Synthesis of star poly(1,3‐cyclohexadiene): Grafting reaction of poly(1,3‐cyclohexadienyl)lithium onto C60

The grafting reaction of poly(1,3‐cyclohexadienyl)lithium onto fullerene‐C₆₀ (C₆₀) was strongly affected by the nucleophilicity of poly(1,3‐cyclohexadiene) (PCHD) carbanions and the polymer chain microstructure, and progressed via step‐by‐step reactions. A star‐shaped PCHD, having a maximum of four arms, was obtained from poly(1,3‐cyclohexadienyl)lithium composed of all 1,4‐cyclohexadiene (1,4‐CHD) units. The rate of the grafting reaction was accelerated by the addition of amine. The grafting density of PCHD arms onto C₆₀ decreased with an increase in the molar ratio of 1,2‐cyclohexadiene (1,2‐CHD) units. The electron‐transfer reaction from PCHD carbanions to C₆₀ did not occur in either a nonpolar solvent or a polar solvent. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3282–3293, 2008.     

Oxidation of poly(1,3‐cyclohexadiene): Influence of the polymer chain structure

The influence of the microstructure on the oxidation of poly(1,3‐cyclohexadiene) (PCHD) homopolymer, obtained by anionic polymerization with alkyllithium/amine systems, was investigated for the first time. PCHD has a structure consisting of a main chain formed by 1,2‐addition (the 1,2‐CHD unit) and 1,4‐addition (the 1,4‐CHD unit). The molar ratio of 1,2‐CHD/1,4‐CHD units in the polymer chain strongly influenced the extent of oxidation of PCHD. A polymer chain with a high content of 1,4‐CHD units was easily oxidized by air and 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ). In contrast, the progress of oxidation was prevented in the case of PCHD containing 52% of 1,2‐CHD units. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 837–845, 2006     

Synthesis of poly(p‐phenylene)‐poly(4‐diphenylaminostyrene) bipolar block copolymers with a well‐controlled and defined polymer chain structure

A poly(p‐phenylene) (PPP)‐poly(4‐diphenylaminostyrene) (PDAS) bipolar block copolymer was synthesized for the first time. A prerequisite prepolymer, poly(1,3‐cyclohexadiene) (PCHD)‐PDAS binary block copolymer, in which the PCHD block consisted solely of 1,4‐cyclohexadiene (1,4‐CHD) units, was synthesized by living anionic block copolymerization of 1,3‐cyclohexadiene and 4‐diphenylaminostyrene. To obtain the PPP‐PDAS bipolar block copolymer, the dehydrogenation of this prepolymer with quinones was examined, and tetrachloro‐1,2‐(o)‐benzoquinone was found to be an appropriate dehydrogenation reagent. This dehydrogenation reaction was remarkably accelerated by ultrasonic irradiation, effectively yielding the target PPP‐PDAS bipolar block copolymer. The hole and electron drift mobilities for PPP‐PDAS bipolar block copolymer were both on the order of 10^?3 to 10^?4 cm²/V·s, with a negative slope when plotted against the square root of the applied field. Therefore, this bipolar block copolymer was found to act as a bipolar semi‐conducting copolymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Aggregation of poly(1,3‐cyclohexadiene): Effects of molecular weight and polymer chain structure

The aggregation of poly(1,3‐cyclohexadiene) (PCHD), obtained by anionic polymerization with alkyllithium/amine systems, was examined using size exclusion chromatography (SEC) and size exclusion chromatography coupled with a multiangle laser light scattering photometer (SEC‐MALS). The PCHD polymer chain has a structure consisting of a main chain formed by 1,2‐addition (the 1,2‐CHD unit) and 1,4‐addition (the 1,4‐CHD unit). Mild stirring with relatively low temperature in the polymerization reaction forms an aggregation of PCHD. The molecular weight and molar ratio of 1,2‐CHD/1,4‐CHD units in the polymer chain strongly influence the aggregation of PCHD. In a high molecular weight PCHD, containing ～50% 1,2‐CHD units, an aggregation of the polymer was observed in tetrahydrofuran (THF) solution at room temperature. This aggregation of PCHD was soluble in 1,2,4‐trichlorobenzene (TCBz) and could be separated into each polymer molecule. In contrast, a polymer chain with a high content of 1,4‐CHD units having a relatively low cis‐stereospecificity was easily soluble in THF and TCBz without aggregating. A long polymer chain structure with a high content of 1,2‐CHD units is considered to be the reason for the generation of strong intermolecular forces contributing to the aggregation of PCHD with the solvophobic interactions. The degree of aggregation could be controlled by the conditions of the PCHD polymer solution. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1442–1452, 2006     

