Development of new methodology for precision polycondensation by means of polymerization-induced oligomer crystallization

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In this study, novel methodology for precision polycondensation was examined based on the new concept of the connection between solution oligomerization and solid-state polymerization by reaction-induced crystallization of oligomers.Fractional polycondensation: Polymerization of p-acetoxybenzoic acid (p-ABA) and m-acetoxybenzoic acid (m-ABA) were carried out in liquid paraffin (LPF) at 300℃ for 6 hours. Needle-like polymer crystals were obtained by the crystallization of oligomers when the molar ratio of m-ABA in feed was less than 30 mol %. The obtained crystals were comprised of poly(p-oxybenzoyl) and it was concluded that the fractional polycondensation was induced by the difference on the crystallizability between homo- and co-oligomers.Sequence control polycondensation: Copolymerizations of p-ABA and S-acetyl-4-mercaptobenzoic acid were carried out in LPF at 300℃. In the case of random copolymerization, spherical polymer products which did not possess any crystal habits were forme … More d in the middle copolymerization ratio due to the lack of crystallizability as well as tendency of liquid-liquid phase separation of oligomers. On the other hand, the copolymerization of dimers or trimers comprised from p-oxybenzoyl and p-mercaptobenzoyl units yield the whiskers at even middle copolymerization ratio. The oligomers prepared from dimers or trimers were precipitated by the crystallization due to the enhancement of sequence regularity and therefore, the copolymer whiskers were formed.Polycondensation of unstoichiometric condition: p-ABA was polymerized with p-hexyloxybenzoic acid (HOBA) or p-decyl oxybenzoic acid (DOBA) to break the balance of stoichiometry between acetoxy and carboxylic end groups. The polymer crystals prepared with HOBA of which the molar ratio in feed was 60 % exhibit very high Mn of 4.08×10^3. And those prepared with DOBA of which the molar ratio was 30 % exhibit quite high Mn of 2.78×10^4. It was concluded that Mn increased with eliminating of oligomer end groups terminated by monocarboxylic acids by trans-esterification which occurred simultaneously with crystallization.Simultaneous one-pot synthesis of poly(p-oxybenzoyl) and poly(p-aminobenzoyl) Simultaneous one-pot synthesis of poly(p-oxybenzoyl) (POB) and poly(p-aminobenzoyl) (PAB) was examined by means of the reaction induced crystallization of oligomers during solution polymerization. The copolymerizations of p-ABA and p-acetoamidobenzoic acid (AABA) were carried out in triethylbiphenyl mixture at 300℃. Needle-like and plate-like crystals were formed separately at ABA/AABA of 50 〜 30 mol%. Former crystals are mainly comprised of POB and the latter are done of PAB. The miscibility of PAB oligomer to the solvent is much lower than that of POB oligomers due to hydrogen bonding, and hereby the average DPn of phase-separated oligomer of PAB is lower, of which POB oligomer is estimated as 1.90 and PAB oligomer is done as 1.04. Kinetic study reveals that ABA can react four times faster than AABA and this difference leads to the fluctuation of composition in oligomers. Therefore, PAB oligomers tend to be precipitated earlier and PAB crystals are formed at the beginning of the polymerization. Then POB oligomers are precipitated gradually in the middle of polymerization. Less