Measurements on the degree of crosslinking of high‐conversion post‐gelation methyl methacrylate—methylene dimethacrylate copolymers

Abstract

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.

Environmentally‐Friendly Acrylates‐Based Polymer Latices

“…Th e copolymers were characterized by FTIR, 1 H-NMR, DSC, and a solubility test, and they were random in nature having similar composition as in the monomer feed. Hwa [27] synthesized MMA and methylene dimethacrylate copolymer by suspension polymerization at 60°C in the presence of a free radical catalyst.…”

Co-polymerization of Acrylates

“…The resulting particle shapes were observed by transmission electron microscopy and the presence of carboxyl groups on the surface of the particles was confirmed by Fouriertransform infrared spectroscopy (FT-IR). Hwa [7] synthesized cross-linked MMAmethylene dimethacrylate co-polymers by suspension polymerization at 60 • C in the presence of a free radical catalyst. They determined the degree of crosslinking by γ -irradiation, extraction and swelling experiments.…”

“…Size mono-dispersed MMA-EGDMA co-polymer packing material for HPLC was prepared by a multi-step swelling polymerization method with cyclohexanol as porogenic solvent. Measurements on the degree of cross-linking of high conversion post-gelation MMA-methylene dimethacylate co-polymers were done by Hwa [7]. The co-polymers containing 0.2, 0.5 and 1.0 mol% cross-linker were prepared by suspension polymerization at 60 • C with a free radical catalyst.…”

Mechanismus der Dreidimensionalen Polymerisation von Glykolmethacrylaten

“…Die Konzentration der Querbindungen wurde aus der Gleichgewichtsquellung und aus der Abhangigkeit der Deformation von der Spannung mit Anwendung der Beziehung von Flory" bestimmt: 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 (4) wobei B o der Anfangsgehalt des Vernetzungsmittels ist, der gleich 100 ist. Bei gleichen Copolymerisationsparametern sollte der Umsatz ein Mass der Wahrscheinlichkeit sein, so dass der theoretische Gehalt der Querbindungen (Ye) durch die Beziehung (5) ausgedruokt werden sollte, Daraus folgt der theoretische Gehalt der hangenden Vinyle Ci3 e)…”