Controlled Synthesis Of Multiple Responsive Block Copolymers And Their Applications

Conjugated polymers, especially poly(3-hexylthiophene) (P3HT) has attracted considerable research attention in recent years due to their excellent electronic properties and environmental stability. Generally, P3HT is commonly prepared by Grignard metathesis polymerization (GRIM) via the quasi-living catalyst-transfer polycondensation mechanism. Taking advantage of the living nature of GRIM, various end-functionalized P3HTs have been developed, some of which were further fabricated into block copolymers to control the patterning and optimize the optoelectronic properties. The typical methods for synthesis of hybrid P3HT multiple block copolymers including either the coupling preformed homopolymers with complementary end-functionalitiesor elaborating an end-functionalized polythiophene into an appropriate macroinitiator for the chain extension of two second blocks via a polymerization process that are mechanistically distinct from that of P3HT. However,these methodologies usually require mass synthesis manipulation and can be inefficient and complex and frequently result in materials containing impurities that difficult to separate. Therefore,development of novel synthetic strategy for facilely synthesis of P3HT triblock block copolymers is of great desire.In the first part of our work,a family of coil-rod-coil ABA triblock copolymers containing poly(3-hexylthiophene) (P3HT) and poly(hexadecyloxyallene) (PHA) were facilely synthesized in one-pot via three sequential living polymerizations of hexadecyloxyallene, 2-bromo-3-hexyl-5-chloromagnesiothiophene, and hexadecyloxyallene using the ?-allylnickel complex as a single catalyst. Although the different monomers were polymerized under distinct polymerization mechanisms, the one-pot block copolymerization were revealed to proceed in a living/controlled chain-growth manner, affording well defined PHA-b-P3HT-b-PHA triblock copolymers in high yields with controlled molecular weights and tunable compositions. The isolated triblock copolymers were found to self-assemble into well-defined supramolecular helical polymers with equivalent of right- and left-handedness. The helicity of the assemblies can be facilely tuned through the induction of chiral cholesteryl pendants introduced on the polyallene segments. Moreover, by using this synthetic method,amphiphilic P3HT triblock copolymers containing hydrophobic P3HT and hydrophilic poly(triethylene glycol allene) (PTA) were readily prepared. Such water-soluble PTA-b-P3HT-b-PTA triblock copolymer exhibited multiresponsiveness including solvent,pH, and temperature.Multi-block copolymers with tunable sequence have attracted considerable research attentions in recent years. In the second section, a family of well-defined, sequence-controlled triblock copolymers comprised of poly(3-hexylethiophene) (P3HT),poly(hexadecyloxylallene) (PHA), and poly(phenyl isocyanide) (PPI) were facilely synthesized in one-pot. The sequence of the blocks can be facilely tuned through the variation on the order of the monomer additions. Although the structures of the three monomers are completely different to each other and were polymerized under distinct polymerization mechanisms, the one-pot sequential block copolymerizations were revealed to proceed in living/controlled chain-growth manners. Thus, a series of well-defined triblock copolymers with controlled block sequence, defined molecular weights(Mns),narrow molecular weight distributions (Mw/MnS),and tunable compositions were readily prepared just by varying the ratios of monomers to the catalyst. Taking advantage of this efficient synthetic method, amphiphilic triblock copolymers containing hydrophobic P3HT and hydrophilic poly(triethylene glycol allene) and hydrophilic poly(phenyl isocyanide)s bearing triethylene glycol monomethyl ether chains was synthesized. Interestingly,the amphiphilic triblock copolymer exhibited interesting tunable light emissions with responsive to various environmental stimuli such as solvent, pH and temperature. Remarkably, white-light emission can be readily achieved in solution, in organogel, and in film state by using this triblock copolymer.