Poly(p-phenylenevinylene) Containing Block Copolymers

Abstract

Organic conjugated polymers have attracted immense attention in academia and industry due to their favourable optoelectronic properties. They have found application in the active layer of photovoltaic cells, electroluminescent displays, organic field-effect transistors and sensors. To improve the performance and reproducibility of the device it is important to synthesise conjugated polymers with well-defined molecular weight (Mn), low polydispersity and low backbone defects. The synthesis of soluble poly(p-phenylenevinylene) (PPV) via ring opening metathesis polymerisation (ROMP) of highly strained paracyclophane-1,9-dienes has been established as an advantageous approach to prepare controlled conjugated polymer structures. In an extension to previous work, alkyl substituted paracyclophane-1,9-dienes were synthesised on a multi-gramme scale. These were used to prepare alkyl substituted PPVs with controlled Mn, low polydispersity and well-defined functional end groups via ROMP. A detailed study of the mechanism and the reaction kinetics associated with the ROMP of alkoxy and alkyl substituted paracyclophane-1,9-dienes using Grubbs™ II and III initiators was performed. Using in-situ 1H and 31P NMR spectroscopy all the propagating species present in the polymerisation were identified. High-resolution 13C NMR spectroscopy of selectively labeled 13C-PPV showed that no backbone defects were formed during ROMP, in context to the PPVs obtained via sulfinyl, dithiocarbamate and Gilch route. Only aldehyde defects were observed for PPV prepared by ROMP at the end of polymer chain due to inefficient quenching of the polymerisation using ethyl vinyl ether. The well-controlled living polymerisation of paracyclophane-1,9-dienes enables the preparation of conjugated block copolymers by sequential monomer addition to give poly(p-phenylenevinylene)-b-poly(oxanorbornene) (PPV-b-PONB) with the different volume fraction of PONB segments. Rod-coil block copolymers can selfassemble to interesting supramolecular architectures. In summary, cyclic highly strained alkoxy and alkyl substituted [2.2]paracyclophane-1,9-diene monomers have been successfully synthesised in multi-gramme quantities (5 g). These monomers have been used to synthesise PPV homopolymers, PPV containing block copolymers and to study the ROMP mechanism and the reaction kinetics. Additionally, a 13C-labeled alkoxy substituted paracyclophane-1,9-diene has been synthesised, this 13C-labeled monomer was subjected to ROMP to give 13C-labeled PPV and by quantitative NMR spectroscopy, the defects generated during the polymerisation were investigated.

Date of Award	31 Dec 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Peter Quayle (Supervisor) & Michael Turner (Supervisor)