Novel Methylaluminoxane‐Activated Neodymium Isopropoxide Catalysts for 1,3‐Butadiene Polymerization and 1,3‐Butadiene/Isoprene Copolymerization

The homo‐ and copolymerizations of 1,3‐butadiene and isoprene are examined by using neodymium isopropoxide [Nd(Oi‐Pr)₃] as a catalyst, in combination with a methylaluminoxane (MAO) cocatalyst. In the homopolymerization of 1,3‐butadiene, the binary Nd(Oi‐Pr)₃/MAO catalyst works quite effectively, to afford polymers with high molecular weight ( ≈ 10⁵ g mol^‐1), narrow molecular‐weight distribution (MWD) (/ = 1.4–1.6), and cis‐1,4‐rich structure (87–96%). Ternary catalysts that further contain chlorine sources enhance both catalytic activity and cis‐1,4 selectivity. In the copolymerization of 1,3‐butadiene and isoprene, the copolymers feature high , unimodal gel‐permeation chromatography (GPC) profiles, and narrow MWD. Most importantly, the ternary Nd(Oi‐Pr)₃/MAO/t‐BuCl catalyst affords a copolymer with high cis‐1,4 content in both monomer units (>95%).

     

A New Insight into the Mechanism of 1,3‐Dienes Cationic Polymerization III: Polymerization of 1,3‐Pentadiene with CF3COOD/TiCl4 Initiating System: Chain‐Ends Structure and Kinetics

A novel method for the investigation of the chain‐end structure of poly(1,3‐pentadiene)s synthesized using the CF₃COOD/TiCl₄ initiating system is developed. It is shown for the first time that the content of trans‐1,2‐structures in the first monomer unit is considerably higher than the content of trans‐1,4‐structures, whereas the content of trans‐1,4‐units is substantially higher than trans‐1,2‐units for the polymer chain as a whole. Another important observation is that chain transfer to monomer is significant even at the earlier stages of the 1,3‐pentadiene polymerization (after 1 s of reaction). The very low functionality at the ω‐end (F_n (Cl) < 0.15) confirms the intensive chain transfer to monomer. This method is also applied for the estimation of the concentration of active species and the rate constant for propagation (k _p) for the cationic polymerization of 1,3‐pentadiene using the CF₃COOD/TiCl₄ initiating system: rate constants for propagation, k _p, of 1.5 × 10³ and 3.3 × 10³ L mol^?1 min^?1 are determined for 1,3‐pentadiene polymerization at 20 and –78 °C, respectively.

     

Flame‐Retardant Polypropylene/Multiwall Carbon Nanotube Nanocomposites: Effects of Surface Functionalization and Surfactant Molecular Weight

Flame‐retardant polypropylene (PP)/carbon nanotubes (CNTs) nanocomposites influenced by surface functionalization and surfactant molecular weights are studied. 3‐Aminopropyl‐triethoxysilane (APTES) is utilized to modify the CNTs (f‐CNTs), and maleic‐anhydride‐grafted PP (MAPP) with two molecular weights ( of 800 and 8000 g mol^?1) is used to further improve the dispersion of f‐CNTs in the PP matrix. Thermal gravimetric analysis (TGA) and microscale combustion calorimetry (MCC) reveal that the molecular weight of MAPP directly affects the thermal stability and flammability of PP/f‐CNTs PNCs: both MAPP polymers ( of 800 and 8000 g mol^?1) increase the thermal stability of PP; however, the heat release rate of PP/f‐CNTs is reduced in the presence of MAPP ( of 800 g mol^?1) and increased in the presence of MAPP ( of 8000 g mol^?1). MAPP ( of 800 g mol^?1) also results in a lower viscosity of the PP/f‐CNTs PNCs compared with pure PP.

