Triphenylene-Based Side Chain Liquid Crystalline Block Copolymers Containing a PEG block: Controlled Synthesis, Microphase Structures Evolution and Their Interplay with Discotic Mesogenic Orders

Abstract

Triphenylene (TP) derivatives are typical and probably the most widely studied discotic liquid crystalline (DLC) materials. Through polymer analogous reactions to attach TP mesogens to the well-synthesized poly(ethylene glycol)-b-poly(2-hydroxyethyl acrylate) (PEG–PHEA) by ATRP, a series of well-defined side chain DLC diblock copolymers PEG–poly(TPm) (m = 6 or 10) with DLC block weight fraction (f w,DLC) ranging from 37% to 90% have been successfully prepared with narrow molecular weight distribution (PDI ≤ 1.11). An intriguing microphase-separated superstructure evolution and the correlation between overall morphologies and discotic mesogenic orders as a function of f w,DLC and temperature have been demonstrated by combination of DSC, POM, and variable temperature SAXS/WAXS. Those copolymers with lower DLC contents (f w,DLC = 37% and 43%) and at lower temperatures formed lamellar structures of variant periods and underwent order–order transitions upon PEG region crystallization at 45 °C and different discotic mesophases of ND or Ncol transition at about 25 °C. For the copolymer with intermediate f w,DLC = 62%, a high temperature hexagonal packed cylinder (HPC) structure of amorphous PEG nanocylinders in the matrix of DLC was formed above 35 °C, while upon cooling below 35 °C it turned into a mixed lamellar structure with PEG region crystallization. The higher f w,DLC (67% ∼ 80%) copolymers exhibited HPC structures with the DLC matrix showing Ncol or ND mesophases. For copolymers with the highest f w,DLC around 90%, an overall ND phase was developed in sharp contrast to the ordered columnar phase formed by their corresponding DLC homopolymers, which was quite inspiring and might suggest another pathway of attaining this important nematic discotic phase through introducing a suitable copolymerized block. The better understanding of the interrelation of microstructures and discotic mesogenic orders constitutes the key basis for utilizing such type of organic semiconductor materials and could help to guide the design of complex DLC polymer materials with hierarchical structures for variant applications.

Synthesis, Mesomorphism and Photoluminescence of a New Class of Anthracene-based Discotic Liquid Crystals

“…The low intensity and broad shape of the reflections indicate poor molecular packing and hence reduced interaction. So, from the aforesaid data, it is confirmed that compound 4.4 shows columnar nematic phase (N Col ), which is uncommon in the family of discotics.…”

Controlled synthesis and microstructure tuning of PEG-containing side-chain discotic liquid crystalline block copolymers via RAFT polymerization

“…Calamitic mesogens based LCBCPs have been extensively explored as synthesized through various “living” or controlled polymerization techniques such as anionic polymerization, atomic transfer radical polymerization (ATRP), and reversible addition‐fragmentation chain‐transfer (RAFT) polymerization . However, so far there appeared very few reports on LCBCPs bearing discotic mesogens, including a few examples of side‐chain discotic LCBCPs through polymer analogous reaction, or via ATRP with some limitations, and several main‐chain type discotic LCBCPs . Such underdeveloped situation may largely result from the synthesis difficulties of discotic LCBCPs as compared to their calamitic counterparts in a controlled preparation approach, since it is a significant challenge even for the controlled synthesis of discotic liquid crystalline homopolymers .…”

“…However, so far there appeared very few reports on LCBCPs bearing discotic mesogens, including a few examples of side‐chain discotic LCBCPs through polymer analogous reaction, or via ATRP with some limitations, and several main‐chain type discotic LCBCPs . Such underdeveloped situation may largely result from the synthesis difficulties of discotic LCBCPs as compared to their calamitic counterparts in a controlled preparation approach, since it is a significant challenge even for the controlled synthesis of discotic liquid crystalline homopolymers . Therefore, it is interesting and appealing to precisely prepare discotic LCBCPs in a feasible controlled way and further explore their organized structure and potential functional applications.…”

“…Our group have ever attempted to synthesize triphenylene(TP)‐based side‐chain discotic LCBCPs directly via ATRP but it turned out not to be so simple and straightforward, then an indirect pathway was adopted by combining ATRP with polymer analogous reaction . A systematic exploration for thus obtained LCBCPs showed an intriguing microphase separated superstructure evolution and close correlation between overall morphologies and discotic mesogenic order .…”

“…Our group have ever attempted to synthesize triphenylene(TP)‐based side‐chain discotic LCBCPs directly via ATRP but it turned out not to be so simple and straightforward, then an indirect pathway was adopted by combining ATRP with polymer analogous reaction . A systematic exploration for thus obtained LCBCPs showed an intriguing microphase separated superstructure evolution and close correlation between overall morphologies and discotic mesogenic order . But owing to the inevasible disadvantage of polymer analogous reaction, it is almost impossible to achieve a quantitative complete conversion thus the randomly distributed residual precursor groups may result in some uncertainty on the molecular components, structure, and even microphase separated morphologies of the block polymers obtained from polymer analogous reaction.…”