Synthesis and white electroluminescent properties of multicomponent copolymers containing polyfluorene,oligo(phenylenevinylene), and porphyrin derivatives

Two novel multicomponent copolymers ( P1 and P2 ) containing polyfluorene (PF), oligo(phenylenevinylene) ( OPV ), and porphyrin ( Por ) derivatives were synthesized according to the Suzuki polymerization method. The structures, optical, and electrochemical properties of the two model compounds ( OPV and Por ) and multicomponent copolymers were characterized by ¹H NMR, FTIR, elemental analysis, UV–vis spectroscopy, photoluminescence, and cyclic voltammetry, respectively. Both of the copolymers exhibit thermotropic liquid crystalline properties and represent the characteristic Schlieren textures in a wide temperature range. Electroluminescence spectra of these copolymers exhibit broadband emissions covering the entire visible region from 400 to 700 nm. The single layer polymer light emitting diodes device based on P2 with a configuration of indium tin oxide/poly(ethylenedioxythiophene):poly(styrenesulfonic acid)/polymers/Ca/Al emits white light with the Commission Internationale de l′Eclairage chromaticity coordinates of (0.29, 0.30), maximum brightness of 443 cd/m². The white‐light‐emitting devices based on the novel multicomponent copolymers exhibit low turn‐on voltage, and good color stability at different driving voltages as well. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5291–5303, 2009     

Synthesis and characterization of poly(fluorene)‐based copolymers containing various 1,3,4‐oxadiazole pendants

A series of soluble alternating poly(fluorene)‐based copolymers containing electron‐transporting 1,3,4‐oxadiazole (OXD) and hole‐transporting carbazole pendants attached to the C‐9 position of fluorene units by long alkyl spacers were synthesized. These copolymers possess mesogenic and nonmesogenic pendants attached to a rigid mesogenic poly(fluorene) (PF) backbone. All these polymers exhibit glass‐forming liquid crystalline properties, including the nematic and smectic A (SmA) phases, and reveal much wider mesophasic temperature ranges than that of PF. The thermal properties and mesomorphism of these conjugated polymers are mainly affected by the nature of these pendants, and thus the mesophasic temperature ranges and glass‐forming properties are greatly enhanced by introducing the OXD pendants. In addition, the tendencies of crystallization and aggregation of PF are also suppressed by introducing the OXD pendants. A single layer device with P4 as an emitter shows a turn‐on voltage of 5 V and a bright luminescence of 2694 cd/m² at 11 V with a power efficiency of 1.28 cd/A at 100 mA/cm². © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2700–2711, 2005     

Synthesis and chiroptical properties of chiral binaphthyl‐containing polyfluorene derivatives

New chiral binaphthyl‐containing polyfluorene (PF) derivatives, PFOH , PFMOM , and PFP , bearing different binaphthyl units ((S)‐2,2′‐bis(methoxymethoxy)‐1,1′‐binaphthyl for PFMOM , (S)‐1,1′‐binaphthyl‐2,2′‐diol for PFOH , and (S)‐2,2′‐bis(diphenylphosphinyl)‐1,1′‐binaphthyl for PFP ) in the backbone have been designed and synthesized through Pd‐catalyzed Suzuki polycondensation. Their properties have been investigated in detail by ¹H NMR, ¹³C NMR, TGA, DSC, UV–vis, photoluminescence (in solutions, in thin films before and after annealing), and circular dichroism (CD) spectroscopic methods compared with poly(9,9‐dihexylfluorene‐2,7‐diyl) ( PF ). The resulting copolymers possessed excellent solubility in organic solvents and emitted strong blue light. The phosphine oxide‐containing copolymers PFP and PFMOM exhibited higher quantum yields and better thermal spectral stability in comparison with PF . All the copolymers exhibited obviously the linearly polarized photoluminescent properties both in solutions and in solid states. High emission polarization ratios (R_PL) of PFP were observed with no obvious decrease upon thermal annealing. In addition, investigation of the CD spectroscopic properties of these copolymers in THF solutions indicated that the chirality of the binaphthyls could be transferred to the whole PF backbone. All these results demonstrated that introduction of the chiral binaphthyls, particularly BINAPO, into the backbone could effectively improve the performances of the copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Effect of higher nonbenzenoids in optical properties of dihydropyrene–thiophene and dihydropyrene–phenylenevinylene copolymers

