磷钨酸对对苯撑乙烯撑寡聚物-b-聚(2-乙烯基吡啶)自晶种行为的影响

Effect of Phosphotungstic Acid on Self-seeding of Oligo(p-phenylenevinylene)-b-poly(2-vinylpyridine)

自晶种具有操作简便和聚合物组装基元适用性广的优点,它是利用结晶-柔性(crystalline-coil)两嵌段共聚物活性结晶驱动自组装制备长度和组成可控的聚合物纳米纤维的重要策略.而多金属氧酸及其衍生物具有独特的化学组成和几何结构以及优异的电/磁/光等物理性能.以对苯撑乙烯撑寡聚物-b-聚(2-乙烯基吡啶)(OPV_(5)-b-P2VP_(42))和磷钨酸(H_(3)O_(4)0PW_(12))分别为模型结晶-柔性两嵌段共聚物和多金属氧酸,系统考察了磷钨酸对OPV_(5)-b-P2VP_(42)自晶种行为的影响.研究发现OPV_(5)-b-P2VP_(42)的种子纤维在加热退火时的抗溶解能力随着磷钨酸的量增大而增强.这可能是由于P2VP中的吡啶基元与磷钨酸金属原子间的络合作用,而非吡啶与磷钨酸间的氢键作用,使P2VP链间发生交联/聚集,这不仅可平衡或减弱P2VP链间的排斥力和拉伸作用,还将提升种子纤维断裂和解离所需的能量.

Self-seeding route of living crystallization-driven self-assembly with merits of easily-handling and excellent compatibility with various block copolymers(BCPs)has been considered as one of the most important strategies to generate uniform nanofibers of controlled length and composition.Polyoxometalates with unique structure and shape are usually en-dowed with attractive electric/magnetic/optical properties.Herein,the influence of phosphotungstic acid(H_(3)O_(4)0PW_(12))on the self-seeding of oligo(p-phenylenevinylene)-b-poly(2-vinylpyridine)(OPV_(5)-b-P2VP_(42),the subscripts represent the number of repeat unit of each block)was systematically examined aiming to get more insight on the effect of polyoxometalates on living crystallization-driven self-assembly.Uniform fiber-like micelles of OPV_(5)-b-P2VP_(42)are formed with addition of different molar ratios of phosphotungstic acid to pyridyls of P2VP,α_(acid/v),from 0 to 0.20.The percentage of surviving seed micelles decreased exponentially with increasing annealing temperature regardless ofαacid/v from 0 to 0.10,demonstrating the typical characteristics of self-seeding behaviors.The most striking finding of this work is that the resistance of seed micelles toward the dissolution upon annealing is enhanced significantly with the increasing ofαacid/v,leading to the formation of shorter fi-ber-like micelles with a higherαacid/v.For example,fiber-like micelles with average length of 1325,232,137 and 73 nm were formed withα_(acid/v) of 0,0.01,0.05 and 0.10,respectively,upon the heating of seed micelles of OPV_(5)-b-P2VP_(42)with average length of 22 nm at 60℃for 45 min,followed by cooling/aging at 30℃for 24 h.It is likely that the coordination,instead of hydrogen bonding interaction,between phosphotungstic acid and pyridyls,contributes to the enhancement of resistance of seed micelles toward the dissolution.The tight and multi-dentate coordination between phosphotungstic acid and pyridyls of P2VP chains would make the P2VP chain crosslink.The crosslinking would weaken the repulsion within P2VP chains and increase the energy for the dissolution of micelles.This work not only provides more information to deepen our understand-ing on the influence of nature of corona chains on living crystallization-driven self-assembly(CDSA),especially self-seeding process,but also presents a new platform to generate uniform hybrid polyoxometalate/polymer nanofibers of controlled length.