     

Reverse Iodine Transfer Polymerization (RITP) of 1,1,2,2‐Tetrahydroperfluorodecyl Acrylate in Supercritical Carbon Dioxide

Reverse iodine transfer polymerization (RITP) of 1,1,2,2‐tetrahydroperfluorodecyl acrylate (FDA) is successfully performed in supercritical carbon dioxide (scCO₂) at 70 °C under a CO₂ pressure of 300 bar. PolyFDA (PFDA) of increasing molecular weights (from 10 000 to 100 000 g mol^?1) is synthesized with good agreement between theoretical, ¹H NMR spectroscopy and and size exclusion chromatography/refractive index/right‐angle laser‐light scattering/differential viscometer (SEC/RI/RALLS/DV)‐estimated molecular weights (). Furthermore, the increase of goes with a decrease of the dispersity of the polymers (? from 2.06 to 1.33), which is consistent with a controlled radical polymerization (CRP). Lastly, the structure of final PFDA and therefore the RITP process are confirmed by matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) analyses.

     

Controlled One‐Pot Synthesis of Polystyrene‐block‐Polycaprolactone Copolymers by Simultaneous RAFT and ROP

A convenient one‐pot method for the controlled synthesis of polystyrene‐block‐polycaprolactone (PS‐b‐PCL) copolymers by simultaneous reversible addition–fragmentation chain transfer (RAFT) and ring‐opening polymerization (ROP) processes is reported. The strategy involves the use of 2‐(benzylsulfanylthiocarbonylsulfanyl)ethanol (1) for the dual roles of chain transfer agent (CTA) in the RAFT polymerization of styrene and co‐initiator in the ROP of ε‐caprolactone. One‐pot poly­merizations using the electrochemically stable ROP catalyst diphenyl phosphate (DPP) yield well‐defined PS‐b‐PCL in a relatively short reaction time (≈4 h; = 9600?43 600 g mol^?1; / = 1.21?1.57). Because the hydroxyl group is strategically located on the Z substituent of the CTA, segments of these diblock copolymers are connected through a trithiocarbonate group, thus offering an easy way for subsequent growth of a third segment between PS and PCL. In contrast, an oxidatively unstable Sn(Oct)₂ ROP catalyst reacts with (1) leading to multimodal distributions of polymer chains with variable composition.

     

Molar‐Mass Analysis of Dendrigraft Poly(l‐lysine) (DGL) Polyelectrolytes by SEC‐MALLS: The “Cornerstone” Refractive Index Increment

Dendrigraft poly(l ‐lysine) (DGL) polyelectrolytes, obtained by iterative polycondensation of N‐trifluoroacetyl‐l ‐lysine‐N‐carboxyanhydride, constitute very promising candidates in many biomedical applications. In order to get a better understanding of their structure–property relationships in these applications, their absolute average molecular weights have to be accurately measured. Size‐exclusion chromatography coupled to a multi‐angle laser‐light‐scattering detector (SEC‐MALLS) is known to be the most appropriate analytical tool. These measurements require the determination of the refractive index increment, dn/dc, of these highly branched polycationic macromolecules in aqueous solution. This optical property has to be measured in the same aqueous conditions as SEC‐MALLS eluents. Consequently, data are determined and discussed as a function of different aqueous SEC‐MALLS eluents, as well as different counter‐ions of the many ammonium groups of DGL (generation 3, DGL‐3, used as a model herein). The resulting number‐average molecular weights, , are found to be very dissimilar when the measured dn/dc values are directly considered. In contrast, very close values are obtained (average = 18 700, standard error of 1110 g mol^?1) with a low coefficient of variation for such data (ca. 6% for six analyses), when the dn/dc are corrected by the exact lysine amount (measured by the total Kjeldahl nitrogen method).

     

One‐Pot Synthesis of Polyester–Polyolefin Copolymers by Combining Ring‐Opening Polymerization and Carbene Polymerization

The ring‐opening polymerization (ROP) of a cyclic ester using alkyl acetate carbene (ROCOCH:) is generated from diazoacetate as organocatalyst under microwave irradiation, which enables the one‐pot preparation of copolymers of polyester and polyolefin. The chemical structure of the polymerized product is characterized by NMR, Fourier transformed infrared (FTIR), and UV–vis spectroscopy. The incorporation of the azo group into the obtained copolymer is determined by elemental analysis, which indicates that 1.38–6.21% nitrogen is contained in the obtained copolymers. The influences of catalyst and microwave irradiation parameters on the polymerization are investigated. Both the microwave power and irradiation time have great influences on the copolymerization. Moreover, the molar mass of the obtained polymers is calculated with polystyrene standards, which gradually increases from 600 to 36 100 g mol^?1 as the reaction temperature increases from 60 to 120 °C. Poly­mer with of 36 100 g mol^?1 and PDI of 1.86 is produced under optimized conditions. The combination of ROP and carbene polymerization offers a new and convenient pathway to synthesize copolymers of polyesters and polyolefins.