Anionic polymerization of 1,3‐cyclohexadiene with alkyllithium/amine system in an aromatic hydrocarbon solvent: Predominant formation of 1,2‐addition product

Steric hindrance of the amine strongly affected the formation of the dominant 1,2‐addition product from the anionic polymerization of 1,3‐cyclohexadiene (1,3‐CHD) initiated by the alkyllithium (RLi)/amine system in an aromatic hydrocarbon solvent. 1,2‐Cyclohexadiene (1,2‐CHD)/1,4‐cyclohexadiene (1,4‐CHD) unit molar ratios from 85/15 to 93/7 were obtained using an RLi/N,N,N′,N′‐tetramethylethylenediamine (TMEDA) system in toluene. The C? Li bonds of poly(1,3‐cyclohexadienyl)lithium (PCHDLi)/TMEDA complex in toluene appeared to be strongly polarized with small steric hindrance. Intermolecular forces contributing to the aggregation were strong for high‐molecular‐weight poly(1,3‐cyclohexadiene) (PCHD) consisting of almost all 1,2‐CHD units. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6604–6611, 2008     

Synthesis of soluble poly(para‐phenylene) with a long polymer chain: Characteristics of regioregular poly(1,4‐phenylene)

Soluble poly(para‐phenylene) having a long polymer chain (more than six repeat units) was synthesized with a tert‐butyl end‐group (t‐PPP) and was found to have improved solubility and excellent optical properties. Poly(1,3‐cyclohexadiene) (PCHD) consisting of only 1,4‐cyclohexadiene (1,4‐CHD) units was synthesized with a tert‐butyl end‐group (t‐PCHD), and completely dehydrogenated to obtain t‐PPP. This end‐group effectively prevented the crystallization of t‐PPP, and polymers containing up to 16 repeat units were soluble in tetrahydrofuran. Soluble t‐PPP obtained had an ability to form a tough thin film prepared by spin‐coating method. Optical analyses of t‐PPP provided strong evidence for a linear polymer chain structure. A block copolymer of t‐PPP and a soluble polyphenylene (PPH) was then synthesized, and the excellent optical properties were retained by this block copolymer along with its solubility. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5223–5231, 2008     

Diblock copolymers of polystyrene‐b‐poly(1,3‐cyclohexadiene) exhibiting unique three‐phase microdomain morphologies

The synthesis and molecular characterization of a series of conformationally asymmetric polystyrene‐block‐poly(1,3‐cyclohexadiene) (PS‐b‐PCHD) diblock copolymers (PCHD: ～90% 1,4 and ～10% 1,2), by sequential anionic copolymerization high vacuum techniques, is reported. A wide range of volume fractions (0.27 ≤ ?_PS ≤ 0.91) was studied by transmission electron microscopy and small‐angle X‐ray scattering in order to explore in detail the microphase separation behavior of these flexible/semiflexible diblock copolymers. Unusual morphologies, consisting of PCHD core(PCHD‐1,4)–shell(PCHD‐1,2) cylinders in PS matrix and three‐phase (PS, PCHD‐1,4, PCHD‐1,2) four‐layer lamellae, were observed suggesting that the chain stiffness of the PCHD block and the strong dependence of the interaction parameter χ on the PCHD microstructures are important factors for the formation of this unusual microphase separation behavior in PS‐b‐PCHD diblock copolymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1564–1572     

Microphase‐separated structure of 1,3‐cyclohexadiene/butadiene triblock copolymers and its effect on mechanical and thermal properties

We report the effect of microphase‐separated structure on the mechanical and thermal properties of several poly(1,3‐cyclohexadiene‐block‐butadiene‐block‐1,3‐cyclohexadiene) triblock copolymers (PCHD‐block‐PBd‐block‐PCHD) and of their hydrogenated derivatives: poly(cyclohexene‐block‐ethylene/butylene‐block‐cyclohexene) triblock copolymers (PCHE‐block‐PEB‐block‐PCHE). Both mechanical strength and heat‐resistant temperature (ex. Vicat Softening Temperature: VSPT) tended to increase with an increase in the 1,3‐cyclohexadiene (CHD)/butadiene ratio. On the other hand, heat resistance of the hydrogenated block copolymer was found to be higher than that of the unhydrogenated block copolymer. However, the mechanical strength was lower than those of the unhydrogenated block copolymer with the same ratio of CHD to butadiene. To clarify the relationship between the higher order structures of those block copolymers and their properties, we observed the microphase‐separated structure by transmission electron microscope (TEM). Hydrogenated block copolymers were found to have more finely dispersed microphase‐separated structures than those of the unhydrogenated block copolymers with the same CHD/Bd ratios through the use of TEM and the small‐angle X‐ray scattering (SAXS) technique. Those results indicated that the segregation strength between the PCHE block sequence and the PEB block sequence increased, depending on hydrogenation of the unhydrogenated precursor. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 13–22, 2001     

