Q 14-14-42 E
Question
Diene polymers contain occasional vinyl branches along the chain.
How do you think these branches might arise?
Step-by-Step Solution
VerifiedA vinyl branch in diene polymer is due to the result of an occasional 1,2 double bond addition to the polymer chain rather than the usual 1,4 addition.
A reaction is said to be an electrophilic reaction if a substrate is initially attacked by an electrophile, and the overall result is the addition of one or more relative simple molecule across a multiple bond.
One of the most striking differences between conjugated dienes and typical alkenes is their behavior in electrophilic addition reactions. To review briefly, the addition of an electrophile to a carbon–carbon double bond is a general reaction of alkenes.
Conjugated dienes also undergo electrophilic addition reactions readily, but mixtures of products are invariably obtained.
Addition of HBr to 1,3-butadiene, for instance, yields a mixture of two products (not counting cis–trans isomers). 3-Bromo-1-butene is the typical Markovnikov product of 1,2-addition to a double bond, but 1-bromo-2-butene seems unusual.
The double bond in this product has moved to a position between carbons 2 and 3, and HBr has added to carbons 1 and 4, a result described as 1,4-addition.
Electrophilic addition