Special Reactions for Preparation of Block Copolymers
Aspecial case is the use of the Witting reaction. Poly (p-phenylene pentadienylene) [415] is prepared by this reaction first. This is utilized in a preparation of a block copolymer [456] according to the following scheme:
Apreparation of block copolymers by “living” ring-opening olefin metathesis polymerization was reported [417]. Initially, norbornene or exo-dicyclopentadiene are polymerized by bis (Z5-cyclopen tadienyl) titanacyl butane. The resulting living polymers are then reacted with terephthaldehyde to form polymers with terminal aldehyde groups. The aldehyde groups in turn initiate polymerizations of t-butyldimethylsilyl vinyl ether by aldol-group transfer polymerizations [418]. Following is an illustration of the process:
Subsequently, the terminal aldehyde group is reduced with NaBH4 and the silyl groups cleaved off by treatment with tetrabutylammonium fluoride to produce a hydrophobic-hydrophilic A—B diblock copolymers.
Living metathesis type polymerization was also employed to form block copolymers from norbornene and its derivative with bimetallic ruthenium catalysts, (PR3)2Cl2Ru(=CH-p-C6H4CH=) RuCl2(PR3)2 [434]. This can be illustrated as follows [434]:
Pitet and Hillmyer [436]formed triblock copolymers from 1,5-cycloocatadieneandDL-Lactideby combining ring opening metathesis polymerization with cyclic ester ring opening polymerization.
Proto et al. [434] living isoselective coordination polymerization of styrene to form isoselective block copolymers. This was accomplished by sequential monomer addition.