One dihydropyrene–thiophene and a series of three dihydropyrene–phenylenevinylene copolymers were synthesized in this work. The core dihydropyrene unit was shown to remain intact in the polymer backbone by ¹H NMR studies. Thermal studies indicated higher stability of the dihydropyrene unit in the copolymers compared with the parent molecule, with one of the dihydropyrene–phenylenevinylene copolymers exhibited a single‐step onset degradation temperature at 400 °C. Extended conjugation effect in the copolymers was evident based on spectroscopic analysis despite a mismatch of macrocyclic dihydropyrene units and small conjugation partners (thiophene and phenylenevinylene). The copolymers exhibited relatively small bandgaps. All four copolymers exhibit blue light emission in photoluminescence studies. Their emission spectra are essentially identical, suggesting that their emission properties were dominated by the dihydropyrene chromophore but independent of the spacer group (thiophene or phenylenevinylene). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1795–1803, 2009     

Chain composition dependence of luminescence properties for copolymers of 2‐methoxy‐5‐2′‐ethyl‐hexyloxy‐1,4‐phenylenevinylene and 2,3‐diphenyl‐5‐octyl‐1,4‐phenylenevinylene

The copolymers of 2‐methoxy‐5‐2′‐ethyl‐hexyloxy‐1,4‐phenylenevinylene (MEH‐PV) and 2,3‐diphenyl‐5‐octyl‐1,4‐phenylenevinylene were prepared via the Gilch route with their chain compositions and the reactivity ratios of the monomers estimated by ¹H NMR spectroscopy. The results indicated that the copolymers tended to form an alternative copolymer as the feed ratio of the monomers closed to one‐half. When an individual copolymer solution in tetrahydrofuran was spun‐cast to form a film, the MEH‐PV units were able to attract the like units from the adjacent chains. As a result, the ultraviolet–visible absorption spectrum of the alternative copolymer in film form was broader than the spectra of those with different compositions. The photoluminescence spectra of the copolymers in film form exhibited the characteristic shoulder of poly(2‐methoxy‐5‐2′‐ethyl‐hexyloxy‐1,4‐phenylenevinylene), even though the content of MEH‐PV units was not great enough for the formation of repeat units in sequence. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2180–2186, 2003     

High‐efficiency poly(phenylenevinylene)‐co‐fluorene copolymers incorporating a triphenylamine as the end group for white‐light‐emitting diode applications

We have synthesized a series of PPV copolymers and investigated the relationships between their chemical structures, thermal stabilities, and optoelectronic properties. Initially, we monitored the effects of the end group and the molecular weight on the behavior of polymer light emitting diodes (PLEDs) prepared from a series of oligo(phenylenevinylene) (OPV)‐fluorene luminescent copolymers. We found that the nature of the end‐capping group was an important factor affecting the luminescence properties of devices, which were improved especially when applying a triphenylamine end group. The molecular weight mainly affected the film quality of the manufactured device; that is, it improved to a certain degree when the molecular weight increased. Based on the luminescence conversion mechanism, we used a simple spin‐coating process to fabricate a high‐efficiency LED displaying white‐light CIE 1931 (coordinates of 0.31, 0.34). The device exhibited a high current‐efficiency of 3.5 cd/A and a brightness of 973 cd/m². © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4504–4513, 2007     

Synthesis and characterization of poly(fluorene)‐based copolymer containing triphenylamine group

The copolymers that are composed of poly(fluorene) (PF), poly(p‐phenylene), and Poly(p‐phenylenevinylene) as backbone and a large 4′‐(N,N′‐diphenylamino)diphenyl or 4′‐(N,N′‐diphenylamino)phenyl as pendent group were synthesized by the nickel(0)‐mediated polycoupling. The composition of the obtained copolymers was confirmed by H NMR. All the copolymers possessed a high weight‐average molecular weight and good solubility in common organic solvents. As the content of triphenyl amine pendants increases, the copolymers showed increased thermal stability due to increased glass transition temperature and increased hole injection ability because of decreased onset of the oxidation potential. In the photoluminescence spectra of copolymers, poly (BDAV₃₀‐co‐DHF₇₀) and poly(BDAPV₃₀‐co‐DHF₇₀) showed efficient energy transfer. indium tin oxide/poly(styrene sulfonate)‐doped poly(3,4‐ethylene dioxythiophene)/poly (BDAV₃₀‐co‐DHF₇₀)/LiF/Al device showed maximum brightness of 2267 cd/m² and efficiency of 0.80 cd/A, with turn‐on voltage at 9.1 V. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 172–182, 2006     