     

Imidazolium‐Based Ionic Liquids as Initiators in Ring Opening Polymerization: Ionic Conduction and Dielectric Response of End‐Functional Polycaprolactones and Their Block Copolymers

Imidazolium alcohols, [R‐Im‐Z‐OH]⁺[X]^?, are investigated as initiators for ring opening poly­merization (ROP) of ε‐caprolactone (CL). Two monomeric imidazolium alcohols { I [R = HOOC(CH₂)₅, Z = (CH₂)₁₁, X = Br] and III [R = n‐Bu, Z = (CH₂CH₂O)₃CH₂CH₂, X = bis(trifluoromethylsulfonyl)imide (TFSI)]} are successfully utilized as initiators for ROP of CL, yielding corresponding polycaprolactones (PCL) Ia‐Br and IIIa‐TFSI . The oligoester II derived from I also acts as an initiator, providing block copolymer IIa‐Br . By anion exchange Ia‐Br and IIa‐Br are converted to Ia‐TFSI and IIa‐TFSI . The TFSI polymers have lower glass transition temperatures (T_g), resulting in higher conductivity, compared to the Br polymers. The ionic conductivities of the PCL block copolymers are higher than those of the PCL homopolymers, despite the similar T_g, because of their higher ionic content. Their static dielectric constants () increase linearly with ion content and exhibit the temperature dependence expected by Onsager, in the liquid state. The semi­crystalline PCL homopolymers, upon crystallization, undergo a significant increase in , owing to a Maxwell–Wagner–Sillars interfacial polarization. The present results demonstrate that with proper design, block copolymers have the potential to provide high ionic conductivities combined with good mechanical strength, key attributes for application of these materials in mechanical actuators.

     

An Alternating Copolymer of a Tetrapeptide and a Tetrathiophene Prepared by a Click Reaction: A Study of the Synthesis and Assembly Behavior

Alternating copolymers of an oligopeptide (N₃‐GVGV‐N₃, where G: glycine; V: valine) and an oligothiophene (5,5′‐bis(ethynyl)‐3,3'‐dioctyltetrathiophene) are prepared by click chemistry. The experimental results discover that these copolymers exhibit strong molecular‐weight‐dependent self‐assembly behaviors. The copolymer P1 with the lowest weight‐average molecular weight ( = 7400 g mol^?1), assembles into well‐ordered fibrous nanostructures. P3 ( = 16 980 g mol^?1) assembles into nano­balls. P2, which has the medium between P1 and P3, ( = 14 800 g mol^?1), exhibits more‐complicated self‐assembly behaviors, more like a transition state between the other two. All of the results suggest the self‐assembly ability of these oligopeptide segments might be the major reason for the nano‐structure evolution.

     

Chain‐Length‐Dependent Termination of Vinyl Acetate and Vinyl Pivalate Bulk Homopolymerizations Studied by SP‐PLP‐EPR

Bulk homopolymerizations of vinyl acetate and vinyl pivalate are studied by EPR experiments between ?65 °C and 60 °C with dicumyl peroxide acting as the photoinitiator. No mid‐chain radicals are seen, which demonstrates that backbiting plays no role. The chain‐length dependence of the termination rate coefficients measured up to 13% monomer conversion is adequately represented by the composite model. The power‐law exponents α_s and α_l for short‐chain and long‐chain radicals are: α_s(VAc) = 0.57 ± 0.05, α_s(VPi) = 0.67 ± 0.15, α_l(VAc) = 0.16 ± 0.07, and α_l(VPi) = 0.16 ± 0.07. The crossover chain lengths differ largely: i_c(VAc) = 20 ± 10 and i_c(VPi) = 110 ± 30. The rate coefficient for termination of two radicals of chain length unity, , which is the fourth composite‐model parameter, depends on temperature, as does the monomer fluidity.

