Synthesis and Self-Assembly of Poly(diethylhexyloxy-p-phenylenevinylene)-b-poly(methyl methacrylate) Rod−Coil Block Copolymers

Abstract

A series of poly(diethylhexyloxy-p-phenylenevinylene-b-methyl methacrylate) (DEH-PPVb-PMMA) polymers with narrow polydispersity (PDI < 1.1) were synthesized using Siegrist polycondensation and anionic polymerizations followed by "click" chemistry. Alkyne-terminated DEH-PPV and azidoterminated PMMA were synthesized first, and then the two functionalized polymers underwent 1,3-cycloaddition reaction to obtain copolymers. Both the conversion of the end-functionalization of the homopolymers and the yield of the "click" reaction were higher than 98% as determined by 1 H nuclear magnetic resonance ( 1 H NMR) and gel permeation chromatography (GPC). Transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies reveal the details of copolymer morphology. The DEH-PPV-b-PMMA system presented here has higher block segregation strength than many previously studied rod-coil block copolymers yet still shows experimentally accessible phase transitions with respect to temperature. As a result, this molecule offers new insight into the competition between rod-rod and rod-coil interactions that occurs in the system. The DEH-PPV rods are organized as a monolayer that is inclined with the lamellar normal (smectic C) for the copolymers containing low volume fraction of PMMA coil (<54%). However, as the coil fraction increases, the strips containing DEH-PPV pack into hexagonal lattice. In contrast to previous work which demonstrated similar morphologies, the sequence of reversible liquid crystalline and microphase phase transitions is altered as a result of the increased block segregation. Upon heating, the low coil fraction copolymers exhibit a series of clear transitions of smectic-lamellar to amorphous-lamellar to disordered structures. In high coil fraction copolymers, the transitions between smectic-hexagonal to amorphous-hexagonal and smectic-hexagonal to disorder structures could not be clearly differentiated. The order-to-disorder temperature (ODT) decreases slowly with increasing coil fraction while the smectic-to-isotropic transition (SI) temperature stays relatively unchanged. The steady SI temperature suggests that the strong rod-rod interaction keeps the liquid crystalline rod in the nanodomain structure regardless of the amount of coil segment in the copolymers.

Synthesis and Hierarchical Self-Assembly of Rod−Rod Block Copolymers via Click Chemistry between Mesogen-Jacketed Liquid Crystalline Polymers and Helical Polypeptides

“…To the best of our knowledge, this is the first example of utilizing a facile and efficient click coupling reaction to prepare rod-rod diblock copolymers containing an R-helical polypeptide and a rigid vinylic polymer, although syntheses of rod-coil BCPs by click chemistry have been reported in literature. 36,37 Experimental Section Materials. 2-Bromo-2-methylpropionyl bromide (98%, Acros), 3-chloropropylamine hydrochloride (98%, Acros), propargyl alcohol (99%, Aldrich), sodium azide (99%), N,N,N 0 ,N 00 ,N 00 -pentamethyl diethylenetriamine (PMDETA) (98%, TCI), and triethylamine (98%) were used as received.…”

Nanowire Shish‐Kebab Structures and Molecular Orientation Control of All‐Conjugated Diblock Copolymers

“…The edge-on orientation with the a axis perpendicular to the substrate and both b and c axes lying in the plane of the substrate is favored for charge transport in OFETs. [15][16][17][18] In most examples of BCPs, the addition of coil-like segments has an effect on the crystallinity and leads to new morphological behavior. In other words, nanocrystals with a preferential face-on orientation with (010) planes parallel to the substrate are beneficial for charge transport along the vertical direction.…”

Enhanced Preparation of Alkoxyamine‐Functionalized Poly(p‐phenylene)s and Their Use as Macroinitiators for the Synthesis of Stimuli‐Responsive Coil‐Rod‐Coil Block Copolymers

“…One route starts from separately synthesized rod and coil homopolymers with specific functionalized end groups. Their combination is achieved, for example, with click chemistry 13. The other way is the use of macroinitiators to obtain the desired rod‐coil block copolymers 14, 15.…”