Low Conversion 4‐Acetoxystyrene Free‐Radical Polymerization Kinetics Determined by Pulsed‐Laser and Thermal Polymerization

Summary: The free‐radical polymerization kinetics of 4‐acetoxystyrene (4‐AcOS) is studied over a wide temperature range. Pulsed‐laser polymerization, in combination with dual detector size‐exclusion chromatography, is used to measure k_p, the propagation rate coefficient, between 20 and 110 °C. Values are roughly 50% higher than those of styrene, while the activation energy of 28.7 kJ · mol⁻¹ is lower than that of styrene by 3–4 kJ · mol⁻¹. With known k_p, conversion and molecular weight data from 4‐AcOS thermal polymerizations conducted at 100, 140, and 170 °C are used to estimate termination and thermal initiation kinetics. The behavior is similar to that previously observed for styrene, with an activation energy of 90.4 kJ · mol⁻¹ estimated for the third‐order thermal initiation mechanism.

Joint confidence (95%) ellipsoids for the frequency factor A and the activation energy E_a from non‐linear fitting of k_p data for 4‐AcOS (black) and styrene (grey).     

Ring Opening Metathesis Polymerization (ROMP) of cis‐ and trans‐3,4‐Bis(acetyloxymethyl)cyclobut‐1‐enes and Synthesis of Block Copolymers

Summary: The synthesis and living ring opening metathesis polymerization (ROMP) of diacetate functionalized cyclobutene derivatives cis‐3,4‐bis(acetyloxymethyl)cyclobutene ( 2 ) and trans‐3,4‐bis(acetyloxymethyl)cyclobutene ( 3 ) were investigated with the functional group tolerant initiators (PCy₃)₂(Cl)₂Ru?CHPh ( I ) and (SIMes)(PCy₃)(Cl)₂Ru?CHPh ( II ) (SIMes: 1,3‐dimesityl‐4,5‐dihydroimidazol‐2‐ylidene). The kinetic parameters of the ROMP initiated by the ruthenium alkylidene complexes I and II were determined and correlated to monomer stereochemistry. The cis isomer 2 was found to be more reactive than the trans isomer 3 and to generate functional polymers of narrow molecular weight distribution especially with the classical “first generation Grubbs catalyst” I . Block copolymers containing 2 and cyclooctadiene ( COD ) or norbornene ( NBE ) were synthesized. Block copolymer poly(2‐ b ‐COD) was hydrolyzed and converted to a material with a block bearing hydrophilic alcohol functional groups and hydrophobic block.

SEC elution profiles: poly(2) prepolymer and block copolymer poly(2‐ b ‐COD) .     

Polyrotaxanes of Pyrene–Triazole Conjugated Azomethine and α‐Cyclodextrin with High Fluorescence Properties

The paper reports on the preparation of a new 2‐rotaxane monomer through an acid coupling reaction between 1‐pyrenecarboxaldehyde and α‐CD/3,5‐diamino‐1,2,4‐triazole inclusion complex. Pyrenyl groups are large enough to provide a blocking effect toward cyclodextrin de‐threading. The oxidative C? C coupling of 2‐rotaxane in the presence of RuCl₃ catalyst afforded conjugated azomethine polyrotaxanes. The expected modifications of the solubility, morphology, film forming ability for rotaxane polymer were proved. As shown by fluorescence and UV‐vis spectroscopy, a material with optical properties appropriate for use in photonics was obtained.

     

Cyclodextrins in polymer synthesis: Steric retardation of the free‐radical polymerization in aqueous medium of 4‐vinylbenzaldehyde/methylated β‐cyclodextrin complex

4‐Vinylbenzaldehyde ( 3 ) was complexed with methylated β‐cyclodextrin ( 4 ) (me‐β‐CD) yielding the water soluble host‐guest complex ( 5 ). Radical polymerization was initiated with K₂S₂O₈/Na₂S₂O₅ in water at room temperature and also at 70 °C. The polymerization tendency of this complex ( 5 ) is lower compared to the styrene/me‐β‐CD‐complex ( 7 ). Also copolymerizations of 5 and complexed styrene ( 6 ) at these two temperatures were carried out and the results are discussed in respect to the behavior of the homopolymerization. The resulting polymers ( 8a‐k , 9a , 9b ) were characterized by SEC‐measurements and ¹H NMR spectroscopy. TEM‐measurements of the homopolymers 8f and 8k show differences in the particle size depending on the amount of me‐β‐CD.

