Читать книгу Poly(lactic acid) - Группа авторов - Страница 95

End‐functionalized poly(3‐alkylthiophene) (P3AT), where the alkyl side chain of thiophene moiety contains either 6 or 12 carbons in length, was used as a macroinitiator for ROP of LA, thereby yielding rod‐coil block copolymers as shown in Figure 4.11 [127].

A semicrystalline block copolymer PLA‐b‐P3AT‐b‐PLA showed a tendency to phase segregate due to a self‐assembly process. Alkaline etching of LA blocks from the polythiophene matrix led to the formation of nanoporous templates, which is useful to generate ordered nanostructures. Other block copolymers can be prepared by combining 3‐(2′‐ethyl)hexylthiophene (3EHT) and LA using a change‐of‐mechanism polymerization technique that utilizes two controlled polymerization techniques. A Grignard metathesis (GRIM) reaction is used to polymerize 3EHT to form bromine‐terminated P3EHT, which is then end‐functionalized with a hydroxyl group through a Suzuki coupling reaction to form the P3EHT–OH macroinitiator. Subsequent controlled ROP of D,L‐LA using triethylaluminum results in the synthesis of P3EHT–PLA block copolymers [128]. It is unlikely to obtain complete functionalization of the P3EHT–CH₂OH parent homopolymer with PLA, residual P3EHT in the reaction mixture was removed from P3EHT–PLA by selective precipitation in petroleum ether. Other block copolymers containing PEG and thiophene unit as 3‐hexylthiophene (3HT), 3‐dodecylthiophene (3DDT), and 3‐(2′‐ethyl)hexylthiophene (3EHT) blocks are also reported via azide‐alkyne coupling reaction [129]. Thienyl‐difluoroboron‐PLA have been synthesized and used to explore oxygen‐sensing capability based on phosphorescence [130].

FIGURE 4.11 Synthesis of 3‐alkylthiophene and LLA‐based block copolymer [127].