Synthesis and characterization of thieno[3,4-c]pyrrole-4,6-dione and pyrrolo[3,4-c]pyrrole-1,4-dione-based random polymers for photovoltaic applications

New random poly{benzo[1,2-b:4,5-b']dithiophene-thieno[3,4-c]pyrrole-4,6-dione-pyrrolo[3,4-c]pyrrole-1,4-dione} (PBDT-TPD-DPP) based on benzo[1,2-b:4,5-b']dithiophene (BDT) as donor and thieno[3,4-c]pyrrole-4,6-dione (TPD, 60–90%), pyrrolo[3,4-c]pyrrole-1,4-dione (DPP, 10–40%) as acceptors were synthesized through Stille coupling reaction. The photophysical, electrochemical and photovoltaic properties of random polymers were investigated. The random polymers with high molecular weight (M_n = 33.5–41.7 kDa) exhibited broad and strong absorption covering the spectra range from 350 nm up to 922 nm with absorption maxima at around 700 nm, the relatively deep highest occupied molecular orbital (HOMO) energy levels vary between ?5.25 and ?5.42 eV and suitable lowest unoccupied molecular orbital (LUMO) energy levels ranging from ?3.85 to ?3.91 eV. Polymer solar cells (PSC) based on these new random polymers were fabricated with device structures of ITO/PEDOT: PSS/random polymers: PC₇₁BM (1:2, w/w)/Ca/Al. The photovoltaic properties of random polymers were evaluated under AM 1.5G illumination (100 mW/cm²). Devices based on the random polymers showed open circuit voltage (V_oc) of 0.71–0.83 V, and power conversion efficiency (PCE) of 0.82–1.80%.     

Charge transport and glassy dynamics in polyisoprene

The ac conductivity (σ _ac) and electric modulus (M′′) of polyisoprene (PI) with various molecular weights, 652 ≤ M _w ≤ 4,470, were analyzed. The scaling of both the σ _ac and M′′ data suggested that the investigated PI samples follow a temperature-independent conductivity distribution relaxation mechanism. An intense peak was observed in M′′(f) and attributed to the dc conductivity (σ _dc). The temperature dependence of σ _dc and the characteristic relaxation times, τ _c, verified Vogel–Fulcher–Tamman equations. Unlike the other studied samples, the PI samples with M _w = 1,370 and 4,470 exhibited non-decoupling between the α-relaxation time, τ _α, and σ _dc. The fractional Debye–Stokes–Einstein law was well verified for PI samples with M _w = 652, 790, 1,040 and 1,920.     

Lipase-catalyzed synthesis of aliphatic polyesters via copolymerization of lactide with diesters and diols

Aliphatic lactate-bearing copolyesters were successfully synthesized via copolymerization of L-lactide (LLA) with diesters and diols using Candida antarctica lipase B (CALB) as the catalyst. The resultant copolymers had a M_w up to 38,000 Da with M_w/M_n between 1.5 and 2.0, and contained L-lactate units (up to 53 mol%), C₆–C₁₂ diester units, and C₄–C₆ alkylene units in the polymer chains. The lactate repeat units were present primarily as lactate–lactate diads in the polymers. The LLA-diester-diol copolymers were purified in good yield (70–85%) and all purified copolymers were optically active. Hydrolytic degradation study shows that LLA-diethyl adipate-1,6-hexanediol (LLA-DEA-HD) copolymers are degradable polymers as the molecular weight (M_w) of the copolymer with 53% lactate units decreased by ∼70% upon incubation in PBS solution under physiological conditions (37 °C, pH of 7.4) for 80 days. The LLA-diester-diol copolymers are thermally stable up to at least 300 °C with the temperature of maximum degradation rate ranging from 380 to 410 °C. The copolymers exhibit a wide range of physical properties (e.g., from white solid to wax and liquid) depending on their structure and composition. In particular, the LLA-DEA-HD and LLA-DEA-1,4-butanediol copolymers with ∼50 mol% lactate units are colorless, viscous liquids at ambient temperature. Biodegradable liquid polymers are potentially useful biomaterials for drug delivery to treat ocular ailments because of their good compatibility with sensitive soft tissues.     