Novel amphiphilic block copolymers derived from the selective fluorination and sulfonation of poly(styrene‐block‐1,3‐cyclohexadiene)

Diblock copolymers of polystyrene‐block‐(1,3‐cyclohexadiene) (PS‐b‐PCHD), with varied molecular weights and compositions, were synthesized by sequential polymerization of styrene and 1,3‐cyclohexadiene (CHD) initiated by sec‐butyllithium in cyclohexane in the presence of appropriate additives during formation of the PCHD block. The residual double bonds in the PCHD block were saturated by addition of in situ generated difluorocarbene and/or hydrogen to enhance thermal and chemical stability. The fluorinated and/or hydrogenated polydiene blocks were chemically stable, allowing for controlled sulfonation of the PS blocks using acetyl sulfate. ¹H NMR and FT‐IR characterization confirmed successful fluorination/hydrogenation and sulfonation of the respective blocks. The resulting amphiphilic block copolymers consist of a semiflexible fluorine‐containing hydrophobic block having a bridged double ring structure and a hydrophilic sulfonated PS block. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A new insight into the mechanism of 1,3‐dienes cationic polymerization. II. Structure of poly(1,3‐pentadiene) synthesized with tBuCl/TiCl4 initiating system

The microstructure of poly(1,3‐pentadiene) synthesized by cationic polymerization of 1,3‐pentadiene with ^tBuCl/TiCl₄ initiating system is analyzed using one‐dimensional‐ and two‐dimensional‐NMR spectroscopy. It is shown that unsaturated part of chain contains only homo and mixed dyads with trans?1,4‐, trans?1,2‐, and cis?1,2‐structures with regular and inverse (head‐to‐head or tail‐to‐tail) enchainment, whereas cis?1,4‐ and 3,4‐units are totally absent. The new quantitative method for the calculation of content of different structural units in poly(1,3‐pentadiene)s based on the comparison of methyl region of ¹³C NMR spectra of original and hydrogenated polymer is proposed. The signals of tert‐butyl head and chloromethyl end groups are identified in a structure of poly(1,3‐pentadiene) chain and the new approaches for the quantitative calculation of number‐average functionality at the α‐ and ω‐end are proposed. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3297–3307     

Synthesis of novel hydrocarbon polymers containing 6‐membered rings in the main chain: living anionic polymerization of 1,3‐cyclohexadiene

The n‐butyllithium (n‐BuLi)/N,N,N',N'‐tetrametylethylene‐diamine (TMEDA) system (the molar ratio of TMEDA to n‐BuLi higher than 4/4) has been found to polymerize 1,3‐cyclohexadiene (1,3‐CHD) to produce “living” polymer having narrow molecular weight distribution with well‐controlled polymer chain length. Binary and ternary block copolymers with narrow molecular weight distribution could be synthesized from 1,3‐cyclohexadiene, styrene, and butadiene with very high efficiency. These polymers and their hydrogenated derivatives have excellent thermal, mechanical, chemical, and optical properties for the new industrial materials.     

Thermal stability of a star‐shaped poly(1,3‐cyclohexadiene)

A star‐shaped poly(1,3‐cyclohexadiene) (PCHD) with a fullerene‐C₆₀ (C₆₀) core (C₆₀‐PCHD) was prepared to examine the thermal stability of the covalent bond between the C₆₀ and PCHD arm in the C₆₀‐PCHD. The covalent bond between the C₆₀ and PCHD arm formed by a 1,2‐cyclohexadiene (CHD) unit on the C₆₀ was stronger than that formed by a 1,4‐CHD unit. The double bond in the CHD unit adjoining the C₆₀ core was a key structure for the stability of that covalent bond. The hydrogenated C₆₀‐PCHD, which did not contain a double bond, possessed significantly higher thermal stability compared to C₆₀‐PCHD. The mechanism of elimination of PCHD arm molecules from the C₆₀ core was thought to proceed via a 1,5‐sigmatropic H‐shift. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2132–2142, 2009     

Copolymerization of propylene with 1,3‐butadiene using isospecific zirconocene catalysts