Synthesis and characterization of new light‐emitting copolymers in polymeric‐light‐emitting‐diode device fabrications

A series of thiophene‐containing photoactive copolymers consisting of alternating conjugated and nonconjugated segments were synthesized. The ¹H NMR spectra corroborated the well‐defined structures, and the copolymers not only were soluble in common organic solvents but also had high glass‐transition temperatures (ca. 130 °C) and good thermal stability up to 390 °C. Introducing aliphatic functional groups, such as alkyl or alkoxyl, into chromophores of the copolymers redshifted the photoluminescence spectra and lowered the optical bandgaps. The electrochemical bandgaps calculated from cyclic voltammetry agreed with the optical bandgaps and thus indicated that electroluminescence and photoluminescence originated from the same excited state. The energy levels (highest occupied molecular orbital and lowest unoccupied molecular orbital) of all the copolymers were lower than those of poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1.4‐phenylenevinylene] MEH–PPV, indicating balanced hole and electron injection, which led to improved performance in both single‐layer and double‐layer polymeric‐light‐emitting‐diode devices fabricated with these copolymers. All the copolymers emitted bluish‐green or green light above the threshold bias of 5.0 V under ambient conditions. At the maximum bias of 10 V, the electroluminescence of a device made of poly(2‐{4‐[2‐(3‐ethoxy phenyl)ethylene]phenyl}‐5‐{4‐[2‐(3‐ethoxy,4‐1,8‐octanedioxy phenyl)ethylene]phenyl}thiophene) was 5836 cd/m². The external electroluminescence efficiency decreased with the lifetime as the polymer degraded. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3954–3966, 2004     

Synthesis of a novel liquid crystal rod–coil star block copolymer consisting of poly(methyl methacrylate) and poly{2,5‐bis[(4‐methoxy‐phenyl)oxycarbonyl] styrene} via atom transfer radical polymerization

A bromine capped star‐shaped poly(methyl methacrylate) (S‐PMMA‐Br) was synthesized with CuBr/sparteine/PT‐Br as a catalyst and initiator to polymerize methyl methacrylate (MMA) according to atom transfer radical polymerization (ATRP). Then, with S‐PMMA‐Br as a macroinitiator, a series of new liquid crystal rod–coil star block copolymers with different molecular weights and low polydispersity were obtained by this method. The block architecture {coil‐conformation of the MMA segment and rigid‐rod conformation of 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl] styrene segment} of the four‐armed rod–coil star block copolymers were characterized by ¹H NMR. The liquid‐crystalline behavior of these copolymers was studied by differential scanning calorimetry and polarized optical microscopy. We found that the liquid‐crystalline behavior depends on the molecular weight of the rigid segment; only the four‐armed rod–coil star block copolymers with each arm's M_n,_GPC of the rigid block beyond 0.91 × 10⁴ g/mol could form liquid‐crystalline phases above the glass‐transition temperature of the rigid block. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 733–741, 2005     

One‐ and two‐dimensional NMR characterization of N‐vinyl‐2‐pyrrolidone/methyl acrylate copolymers

N‐vinyl‐2‐pyrrolidone/methyl acrylate (V/M) copolymers were prepared by free‐radical bulk polymerization using benzoyl peroxide as an initiator. The copolymer composition of these copolymers was calculated from ¹H NMR spectra. The radical reactivity ratios for N‐vinyl‐2‐pyrrolidone (V) and methyl acrylate (M) were r_V = 0.09, r_M = 0.44. These reactivity ratios for the copolymerization of V and M were determined using the Kelen–Tudos and nonlinear least‐squares error‐in‐variable methods. The ¹³C{¹H} and ¹H NMR spectra of these copolymers overlapped and were complex. The complete spectral assignment of the ¹³C and ¹H NMR spectra were done with distortionless enhancement by polarization transfer and two dimensional ¹³C‐¹H heteronuclear single quantum correlation spectroscopic experiments. The two‐dimensional ¹H‐¹H homonuclear total correlation spectroscopic NMR spectrum showed the various bond interactions, thus inferring the possible structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2225–2236, 2002     

One‐ and two‐dimensional NMR characterization of N‐vinyl‐2‐pyrrolidone/methyl acrylate copolymers

N‐vinyl‐2‐pyrrolidone/methyl acrylate (V/M) copolymers were prepared by free‐radical bulk polymerization using benzoyl peroxide as an initiator. The copolymer composition of these copolymers was calculated from ¹H NMR spectra. The radical reactivity ratios for N‐vinyl‐2‐pyrrolidone (V) and methyl acrylate (M) were r_V = 0.09, r_M = 0.44. These reactivity ratios for the copolymerization of V and M were determined using the Kelen–Tudos and nonlinear least‐squares error‐in‐variable methods. The ¹³C{¹H} and ¹H NMR spectra of these copolymers overlapped and were complex. The complete spectral assignment of the ¹³C and ¹H NMR spectra were done with distortionless enhancement by polarization transfer and two dimensional ¹³C‐¹H heteronuclear single quantum correlation spectroscopic experiments. The two‐dimensional ¹H‐¹H homonuclear total correlation spectroscopic NMR spectrum showed the various bond interactions, thus inferring the possible structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2225–2236, 2002     

Renewable resource‐based poly (m‐phenylenevinylene)s and their statistical copolymers: Synthesis,characterization, and probing of molecular aggregation and Forster energy transfer processes

We report a novel poly (m‐phenylenevinylene)s and their copolymers based on renewable resource starting material 3‐pentadecylphenol to trace the Forster energy transfer process and molecular aggregation in the π‐conjugated polymers. The new bisylide monomer was polymerized with bisaldehyde (or benzaldehyde) under Wittig‐Horner reaction conditions to prepare poly [(4‐methoxy‐6‐pentadecyl‐1, 3‐phenylenevinylene)‐alt‐(1, 3‐phenylenevinylene)] (m‐PPV) and its para‐counterpart poly [(4‐methoxy‐6‐pentadecyl‐1, 3‐phenylenevinylene)‐alt‐(1, 4‐phenylenevinylene)] (p‐PPV) and oligo‐phenylenevinylene model compound 4‐methoxy‐6‐pentadecyl‐1, 3‐distyrylbenzene (OPV). A series of with m‐ or p‐conjugated segments were also prepared by varying the m‐ and p‐content from 0 to 100% in the feed. The selective excitation of m‐conjugated segments in the copolymer by 310 nm light showed emission properties of pure p‐conjugated segments indicating the efficient Forster energy transfer process in segmented copolymers. Both solution quantum yields and the emission intensities increase up to 75% of para‐content in the copolymers. In the solid state, the increase in the p‐incorporation in the copolymer decreases the photoluminescent intensity almost by four times as compared to that of pure meta‐substituted PPV. The excitation spectra of the polymers confirmed a new peak at 400 nm corresponding to the aggregated polymer chains in the film, which is absent in the solution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3241–3256, 2008     

Copolymers of 2,5‐bis[(4‐methoxyphenyl) oxycarbonyl]styrene with styrene and methyl methacrylate: Synthesis,monomer reactivity ratios,thermal properties,and liquid crystalline behavior

Copolymers of a liquid crystalline monomer, 2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene (MPCS), with St and MMA were prepared by free radical polymerization at low conversion in chlorobenzene with 2,2′‐azobisisobutyronitrile (AIBN) as initiator. The copolymers of poly(MPCS‐co‐St) and poly(MPCS‐co‐MMA) were characterized by ¹H NMR and GPC. The monomer reactivity ratios were determined by using the extended Kelen–Tudos (EKT) method. Structural parameters of the copolymers were obtained from the possibility statistics and monomer reactivity ratios. The influence of MPCS content in copolymers on the glass transition temperatures of copolymers was investigated by DSC. The thermal stabilities of the two copolymer systems increased with an increase of the molar fraction of MPCS in the copolymers. The liquid crystalline behavior of the copolymers was also investigated using DSC and POM. The results revealed that the copolymers with high MPCS molar contents exhibited liquid crystalline behaviors. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2666–2674, 2005     

Novel saturated red‐emitting poly(p‐phenylenevinylene) copolymers with narrow‐band‐gap units of 2,1,3‐benzothiadiazole synthesized by a palladium‐catalyzed Stille coupling reaction

