Effects of ionizing radiation on linear aromatic polyesters

Abstract

The influence of chemical structure on the response of aromatic polyesters to high‐energy ionizing radiation was studied. Systematic variations of polymers related to poly(ethylene terephthalate) were subjected to γ radiation, and the competitive chain scission and crosslinking reactions were determined by measuring changes in intrinsic viscosity and molecular weights. It was found that an increase in the paraffinic glycol segment of polyterephthalates facilitated crosslinking, while the protective nature of aromatic groups was demonstrated by modifying the dibasic acid segments. The influence of substituents on the terephthalate moiety was mixed: electronegative groups led to chain scission (as evidenced by decreased viscosities), but electropositive substituents exerted a stabilizing effect on polymer viscosity. In almost all cases, number‐average molecular weights were decreased by exposure to γ radiation, regardless of viscosity behavior. Crystalline melting temperatures of the polymers generally were decreased by the combined radiation effects of chain scission and crosslinking.

Fire Retardance in Poly(butylene terephthalate). The Effects of Red Phosphorus and Radiation‐Induced Cross‐Links

“…[12][13][14][15] This was recently documented by rather low values of the free radical yield G(R.) obtained by ESR measurements. [16] For PBT G(R.) ¼ 0.27 (77 K) and 0.05 (298 K) were reported.…”

“…Bell and Pezdirtz reported for a PBT sample of molar mass M n ¼ 1.9 Â 10 4 g Á mol À1 that D gel , the absorbed dose for incipient gel formation, is in the order of 10 MGy. [13] For the PBT sample used in this work D gel is expected to be of the same order of magnitude because its molar mass is only slightly larger than that of the sample used by Bell and Pezdirtz. Therefore, the usage of a cross-linking promoter permitting the formation of an intermolecular network at an absorbed dose significantly less than 10 MGy appeared indicated.…”

Radiation‐induced crosslinking of acetylene‐impregnated polyesters. II. Effects of preirradiation crystallinity, molecular structure, and postirradiation crosslinking on mechanical properties

“…Such increases in the degree of crosslinking and decreases in main chain scission were observed in our previous work, 5 and to a lesser extent, in that of Bell and Pezdirtz. 2 The latter study demonstrated an increase in viscosity when increasing the aliphatic chain length from PET though PBT to PDMT, following the degree of in vacuo irradiation. In the current study and our previous study, we found dramatic increases in gel fraction when acetylene is also used in conjunction with increasing the aliphatic chain length in situations of low crystallinity.…”

“…Hence, the proportion of ET in the copolyesters appears to be of little consequence. From previous studies on alkyl polymers 2 and aromatic polyesters 5 and knowledge of molecular dimensions, it is known that acetylene enhances crosslinking only in the amorphous regions, because it does not penetrate into the crystallites. This was demonstrated by the PBT film and fiber in the present study.…”

“…Previous radiation studies of poly(ethylene terephthalate) (PET) 1,2 have shown that high doses are required for reasonable levels of crosslinking to be achieved. This is because the alkyl radical, which is the predominantly observed reactive species, 3 is prone to undergo rapid ␤-bond scission, resulting in the production of the carboxyl radical.…”