Poly(propylene‐ran‐1,3‐butadiene) was synthesized using isospecific zirconocene catalysts and converted to telechelic isotactic polypropylene by metathesis degradation with ethylene. The copolymers obtained with isospecific C₂‐symmetric zirconocene catalysts activated with modified methylaluminoxane (MMAO) had 1,4‐inserted butadiene units ( 1,4‐BD ) and 1,2‐inserted units ( 1,2‐BD ) in the isotactic polypropylene chain. The selectivity of butadiene towards 1,4‐BD incorporation was high up to 95% using rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride (Cat‐A)/MMAO. The molar ratio of propylene to butadiene in the feed regulated the number‐average molecular weight (M_n) and the butadiene contents of the polymer produced. Metathesis degradations of the copolymer with ethylene were conducted with a WCI₆/SnMe₄/propyl acetate catalyst system. The ¹H NMR spectra before and after the degradation indicated that the polymers degraded by ethylene had vinyl groups at both chain ends in high selectivity. The analysis of the chain scission products clarified the chain end structures of the poly(propylene‐ran‐1,3‐butadiene). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5731–5740, 2007     

Molecular dynamics study of the stereostructure of 1,4‐linked poly(cyclohexa‐1,3‐diene) obtained with π‐allylnickel‐based catalysts

Temperature‐constant and pressure‐constant molecular dynamics simulations of crystalline 1,4‐linked poly(cyclohexa‐1,3‐diene) (CHD) were performed using the COMPASS force field. Powder X‐ray diffraction spectra calculated from the simulated atomic coordinates were compared with the measured spectrum of the crystal of 1,4‐linked poly(CHD), obtained using a bis(allylnickel bromide) (ANiBr)/methylaluminoxane (MAO) catalyst. As a result of the comparison, the geometrical isomerism of the 1,4‐linked poly(CHD) obtained with the ANiBr/MAO catalyst was found to be cis syndiotactic. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 973–978, 2001     

Polymerization of 1,3‐cyclohexadiene with nickel/MAO catalytic systems

The polymerization of 1,3‐cyclohexadiene with nickel bis(acetylacetonate) activated by methylaluminoxane affords poly(1,3‐cyclohexadiene) in high yields; the same catalyst is unable to polymerize larger conjugated cyclic diolefins or copolymerize 1,3‐cyclohexadiene with styrene. In the latter case, the homopolymer of the diolefin is obtained. The catalyst activity increases with increasing reaction temperature, nickel concentration, and aluminum/nickel ratio or with the addition of triisobutylaluminum to the reaction medium. The obtained poly(1,3‐cyclohexadiene) samples are high‐melting crystalline polymers (melting temperature ∼ 320 °C) that are insoluble in all common organic solvents. With bis(cyclopentadienyl)nickel in place of nickel bis(acetylacetonate), the activity is much lower, but the polymer is more stereoregular, as indicated by the slightly higher value of the melting temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3004–3009, 2000     

Facile synthesis of conjugated rod‐coil block copolymers

A facile synthetic approach of conjugated rod‐coil block copolymers with poly(para‐phenylene) as the rod block and polystyrene or polyethylene glycol as the coil block was developed. The block copolymers were synthesized through a TEMPO‐mediated radical polymerization of 3,5‐cyclohexadiene‐1,2‐diol‐derived monomers (diacetate, dibenzonate, and dicarbonate), followed by thermal aromatization of the polymer precursor. The living character of the polymerization and the structure of the copolymers were studied by NMR, GPC, TGA, and UV–vis spectroscopy. The average conjugation lengths of the copolymers were calculated according to their maxima in UV–vis spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 800–808, 2007     

Effect of solvent on the dehydrogenation of poly(1,3‐cyclohexadiene): Formation and characteristics of benzoquinone–aromatic hydrocarbon charge‐transfer complexes

The effect of solvent on the dehydrogenation of poly(1,3‐cyclohexadiene) (PCHD) with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) [or 2,3,5,6‐tetrachloro‐1,4‐(p‐)‐benzoquinone (TCQ)] was examined to improve the reactivity of benzoquinones for this dehydrogenation reaction. The dehydrogenation of PCHD with DDQ (or TCQ) was strongly affected by the type of solvent, and aromatic hydrocarbon based solvents were appropriate for this dehydrogenation reaction. A charge‐transfer complex between DDQ (or TCQ) and aromatic hydrocarbons was formed in the reaction mixture, and the reactivity of the complex was much higher than that of free DDQ (or TCQ). The formation of a DDQ–aromatic hydrocarbon complex, which has a large diamagnetic shift of the ¹³C NMR signals with respect to DDQ, was the primary factor for improvement of the reactivity of DDQ. For the TCQ–aromatic hydrocarbon complex, the existence of an electron‐withdrawing group on the aromatic hydrocarbon was the major factor for improvement of the reactivity of TCQ. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 342–350, 2010     

