摘要:

PVC samples were prepared in bulk by using AIBN and UV radiation as the initiator system. The polymerization temperatures were 40, 0, -25, and -50oC. The samples were fractionated by means of successive extractions with dioxane, tetrahydro-furan, and cyclohexanone, and two fractions of each sample were characterized in order to study their thermal degradation. This was carried out by conductivity measurements with the use of a differential conductimetry cell for degradations up to 0.1% and a single cell for degradations up to 0.4%. From the UV-visible spectra of equally degraded samples it is concluded that the higher the tacticity of PVC, the higher the proportion of long polyene sequences is; this behavior is independent of the conversion. The degraded samples were ozonized in order to measure the number of scissions per chain. This number was found to be low for syndiotactic samples and high for atactic samples, which is accounted for by the increased clustering of double bonds to form long polyene sequences in the more syndiotactic polymers. Previous results suggesting increased ease of propagation along syndiotactic sequences are therefore confirmed more quantitatively.

ISSN:0022-233X    

DOI:10.1080/00222337808063160

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The thermal degradation behavior of blends of polyvinyl chloride) with polyacrylonitrile, poly(n-butyl methacrylate), poly-acrylamide, poly(N-butyl methacrylamide) and poly(methyl acrylate) is discussed, and the results for these blends and five other binary polyblends containing PVC previously studied are compared. The various types of interactions which can occur in these heterogeneous systems are considered, and the mechanisms of degradation are compared with those of each polymer when degraded alone. The most important interactive effects result when a small reactive species produced in the degradation of one of the two polymers in the blend diffuses into the domains of the other polymer in the two-phase system and reacts with that polymer.

ISSN:0022-233X    

DOI:10.1080/00222337808063161

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The mechanism of vinyl chloride polymerization by the tri-ethylaluminum-Lewis base-carbon tetrachloride catalyst system and the thermal stability of the resulting polymer were investigated. When the Lewis base is multidentate, the resultant complex with triethylaluminum shows significantly high catalytic activity for radical polymerization of vinyl chloride in the presence of carbon tetrachloride to give a white powder with high molecular weight. Carbon tetrachloride accelerates the rate of polymerization and participates in an initiating process rather than in a propagating step. The thermal stability of the polymer prepared with this catalyst system is much superior to that of commercial polyvinyl chloride), although the numbers of the double bonds in a chain end and of the head-to-head linkage are similar in both samples, suggesting that the thermally unstable structures of the former react with triethylaluminum to give the thermally stable structure on the polymerization process.

ISSN:0022-233X    

DOI:10.1080/00222337808063162

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The photooxidation of PVC was followed by IR titration of C˭O groups. The kinetics of formation of these groups is characterized by an initial autocatalytic behavior. This feature disappears after a few hundred hours of exposure, and a marked decrease of the rate of reaction is then observed. We have shown that no relation exists between these variations of the reaction rate and the variation of UV absorption of films. HC1 is formed in the reactions of photooxidation and photoelimination. The auto-catalysis and the autoinhibition are favored when the accumulation of HC1 is itself favored.

ISSN:0022-233X    

DOI:10.1080/00222337808063163

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A range of techniques has been applied to the assessment of resistance to weathering of rigid PVC. Of the techniques evaluated, only ATR spectroscopy appears to satisfy the requirements of sensitivity and reliability to justify its use for the prediction, based on short periods of weathering, of the likely long-term stability of PVC compounds. However, confirmation of this potential use depends on more extensive correlations between predictions and practical observations.

ISSN:0022-233X    

DOI:10.1080/00222337808063164

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

During the γ-irradiation and UV-light photolysis of polyvinyl chloride) (PVC), free radicals are formed which may be detected by electron spin resonance (ESR) spectroscopy. In this paper interpretations of the ESR spectra and decomposition mechanisms of PVC are presented.

ISSN:0022-233X    

DOI:10.1080/00222337808063165

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Pure and peroxided PVC films were irradiated under monochromatic ultraviolet light between 300 and 400 nm. The degradation state of PVC is measured by means of carbonyl absorption in the infrared spectra and polyene content by UV spectroscopy. The initial rate of carbonyl formation depends on the wavelengths and oxidized impurities content. Peroxided PVC is oxidized faster than pure PVC with wavelengths above 320 nm. Two hazardous ranges of wavelengths have been detected: 300–320 and 350–370 nm. Good protection of PVC against UV radiation can be assured by the exclusion of wavelengths under 380 nm.

ISSN:0022-233X    

DOI:10.1080/00222337808063166

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0022-233X    

DOI:10.1080/00222337808063159

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor