Synthesis and Optical Properties of Poly[2‐{N‐Methyl‐N‐(4‐(4‐ethynylphenylazo)phenyl)amino}ethyl butyrate]

Summary: The high‐molecular‐weight functional polyacetylene that contain a para‐aminoazobenzene chromophore, poly[2‐{N‐Methyl‐N‐(4‐(4‐ethynylphenylazo)phenyl)amino}ethyl butyrate] [poly(EAPAB)], was synthesized in moderate yield and characterized by FT‐IR, ¹H NMR, UV‐vis, TGA, and GPC. The nonlinear optical and optical limiting properties were performed with 8 ns pulse width at 532 nm wavelength. The results show that the introduction of the flexible amino group effectively improved the solubility of polymer [poly(EAPAB)] in common organic solvent, such as CHCl₃, THF, and dioxane, while poly(4‐ethynylazobenzene) [poly(4EAB)] without the flexible amino group shows poor solubility in common organic solvent. Simultaneously, poly(EAPAB) still shows good thermal stability, large third‐order nonlinear optical property, and novel optical limiting property owing to the functionalization of the para‐aminoazobenzene chromophore.

Polymerization of EAPAB by Rh(nbd)Cl₂‐Et₃N to poly(EAPAB).     

Anionic Copolymerization of 5‐(N,N‐Dialkylamino)isoprenes

Summary: The anionic copolymerization of various 5‐(N,N‐dialkylamino)isoprenes initiated by sec‐butyllithium in hexane is investigated. The bulkiness of the alkyl side chains has a strong influence on the copolymerization behavior, monomer reactivity decreasing in the order of alkyl groups methyl > ethyl ≈ propyl > isopropyl. Polymer structures vary from nearly block over tapered and gradient to random, depending on the relative reactivities of comonomers. Since the basicity of the tertiary amino groups depends on the nature of the alkyl groups, it is possible to vary the basicity along the polymer backbone by a suitable choice of the comonomers. Copolymerization kinetics do not seem to follow first‐ or second‐order with respect to monomer conversion and they cannot be described using the terminal model.

General structure of obtained polymers.     

Influence of β‐Cyclodextrin on the Free‐Radical Copolymerization of N‐(4‐Methylphenyl)maleimide with N‐Vinylpyrrolidone in Water

Randomly methylated β‐cyclodextrin (me‐β‐CD) is used to include the hydrophobic monomer N‐(4‐methylphenyl)maleimide (MPM) ( 1 ) yielding the corresponding water‐soluble host‐guest structure 1a . Free‐radical copolymerization of 1a with N‐vinylpyrrolidone (NVP) ( 2 ) is performed and the reactivity ratios r₁ and r₂ are determined: 0.24 ± 0.03 (r₂) and 1.10 ± 0.05 (r_1a). This indicates a preferred incorporation of complexed maleimide into the copolymer chain. In contrast to that, the copolymerization of the uncomplexed monomers 1 and 2 is carried out using organic solvent (DMF/H₂O) showing reactivity ratios corresponding to nearly alternating copolymerization (r₂ = 0.09 ± 0.02; r₁ = 0.34 ± 0.03).

     

Synthesis and Photovoltaic Properties of 1,8‐Carbazole‐Based Donor–Acceptor Type Conjugated Polymers

1,8‐Diethynylcarbazole‐based conjugated polymers were synthesized by the acetylenic oxidative coupling reaction or Pd‐catalyzed Sonogashira reaction of the newly designed 3,6‐dialkylated 1,8‐diethynylcarbazole monomers. In particular, the Sonogashira polycondensation was effective for the preparation of donor–acceptor type alternating copolymers. The UV‐vis absorption and fluorescence spectra of the polymers revealed the strength of the donor–acceptor interactions as well as their self‐assembling features. The combination of electrochemical redox potentials and optical band gaps enabled the estimation of the polymer energy levels. The bulk‐heterojunction solar cells composed of these promising polymers and PCBM exhibited a photoconversion efficiency (PCE) of 0.24%. It was determined that the partial doping of the bulk‐heterojunction layer increased the open‐circuit voltage (V_oc), but decreased the short‐circuit current (J_sc).     

3‐Butyl‐2‐yl‐ and Propargyl Cholesteryl Carbonates. Chiroptical and Liquid Crystalline Properties of their Polymers

Novel chiral acetylene monomers containing cholesteryl groups, (R)‐3‐butyn‐2‐yl cholesteryl carbonate ( 1 ), (S)‐3‐butyn‐2‐yl cholesteryl carbonate ( 2 ), and propargyl cholesteryl carbonate ( 3 ) were synthesized and polymerized with (nbd)Rh⁺[η⁶‐C₆H₅B^?(C₆H₅)₃] to give the corresponding polymers with number‐average molecular weights of 32 900–97 000 in 84–85% yields. Circular dichroism spectroscopic studies revealed that poly( 1 ) and poly( 2 ) predominantly took one‐handed helical structure in CHCl₃ and THF. The helical conformation was stable to heat and to addition of MeOH. The copolymerization of 1 and 2 was carried out with the rhodium catalyst to afford copolymers with number‐average molecular weights ranging from 53 400 to 88 700 in 83–98% yields. The copolymer with a large diastereomeric excess showed a large specific rotation and an intense Cotton effect in THF, indicating that the predominance of one‐handed helicity was high. Poly( 1 ₅₀‐co‐ 2 ₅₀) showed lyotropic liquid crystalline property.

     

A Novel Branched Polyoxymethylene Synthesized by Cationic Copolymerization of 1,3,5‐Trioxane with 3‐(Alkoxymethyl)‐3‐ethyloxetane

Novel branched polyoxymethylene copolymers are synthesized by cationic copolymerization of 1,3,5‐trioxane (TOX) with 3‐(alkoxymethyl)‐3‐ethyloxetane (ROX) using BF₃·Et₂O as an initiator. Four oxetane derivatives with different side‐chain lengths (from 1 to 6 carbons) are tested for copolymerization. The copolymer composition is controlled by the feed ratio of ROX, and influenced by the chain length of alkyl group on ROX. The incorporation ratio and side‐chain length of the ROX unit have great influence on the thermomechanical properties and crystallinity of the copolymers.

     

Radical Copolymerization Reactivity of N‐Substituted Maleimides with α‐Substituted Styrenes with Various N‐ and α‐Substituents and the Thermal and Optical Properties of the Resulting Copolymers

The radical alternating copolymerization of N‐substituted maleimides (RMIs) with N‐methyl, n‐butyl, and 2‐ethylhexyl groups and styrene derivatives with various α‐substituents (RSs) is carried out. The yield and the molecular weight of the obtained copolymers significantly decrease with an increase in the size of the α‐substituent of RSs, but are independent of the N‐substituents. The glass‐transition temperature of the copolymers increases on the introduction of the large substituents into the RS repeating units. The high‐molecular‐weight poly(RMI‐alt‐RS)s are soluble in organic solvents and provide flexible and transparent films with excellent transparency by casting the solutions.

     

Networks Based on Poly(α‐methylene‐δ‐valerolactone‐co‐δ‐valerolactone): Crosslinking Through Free‐Radical Vinyl Copolymerization

Unsaturated polyesters are synthesized via ring‐opening copolymerization of α‐methylene‐δ‐valerolactone and δ‐valerolactone. These polyesters 4a–c are mixed with ethyl methacrylate (EMA), 2‐hydroxyethyl methacrylate (HEMA), and α‐methylene‐δ‐valerolactone (α‐MVL), respectively. Then, crosslinking is carried out by free radical polymerization initiated by an azo‐initiator. A second glass transition is found with incorporation of HEMA and α‐MVL. These findings indicate the formation of phase‐separated polyester blocks crosslinked with the poly(meth)‐acrylic‐segments, respectively poly(α‐methylene‐δ‐valerolactone) segments.

     

New Group IV Metallocene Systems Active in the Copolymerization of α‐Olefins and Conjugated Dienes

Summary: Rac‐[CH₂(2,4‐di‐tert‐butyl‐cyclopentadienyl)₂]ZrCl₂ ( 1 ), rac‐[CH₂(3‐tert‐butyl‐4,5,6,7‐tetrahydroindenyl)₂]ZrCl₂ ( 2 ), rac‐[CH₂(3‐isopropyl‐4,5,6,7‐tetrahydroindenyl)₂]ZrCl₂ ( 3 ), and rac‐[CH₂(3‐methyl‐4,5,6,7‐tetrahydroindenyl)₂]ZrCl₂ ( 4 ) were synthesized and characterized by ¹H NMR analysis. These C₂ symmetric ansa‐zirconocenes, activated with methylaluminoxane (MAO), were able to promote copolymerization of ethene and 1,3‐butadiene. The structures of the copolymers are strongly influenced by zirconocene utilized as catalytic precursor. Depending on the reaction conditions polyethenes containing cyclopropane and cyclopentane rings, or 1,1‐ 1,3‐butadiene inserted constitutional units, were obtained.

Structures of the synthesized catalytic precursors.     

From Old to New: Polymers from Mono‐α‐Alkylated N‐vinylcaprolactam

N‐vinylcaprolactam (NVCL) is modified via alkylation at the α‐position. The α‐substituents are ethyl (3‐ethyl‐1‐vinylcaprolactam), dodecyl (3‐dodecyl‐1‐vinylcaprolactam), octadecyl (3‐octadecyl‐1‐vinylcaprolactam), 1‐propanol (3‐(3‐hydro­xy‐propyl)‐1‐vinylcaprolactam), and PEG₃ bromide (3‐PEG₃‐bromide‐1‐vinylcaprolactam). These monomers are homo‐ and copolymerized with N‐(4‐methylphenyl)­maleimide by the free radical mechanism. The structures of the obtained polymers are characterized by means of ¹H NMR and IR spectroscopy, gel permeation chromatography (GPC), and by use of differential scanning calorimetry (DSC) (T_g).

     

Zwitterionic Copolymerization of β‐Butyrolactone with Styrene

The hybrid copolymerization of vinyl monomers with cyclic esters endows the formed copolymers new features, such as biodegradability and functionality. However, the recently reported hybrid copolymerizations are mainly based on polar vinyl monomers and cyclic esters catalyzed by organocatalysts. The copolymerization of non‐polar vinyl monomers with cyclic esters is still a challenge. In this work, the copolymerization of β‐butyrolactone (β‐BL) with styrene catalyzed by B(C₆F₅)₃ in the absence of coinitiators is reported. The density functional theory studies suggest the formation of zwitterion between β‐BL and B(C₆F₅)₃. It is found that β‐BL and styrene are concurrently copolymerized through the macro‐zwitterion intermediates. The obtained copolymers are carefully examined by ¹H NMR, 2D ¹H‐¹³C HMBC, differential scanning calorimetry, thermogravimetric analysis, hydrolysis experiments, as well as Brady's reagents.     

High‐Pressure Kinetics of Oxidative Copolymerization of Styrene with α‐Methylstyrene

This is the first report on the study carried out on high‐pressure free‐radical initiated oxidative copolymerization of styrene (STY) with α‐methylstyrene (AMS) at various temperatures (45–65 °C) at constant pressure (100 psi) and then at various pressures (50–300 psi) keeping the temperature (50 °C) constant. The compositions of the copolyperoxides obtained from the ¹H NMR spectra were utilized to determine the reactivity ratios of the monomers. The reactivity ratios indicate that STY forms an ideal copolyperoxide with AMS and the copolyperoxide is richer in AMS. The effect of temperature and oxygen pressure on the reactivity ratios of the monomers was studied. The rates of copolymerization (R_P) were used to determine the overall activation energies (E_a) and activation volume (ΔV^#) of copolymerization. The unusually higher values of the ΔV^# may be due to the pressurizing fluid oxygen which itself is a reactant in the copolymerization, the side reactions, and the chain‐transfer reactions occurring during copolymerizations.

The Arrhenius plots for the rate of the copolymerization of STY‐AMS‐O₂ system at 100 psi of oxygen pressure.     

Effect of Rotaxane Formation on the Photophysical,Morphological, and Adhesion Properties of Poly[2,7‐(9,9‐dioctylfluorene)‐alt‐(5,5'‐bithiophene)] Main‐Chain Polyrotaxanes

In order to investigate the effect of rotaxane formation on the photophysical and morphological properties of π‐conjugated materials, a new main chain polyrotaxane was synthesized through Suzuki coupling between the inclusion complex of 5,5'‐dibromo‐2,2'‐bithiophene with randomly methylated β‐cyclodextrin and 9,9‐dioctylfluorene‐2,7‐trimethylene diborate. Due to rotaxane formation, a blue shift in the absorption spectra as well as in the fluorescence spectra was observed, while the fluorescence quantum yields and fluorescence lifetimes remained unchanged. This study demonstrates that rotaxane formation can alter the electronic and morphological properties of the threaded copolymer, which is of great interest for electronic applications.

     

Ring‐Opening Homo‐ and Copolymerization of Cis/Trans‐3‐oxa‐4‐oxobicyclo‐ and Cis/Trans‐4‐oxa‐3‐oxobicyclo[5.4.0]undecane

Ring‐opening polymerization of the bicyclic lactone mixture 2 , cis/trans‐3‐oxa‐4‐oxo‐ and cis/trans‐4‐oxa‐3‐oxobicyclo[5.4.0]undecane with Sn(Oct)₂ as a catalyst was investigated for the first time (Scheme 1 ). The lactones were obtained by Baeyer–Villiger oxidation of cis/trans‐2‐decalone 1 (Scheme 2 ). Additionally, copolymerization of 2 with ε‐caprolactone in different ratios was performed. GPC measurements and ¹H NMR spectroscopy proved that 2 was quantitatively incorporated into the polymer, leading to polycaprolactone with cyclohexane moieties in its backbone. values were up to 25 000 with ≤ 2.4. DSC measurements revealed a linear dependence of the melting points and the glass transition temperatures of the polymers on the feed of the bicyclic lactone 2 . Additionally, the time dependence of the cis/trans ratio of the residual monomers was followed during the course of polymerization reaction by gas chromatography. The crystallinity of the resulting copolymers was investigated via polarization microscopy. Finally, it was shown that the mixture of 2 with ε‐caprolactone could be selectively polymerized with lipase. Only ε‐caprolactone was converted, while 2 remained unreacted in the residue.