TEM recordings of the polymers 8f (left) and 8k (right).     

Synthesis and Optical Properties of π‐Conjugated Polymers Composed of Benzo[1,2‐b:4,5‐b′]dithiophene and Thiophenes Bearing Electron‐Deficient Ethenyl Groups in the Side Chains

π‐Conjugated polymers composed of dialkoxybenzo[1,2‐b:4,5‐b′]dithiophene and thiophenes bearing cyano‐alkoxycarbonylethenyl [? CH?C(CO₂R)CN] and bis(alkoxycarbonyl)ethenyl groups [? CH?C(CO₂R)₂] were prepared. The optical properties of the obtained polymers were investigated by UV‐vis and photoluminescence spectroscopy to demonstrate that the absorption maxima of the polymers were tunable by varying the substituent of thiophene unit. The photoluminescence wavelengths and intensities of the polymer in solution were significantly dependent on the polymer side chain. The HOMO energy level of the polymer was lowered by up to ?5.51 eV by introducing electron‐deficient cyano groups. Polymer solar cells based on the new polymers were fabricated to achieve a PCE of 1.90%.

     

Synthesis of AB2 3‐ and AB4 5‐Miktoarm Star Copolymers Initiated from Dendritic Tri‐ and Penta‐Functional Initiators by Combination of Ring‐Opening Polymerization of ε‐Caprolactone and Nitroxide‐Mediated Radical Polymerization of Styrene

Summary: Well‐defined AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers were prepared by combination of ring‐opening polymerization (ROP) and nitroxide‐mediated radical polymerization (NMRP) using dendritic tri‐ and penta‐functional initiators. Initially, two kinds of dendritic initiators having one benzylic OH and two or four TEMPO‐based alkoxyamine moieties were prepared. Using them, ROP of ε‐caprolactone was carried out at room temperature to give poly(ε‐caprolactone)s carrying two or four alkoxyamine moieties. NMRP of styrene from the poly(ε‐caprolactone)s was carried out at 120 °C to give AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers, which were analyzed by ¹H NMR and SEC. The increased linearly with conversion and the were in the range 1.10–1.37, showing that well‐defined AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers were formed.

Well‐defined AB₂ 3‐ and AB₄ 5‐miktoarm star copolymers were prepared by combination of ring‐opening polymerization (ROP) and nitroxide‐mediated radical polymerization (NMRP) using dendritic tri‐ and penta‐functional initiators.     

Anionic Polymerizations of 1‐Adamantyl Methacrylate and 3‐Methacryloyloxy‐1,1′‐biadamantane

Anionic polymerizations of 1‐adamantyl methacrylate ( 1 ) and 3‐methacryloyloxy‐1,1′‐biadamantane ( 2 ) were carried out in THF at ?50 to ?78 °C for 24 h. The initiator employed was either [1,1‐bis(4′‐trimethylsilylphenyl)‐3‐methylpentyl]lithium ( 3 )/lithium chloride, or diphenylmethylpotassium. The polymerizations of 1 and 2 proceeded quantitatively to afford the polymers having the predicted molecular weights based on the molar ratios of monomers and initiators and the narrow molecular weight distributions (M _w/M _n = 1.05–1.18), indicating the living character of the polymerization systems of 1 and 2 . Novel well‐defined block copolymers, poly[ 2 ‐block‐(tert‐butyl methacrylate)], poly( 2 ‐block‐isoprene‐block‐ 2 ), and poly[[(2,2‐dimethyl‐1,3‐dioxolan‐4‐yl)methyl methacrylate]‐block‐ 2 ], were anionically synthesized by the sequential copolymerization of 2 and comonomers. The poly( 2 ) had the significantly higher glass transition temperature (T_g) of 236 °C and decomposed over 370 °C, while poly( 1 ) started to decompose at around 320 °C before its T_g was reached. This thermal stability can be explained by the substituent effects of the bulky adamantyl and 1,1′‐biadamantyl moieties.

