Inspite of having higher Tg, Epoxidized natural rubber (with 25 and 50 mol% epoxidation level) exhibit higher stickiness than the synthetic polyisoprene (cis). Why?
Stickiness is a very complex phenonenon. If we limit ourselves to adhesion (which is rleated to tack) the most probable reason in the incresed concentration of polar groups in epoxidized rubber as compared to isoprene rubber, bieng a low polarity molecule. Epoxide goups may partly open up resulting in OH gorups amenable to H-bond formation to various high surface energy susbtrates as metals, glass, ceramics.
This seems to be an obvious answer: highthened concentration of oxigen at polymer matrix can improve H bonding, besides other ionic interaction with more chemical species.