation of an insoluble network. The primary faetor determining the behavior is the relative incidence of fracture of the main chain of carbon atoms to crosslink formation. The ratio of fractures to crosslinks β has usually been estimated from studies of the solubility of irradiated polymers. Most of this work has been on polyethylenes, but even under comparable experimental conditions widely differing estimates of β have been reported. The use of stress-relaxation measurements to detect the fracture of network chains during irradiation has also been reported. A recent study of the elastic behavior of crosslinked networks has indicated that comparative estimates of the number-average molecular weights of both (1) the chain segments lying between adjacent crosslinks and (2) the molecular chains crosslinked into the network may be obtained from stress-strain measurements alone. In the present work an attempt has been made to apply all three methods in a study of chain fracture occurring during the irradiation of purified natural rubber in vacuo.

scholarly journals Bis-Tridendate Ir(III) Polymer-Metallocomplexes: Hybrid, Main-Chain Polymer Phosphors for Orange–Red Light Emission

Polymers ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 2976
Author(s):  
Konstantinos Andrikopoulos ◽  
Charalampos Anastasopoulos ◽  
Joannis K. Kallitsis ◽  
Aikaterini K. Andreopoulou
Keyword(s):  
Main Chain ◽  
Light Emission ◽  
Red Light ◽  
Molecular Complexes ◽  
Hydroxyl Groups ◽  
Iridium Complexes ◽  
Light Emitters ◽  
Chain Polymer ◽  
Molecular Weights ◽  
Pyridine Moiety

In this work, hybrid polymeric bis-tridentate iridium(III) complexes bearing derivatives of terpyridine (tpy) and 2,6-di(phenyl) pyridine as ligands were successfully synthesized and evaluated as red-light emitters. At first, the synthesis of small molecular bis-tridendate Ir(III) complexes bearing alkoxy-, methyl-, or hydroxy-functionalized terpyridines and a dihydroxyphenyl-pyridine moiety was accomplished. Molecular complexes bearing two polymerizable end-hydroxyl groups and methyl- or alkoxy-decorated terpyridines were copolymerized with difluorodiphenyl-sulphone under high temperature polyetherification conditions. Alternatively, the post-polymerization complexation of the terpyridine-iridium(III) monocomplexes onto the biphenyl-pyridine main chain homopolymer was explored. Both cases afforded solution-processable metallocomplex-polymers possessing the advantages of phosphorescent emitters in addition to high molecular weights and excellent film-forming ability via solution casting. The structural, optical, and electrochemical properties of the monomeric and polymeric heteroleptic iridium complexes were thoroughly investigated. The polymeric metallocomplexes were found to emit in the orange–red region (550–600 nm) with appropriate HOMO and LUMO levels to be used in conjunction with blue-emitting hosts. By varying the metal loading on the polymeric backbone, the emitter’s specific emission maxima could be successfully tuned.

THE VISCOSITY – MOLECULAR WEIGHT RELATION FOR POLY-levo-2,3-BUTANEDIYL o-PHTHALATE

1948 ◽  
Vol 26b (12) ◽  
pp. 783-797
Author(s):  
R. W. Watson ◽  
N. H. Grace
Keyword(s):  
Molecular Weight ◽  
High Purity ◽  
Molecular Orientation ◽  
Degree Of Polymerization ◽  
Solution Viscosity ◽  
Dilute Solution ◽  
Molecular Weights ◽  
Complex Relation ◽  
End Group ◽  
Long Chain

The inherent viscosities of dilute solutions of acidic polyesters of high purity have been compared with number average molecular weights accurately determined by end-group titration. For unfractionated resins with a degree of polymerization from 2 to 11 [Formula: see text] the viscosity – molecular weight relation is linear in chloroform at 25 °C. Where [Formula: see text], K = 1.923 × 10−5 and β = 0.0176. For fractionated polyesters from DP 5 to 8, K = 1.959 × 10−6 and β = 0.0161. For unfractionated resins with a DP > 11, molecular weights increase more rapidly than inherent viscosities. Above [Formula: see text] for fractionated resins linearity is resumed, and the slope increases. Several attempts have been made to explain this complex relation. Apparently the short chains remain linear, and the formation of anisotropic fibers at a DP close to 100 establishes a degree of molecular orientation in the long-chain superpolyesters. Isomerization of levo-diol to the diastereoisomer during polycondensation is without effect on the dilute solution viscosity of the resulting resin. Preferential degradation of the longer chains is assumed to be partially responsible for the decreasing slope from DP 11 to 65. As yet it has not been possible to assess the roles played by changes in size distribution, and variation in solvation with increasing chain length, but the data point to a curved viscosity – molecular weight relation in chloroform at 25 °C.

