Polymer Chains In Solid State Research Articles

Synthesis and Characterization of Poly(3‐Hexylthiophene) for Organic Solar Cells

Poly(3‐hexylthiophene) (P3HT) has been successfully synthesized through McCullough route. The influence of nickel catalyst content on molar mass (Mn and Mw), dispersity (Đ), regioregularity (rr), as well as optical, thermal, and morphological properties is systematically investigated. The results evidence that polymer dispersities are narrow, Mn and rr values decrease with the augmentation of catalyst content. Polymer solution in different solvents (chloroform and dichlorobenzene) show similar optical band gaps. Solid state band gap of obtained material is lower than in solution, which confirms the reorganization of polymer chains in solid state. Both polymers show good thermal stability and their morphologies are tightly influenced by the monomer/catalyst ratio in the synthesis. Two main morphologies are obtained, for the higher molar mass P3HT it is nodule‐like, while the lower Mn presented rod form. The fore polymer combined with PCMB results in lower root mean square (RMS) indicating smoother morphology, which is more appropriate for solar cells application.

Ethylene/1‐heptene copolymers as interesting alternatives to 1‐octene‐based LLDPE: Molecular structure and physical properties

ABSTRACTClassical linear low density polyethylenes (LLDPEs) are copolymers of ethylene and 1‐octene or 1‐hexene, respectively. In the past, other 1‐olefins have been tested as comonomers but the resulting LLDPEs were never commercialized as large scale products. The present study focuses on the use of 1‐heptene as an interesting comonomer for the synthesis of LLDPE. For a comparison of the molecular structure and the physical properties of 1‐heptene‐ and 1‐octene‐based LLDPEs, five Ziegler–Natta LLDPEs of varying comonomer contents based on 1‐heptene and 1‐octene, respectively, were acquired and analysed using advanced methods. The comonomer contents of the resins were between 0.35 and 6.4 mol %. Crystallization‐based techniques revealed similar bimodal distributions that are due to the formation of copolymer and polyethylene homopolymer fractions. The compositional distribution of the copolymers was studied by high‐temperature (HT) HPLC and HT‐2D‐LC. The analytical results indicate similar chemical heterogeneities and molar mass distributions of the two sets of LLDPE up to a comonomer content of 3 mol %. Similar to the molecular structure, the physical properties of the materials are quite similar. At comonomer contents of ≥3 mol % differences between the two sets of samples are seen that are attributed to differences in the abilities of 1‐heptene and 1‐octene in disrupting the crystal arrangements of the polymer chains in solid state. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 962–975

Cold crystallization and postmelting crystallization of PLA plasticized by compressed carbon dioxide

AbstractThe cold crystallization at temperature Tcc (melting > Tcc > glass transition) and the postmelting crystallization of polylactic acid plasticized by compressed carbon dioxide (CO2) were studied using a high‐pressure differential scanning calorimeter. The kinetics of the two kinds of crystallization were evaluated by the Avrami equation as a function of pressure at certain temperatures. The effects of using talc as a nucleation agent on the two types of crystallization under pressure were also investigated. The results show that compressed CO2 increased the mobility of the polymer chains in solid state, resulting in an increased rate of cold crystallization. The decreased rate of postmelting crystallization was mainly in the nucleation‐controlled region, which indicates that the number of nuclei was decreased by the compressed CO2. The growth rate of the two crystallization types followed the Avrami equation, but the kinetics of each depended upon temperature and pressure. The inclusion of talc accelerated postmelting crystallization but had little effect on cold crystallization. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2630–2636, 2008

Non-dispersive hole transport in a novel trifluoromethylbiphenylyl substituted PPV derivative

We have studied the optical and electrical properties of a novel electroluminescent polymer, poly[2−(2'-p−trifluoromethyl-phenyl-4',5'-bis(3’’-methylbutoxy))phenyl-1,4- phenylene vinylene], using absorption, photoluminescence (PL), photoluminescent quantum yield (ηPL) and time of flight (TOF) photoconductivity techniques. The absorption spectrum in chloroform shows a broad absorption band peaked at 2.92 eV and the PL spectrum shows a maximum at 2.52 eV with vibronic shoulders at 2.38 eV and 2.24 eV. The film state absorption and PL spectra shifted towards the low energy region and the vibronic features are more pronounced compared to that in dilute solution. This is due to the increase of effective conjugation length in the solid state compared to that in solution. The PL quantum yield of the polymer was found to be 44 % in chloroform and 52 % in solid state. The increase of ηPL in solid state compared to liquid state is due to the constraint on the twisting or bending motion of the polymer chains in solid state. The room temperature TOF transients for positive charges showed non-dispersive nature of transport with a mobility of 3.83 × 10−6 cm2/Vs at an electric field of 2 × 105 V/cm. The variation of hole mobility with applied electric field has been studied and analyzed according to disorder formalism.