     

Synthesis,Characterization, and Intramolecular End‐to‐End Ring Closure of α‐Isopropylidene‐1,1‐dihydroxymethyl‐ω‐diethylacetal Polystyrene‐block‐polyisoprene Block Copolymers

Cyclic polystyrene‐block‐polyisoprenes of controlled dimensions have been synthesized for the first time by the direct coupling of α‐isopropylidene‐1,1‐dihydroxymethyl‐ω‐diethylacetal‐heterodifunctional linear polystyrene‐block‐polyisoprene precursors previously prepared by living anionic polymerization. Cyclization is achieved under high dilution by intramolecular coupling of the polymer ends under acid catalyst conditions. Using this strategy polystyrene‐block‐polyisoprene macrocycles of controlled chain dimensions are prepared in high yield (> 90%). Pure cycles were finally recovered by flash chromatography. The synthesis and characterization of both the linear α,ω‐heterodifunctional polystyrene‐block‐polyisoprenes block copolymers precursors and of the corresponding cyclized chain architectures are reported.

200 MHz ¹H NMR spectrum (CDCl₃) of cyclized polystyrene‐block‐polyisoprene copolymer (M _n = 12 000).     

Control of the radical polymerization by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl and its sodium salt

The control of the radical polymerization of styrene by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl is reported here in bulk at 90 °C, 120 °C and in miniemulsion. Similarly, the control by its sodium complex is reported in bulk at 90 °C.

M _n vs. conversion for 3 , 3Na , and TEMPO.     

Novel Random Low‐Band‐Gap Fluorene‐Based Copolymers for Deep Red/Near Infrared Light‐Emitting Diodes and Bulk Heterojunction Photovoltaic Cells

Summary: Novel readily soluble random low‐band‐gap conjugated copolymers (PFO–DTTP, E_g ≈ 1.77–2.00 eV) derived from 9,9‐dioctylfluorene (DOF) and 2,3‐dimethyl‐5,7‐dithien‐2‐yl‐thieno[3,4‐b]pyrazine (DTTP) were prepared. The solutions and the solid thin films of the copolymers absorbed light from 300–690 nm. Prototype photovoltaic cells from solid state composite films with the copolymer PFO–DTTP30 and [6,6]‐phenyl C₆₁ butyric acid methyl ester (PCBM) showed power conversion efficiencies up to 0.83% under an AM1.5 solar simulator (100 mW · cm⁻²). For electroluminescent devices, the emission peaks were around 734–780 nm. This indicates that the low band gap copolymers are promising materials for polymeric solar cells and deep red/near infrared light‐emitting diodes.

Synthesis of novel low‐band‐gap fluorene‐based copolymer.     

Pressure‐Induced cis‐to‐trans Isomerization of Poly[(p‐methylthiophenyl)acetylene] Prepared with a [Rh(norbornadiene)Cl]2 Catalyst – A Raman,UV‐Vis,and ESR Study

Summary: A stereospecific polymerization of a novel aromatic acetylene containing an alkyl sulfide group, i.e., (p‐methylthiophenyl)acetylene (pMeSPA) was successfully performed to selectively give the corresponding polymer bearing a cis‐transoid structure as a main geometrical form and a very high molecular weight, = 1.7–5.8 × 10⁶ in high yields. This was accomplished when a Rh complex catalyst, [Rh(norbornadiene)Cl]₂, was used in the presence of triethylamine (TEA) solvent as a cocatalyst and its mixed solvents with TEA, together with a detailed characterization of the resulting polymers before and after compression at room temperature. Based on the data obtained before and after compression, it was concluded that compression of the PpMeSPA polymers induced a cis‐to‐trans isomerization at room temperature under vacuum even in the solid state (the Figure shows the radical generated by compression).