Synthesis of poly(2,6-dimethyl-1,4-phenylene oxide) derivatives in water using water-soluble copper complex catalyst with natural ligands

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was synthesized by oxidative polymerization of 2,6-dimethylphenol (DMP) using a water-soluble copper complex catalyst under oxygen and with natural ligands in alkaline water. Arginine, guanine, adenine, cytosine, histidine, and folic acid were used as ligands for the copper complex. Arginine performed the best, with a yield of 72%, a number-average molecular weight (M_n) of 4400, and a molecular weight distribution (M_w/M_n) of 1.7. It was then used to optimize reaction conditions. Surfactants, temperature, and sodium hydroxide concentration were varied in copolymerization of DMP and 2-allyl-6-methylphenol (AMP) to produce allyl-containing PPO with 77% yield (M_n = 4500; M_w/M_n = 1.8). The optimum conditions were applied to copolymerization of DMP, AMP, and bisphenol A, leading to dihydroxyl PPO analogs containing thermally cross-linkable allyl groups. The thermal properties of these thermosetting PPOs were studied by differential scanning calorimetry, thermogravimetric analysis, and Fourier-transform infrared spectroscopy.     

Synthesis and characterization of naphthalene diimide/diethynylbenzene copolymers

A series of conjugated polymers has been synthesized by Sonogashira coupling of N,N′-bis(2-octyldodecyl)-2,6-dibromonaphthalene-1,4,5,8-bis(dicarboximide) and four para-diethynylbenzene derivatives: 1,4-diethynyl-2,5-dihexadecyloxybenzene, 1,4-diethynyl-2,5-bis(2-octyldodecyloxy) benzene, 1,4-bis(2-ethylhexyl)-2,5-diethynylbenzene, 1,4-diethynyl-2,5-bis(trifluoromethyl)benzene. The polymers display absorption maxima at wavelengths ranging from 530 nm to 654 nm with molar absorptivities ranging from ca. 4 to 7 × 10⁴ M^?1 cm^?1. The peak reduction potentials, determined by differential pulse voltammetry, for polymer films varied from ?0.93 to ?1.14 V vs. ferrocenium/ferrocene with the trifluoromethyl-substituted derivative being the most readily reduced. All four polymers exhibited electron transport characteristics in bottom-gate/top-contact field-effect transistors, showing average electron mobility values ranging from 1.4 × 10^?4 to 3.7 × 10^?3 cm² V^?1 s^?1.     

Synthesis and characterization of thioether-containing polyimides with high refractive indices

Colorless and transparent polymers with high refractive indices and high temperature resistance have aroused great interest in the industrial community. Here, a series of polyimides (PIs) were prepared from a newly synthesized thioether-containing dianhydride, 1,4-bis(3,4-dicarboxy-phenylenesulfanyl)-benzene dianhydride, and various diamines by a two-step polycondensation reaction. Some flexible and tough films were obtained by casting solutions of them in poly(amic acid) (PAA). The tensile strengths and elongations at break of these PI films were greater than 58 MPa and 10%, respectively. All of them were thermally stable up to 500 °C in both air and nitrogen. Their glass transition temperatures were in the range from 204.5 to 265.8 °C. PI films with a thickness of 10–20 μm showed good optical transparency in the visible light region. Their cutoff wavelengths were lower than 400 nm and their transmittance was higher than 80% at 460 nm. The thioether linkages in the PIs endowed them with high average refractive indices (n _AV) of 1.68–1.74 and low birefringence values (Δn) of 0.0085–0.0120.     

