Prakash Sista

Grignard metathesis (GRIM) polymerization for the synthesis of conjugated block copolymers containing regioregular poly(3-hexylthiophene)

The synthesis of various conjugated block copolymers of regioregular poly(3-hexylthiophene) by Grignard metathesis (GRIM) polymerization is described.

Synthesis and Characterization of a Block Copolymer Containing Regioregular Poly(3‐hexylthiophene) and Poly(γ‐benzyl‐L‐glutamate)

Poly(3-hexylthiophene)-b-poly(γ-benzyl-L-glutamate) (P3HT-b-PBLG) rod-rod diblock copolymer was synthesized by a ring-opening polymerization of γ-benzyl-L-glutamate-N-carboxyanhydride using a benzylamine-terminated regioregular P3HT macroinitiator. The opto-electronic properties of the diblock copolymer have been investigated. The P3HT precursor and the P3HT-b-PBLG have similar UV-Vis spectra both in solution and solid state, indicating that the presence of PBLG block does not decrease the effective conjugation length of the semiconducting polythiophene segment. The copolymer displays solvatochromic behavior in THF/water mixtures. The morphology of the diblock copolymer depends upon the solvent used for film casting and annealing results in morphological changes for both films deposited from chloroform and trichlorobenzene.

Electronic Properties-Morphology Correlation of a Rod–Rod Semiconducting Liquid Crystalline Block Copolymer Containing Poly(3-hexylthiophene)

The influence of the solvent and annealing temperature on the field-effect mobilities and morphologies of poly(3-hexylthiophene)-b-poly(γ-benzyl-L-glutamate) (P3HT-b-PBLG) rod-rod diblock copolymer has been investigated. Thin film X-ray diffraction studies show peaks originating from both P3HT and PBLG indicating that the crystalline nature of both the blocks is conserved after the formation of the block copolymer. It has been observed that the field-effect mobilities of the diblock copolymer are independent of the annealing temperatures for thin films deposited from both 1,2,4-trichlorobenzene and chloroform solvents. The correlation between the field-effect mobility and morphology indicates that the P3HT block self-assembles at the surface SiO(2) dielectric.

Nickel(II) α-Diimine Catalyst for Grignard Metathesis (GRIM) Polymerization

A nickel α-diimine catalyst was used for Grignard metathesis (GRIM) polymerization of 2,5-dibromo 3-hexylthiophene and 2-bromo-5-iodo-3-hexylthiophene monomers. GRIM polymerization of 2-bromo-5-iodo-3-hexylthiophene generated regioregular polymers with molecular weights ranging from 3,000 to 12,000 g · mol(-1). The nickel α-diimine catalyst was also successfully used for the GRIM polymerization of a bulky benzodithiophene monomer.

Temperature-sensitive aliphatic polyesters: synthesis and characterization of γ-substituted caprolactone monomers and polymers

Synthesis and ring-opening polymerization of γ-substituted e-caprolactone monomers containing octyloxy and 2-[2-(2-methoxyethoxy)ethoxy]ethoxy functional groups is reported. An amphiphilic block copolymer containing hydrophobic poly(γ-octyloxy-e-caprolactone) and hydrophilic poly{γ-2-[2-(2-methoxyethoxy)ethoxy]ethoxy-e-caprolactone} forms micelles in aqueous solution above the critical micellar concentration of 1.74 × 10−3 g L−1. Poly{γ-2-[2-(2-methoxyethoxy)ethoxy]ethoxy-e-caprolactone} and its block copolymer with poly(γ-octyloxy-e-caprolactone) are thermoresponsive polymers. The LCST measured for poly{γ-2-[2-(2-methoxyethoxy)ethoxy]ethoxy-e-caprolactone} is 47.5 °C, while the LCST decreased to 37.5 °C for the amphiphilic block copolymer poly{γ-2-[2-(2-methoxyethoxy)ethoxy]ethoxy-e-caprolactone}-b-poly(γ-octyloxy-e-caprolactone).

Solvatochromism and Conformational Changes in Fully Dissolved Poly(3-alkylthiophene)s

Absorption spectroscopy is commonly utilized to probe optical properties that can be related, among other things, to the conformation of single, isolated conjugated polymer chains in solution. It is frequently suggested that changes in peak positions of optical spectra result from variations in the stiffness of polymer chains in solution because this modifies the conjugation length. In this work we utilize ultraviolet-visible (UV-vis) spectroscopy, small angle neutron scattering (SANS), and all atom molecular dynamic (AA-MD) simulations to closely probe the relationship between the conformation of single-chains of poly(3-alkylthiophene)s (P3ATs) and their optical properties. SANS results show variations in the radius of gyration and Kuhn length as a function of alkyl chain length, and structure, as well as the solvent environment. Furthermore, both SANS and MD simulations show that dissolved P3HT chains are more rigid in solvents where self-assembly and crystallization are possible. Shifts in P3AT optical properties were also observed for different solvent environments. However, these changes were not correlated to the changes in polymer conformation. Furthermore, changes in optical properties could not be perfectly described by generalized solvent-solute interactions. AA-MD simulations provide new insights into specific polymer-solvent interactions not accounted for in generalized solvatochromic theory. This work highlights the need for experiments and molecular simulations that further inform the specific role of solvent molecules on local polymer conformation and on optical properties.

Progress in the Synthesis of Poly (3-hexylthiophene)

Polythiophene synthesis has undergone a multitude of changes, starting from the initial methods of acid-catalyzed polymerizations with low yields of oligomeric polythiophenes to modern methods using transition metal-based catalysts that allow controlled synthesis of poly(alkylthiophene)s with high molecular weight and regioregularity. The discovery of the opto-electronic properties of conjugated polymers played a major role in this development. Further improvements such as externally initiated polymerization not only enabled the synthesis of polymers that are almost 100% regioregular, but also gave the capability for in situ synthesis of these polymers on substrates, which increases their applicability in opto-electronic devices. This chapter summarizes developments in the methodology of polythiophene synthesis.

Self-assembly of a conjugated triblock copolymer at the air–water interface

Controlling the self-assembly of highly luminescent conjugated polymers is essential for preparing various optoelectronic devices. In this study, a polyisoprene-b-polystyrene-b-poly(3-hexylthiophene) (PI-PS-P3HT) triblock copolymer was synthesized and readily self-assembled into network-like morphologies via dewetting at the air–water interface. Interestingly, the monolayer thick film displayed high photoluminescence (PL) as a result of successfully transferring the amorphous conjugated P3HT chains in the PI-PS-P3HT triblock copolymer from the solution state to the solid state. A model was proposed to illustrate the supramolecular organization of the PI-PS-P3HT monolayer. To the best of our knowledge, this is the first study of a hydrophobic conjugated block copolymer at the air–water interface, from which the conjugated polymer-based monolayer with highly efficient PL formed by dewetting was achieved.