     

Synthesis of π‐Conjugated Organometallic Polymer Networks

The present paper reports the synthesis of π‐conjugated organometallic polymer networks based on poly[2,5‐dioctyloxy‐1,4‐diethynyl‐phenylene‐alt‐2,5,‐bis(2′‐ethylhexyloxy)‐1,4‐phenylene] (EHO‐OPPE), a soluble poly(p‐phenylene ethynylene) (PPE) derivative. The ethynylene moieties of the polymer coordinate to Pt⁰ centers, which act as conjugated cross‐links. These materials are readily accessible through ligand‐exchange reactions between the linear PPE and Pt(styrene)₃. The in‐situ NMR investigation of model reactions of Pt(styrene)₃ with diphenylacetylene (DPA) has shown that the ethynylene moieties comprised in the PPE readily coordinate to Pt⁰ centers under release of the relatively weakly‐bound styrene ligands. Spin‐coating has resulted in cross‐linked films of good optical quality. We also have been able to produce PPE‐Pt‐gels with high solvent content (> 95 wt.‐%). As expected, the coordination of Pt markedly influences the photophysical characteristics of the PPE. The photoluminescence is efficiently quenched, and the absorption maximum in the visible regime experiences a hypsochromic shift.

Ligand‐exchange reaction between EHO‐OPPE and [Pt(PhCH?CH₂)₃] leading to the target EHO‐OPPE‐Pt⁰ networks.     

High‐Molecular‐Weight Polyketones from Higher α‐Olefins: A General Method

Summary: A method to optimize the polymerization conditions in order to favor chain propagation is described for the synthesis of polymers containing low reactive, long, linear 1‐olefins and carbon monoxide (CO). It consists of the use of the olefin monomer as the polymerization solvent, together with the emulsification of a carefully chosen immiscible activator. This is given as a general method applicable to different families of catalyst able to produce 1,4‐polyketones. When the catalyst precursor is [dpppPd(NCCH₃)₂](BF₄)₂, which has been extensively studied, the polymerization degrees are the highest published (up to 2.4 × 10⁵ g · mol^?1). The influence of parameters like temperature, CO pressure, volume of activator, and catalyst counter ion or ligand substitutions are reported. Some chemical and physical properties of the polymers, such as glass transition temperature, melting processes, and mechanical behavior, are examined and compared with the linear 1‐olefin homologues from C3 to C10. These properties are shown in some cases to be unprecedented.

DSC profiles from the 1st scan for α‐olefin/CO copolymers.     

Synthesis and aqueous phase behavior of thermoresponsive biodegradable poly(D,L‐3‐methylglycolide)‐block‐poly(ethylene glycol)‐block‐poly(D,L‐3‐methylglycolide) triblock copolymers

Novel biodegradable thermosensitive triblock copolymers of poly(D ,L ‐3‐methylglycolide)‐block‐poly(ethylene glycol)‐block‐poly(D ,L ‐3‐methylglycolide) (PMG‐PEG‐PMG) have been synthesized. Ring‐opening polymerization of D ,L ‐3‐methyl‐glycolide (MG) initiated with poly(ethylene glycol) (PEG) and Ca[N(SiMe₃)₂]₂(THF)₂ provided triblock copolymers with alternating lactyl/glycolyl sequences of controlled molecular weight, low polydispersity index and uniform chain structure. At relatively low temperatures (≈ 10 °C) these copolymers formed clear solutions in water up to high concentrations (50 wt.‐%). Depending on molecular mass ratios of PMG and PEG blocks, a sol‐gel transition or an increase in viscosity without gel formation was observed upon increasing the temperature of the aqueous solutions. The temperature‐induced gelation was ascertained by rheology and dynamic differential scanning calorimetry (DDSC).

Phase diagram of PMG‐PEG‐PMG 1 400‐1 450‐1 400 in an aqueous solution.     

Crystallization and Ring‐Banded Spherulite Morphology of Poly(ethylene oxide)‐block‐Poly(ε‐caprolactone) Diblock Copolymer

Summary: The crystallization behavior of crystalline‐crystalline diblock copolymer containing poly(ethylene oxide) (PEO) and poly(ε‐caprolactone) (PCL), in which the weight fraction of PCL is 0.815, has been studied via differential scanning calorimeter (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized optical microscopy (POM). DSC and WAXD indicated that both PEO and PCL blocks crystallize in the block copolymer. POM revealed a ring‐banded spherulite morphology for the PEO‐b‐PCL diblock copolymer.

DSC heating curve for the PEO‐b‐PCL block copolymer.     