Chain‐end modification of living anionic polybutadiene with diphenylethylenes and styrenes

The first step in the transformation of poly(butadienyl)lithium into a macromolecular atom transfer radical polymerization initiator or reversible addition–fragmentation chain transfer agent is the modification of the anionic chain end into a suitable leaving/reinitiating group. We have investigated three different modification reactions to obtain a styrenic end group at the chain end of poly(butadienyl)lithium. In all cases, we have looked at the influence of a Lewis base on the progress of the reaction. The first modification reaction with α‐methylstyrene leads to partial functionalization and oligomerization. The second reaction with 1,2‐diphenylethylenes, particularly trans‐stilbene, results in monoaddition to the poly(butadienyl)lithium chain ends. Quantitative functionalization is not obtained, possibly because of a hydrogen abstraction reaction, which causes termination. In the third modification reaction, a small polystyrene block is successfully added to the chain ends, as shown by a detailed matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis of the block copolymers. Nearly quantitative block copolymer formation is achieved, with an average styrene block size of four monomer units and a polydispersity index of 1.19 for the polystyrene block. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2536–2545, 2005     

Influence of tertiary diamines on the synthesis of high‐molecular‐weight poly(1,3‐cyclohexadiene)

The living synthesis of poly(1,3‐cyclohexadiene) was performed with an initiator adduct that was synthesized from a 1:2 (mol/mol) mixture of N,N,N′,N′‐tetramethylethylenediamine (TMEDA) and n‐butyllithium. This initiator, which was preformed at 65 °C, facilitated the synthesis of high‐molecular‐weight poly(1,3‐cyclohexadiene) (number‐average molecular weight = 50,000 g/mol) with a narrow molecular weight distribution (weight‐average molecular weight/number‐average molecular weight = 1.12). A plot of the kinetic chain length versus the time indicated that termination was minimized and chain transfer to the monomer was eliminated when a preformed initiator adduct was used. Chain transfer was determined to occur when the initiator was generated in situ. The polymerization was highly sensitive to both the temperature and the choice of tertiary diamine. The use of the bulky tertiary diamines sparteine and dipiperidinoethane resulted in poor polymerization control and reduced polymerization rates (7.0 × 10⁻⁵ s⁻¹) in comparison with TMEDA‐mediated polymerizations (1.5 × 10⁻⁴ s⁻¹). A series of poly(1,3‐cyclohexadiene‐block‐isoprene) diblock copolymers were synthesized to determine the molar crossover efficiency of the polymerization. Polymerizations performed at 25 °C exhibited improved molar crossover efficiencies (93%) versus polymerizations performed at 40 °C (80%). The improved crossover efficiency was attributed to the reduction of termination events at reduced polymerization temperatures. The microstructure of these polymers was determined with ¹H NMR spectroscopy, and the relationship between the molecular weight and glass‐transition temperature at an infinite molecular weight was determined for polymers containing 70% 1,2‐addition (150 °C) and 80% 1,4‐addition (138 °C). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1216–1227, 2005     

Copolymerization of ethylene with cycloolefins or cyclodiolefins by a constrained‐geometry catalyst

The copolymerization of ethylene and cycloolefins [cyclopentene (CPE), cyclohexene (CHX), cycloheptene (CHP), cyclooctene (COT), cyclododecene (CDO), norbornene (NB), and 5,6‐dihydrodicyclopentadiene HDCPD] and cyclodiolefins [1,3‐cyclopentadiene (CPD), 1,4‐cyclohexadiene (CHD), 1,5‐cyclooctadiene (COD), 2,5‐norbornadiene (NBD), and dicyclopentadiene (DCPD)] was investigated with a constrained‐geometry catalyst, dimethylsilylene(tetramethylcyclopentadienyl)(N‐tert‐butyl)titanium dichloride, with methyl isobutyl aluminoxane as a cocatalyst. In the copolymerization with cycloolefins, the olefins, except for CHX, CDO, and HDCPD, were copolymerized via the 1,2‐insertion mode with the following reactivity: NB > CHP > COT > CPE. In the copolymerization with cyclodiolefins, corresponding copolymers, except for copolymerization with CHD, were obtained. A crosslinking fraction was detected in the copolymers with COD and NBD. The reactivity of the cyclodiolefins, except for COD, was higher than that of the cycloolefins. CPD was copolymerized via 1,2‐insertion, 1,4‐insertion or 1,2‐insertion of dimerized DCPD. The copolymerization with COD showed peculiar behavior under the copolymerization condition of a high COD concentration in the feed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1285–1291, 2005