Living polymerization of 1,3-butadiene by a Ziegler-Natta type catalyst composed of iron(III) 2-ethylhexanoate, triisobutylaluminum and diethyl phosphite

Living characteristics of facilely prepared Ziegler-Natta type catalyst system consisting of iron(III) 2-ethylhexanoate, triisobutylaluminum and diethyl phosphite have been found in the polymerization of 1,3-butadiene in hexane at 40 °C. The characteristics have been well demonstrated by: a first-order kinetics with respect to monomer conversion, a narrow molecular weight distribution (M_w/M_n = 1.48-1.52) of polybutadiene in the entire range of polymerization conversion and a good linearity between M_n and the yield of polymer. Feasible post-polymerization of 1,3-butadiene and block co-polymerization of 1,3-butadiene and isoprene further support the living natures of the catalyst bestowed with. The current catalyst system is highly active (yield > 80%, 35 min), providing polybutadiene with 1,2, cis-1,4 and trans-1,4 units about 44.0%, 51.0% and 5.0%, respectively.     

Synthesis of poly(N-vinyl carbazole)-based block copolymers by sequential polymerizations of RAFT–ATRP

Poly(N-vinylcarbazole) (PNVK) is one of the extensively studied photoconductive polymers because of its wide ranges of applications. Through the reversible addition-fragmentation chain transfer/macromolecular design via the interchange of xanthates (RAFT/MADIX) polymerizations, in this study we investigated the syntheses of PNVK-based block copolymers (BCPs) with styrene (St) and methyl methacrylate (MMA). A variety of difunctional haloester-xanthate inifers were prepared and subjected to sequential polymerizations through RAFT and ATRP. In the presence of small amounts of bromoxanthate inifers, the ¹H NMR spectra showed nearly complete consumption of the NVK monomer, but without formation of PNVK. The bromoxanthate inifer could act as acidic moieties that protonated the highly basic NVK monomer. Through ¹H NMR and MALDI-TOF spectroscopic analyses, the structures of byproducts were indentified and a plausible mechanism for their formation was proposed. Alternatively, RAFT/MADIX polymerizations of NVK with two chloroxanthate inifers S-[1-methyl-4-(6-chloropropionate)ethyl acetate] O-ethyl dithiocarbonate and S-[1-methyl-4-(6-chloroisobutyrate)ethyl acetate] O-ethyl dithiocarbonate) provided first-order kinetic plots and well-controlled PNVK-Cl MIs (M_n ≈ 6000–40,000; M_w/M_n < 1.35). Using a suitable ATRP-initiating groups and optimization of the reaction conditions, the BCPs PNVK-b-PSt (M_n ≈ 4900–12,800; M_w/M_n < 1.5) and PNVK-b-PMMA (M_n ≈ 46,000–100,000; M_w/M_n < 1.35) were obtained.     

Optimization of poly(1,4-cyclohexylidene cyclohexane-1,4-dicarboxylate) (PCCD) preparation for increased crystallinity

A key factor, which affects the crystallization temperature on cooling (T_c) of PCCD is the cis/trans isomer ratio of the cyclohexyl diester in the polymer. Isomerization of pure dimethyl-trans-1,4-cyclohexanedicarboxylate can occur during the polymerization, and the T_c on cooling decreases along with the trans content. The isomerization reaction is enhanced with temperature, time and catalyst amount, and these variables should be minimized to prepare PCCD polymers with high T_c. However, these same variables also control the molecular weight growth of the polymer, and so a compromise between the best conditions for high T_c and those for high M_w must be made. A set of optimized conditions were obtained leading to PCCD polymers with M_w of 75,000-80,000 and T_c on cooling of 164-167 °C. Solid state polymerization was used to prepare high molecular weight PCCD with a high level of crystallinity (T_c on cooling ∼193 °C). It was also shown that adding small amounts of supplementary diols facilitates PCCD preparation by ensuring that high molecular weight PCCD polymers will be obtained even when the stoichiometry of monomer feed is off by >3%, i.e. conditions which would otherwise lead to low M_w. Finally, less crystalline PCCD's have been prepared via either incorporation of diethylene glycol or increasing the cis-diester amount in the polymer.     

