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.

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.

scholarly journals Study on adsorption, rheology and hydration behaviours of Polycarboxylate(PCE) superplasticizer synthesized by different acid to ether ratio

2021 ◽  
Vol 2133 (1) ◽  
pp. 012007
Author(s):  
Zhijun Lin ◽  
Xiaofang Zhang ◽  
Zhanhua Chen ◽  
Yue Xiao ◽  
Yunhui Fang
Keyword(s):  
Molecular Weight ◽  
Adsorption Capacity ◽  
Cement Paste ◽  
Cement Hydration ◽  
Main Chain ◽  
Chain Structure ◽  
Hydration Process ◽  
Side Chain ◽  
Structure Parameters ◽  
Polycarboxylate Superplasticizer

Abstract Polycarboxylate superplasticizer is synthesised by different acid to ether ratio, which is changing the main chain structure parameters, obtained different microstructures. The effect of different microstructure PCE superplasticizer on the fluidity of cement paste, rheological thixotropy, adsorption capacity and hydration heat are studied. The results show that dispersing performance in cement with acid to ether ratio of 3.5 is the best, the molecular weight and side chain density have rather little effect on the cement hydration process.

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.

Radiation-induced changes in the structure of polypropylene

1959 ◽  
Vol 253 (1274) ◽  
pp. 322-330 ◽  
Keyword(s):  
Main Chain ◽  
High Energy ◽  
Theoretical Expression ◽  
Cross Linking ◽  
Gel Point ◽  
High Energy Radiation ◽  
Infra Red ◽  
Radiation Induced ◽  
Induced Changes ◽  
Good Agreement

Polypropylene undergoes both cross-linking and random main-chain fracture when exposed to high-energy radiation, the ratio of cross-linking to chain fracture varying with the dose received up to the gel point. An examination of the infra-red absorption spectrum of the irradiated polymer has shown that, in addition, vinylidine unsaturation ( R . R' /C=CH 2 ) is formed in the ratio of one vinylidene double bond to each chain fracture. The rate of main-chain fracture deduced from intrinsic viscosity measurements has been found to be initially (up to a dose of 35 Mrad) a function of the number of chain fractures produced, rather than proportional to the intensity of the radiation, as might have been expected from the behaviour of other polymers. After a dose of 50 to 60 Mrad an insoluble cross-linked gel can be separated from the polymer by solvent extraction, and the sol fraction decreases on further irradiation in accordance with the theoretical expression derived by Charlesby (1953), assuming that for every cross-link formed, one bond between two monomer units is broken. A mechanism for the radiation-induced changes is proposed, based upon the application of classical chemical kinetics, which is in good agreement with the observed phenomena.

Comparison of alpha and gamma radiation effects in polyethylene

1964 ◽  
Vol 277 (1370) ◽  
pp. 348-364 ◽  
Keyword(s):  
Gamma Radiation ◽  
Radiation Effects ◽  
Main Chain ◽  
High Energy ◽  
The Other ◽  
High Energy Radiation ◽  
Polyethylene Films ◽  
Subsequent Exposure ◽  
The Difference ◽  
Thin Polyethylene

Exposure of polyethylene and paraffins to high-energy radiation produces main chain (transvinylene) unsaturation, and this rises to a maximum limiting concentration with increasing dose. On the other hand, vinylun saturation initially present diminishes on irradiation. Comparison of the effects of a- and y-irradiation of thin polyethylene films show that the initial G value for the formation of transvinylene unsaturation is not significantly affected by the l.e.t. of the radiation, but the maximum values reached differ by a factor of over 4. Similarly the decay of vinyl unsaturation is four times slower with a-radiation. The destruction of unsaturation is ascribed to the reaction of H atom s liberated by radiation with the unsaturated groups acting as a scavenger. The difference between a- and y-radiation is due to an l.e.t. effect, more H atoms being available from radiation of lower l.e.t. Estimates are made of the proportion of H atoms which escape from the tracks of the two forms of radiation. The difference is much smaller than in the case of irradiated aqueous solutions. Data are also presented on the formation of carbonyl with a- and y-radiation, both in the presence of air, an d during subsequent exposure.

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