Proton‐Conducting Properties of Acid‐Doped Poly(glycidyl methacrylate)‐1,2,4‐Triazole Systems

1,2,4‐triazole‐functional PGMA polymers have been synthesized and their anhydrous proton‐conducting properties were investigated after doping with phosphoric acid and triflic acid. PGMA was prepared by solution polymerization and then modified with 1H‐1,2,4‐triazole (Tri) and 3‐amino‐1,2,4‐triazole (ATri). FT‐IR, ¹³C NMR and elemental analysis verify the high immobilization of the triazoles in the polymer chain. Phosphoric‐acid‐doped polymers showed lower T_g and higher proton conductivities. PGMA‐Tri 4 H₃PO₄ showed a maximum water‐free proton conductivity of approximately 10^?2 S · cm^?1 while that of PGMA‐ATri 2 H₃PO₄ was 10^?3 S · cm^?1. The structure and dynamics of the polymers were explored by ¹H MAS and ¹³C CP‐MAS solid‐state NMR.

     

Pseudo‐Living Anionic Telomerization of Buta‐1,3‐diene

Low‐molecular‐weight liquid polybutadienes (1 000–2 000 g · mol^?1) consisting of 60 mol‐% poly(buta‐1,2‐diene) repeating units were synthesized via anionic telomerization. Maintaining the initiation and reaction temperature at less than 70 °C minimized chain transfer and enabled the polymerization to occur in a living fashion, which resulted in well‐controlled molecular weights and narrow polydispersity indices. MALDI‐TOF mass spectrometry confirmed that the end groups of liquid polybutadienes synthesized via anionic telomerization contained one benzyl end and one protonated end. In comparison, the end groups of liquid polybutadienes synthesized via living anionic polymerization contained one sec‐butyl or butyl end and one protonated end.

     

Diblock Copolymers Based on 1,4‐Dioxan‐2‐one and ε‐Caprolactone: Characterization and Thermal Properties

Summary: Various poly(ε‐caprolactone‐block‐1,4‐dioxan‐2‐one) (P(CL‐block‐PDX)) block copolymers were prepared according to the living/controlled ring‐opening polymerization (ROP) of 1,4‐dioxan‐2‐one (PDX) as initiated by in situ generated ω‐aluminium alkoxides poly(ε‐caprolactone) (PCL) chains in toluene at 25 °C. 1 ¹H NMR, PCS and TEM measurements have attested for the formation of colloids attributed to a growing PPDX core surrounded by a solvating PCL shell during the polymerization of PDX promoted by ω‐Al alkoxide PCL chains in toluene. The thermal behavior of the P(CL‐block‐PDX) copolymers was studied by DSC; showing two distinct melting temperatures (as well as two glass transition temperatures) similar to those of the respective homopolyesters. Finally, the thermal degradation of the P(CL‐block‐PDX) block copolymers was investigated by TGA simultaneously coupled to a FT‐IR spectrometer and a mass spectrometer for evolved gas analysis (EGA). The degradation occurred in two consecutive steps involving a first unzipping depolymerization of the PPDX blocks followed by the degradation of the PCL blocks via both ester pyrolysis and unzipping reactions.

TEM observation of P(CL‐block‐PDX) block copolyesters ( = 11 600 and = 22 100) as formed by vaporization starting from a diluted suspension in toluene/TCE mixture solvent (50/50 v/v).     

Well‐Defined Miktocycle Eight‐Shaped Copolymers Composed of Polystyrene and Poly(ε‐caprolactone): Synthesis and Characterization

A series of well‐defined miktocycle number‐eight‐shaped copolymers composed of cyclic polystyrene (PS) and cyclic poly(ε‐caprolactone) (PCL) have been successfully synthesized by a combination of atom transfer radical polymerization (ATRP), ring‐opening polymerization (ROP), and “click” reaction. The synthesis involves three steps: 1) preparation of tetrafunctional initiator with two acetylene groups, one hydroxyl group and a bromo group; 2) preparation of two azide‐terminated block copolymers, N₃‐PCL‐(CH?C)₂‐PS‐N₃, with two acetylene groups anchored at the junction; and 3) intramolecular cyclization of the block copolymer through “click” reaction under high dilution. The ¹H NMR, FT‐IR, and gel permeation chromatography (GPC) techniques are applied to characterize the chemical structures of the resulting intermediates and the target polymers. Their thermal behavior is investigated by differential scanning calorimeter (DSC). The decrease in chain mobility of eight‐shaped copolymers restricts the crystallization of PCL.