Simulation study on the relationship between a high resolution αs-plot and the pore size distribution for activated carbon

The effects of the micropore structure of activated carbons on the high resolution α_s-plot for nitrogen adsorption isotherms were examined with the grand canonical Monte Carlo simulation. Adsorption isotherms of nitrogen were simulated in graphitic slit pores at 77 K as a function of the slit width (w). As no pore effect was observed below P/P₀=0.6 for w=3.5 nm, α_s-plots for the simulated adsorption isotherms were constructed using the standard isotherm simulated for w=3.5 nm. The simulated α_s-plots had filling and cooperative swings which were experimentally shown in the previous works, and the shape of the simulated α_s-plot varied with the micropore structure. As the subtracting pore effect (SPE) method for the specific surface area (SSA) determination using the α_s-plot was proposed in the previous experimental works, the theoretical ground for the SPE method was discussed. The best evaluation method of SSA using the α_s-plot was shown, almost agreeing with the SPE method. This simulation study showed clearly that the SPE method is available for pore systems of w≥0.7 nm, whereas even the SPE method underestimates the SSA of the pores of w≤0.6 nm. The observed swings of the α_s-plot were simulated using the different micropore size distribution. The bimodal micropore size distribution lead to both of filling and cooperative swings, while a single pore size distribution <0.9 nm gave only the filling swing. Thus, four representative types of the α_s-plot for activated carbons were proposed and it was shown how to understand the micropore size distribution through the α_s-plot.     

Synthesis of high molecular weight poly(l-lactic acid) and poly(d-lactic acid) with improved thermal stability via melt/solid polycondensation catalyzed by biogenic creatinine

Stereoregular high polymers of poly(l-lactic acid) (PLLA) (M_w 1.2 × 10⁵, isotacticity 96.0%) and poly(d-lactic acid) (PDLA) (M_w 1.0 × 10⁵, isotacticity 98.6%) were successfully synthesized via melt/solid polycondensation (MP/SSP) using a biogenic catalyst creatinine (CR). The follow-up monitor of the polycondensation products with ¹³C NMR technique revealed that the polymerization of MP/SSP proceeded in a stereochemical controlled way throughout the whole process as evidenced by the constant high values of isotacticity (97.8–99.4%) of produced polymers. Thermogravimetric analysis demonstrated that the decomposition temperatures (T_d,init 324.3 °C, T_{d, 5%} 347.0 °C, T_{d, max} 400.2 °C) of PLLA synthesized with catalyst CR are over 100 °C above those of PLLA synthesized with catalyst SnCl₂·2H₂O.     

Synthesis and characterization of highly fluorescent phenylene vinylene containing perfluorocyclobutyl (PFCB) aromatic ether polymers

4-(Trifluorovinyloxy)benzaldehyde was treated under Wittig conditions with 4-dihexyloxy-2,5-xylenebis(triphenylphosphoniumbromide) to form 1,4-bis(2′-(4-trifluorovinyloxyphenyl)ethenyl)-2,5-dihexyloxybenzene, a novel phenylene vinylene-bistrifluorovinyl ether monomer. Cyclopolymerization afforded an insoluble, non-luminescent material likely due to cross-addition reactions between phenylene vinylene olefin and trifluorovinyl ether (TFVE). However, 1,2-bis(4-formylphenoxy)hexafluorocyclobutane was polymerized with 1,4-dihexyloxy-2,5-xylenebis(triphenylphosphoniumbromide) and 1-methoxy-4-(2-ethylhexyloxy)-2,5-xylenebis(triphenylphosphoniumbromide) under Wittig conditions to yield two novel poly(perfluorocyclobutyl-co-phenylene vinylene) polymers. The polymers are of moderate molecular weight (8600-8700 M_n), show excellent thermal stability (T_d = 390-405 °C), and are readily soluble in common organic solvents. The materials are highly fluorescent in both solution and thin film with solution quantum yields of 68 and 71%.     

