Although several phase diagrams of block copolymers prepared by sequential monomer addition are known today, the phase diagrams of the corresponding tapered copolymers have not been reported in detail and this despite the industrial importance of the latter. A phase diagram based on a series of tapered diblock copolymers is reported, generated by the sec-butyllithium initiated statistical anionic copolymerization of styrene and isoprene in cyclohexane. This affords copolymers with polyisoprene volume fractions, f, in the range of 0.43 < f < 0.82 and total molar mass in the range of 46–160 kg mol–1. The phase diagram consists of lamellae, hexagonally packed cylinders, weakly ordered hexagonally packed cylinders (CYL), and perforated (PL) as well as irregular bicontinuous morphologies. The phase state in the tapered copolymers bears some similarities and several distinct differences in comparison to the respective copolymers prepared by conventional sequential monomer addition. It is shown that the weakly ordered CYL/PL morphologies comprise a large part of the phase diagram that is significantly extended in comparison to diblock copolymers prepared sequentially. On the other hand, the composition range for the bicontinuous morphologies is similar in the two systems (0.64 < fPI < 0.68). 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/macp.202200033

Phase Diagram of Tapered Copolymers Based on Isoprene and Styrene

: Graphene nanoribbons (GNRs) have demonstrated great potential for nanoscale devices owing to their excellent electrical properties. However, the application of the GNRs in large-scale devices still remains elusive mainly due to the absence of facile, nonhazardous, and nondestructive transfer methods. Here, we develop a simple acid (HF)-free transfer method for fabricating ﬁ eld-e ﬀ ect transistors (FETs) with a monolayer composed of a random network of GNRs. A polymer layer that is typically used as mechanical support for transferring GNR ﬁ lms is utilized as the gate dielectric. The resultant GNR-FETs exhibit excellent FET characteristics with a large on/o ﬀ switching current ratio of >10 4 . The transfer process enables the demonstration of the ﬁ rst GNR-based nonvolatile memory. The process o ﬀ ers a simple route for GNRs to be utilized in various optoelectronic devices.

Graphene Nanoribbon Field-Effect Transistors with Top-Gate Polymer Dielectrics

In the present work, we report a simple synthesis method for preparation of copolymers and nanocomposites from limonene and styrene using clay as a catalyst. The copolymerization reaction is carried out by using a proton exchanged clay as a catalyst called Mag-H+. The effect of temperature, reaction time and amount of catalyst were studied, and the obtained copolymer structure (lim-co-sty) is characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (1H-NMR) and differential scanning calorimetry (DSC). The molecular weight of the obtained copolymer is determined by gel permeation chromatography (GPC) and is about 4500 g·mol−1. The (lim-co-sty/Mag 1%, 3%, 7% and 10% by weight of clay) nanocomposites were prepared through polymer/clay mixture in solution method using ultrasonic irradiation, in the presence of Mag-CTA+ as green nano-reinforcing filler. The Mag-CTA+ is organophilic silicate clay prepared through a direct exchange process, using cetyltrimethylammonuim bromide (CTAB). The prepared lim-co-sty/Mag nanocomposites have been extensively characterized by FT-IR spectroscopy, X-ray diffraction (XRD), scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM). TEM analysis confirms the results obtained by XRD and clearly show that the obtained nanocomposites are partially exfoliated for the lower amount of clay (1% and 3% wt) and intercalated for higher amounts of clay (7% and 10% wt). Moreover, thermogravimetric analysis (TGA) indicated an enhancement of thermal stability of nanocomposites compared with the pure copolymer.

/pdf/synthesis-and-characterization-of-copolymers-and-3ilns7yx.pdf

Synthesis and Characterization of Copolymers and Nanocomposites from Limonene, Styrene and Organomodified-Clay Using Ultrasonic Assisted Method

High molar mass copolymers with a tapered interface are mechanically tough materials with an accessible order-to-disorder transition temperature and hence processability. We report the first ordering kinetics for a tapered tetrablock copolymer in comparison to a conventional diblock copolymer made sequentially. We show that tapered copolymers belong to the Brazovskii "universality class," where fluctuations play a dominant role. Consequently, the order-to-disorder transition has a very weak, fluctuation-induced first-order character. The ordering kinetics of the lamellar phase from the supercooled disordered melt revealed several distinct differences associated with the range of metastability (increased), the timescales (bimodal), and the exact mechanism of ordering. The results are discussed in terms of the reduced interaction parameter and the introduction of structural defects within the lamellar grains.

Ordering kinetics of a tapered copolymer based on isoprene and styrene.

Grafted Copolymer Electrolytes Based on the Poly(acrylic acid-co-oligo ethylene glycol acrylate) (P(AA-co-OEGA)) Ion-Conducting and Mechanically Robust Block

We report on the phase behavior and the respective dynamics in random P(VDF-TrFE) copolymers using standard and temperature-modulated differential scanning calorimetry, X-ray diffraction, and a combination of temperature- and pressure-dependent dielectric spectroscopy measurements. Depending on the copolymer composition, the coexistence of three/four weakly ordered phases was identified in the vicinity of the Curie transition (Tc). With respect to the dynamics, we demonstrate that the segmental dynamics associated with the relaxation of constrained amorphous VDF segments at the crystal/amorphous “phase” can be used as a marker of the Curie transition. The corresponding segmental relaxation freezes at about 50 K above the lower liquid-to-glass temperature associated with the freezing of amorphous segments away from the interface. Pressure-dependent dielectric measurements provided quantitative insight into (i) the molecular origin of the segmental processes (by employing the pressure sensitivity of relaxation times and the pressure coefficient of the respective Tg’s), (ii) the nature of the phase transition at Tc, and (iii) information about the stability of phases under the variation of temperature and pressure (through the T–P phase diagram). We show that Tc increases linearly with pressure and is accompanied by small volume changes, implying a weakly first-order thermodynamic transition. Furthermore, pressure stabilizes the ferroelectric phase over a broader temperature range. This could extend the operating temperature range of ferroelectric devices based on P(VDF-TrFE) copolymers. 

https://purehost.bath.ac.uk/ws/files/235226583/PVDF_TrFE_final_Accepted.pdf

Dr. Ram Sanehi

Papers

Phase Diagram of Tapered Copolymers Based on Isoprene and Styrene

P(VDF-TrFE) Copolymer Dynamics as a Function of Temperature and Pressure in the Vicinity of the Curie Transition

Ionic Conductivity of a Solid Polymer Electrolyte Confined in Nanopores