     

Structural Analysis of Poly(3‐hexylthiophene) Prepared via Direct Heteroarylation Polymerization

This study reports the synthesis and characterization of poly(3‐hexylthiophene) (P3HT) from a direct heteroarylation polymerization of two isomeric monomers, 2‐bromo‐3‐hexylthiophene (monomer 1 ) and 2‐bromo‐4‐hexylthiophene (monomer 2 ). Using the Herrmann–Beller catalyst along with P(o‐NMe₂Ph)₃, the resulting polymers are obtained in excellent yields and exhibit a good number‐average molecular weight (M_n of 33 and 16 kDa, respectively). Detailed ¹H NMR analyses reveal less than 1% of homocouplings and no evidence of β‐branching. Dehalogenation is identified as the main chain termination step and preferentially occurs on monomer 2 . The melting temperature (237 °C) and hole mobility (up to 0.19 cm² V^?1.s^?1) of the nearly defect‐free P3HT obtained from this simple polymerization of monomer 1 are comparable, if not superior, to those obtained with commercially available GRIM and Rieke samples.

     

Biodegradable Copolyesters of Poly(hexamethylene terephthalate) Containing Bicyclic 2,4:3,5‐Di‐O‐methylene‐d‐Glucarate Units

A set of copolyesters (PHT_xGlux_y) with compositions ranging between 90/10 and 50/50 in addition to the parent homopolyesters poly(hexamethylene terephthalate) (PHT) and PHGlux, are prepared by the melt polycondensation of 1,6‐hexanediol (HD) with mixtures of dimethyl terephthalate (DMT) and dimethyl 2,4:3,5‐di‐O‐methylene‐d ‐glucarate (Glux). The copolyesters have in the 35 000–45 000 g mol^?1 range, their microstructure is random, and they start to decompose at a temperature well above 300 °C. Crystallinity of PHT is repressed by copoly­merization so that copolyesters containing more than 20% of sugar‐based units are essentially amorphous. On the contrary, PHT_xGlux_y displays a T_g that increases monotonically with composition from 16 °C in PHT up to 73 °C in PHGlux. Compared with PHT, the copolyesters show an accentuated susceptibility to hydrolysis and are sensitive to the action of lipases upon incubation under physiological conditions. The degradability of PHT_xGlux_y increases with the content in Glux units.

     

Cationic Main‐Chain Polyelectrolytes with Pyridinium‐Based p‐Phenylenevinylene Units and Their Aggregation‐Induced Gelation

Cationic polyelectrolytes find potential applications in electronic device fabrication, biosensing as well as in biological fields. Herein, a series of cationic main‐chain polyelectrolytes with pyridinium‐based p ‐phenylenevinylene units that are connected via alkylene spacers of varying lengths are synthesized by a base‐catalyzed aldol‐type coupling reaction. Their mean average molecular weights range from 15 000 to 32 000 g mol^‐1, corresponding to about 16–33 repeat units. Due to the presence of alkyl side‐chains and alkylene spacers as well as cationic hard‐charges the polymers are endowed with amphiphilic character and hence, aggregation of these polyelectrolytes at high concentration leads to thermoreversible physical gel formation in dimethyl sulfoxide accompanied by interchain interactions. Morphological analysis shows spherical aggregates in case of C₁₆‐Poly‐S₁₂ in dimethyl sulfoxide. Dependence of gelation behavior on the length of alkyl side‐chains and alkylene spacers of the polyelectrolytes are addressed.

