Rubber

Question 1

natural rubber comes from

Answer 1

plants/trees with a white milky liquid (latex)

harvest latex from rubber trees

Question 2

what is latex

Answer 2

major constituent = homopolymer of isoprene (monomer)

2-methyl-1,3-butadiene

Question 3

polyisoprene

Answer 3

carbon-carbon double bond

rigidity

2 stereoisomers cis/trans

Question 4

cis-polyisoprene

Answer 4

natural rubber

from Hevea brasiliensis tree

Question 5

trans-polyisoprene

Answer 5

gutta percha

from Palaquium oblongitulium tree

Question 6

properties of cis-polyisoprene

Answer 6

rubber is soft, poor chain packing (sterics) ; oozes

not a good elastomer b/c deforms under stress

recovers original dimensions when stress is removed

if high T, more fluid/sticky

low T, more solid (molecules interact more ; brittle

Question 7

properties of trans-polyisoprene

Answer 7

hard @ room T

softens when heated

better packing

Question 8

both cis and trans

Answer 8

25% cis 75% trans

chicle tree

Question 9

role of polyisopenes

Answer 9

less understood

decompose readily when exposed to sunlight or O2 in the air

not useful until 1850s Goodyear Vulcanizaion (Hancock)