Polyelectrolyte hydrogels have the advantage of a high swelling ratio and to respond to changes in pH and ionic strength which gives them useful characteristics for biomedical applications. To investigate the possibility to synthesize hydrogels from vinylphosphonic acid (VPA), first the free radical copolymerization of VPA and methyl acrylate (MA) was investigated at temperatures between 60 and 80 °C. Second free radical copolymerization of VPA with ethylene glycol diacrylate (EGDA) at 80 °C was studied to obtain a hydrogel. These copolymerizations were successful. For poly(VPA-co-MA) the solubility behavior, NMR spectra, and titration curves of the resulting products proved the existence of copolymers, and for poly(VPA−EGDA) gels a high mass swelling ratio in water was observed, showing that they behave as hydrogels. At pH values between 3 and 9 the degree of swelling displayed low dependence on pH, but deswelling upon addition of salt was observed. A total conversion between 15 and 79% was obtained for poly(VPA-co-MA) depending on the percentage of VPA in the feed and on the temperature. A higher conversion was achieved when the percentage of VPA in the feed was lower, and the polymerization temperature was higher. A nonideal behavior of the copolymerization in terms of VPA content in the resulting polymers as a function of VPA in the feed was observed. This was attributed to the participation of VPA−anhydride in the copolymerization process as an intermediate giving rise to cyclopolymerization.

No abstract

Poly(vinyl phosphonic acid) (PVPA) as obtained by free radical polymerization of aqueous vinyl phosphonic acid was studied by light scattering (SLS, DLS) and size exclusion chromatography (SEC) in dilute aqueous solutions containing sufficient salt in order to screen long range electrostatic interactions. Samples of 37<$\overline M _{\rm w}$< 110 × 10(3) were studied. The polymers showed positive A(2) -values in aqueous NaH(2) PO(4) solution (0.04 M), and self-diffusion behavior and R(H) /R(G) -ratios indicative of the structure of random coiled chains. A comparison of the SEC-elugrams of the PVPA-samples with those of commercially available standards of poly(acrylic acid) sodium salt gave a fit to the same calibration curve described by log P(n(PVPA))  = -0.21ν(e)  + 7.0(+0.1) which correlates the number average degree of polymerization (P(n) ) with the elution volume ν(e) . This indicates that PVPA and PAA have the same hydrodynamic structure under given solution conditions.

␣-Tocopherol was compared with a commercial phenolic antioxidant (Irganox 1076) as a long-term and process antioxidant in film-blown and compression-molded linear low-density polyethylene. The antioxidant function of ␣-tocopherol was high in the film-blown material, especially in the processing, according to oxygen induction time measurements with differential scanning calorimetry. The residual content of ␣-tocopherol after processing, determined with chromatographic techniques, was less than that of the commercial phenolic antioxidant in both the film-blown and compression-molded materials. The process stabilizing efficiency was nevertheless higher for the material containing ␣-tocopherol. During the long-term stabilization, the efficiency of ␣-tocopherol was less than that of the commercial phenolic stabilizer Irganox 1076 in the thin films, according to chemiluminescence and infrared measurements. The long-term efficiency in the compression-molded samples stabilized with ␣-tocopherol or Irganox 1076 was equally good because of the low loss of both ␣-tocopherol and Irganox 1076 from the thicker films.