     

Synthesis of Functional Poly(ε‐caprolactone)s via Living Ring‐Opening Polymerization of ε‐Caprolactone Using Functionalized Aluminum Alkoxides as Initiators

The new aluminum compounds 1–3 modified by unsaturated alcohol, Me_3−n Al(O(CH₂)₄OCHCH₂)_n (n = 1 ( 1 ), 2 ( 2 ), 3 ( 3 )), are synthesized and investigated by multinuclear (¹H, ¹³C, ²⁷Al) NMR spectroscopy. The compounds 1 – 3 initiate living ring‐opening polymerization of ε‐caprolactone in bulk at 40–80 °C to afford polyesters with controlled molecular weight (M _n up to 35 000 g mol⁻¹) and relatively narrow molecular weight distribution (M _w/M _n < 1.8). Among initiators studied here, aluminum trialkoxide shows the highest activity, whereas aluminum dialkoxide is a less active. In all cases, the fragment of unsaturated alcohol is transferred to the end of the polymeric chain with high degree of functionality (>85%) yielding macromonomers. These macromonomers are copolymerized with maleic anhydride to give poly(vinyl ether‐co‐maleic anhydride)‐g‐poly(ε‐caprolactone) graft copolymers.

     

Synthesis and Photovoltaic Characterization of Dithieno[3,2‐b:2′,3′‐d]thiophene‐Derived Narrow‐Bandgap Polymers

Three novel dithieno[3,2‐b:2′,3′‐d]thiophene‐based low‐bandgap polymers are synthesized by a Suzuki–Miyaura coupling reaction or by direct arylation polycondensation. The polymers present a high molecular weight (26–32 kDa) and narrow polydiversity (1.3–1.7). With a highest occupied molecular orbital (HOMO) energy level around ?5.20 eV, these polymers exhibit a narrow bandgap of 1.75–1.87 eV. All the polymers display strong absorption in the range of 350–700 nm. Bulk‐heterojunction (BHJ) solar cells are further fabricated by blending the as‐prepared polymer with (6,6)‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) at different weight ratios. The best devices contribute a power conversion efficiency (PCE) of 0.73% under AM 1.5 (100 mW cm^?2).

     

Polycyclotrimers of 1,4‐Diethynylbenzene, 2,6‐Diethynylnaphthalene,and 2,6‐Diethynylanthracene: Preparation and Gas Adsorption Properties

Hyperbranched partly cross‐linked polycyclotrimers of 1,4‐diethynylbenzene, 2,6‐diethynyl­naphthalene, and 2,6‐diethynylanthracene, Pc(1,4‐DEB), Pc(2,6‐DEN), and Pc(2,6‐DEA), respectively, are prepared using TaCl₅/Ph₄Sn catalyst. Brunauer–Emmett–Teller (BET) surface area, microporosity, and maximum sorption capacity for H₂ and CO₂ decrease in the order of decreasing relative content of branching points in polycyclotrimers Pc(1,4‐DEB) > Pc(2,6‐DEN) > Pc(2,6‐DEA), the highest values for Pc(1,4‐DEB) being S_BET = 1299 m² g^?1, a_H2 = 1.26 wt% (100 kPa, 77 K), and a_CO2 = 10.8 wt% (100 kPa, 273 K). N₂ isotherms show that adsorption/desorption hysteresis occurs already at low equilibrium pressures. CO₂ isotherms show that the time allotted to the measurement influences both the maximum adsorption capacity and the hysteresis upon desorption.

     

Synthesis and Optoelectronic Properties of Benzo[1,2‐b:4,5‐b′]dithiophene‐Based Copolymers with Conjugated 2‐(2‐Ethylhexyl)‐3,4‐dimethoxythiophene Side Chains

In order to regulate the electronic ability of benzo[1,2‐b:4,5‐b′]dithiophene (BDT), the new electron‐donating unit (BDTOT) is designed and synthesized which consists of a BDT backbone with conjugated 2‐(2‐ethylhexyl)‐3,4‐dimethoxythiophene side chains. By alternating copolymerization of BDTOT with electron‐accepting units of fluorinated benzothiadiazole (FBT), benzothiadiazole (BT), and pyrrolo[3,4‐c]pyrrole‐1,4‐dione (DPP), three donor–acceptor (D‐A) copolymers (PBDTOT‐FBT, PBDTOT‐BT, and PBDTOT‐DPP) have been developed for PSC applications. The impact of dimethoxythiophene substituent and the electron‐accepting strength of the acceptor units on the absorption, HOMO/LUMO energy levels, and photovoltaic properties of the resultant polymers is investigated in detail. PBDTOT‐BT and PBDTOT‐DPP exhibit relatively narrower bandgaps and PBDTOT‐FBT possesses a down‐shifted HOMO energy level as compared to their corresponding analogs without methoxy groups onto the conjugated thiophene side chains. The screening of the different blend ratio, the processing additive, and polar solvent post‐treatment is conducted to optimize the polymer solar cell (PSC) devices. PSCs with PBDTOT‐FBT as donor deliver a power conversion efficiency (PCE) of 2.55%. By treatment of the active layer with methanol to tailor the morphology, the solar cell based on PBDTOT‐FBT exhibits the remarkably improved PCE of 4.84% with a V _oc of 0.92 V, a J _sc of 8.71 mA cm^?2, and an FF of 60.3%.

