Abstract
A dilute aqueous solution of the temperature-sensitive polymer, poly(vinyl methyl ether) (PVME), was irradiated by a pulsed electron beam in a closed-loop system. At temperatures, below the lower critical solution temperature (LCST), intramolecular crosslinked macromolecules, nanogels, were formed. With increasing radiation dose D the molecular weights M w increase, whereas the dimensions (radius of gyration R g, hydrodynamic radius R h) of the formed nanogels decrease. The structure of the PVME nanogels was analyzed by field emission scanning electron microscopy (FESEM) and globular structures with d=(10–30) nm were observed. The phase-transition temperature of the nanogels, as determined by cloud point measurements, decreases from T cr=36 °C (non-irradiated polymer) to T cr=29 °C ( c p=12.5 mM, D=15 kGy), because of the formation of additional crosslinks and an increase in molecular weights. The same behavior was observed for a pre-irradiated PVME (γ-irradiation) with higher molecular weight due to intermolecular crosslinks. After pulsed electron beam irradiation the molecular weight again slightly increases whereas the dimension decreases. Above D=1 kGy the calculated ρ-parameter ( ρ= R g/ R h) is in the range of ρ=0.5–0.6 that corresponds to freely draining globular structures.
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