     

Radical Copolymerization of N‐Vinylformamide with Methylvinylketone: An Approach to Iminium/Imine Ring Containing Polymers

The free radical copolymerization of N‐vinylformamide (NVF) with methylvinylketone in water and the subsequent alkaline or acidic hydrolysis produce iminium structures containing polymers. It can be concluded from the copolymerization parameters (r_{N ‐vinylformamide} = 0.02, r _{methylvinylketone} = 0.50) that alternating copolymers are formed which contain few amounts with statistically arranged monomer sequences. The acidic hydrolysis of the copolymer results in a water‐soluble polymer bearing five‐membered iminium rings along the polymer chain. A water‐insoluble polymer is generated under alkaline conditions also containing five‐membered imine rings. The formation of the iminium ring polymer is attributed to the fact that generated free amino groups derived from NVF immediately react with the keto groups in the vicinity. The molecular structures of the obtained polymers are characterized by ¹H‐NMR, ¹³C‐NMR, and IR spectroscopy. The assignment of the signals in the novel polymers are confirmed by model compounds.     

Synthesis and Characterization of Conducting Copolymers of (S)‐2‐Methylbutyl‐2‐(3‐thienyl)acetate with Pyrrole and Thiophene

Polymerization of methylbutyl‐2‐(3‐thienyl)acetate (MBTA) was achieved by constant current electrolysis at low temperature. Subsequently, the syntheses of block copolymers of polyMBTA were accomplished in the presence of either pyrrole or thiophene by constant potential electrolysis. Moreover, the copolymer of MBTA with thiophene was obtained with constant potential electrolysis.

The synthesis of monomer MBTA.     

Penultimate Unit and Solvent Effects on 2:1 Sequence Control During Radical Copolymerization of N‐Phenylmaleimide With β‐Pinene

Copolymers with a 2:1 regulated sequence of N‐phenylmaleimide with β‐pinene units (AAB‐type repeating units) are produced during radical copolymerization. The monomer reactivity ratios are determined using the penultimate unit model, and it is demonstrated that they vary depending on the solvent used (tetrahydrofuran, 1,2‐dichloroethane, 2,2,2‐trifluoroethanol, and perfluoro‐tert‐butanol) and the copolymerization temperature (0–100 °C). The interaction of the PhMI repeating units with solvents lead to the production of the 2:1 controlled sequence and a significant change in the relative reactivity of the PhMI radicals by polar and steric effects.     

Controlled Synthesis of Alternating Copolymers by RAFT Copolymerization of N‐Vinylphthalimide with N‐Isopropylacrylamide

A nonconjugated N‐vinyl monomer, N‐vinylphthalimide (NVPI), was copolymerized with various comonomers via reversible addition‐fragmentation chain transfer (RAFT) process. Two different chain transfer agents (CTAs), O‐ethyl‐S‐(1‐ethoxycarbonyl) ethyldithiocarbonate (CTA 1) and benzyl 1‐pyrrolecarbodithioate (CTA 2), were compared for these copolymerizations with 2,2′‐azobis(isobutyronitrile) as an initiator. The effects of the nature of CTA, the comonomer structure, and solvent on the copolymerization were investigated in terms of the controlled character of the copolymerization and alternating structure. The copolymerization of NVPI and N‐isopropylacrylamide using CTA 2 in DMF or MeOH afforded well‐defined copolymers with predominantly alternating structure, controlled molecular weights, and low molecular mass distributions.

     

A Study of Copolymerization of 1‐Hexene with 2,5‐Norbornadiene Using Metallocene Catalysts

Summary: Copolymerization of 1‐hexene with a symmetrical diene, namely 2,5‐norbornadiene was studied using four different metallocene catalysts. Copolymerization was found to occur exclusively through one of the two equally reactive endocyclic double bonds with all the four catalysts. Copolymerization results in low molecular weight oligomers with the number average molecular weight ( ) varying from 1 000–3 000. End group analysis of the co‐oligomers revealed that the β‐hydrogen transfer after 2,1 insertion also occurs in the presence of highly regiospecific catalysts. The regio errors were also found to depend on various reaction parameters such as polymerization time, Al/Zr mol ratio, metallocene concentration and polymerization temperature.

Plots of variation in end groups and NBD incorporation with time.