     

CO2‐Based Non‐ionic Surfactants: Solvent‐Free Synthesis of Poly(ethylene glycol)‐block‐Poly(propylene carbonate) Block Copolymers

Copolymerization of carbon dioxide (CO₂) and propylene oxide (PO) is employed to generate amphiphilic polycarbonate block copolymers with a hydrophilic poly(ethylene glycol) (PEG) block and a nonpolar poly(propylene carbonate) (PPC) block. A series of poly(propylene carbonate) (PPC) di‐ and triblock copolymers, PPC‐b‐PEG and PPC‐b‐PEG‐b‐PPC, respectively, with narrow molecular weight distributions (PDIs in the range of 1.05–1.12) and tailored molecular weights (1500–4500 g mol^?1) is synthesized via an alternating CO₂/propylene oxide copolymerization, using PEG or mPEG as an initiator. Critical micelle concentrations (CMCs) are determined, ranging from 3 to 30 mg L^?1. Non‐ionic poly(propylene carbonate)‐based surfactants represent an alternative to established surfactants based on polyether structures.

     

Visible Light Induced RAFT Polymerization of 2‐Vinylpyridine without Exogenous Initiators or Photocatalysts

The controlled radical polymerization of 2‐vinylpyridine is reported using commercial blue light‐emitting diodes as visible light source in the presence of S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐aceticacid) trithiocarbonate without exogenous initiators or photocatalysts. With this system, poly(2‐vinylpyridine) with well‐regulated molecular weight and narrow dispersity (?) (? = 1.13) and a conversion efficiency of 84.9% is obtained after 9 h irradiation. The polymerization can be instantly switch “on” or “off” in response to visible light while maintaining a linear increase in molecular weight with conversion and first order kinetics. These results demonstrate the simplicity and efficiency of the photocatalysts‐free, visible light mediated reversible addition fragmentation chain transfer polymerization as a platform to achieve well‐defined poly(2‐vinylpyridine) under mild conditions.

     

One‐Pot Synthesis of PTFEMA‐b‐PMMA‐b‐PTFEMA by Controlled Radical Polymerization with a Difunctional Initiator in Conjugation with Photoredox Catalyst of Ir(ppy)3 Under Visible Light

Visible‐light‐induced free radical polymerization of methyl methacrylate (MMA) and 1,1,1‐trifluoroethyl methacrylate (TFEMA) with a difunctional initiator, dimethyl 2,6‐dibromoheptanedioate (DMDBHD), conjugated with a photoredox catalyst, tris(2‐phenylpyridinato)iridium(III) (fac‐[Ir(ppy)₃]), is investigated. Kinetic studies demonstrate that homopolymerizations of both MMA and TFEMA are controlled radical polymerizations. The linear increase of molecular weights with monomer conversion and the narrow PDIs (1.2–1.4) reveal a good living character. In addition, PTFEMA‐b‐PMMA‐b‐PTFEMA triblock copolymer is prepared by a one‐pot process with sequential monomer addition. The of the triblock copolymers increases linearly with monomer conversion and the PDI of block copolymers is still maintained around 1.2–1.4. Experimental data confirm that the products are pure block polymers. Furthermore, the molar fraction of the TFEMA monomeric unit in the block copolymer is about 21.96%, close to the theoretical value 21.00% calculated from the monomer conversion.