ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The degrees of crosslinking of three post-gelation high-conversion copolymers were measured by γ-irradiation, extraction, and swelling experiments. The copolymers containing 0.2, 0.5, and 1.0 mole-% of the crosslinker were prepared by suspension polymerization at 60°C. with a free-radical catalyst. The degree of effective chemical crosslinking for the parent copolymers was calculated by correlating irradiation dose with extractables data after Shultz and the efficiencies of effective crosslinking were 40, 35, and 27% for the three copolymers, respectively. Based on related data by other workers, the low effective crosslinking efficiencies were due partly to incomplete polymerization of some crosslinkers on both ends and partly to wastage of crosslinks by intramolecular cyclization. On correlating the extractables data with the backbone molecular weight of the irradiated and extracted gels after Horikx, similar crosslinking efficiencies were obtained. A new technique has been shown to obtain the latter information by hydrolyzing the copolymer with 80% sulfuric acid under specific conditions and reesterifying the hydrolyzed intermediate with diazomethane. The effective chemical crosslinking of the irradiated and extracted gels, (ve)ir, were calculated from the crosslinking efficiency and extractables data. The degree of effective crosslinking, (ve)sw, for the parent as well as the irradiated gels were calculated from swelling data by means of Flory's swelling equation. It was found that the apparent value of (ve)sw for a given polymer decreased when a better solvent was used in the swelling. This finding was interpreted to be due to failure to correct the polymer-solvent interaction parameter X1, that was used in the swelling equation, for concentration dependence. The aim of this work was to ascertain the validity of the swelling equation with respect to the prediction of (ve)sw. On comparing (ve)ir with (ve)sw, the latter being determined in benzene (X1 = 0.439), the ratios (ve)sw/(ve)ir for the three parent copolymers were between 9 and 10. A large part of the discrepancy was believed to be due to the presence of permanent chain entanglements which acted like physical crosslinks. (ve)sw/(ve)ir for the corresponding irradiated and extracted gels decreased sharply, and all appeared to approach an apparent common limit of about two at large irradiation doses. The theoretical limit should be one. Since the theory of rubber elasticity by James and Guth would require the limit of (ve)sw/(ve)ir to be 0.5 by the present scheme, Flory's theory on which the swelling equation was based seemed to be preferable. This work, however, could not distinguish Flory's theory from a slightly different theory by Hermans.
Additional Material:
9 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1962.1205816644
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