Synthesis of fluorene- and anthracene-based π-conjugated polymers and dependence of emission range and luminous efficiency on molecular weight

In the present work poly[9,9-dioctylfluorene-co-2-pentyl-9,10-bis(4-vinylphenyl)anthracene], a fluorene- and anthracene-based copolymer, is synthesized through a Heck coupling reaction. In order to synthesize polymers with high-molecular weight, DMF (P1), DMF/p-Xylene = 1/1 (P2), p-Xylene (P3), and 1,4-Dioxane (P4) are used as solvents, which are an important factor in the synthesis process. The number of average molecular weights (M_n) of the synthesized polymers P1–P4 do not differ significantly, standing at 22,309, 12,369, 29,192, and 39,464, respectively, while their weight average molecular weights (M_w) show considerable differences (i.e. 50,055; 24,042; 125,406; and 231,053). Polymers P1–P4 demonstrate little difference in the results of a thermal analysis, electrochemical analysis, UV–vis analysis, and photoluminescence (PL) spectrum measurement. With regard to electroluminescence (EL) spectrum measurement, however, P1 and P2 show main luminous peaks at 508 nm, while P3 and P4's luminous peaks are seen at 516 nm. Moreover, luminous shoulder peaks were red-shifted with increase of molecular weight of polymers from 460 to 544 nm. In this process, the luminous area is red-shifted from greenish-blue to yellowish-green. The I–V–L measurement results show that the maximum brightness of P1, P2, and P3 ranges from 164 to 303 cd/m² and their luminous efficiency is low at 0.031–0.054 cd/A. Meanwhile, the turn-on voltage of P4, having greater molecular weight, is 9.5 V, and its maximum brightness and corresponding luminous efficiency are 736 cd/m² and 0.08 cd/A, respectively, implying that the luminous efficiency of devices improves as the molecular weight becomes greater.     

Reversible coordinative chain transfer polymerization of isoprene and copolymerization with ε-caprolactone by neodymium-based catalyst

Coordinative chain transfer polymerization (CCTP) of isoprene was investigated by using the typical Ziegler–Natta catalytic system [Nd(Oi-Pr)₃/Al(i-Bu)₂H/Me₂SiCl₂] with Al(i-Bu)₂H as cocatalyst and chain transfer agent (CTA). The catalyst system exhibited high catalytic efficiency for the reversible CCTP of isoprene and yielded 6–8 polymer chains per Nd atom due to the high chain transfer ability of Al(i-Bu)₂H. The narrow molecular weight distribution (M_w/M_n = 1.22–1.45) of the polymers, the good linear relationship between the M_n and yield of the polymer, and the feasible seeding polymerization of isoprene indicated the living natures of the catalyst species. Moreover, the living Nd-polyisoprene active species could further initiate the ring-opening polymerization of polar monomer (ε-caprolactone) to afford an amphiphilic block copolymer consisting of cis-1,4-polyisoprene and poly(ε-caprolactone) with controllable molecular weight and narrow molecular weight distribution.     

Thermal polymerization of methyl (meth)acrylate via reversible addition-fragmentation chain transfer (RAFT) process

Thermal polymerization of methyl (meth)acrylate (MMA) was carried out using 2-cyanoprop-2-yl-1-dithionaphthalate (CPDN) and cumyl dithionaphthalenoate (CDN) as chain transfer agents. The kinetic study showed the existence of induction period and rate retardation, especially in the CDN mediated systems. The molecular weights of the polymers increased linearly with the monomer conversion, and the molecular weight distributions (M_w/M_ns) of the polymers were relatively narrow up to high conversions. The maximum number-average molecular weights (M_ns) reached to 351?900 g/mol (M_w/M_n = 1.47) and 442?400 g/mol (M_w/M_n = 1.29) in the systems mediated by CPDN and CDN, respectively. Chain-extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA-block-polystyrene (PMMA-b-PSt) copolymer with controlled structure and narrow M_w/M_n. Thermal polymerization of methyl acrylate (MA) in the presence of CPDN, or benzyl (2-phenyl)-1-imidazolecarbodithioate (BPIC) also demonstrated “living”/controlled features with the experimented maximum molecular weight 312?500 g/mol (M_w/M_n = 1.57). The possible initiation mechanism of the thermal polymerization was discussed.     

