Hmm, I no chemist or materials expert but long ago, when I had a 65ft-ish bare copper wire for my SW antenna... it degraded after six months or so. I replace it with a fresh bare copper wire. It sure seemed to make a difference to me!
I eventually got smart and went with #14ga Flexweave which is UV insulated. This stuff is great. You could leave this up for years and not have any signs of weathering, cracking, etc.
It's more expensive but it will last forever. I also preferred the black insulation since it's virtually invisible outdoors (at least around trees.)
From thewireman.com:
544 FLEXWEAVE™ 14 AWG with Black, Army Green, or Clear ultra violet resistant, very flexible PVC jacket. Break strength 143 lbs. 0.30/ft
545 FLEXWEAVE™ 12 AWG with Black, Army Green, or Clear ultra violet resistant, very flexible PVC jacket. Break strength 196 lbs. 0.50/ft