Novel poly(p‐phenylenevinylene) (PPV) copolymers derived from 1‐methoxy‐4‐octyloxyphenylene (MOP), 2,1,3‐benzothiadiazole (BT), and trans‐1,2‐bis(tributylstannyl)ethylene were first prepared by a palladium‐catalyzed Stille coupling reaction. The feed ratios of MOP to BT were 99.5:0.5, 99:1, 95:5, 85:15, 70:30, and 50:50. An efficient energy transfer from the 2‐methoxy‐5‐octyloxy‐p‐phenylenevinylene segment to the narrow‐band‐gap units was observed. The poly(2‐methoxy‐5‐octyloxy‐p‐phenylenevinylene‐2,1,3‐benzothiadiazolevinylene) copolymers emitted deep red light. The maximum electroluminescence emission of these PPV copolymers occurred at 659–724 nm and was accompanied by gradual redshifting with an increasing BT concentration. The photophysical properties were examined in comparison with those of copolymers based on BT and fluorene or N‐alkylcarbazole doped with the same BT concentration in the copolymer main chain. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2325‐2336, 2005     

Synthesis,characterization, and self‐assembly of comb‐dendronized amphiphilic block copolymers

Novel amphiphilic comb‐dendronized diblock copolymers composed of hydrophobic Percec‐type dendronized polystyrene block and hydrophilic comb‐like poly(ethylene oxide) grafted polymethacrylate P(PEOMA) block were designed and synthesized via two steps of atom transfer radical polymerization (ATRP). The comb‐like P(PEOMA) prepared by ATRP of macromonomers (PEOMA) with two different molecular weights (M_n = 300 and 475) were used to initiate the sequent ATRP of dendritic styrene macromonomer (DS). The molecular weights and compositions of the obtained block copolymers were determined by ¹H NMR analysis. The copolymers with relatively narrow polydispersities (1.27–1.38) were thus obtained. The bulk properties of comb‐dendronized block copolymers were studied by using differential scanning calorimetry, polarized optical microscopy and wide‐angle X‐ray diffraction (WAXD). Similar to dendronized homopolymers, the block copolymers exhibited hexagonal columnar liquid‐crystalline phase structure. By using such amphiphilic comb‐dendronized block copolymers as building blocks, the rich self‐assembly morphologies, such as twisted string, vesicle, and large compound micelle (LCM), were obtained in a mixture of CH₃OH and THF. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4205–4217, 2008     

Highly efficient and stable blue‐light‐emitting binaphthol‐fluorene copolymers: A joint experimental and theoretical study of the main‐chain chirality

In a quest for the main‐chain chiral and highly stable blue‐light‐emitting π‐conjugated polymers, a novel series of soluble conjugated random and alternating copolymers (PF‐BN) derived from fluorene and axially chiral 1,1′‐binaphthol (BINOL) were successfully synthesized by Suzuki coupling polymerization. The polymer structures, optical properties, and their electrochemical properties were investigated by ¹H NMR, TGA/DSC, UV‐Vis absorption, photoluminescence, cyclic voltammetry, circular dichroism spectroscopy, and DFT calculations. The blue‐light‐emitting BINOL‐containing copolymers with proper content of BINOL show highly efficient photoluminescence and ultra highly stable light‐emission with almost unchanged fluorescent spectra after annealing at 200 °C in air for 10 h. The joint experimental and theoretical study of the main‐chain chirality reveals that (1) the chirality of BINOL can be transferred to the polymer backbone, (2) the effective conjugation length is about one BINOL and three fluorenes, (3) the main active chiral block in the copolymers is probably composed by one BINOL with the other two or three fluorenes, and (4) the dihedral angle in the PF‐BN copolymers should be larger than 105°. The incorporation of BINOL into the polyfluorene backbone is an effective way to produce highly efficient and stable blue‐light‐emitting main‐chain chiral conjugated polymer with interesting optoelectronic properties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3868–3879, 2010     

ABA‐type liquid crystalline triblock copolymers via nitroxide‐mediated radical polymerization: Design,synthesis, and morphologies

