Abstract A number of commercially available polycarbonates, including formulations made flame retardant by two different modifications, have been exposed to conditions producing moderately rapid hydrolysis. Hydrolysis rates were calculated from molecular weight data determined by gel permeation chromatography and, in some cases, from melt flow rate data. The rates calculated by the two methods are in good agreement. In general, the standard formulations containing minimal additive packages are the most hydrolytically stable. Although one relatively new flame retardant polycarbonate demonstrates generally good resistance to hydrolysis, most of the flame retardant formulations appear to be quite susceptible to hydrolytic degradation. For these materials, hydrolysis under conditions encountered in use could cause significant decreases in impact strength within a few years.
Abstract A viscometric polydispersity index may be calculated by forming the ratio of the viscosity‐average molecular weights of a polymer in a relatively good solvent and in a relatively poor solvent and subtracting 1. This index has been examined by measuring dilute solution viscosities of a polydisperse polystyrene and a polydisperse methyl methacrylate in a variety of solvents, calculating viscosity‐average molecular weights using Mark‐Staudinger‐Houwink equations, and forming the viscometric polydispersity indices. These are compared to Schulz parameters, weight‐average–number‐average molecular weight ratios minus 1, determined from osmotic pressure and light scattering. Viscometric polydispersity indices are more sensitive to polydispersities than expected when compared to Schulz parameters if account is taken of the differences in the powers of molecular weight in the various molecular weight sums. Viscometric polydispersity indices are examined for other polymers, including an almost monodisperse polystyrene. From these measurements it is concluded that the viscometric polydispersity index is valuable for characterizing the polydispersity of polydisperse linear polymers and rough fractions. The weight‐average–viscosity‐average polydispersity index is more sensitive than the viscometric polydispersity index and may be used to characterize relatively monodisperse linear polymers.
Abstract The effect of long‐chain branching must be considered in gel permeation chromatography to evaluate the molecular weight polydispersity of branched polyethylenes. Osmotic molecular weights of fractions of branched polyethylene were correlated with elution volumes; weight‐average and number‐average molecular weights of a branched polyethylene were determined. Molecular weight changes on crosslinking polyethylene by ionizing radiation are accompanied by branching and cannot be simply interpreted by gel permeation chromatography.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolid-state photochemistry of poly(ethylene-co-carbon monoxide). Model studies of polyethylene photochemistryRobert Gooden, Molly Y. Hellman, R. S. Hutton, and Field H. WinslowCite this: Macromolecules 1984, 17, 12, 2830–2837Publication Date (Print):December 1, 1984Publication History Published online1 May 2002Published inissue 1 December 1984https://pubs.acs.org/doi/10.1021/ma00142a067https://doi.org/10.1021/ma00142a067research-articleACS PublicationsRequest reuse permissionsArticle Views108Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRadiation-Induced Cross-linking of ParaffinsR. Salovey and M. Y. HellmanCite this: Macromolecules 1968, 1, 5, 456–459Publication Date (Print):September 1, 1968Publication History Published online1 May 2002Published inissue 1 September 1968https://pubs.acs.org/doi/10.1021/ma60005a017https://doi.org/10.1021/ma60005a017research-articleACS PublicationsRequest reuse permissionsArticle Views67Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Abstract Elevated temperatures and high humidity decrease the molecular weight and impact strength of polycarbonate. Hydrolysis of injection molded polycarbonate (PC) bars stored in glass containers at 85°C and 96% relative humidity (RH) produced brown surface crystals within 30 days. Aging of PC bars at 96% RH and temperatures of 70°C and lower for longer periods of time formed a brown liquid coating on the PC. X‐ray, DSC, and GPC measurements indicated that about 70 wt% of the surface crystals were bisphenol A (BPA). The remaining portion of hydrolysis products appeared to be higher molecular weight oligomers of BPA. The brown liquid was composed of supercooled liquid BPA, BPA oligomers, and water. Initial growth of BPA on the surface of a PC bar took place at the interface between the PC and the glass wall of the container. Apparently a water soluble extract from the glass container accelerated the hydrolytic degradation of PC; nevertheless, hydrolysis of PC occurred in the absence of glass—although at a slower rate. Hydrolysis studies were carried out on several commercial PC formulations. The PC resin containing only a heat stabilizer was least affected. Of the fiame retardant grades, the brominated PC hydrolyzed less rapidly than these particular compositions containing alkali metal sulfonic acid salts. A glass fiber reinforced PC was less stable than its unfilled parent compound. A hydrolytic stabilizer was ineffective against the attack of water under these conditions.
Abstract Preirradiation produced no detectable change in the molecular weight of solution‐ or melt‐crystallized polyethylene etched by fuming nitric acid. This is consistent with crosslinking in areas which are selectively eroded by nitric acid.
