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

本研究基于反应诱导低聚物结晶将溶液齐聚与固相聚合联系起来的新概念，研究了精密缩聚的新方法。分步缩聚：对乙酰氧基苯甲酸(p-ABA)和间乙酰氧基苯甲酸(m-ABA)在液体石蜡中于300℃下聚合6h。当原料中m-ABA的摩尔比小于30mol%时，低聚物结晶得到针状聚合物晶体。得到的晶体由聚对氧基苯甲酰基组成，认为分步缩聚是由于均聚低聚物和共聚低聚物结晶性的差异引起的。顺序控制缩聚：在300℃的条件下，对脱落酸和S-乙酰基-4-巯基苯甲酸在低聚甲醛中进行了共聚。在无规共聚的情况下，形成了不具有任何结晶习性的球形聚合物产品…由于低聚物结晶性差和液液相分离倾向，导致中等共聚比较大。另一方面，由对氧苯甲酰基和对巯基苯甲酰基单元组成的二聚体或三聚体的共聚反应可以得到中等共聚比的晶须。由二聚体或三聚体形成的低聚物由于序列规律性的增强而在结晶过程中析出，从而形成共聚物晶须。非化学计量条件的缩聚：P-ABA与对己氧基苯甲酸(HOBA)或对-十烷氧基苯甲酸(DOBA)聚合，以打破乙酰氧基和羧基端基之间的化学计量比平衡。用原料摩尔比为60%的HOBA制备的聚合物晶体的锰含量很高，达到4.08×10~(-3)，而用摩尔比为30%的DOBA制备的聚合物晶体的锰含量很高，达到2.78×10~(-4)。结果表明，在结晶的同时，通过转酯化反应消除了以一元羧酸为端基的低聚物端基，从而提高了聚合物晶体的锰含量。通过低聚物在溶液聚合过程中的反应诱导结晶进行检测。在三乙基联苯混合物中，于30 0℃下进行了对脱落酸与对乙酰氨基苯甲酸的共聚反应。当ABA/AABA摩尔分数为50~30时，分别形成针状和片状晶体。前者晶体主要由POB组成，后者由PAB组成。由于氢键作用，PAB齐聚物与溶剂的相容性远低于POB齐聚物，相分离的PAB齐聚物的平均DPN较低，其中POB齐聚物为1.90，PAB齐聚物为1.04。动力学研究表明，ABA的反应速度是AABA的4倍，这一差异导致了齐聚物组成的波动。因此，PAB齐聚物倾向于在聚合初期较早沉淀，并形成PAB晶体。然后POB齐聚物在聚合过程中逐渐析出。较少

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