Solubilities and diffusivities of water vapor in poly(methylmethacrylate), poly(2-hydroxyethylmethacrylate), poly(N-vinyl-2-pyrrolidone) and poly(acrylonitrile)

Sorption and diffusion data were obtained for water vapor in four different polymers: poly (methylmethacrylate) (PMMA), poly (2-hydroxyethylmethacrylate) (PHEMA), poly (N-vinyl-2-pyrrolidone) (PVP) and poly (acrylonitrile) (PAN) at 35 °C using a gravimetric sorption method. Highest sorption was for PVP, followed by PHEMA. PMMA and PAN sorbed very little water. All the polymers exhibit a BET type III sorption isotherm; the large upturn at high activity for PVP and PHEMA is probably due to plasticization of the polymers by water vapor. Sorption data were interpreted using Flory-Huggins theory and the Zimm and Lundberg cluster integral.Fickian diffusion is observed for PHEMA. For PVP, the fractional uptake M_t/M_∞ is linear with the square root of the time up to M_t/M_∞=0.6−0.8 for all water activities a_w, but it shows a clear water sorption overshoot at a_w=55.3% and a_w=72.1%, probably due to macromolecular relaxation. PMMA sorption kinetics is also characterized by a maximum in the water uptake. The diffusion coefficient increases significantly with water concentration for PVP and PHEMA, weakly for PMMA, but it is independent of concentration for PAN.     

Polybutadiene modified by epoxidation: 2. The effect of epoxy groups on the crosslinking process with dicumyl peroxide

The process of crosslinking sodium and n-butyllithium polybutadienes as well as the products of their modification obtained by epoxidation has been studied. It has been found that the crosslinking efficiency of epoxy-1,2-polybutadiene is half that of the starting polybutadiene. However, the crosslinking efficiency of epoxy-1,4-polybutadiene was found to be similar to that of the starting 1,4-polybutadiene. The shift in glass transition temperature for epoxy-polybutadienes brought about by the change in the chemical composition (ΔT_g)_M was found to be 67 K for 1,4-polybutadiene, and 51 K for 1,2-polybutadiene. The effect of the epoxy groups and crosslinks on the glass transition temperatures of modified crosslinked polymers is also discussed.     

Polymerization of propynes bearing diphenylamino or indolyl groups

Summary Nitrogen-containing acetylenic monomers including 3-(N,N-diphenylamino)-1-propyne (DPAP), N-(2-propynyl)indole (PI), 2-methyl-N-(2-propynyl)indole (2-MePI) and 3-methyl-N-(2-propynyl)indole (3-MePI) polymerized in the presence of various transition metal catalysts. Poly(DPAP) was obtained with WCl₆, MoCl₅, Rh and Fe catalysts, and its weight-average molecular weights (M _w) reached 140x10³. Polymerization of PI and 2-MePI by Rh and Fe catalysts gave good yields of high molecular weight polymers with M _w of 340x10³ and 640x10³, respectively. Polymerization of 3-MePI by WCl₆- and MoCl₅-based catalysts resulted in a soluble polymer (M_w= 52x10³), whereas the use of Rh and Fe catalysts led to the formation of an insoluble polymer. All the polymers exhibited cutoff wavelengths around 450–500 nm, meaning the moderate to fair conjugation along the polymer backbones. Received: 24 June 1998/Accepted: 5 August 1998     

Microwave-assisted FeCl3-mediated rapid synthesis of poly(9,9-dihexylfluorene) with high molecular weight

Poly(9,9-dihexylfluorene) with high molecular weight (M_w ∼ 81,000) is obtained in 25 min using a microwave-assisted FeCl₃-mediated oxidative polymerization. The effects of microwave power, time, solvent, monomer and catalyst's concentration on the polymerization have been systematically investigated. The structures and thermal properties of obtained polymers are fully characterized using FTIR, NMR, TGA, DSC, UV–visible absorption and fluorescence spectra. The results show that well-defined polymers have been obtained. XPS, ICP and elemental analysis are used to check the residue of iron catalyst, and almost no residue of FeCl₃ is detected in polymers.