Synthesis and Transformation of Polymers

Polymers have intruded into our daily life, and it looks impossible to remain isolated without these molecules. Consequently, a lot of work is being carried out in various research laboratories to synthesize new types of polymers with better physical and chemical properties. The development of different organob-oranes is also contributing significantly for their preparation. Chung et al [ 1 ] have prepared functionalized copolymer by Ziegler-Natta process, employing 9-(5-hexenyl)-9-BBN and 1-octene to yield octane-hexenol copolymer. 

Diblock copolymers having both polydiene and polyalcoholic blocks have been synthesized by the hydroboration of butadiene-isoprene diblock copolymer, followed by H2O2 oxidation [2]. Hydroxyl groups containing polymers have been prepared by the hydroboration of 2,5-norbomadiene with 9-BBN in the presence of a WClg-Me4Sn catalyst, followed by alkaline HjOj to afford poly(exo-5-hydroxy norbornene) (Eq. 21.1) [3]. 

The selective hydroboration of block copolymers containing 1,2-polybutadi-ene blocks and polyisoprene poly 2-methyl-l,3-pentadine, 1,3-polybutadiene blocks, on 1,2-polybutadiene blocks have been achieved using 9-BBN as the hydroborating agent [3]. The resulting hydroborated copolymers on oxidation afford the hydroxylated copolymers having 2 glass temperature, which show the phase-separated nature of the copolymers. 

Copolymers with amorphous A block and liquid crystalline B block have been synthesized. The hydroboration of polybutadiene or butadiene styrene block copolymer with 9-BBN yields the intermediate, which on oxidation, followed by esterification with cholesteryl chloroformate, leads to the formation [4] of the said polymer. 

Surface modifications of polymers is brought about by the introduction of alcohol functionality, e.g., poly(tetrafluoroethylene-co-hexafluoropropylene) on reduction with sodium naphthalide in THF results in an unsaturated modified surface layer, the thickness of which is controlled with reaction time and temperature. The air sensitive surface contains alcohols, ketones, aliphatic C-H bonds in addition to C=C and C C. The more alcoholic groups are introduced by hydroboration-oxidation, but the esterification leads to the formation of ester in lower yield. This reveals that the reactivity of OH group is similar to hindered alcohols. The reactivity of the surface can be enhanced by chain extension of secondary surface alcohols with ethylene oxide to form a surface containing primary alcohols groups separated from the polymer backbone by C-2 spacer. On the other hand, primary alcohols are directly introduced to the surface by reaction of the reduced layer with 9-BBN, followed by carbonylation and reduction [5]. 

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There is very little new synthetic organic chemistry involved in the synthesis and transformation of polymers. The organic chemistry involved is usually the application of known, solution-phase organic reactions to polymeric chemistry. 

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