Viscoelastic relaxation in poly-1-butenes of low molecular weight

1967 ◽  
Vol 300 (1462) ◽  
pp. 356-372 ◽  
Keyword(s):  
Molecular Weight ◽  
Steady Flow ◽  
Simple Liquid ◽  
Viscoelastic Relaxation ◽  
Low Frequencies ◽  
Chain Polymer ◽  
Molecular Weights ◽  
Wide Range ◽  
Volume Equation ◽  
Rouse Theory

Measurements have been made of the viscoelastic properties of a range of poly-1-butene liquids of different molecular weights under cyclic shearing stress. The five liquids studied range in steady-flow viscosity at 20 °C from 5.5 to 9330 P corresponding to number average molecular weights from 448 to 2700. Measurements over the temperature range – 60 to +90 °C were made at frequencies of alternating shear of 64 kc/s, 6, 18 and 30 Mc/s. The liquid of lowest molecular weight (448) was nominally pure, having eight repeat units, while the remaining four each had a distribution of molecular weights. In all cases, the dependence of steady flow viscosity upon temperature follows the equation In η = A + B /(T - T 0 ), (1) which is derived from the free-volume equation with a linear dependence of density upon temperature. Recent measurements on a wide range of pure liquids which have viscosities described by equation (1) have been interpreted in terms of a simple phenomenological model for viscoelastic relaxation which allows the behaviour to be predicted (Barlow, Erginsav & Lamb 1967 b ). Analysis of the present results on the liquid of lowest molecular weight shows that the measured behaviour can also be described by this model. For the four liquids of higher molecular weight a second relaxation process is found at lower frequencies. This is attributed to the increased chain length of the molecules giving rise to 'quasi-Rouse’ modes of motion. At low frequencies the results for these four liquids show a behaviour intermediate between that of a simple liquid and that exhibited by a long chain polymer which conforms to the extended form of the Rouse theory.

Behavior of Rubber Hydrocarbon in a Molecular Still

1939 ◽  
Vol 12 (4) ◽  
pp. 789-793 ◽  
Author(s):  
W. Harold Smith ◽  
Henry J. Wing
Keyword(s):  
Molecular Weight ◽  
Vapor Pressure ◽  
High Molecular Weight ◽  
Molecular Species ◽  
Decomposition Temperature ◽  
Sedimentation Equilibrium ◽  
Chain Molecules ◽  
Molecular Weights ◽  
Average Value ◽  
Long Chain

Abstract Some investigators believe that rubber consists of associated molecules, and others accept Staudinger's view that long-chain molecules are formed by polymerization. Pummerer, Andriessen and Gündel have obtained a molecular weight as low as 600. Meyer and Mark believe that it is approximately 5,000, although they calculated on the basis of osmotic pressures values as high as 350,000. They, as well as Pummerer, consider that rubber is an associated colloid and that high molecular weights are caused by aggregates, sometimes called micelles. Staudinger, however, considers that the long-chain rubber molecule itself has a molecular weight of 200,000 or even 350,000, and that products with lower values, which may be formed in rubber, result from degradation. if the molecules are small it might be possible to distil them if their vapor pressure could be sufficiently increased, but none would distil without decomposition if the molecules are very large. Because the vapor pressure of rubber below its decomposition temperature is low, it appeared of interest to attempt to distil the material in a molecular still. Paraffin wax and sugar, both substances of relatively high molecular weight, have been successfully distilled in this type of apparatus. Subsequent to the work described in this paper, the molecular weight of sol rubber prepared at this Bureau was determined by Kraemer and Lansing of E. I. du Pont de Nemours & Co., Inc. They used the Svedberg method of sedimentation equilibrium in an ultracentrifuge with ethereal solutions of sol rubber. The temperature of the solutions during determinations was approximately 10° C, and an average value of 460,000 was obtained. There was evidenced of a mixture of molecular species.

Relation of Structure to Properties in Polyurethanes. Crosslinking Studies

1961 ◽  
Vol 34 (2) ◽  
pp. 629-638
Author(s):  
E. F. Cluff ◽  
E. K. Gladding
Keyword(s):  
Molecular Weight ◽  
High Energy ◽  
Side Reactions ◽  
Hydroxyl Groups ◽  
Polymer Molecular Weight ◽  
High Energy Radiation ◽  
Elastic Networks ◽  
Site Distribution ◽  
Degradation Reactions ◽  
Curing Systems

Abstract The present work was undertaken to assess the effect of crosslink structure on the properties of the elastic network derived from a linear polyetherurethane elastomer. In order to study this effect, a polyetherurethane was synthesized which contained two types of reactive sites suitable for establishing crosslinks— pendant hydroxyl groups for reaction with diisocyanate curatives and pendant double bonds for vulcanization with sulfur. Incorporation of both types of curing sites within the same linear polymer served to hold constant variables which might otherwise influence vulcanizate properties. Thus, the elastic networks formed by both curing systems were produced from the same polymer, and such factors as polymer molecular weight and molecular weight distribution, interchain forces and cure site distribution remained constant. Furthermore, the curing sites have been placed on pendant groups, well removed from the main polymer chain, in order to avoid degradation of the polymer by side reactions which may accompany sulfur vulcanization. It is recognized that common elastomers with internal unsaturation, such as SBR and natural rubber, can be crosslinked by more than one method (e.g., with sulfur, peroxides, or high energy radiation), but the extent and nature of side reactions which may occur is not known with certainty. There are possibilities of polymer degradation reactions with all of these curing systems, and the occurrence of such degradation reactions would cloud any conclusions concerning the relation between crosslink structure and vulcanizate properties.

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