We have designed and synthesized rod–coil–rod triblock copolymers of controlled molecular weight by two‐step nitroxide‐mediated radical polymerization, where the rod part consists of “mesogen‐jacketed liquid crystalline polymer” (MJLCP). The MJLCP segment examined in our studies is poly{2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene} (MPCS) while the coil part is polyisoprene (PI). Characterization of the triblock copolymers by GPC, ¹H and ¹³C NMR spectroscopies, TGA, DSC confirmed that the triblock copolymers were comprised of microphase‐separated low T_g amorphous PI and high T_g PMPCS blocks. Analysis of POM and 1D, 2D‐WAXD demonstrated that the triblock copolymers formed nematic liquid crystal phase. Morphological studies using TEM indicated the sample formed lamellar structure. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5949–5956, 2007     

Control of molecular aggregation in symmetrically substituted π‐conjugated bulky poly(p‐phenylenevinylene)s and their copolymers

A new series of symmetrically substituted bulky PPV‐copolymers based on poly(bis‐2,5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene) ( BEH‐PPV ) bearing tricyclodecane (TCD) pendants were synthesized to study the effect of chain aggregation in the π‐conjugated polymer backbone. The composition of the copolymers was varied up to 100 mol % and the structures of the copolymer were confirmed by NMR and FTIR. The molecular weights of the copolymers were obtained as M_w = 11,500–1,78,800 depending on the TCD‐incorporation in BEH‐PPV. The origin of the π‐aggregation was investigated using mixture of solvents (polar or nonpolar) or temperature as external stimuli. Absorption, photoluminescence, and time‐resolved fluorescence decay techniques were employed as tools to trace molecular aggregation in solution and solid state. The TCD‐substituted bulky copolymers showed almost twice the enhancement in photoluminescence compared with that of BEH‐PPV . Solvent‐induced aggregation studies of copolymers revealed the existence of strong molecular aggregation in BEH‐PPV compared with that of bulky copolymers. Variable temperature studies further evidence for the reversibility of molecular aggregation on heating/cooling cycles and showed isosbetic points with respect to free and aggregated polymer chains. Time‐resolved fluorescent studies confirmed the existence of free and aggregated π‐conjugated species with a life time of 0.1 to 1.0 ns. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2631–2646, 2009     

Studies on the phase structure of ethylene‐vinyl acetate copolymers by solid‐state 1H and 13C NMR

The phase structure of a series of ethylene‐vinyl acetate copolymers has been investigated by solid‐state wide‐line ¹H NMR and solid‐state high‐resolution ¹³C NMR spectroscopy. Not only the degree of crystallinity but the relative contents of the monoclinic and orthorhombic crystals within the crystalline region varied with the vinyl acetate (VA) content. Biexponential ¹³C NMR spin–lattice relaxation behavior was observed for the crystalline region of all samples. The component with longer ¹³C NMR spin–lattice relaxation time (T₁) was attributed to the internal part of the crystalline region, whereas the component with shorter ¹³C NMR T₁ to the mobile crystalline component was located between the noncrystalline region and the internal part of the crystalline region. The content of the mobile crystalline component relative to the internal part of the crystalline region increased with the VA content, showing that the ¹³C NMR spin–lattice relaxation behavior is closely related to the crystalline structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2199–2207, 2002     

Synthesis and characterization of side‐chain liquid crystalline ABC triblock copolymers with p‐methoxyazobenzene moieties by atom transfer radical polymerization

A series of novel side‐chain liquid crystalline ABC triblock copolymers composed of poly(ethylene oxide) (PEO), polystyrene (PS), and poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] (PMMAZO) were synthesized by atom transfer radical polymerization (ATRP) using CuBr/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) as a catalyst system. First, the bromine‐terminated diblock copolymer poly(ethylene oxide)‐block‐polystyrene (PEO‐PS‐Br) was prepared by the ATRP of styrene initiated with the macro‐initiator PEO‐Br, which was obtained from the esterification of PEO and 2‐bromo‐2‐methylpropionyl bromide. An azobenzene‐containing block of PMMAZO with different molecular weights was then introduced into the diblock copolymer by a second ATRP to synthesize the novel side‐chain liquid crystalline ABC triblock copolymer poly(ethylene oxide)‐block‐polystyrene‐block‐poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] (PEO‐PS‐PMMAZO). These block copolymers were characterized using proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatograph (GPC). Their thermotropic phase behaviors were investigated using differential scanning calorimetry (DSC) and polarized optical microscope (POM). These triblock copolymers exhibited a smectic phase and a nematic phase over a relatively wide temperature range. At the same time, the photoresponsive properties of these triblock copolymers in chloroform solution were preliminarily studied. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4442–4450, 2008