Preparation of oriented β‐form poly(L‐lactic acid) by solid‐state extrusion

Melt‐crystallized, low molecular weight poly(L ‐lactic acid) (PLLA) consisting of α crystals was uniaxially drawn by solid‐state extrusion at an extrusion temperature (T_ext) of 130–170 °C. A series of extrusion‐drawn samples were prepared at an optimum T_ext value of 170 °C, slightly below the melting temperature (T_m) of α crystals (～180 °C). The drawn products were characterized by deformation flow profiles, differential scanning calorimetry (DSC) melting thermograms, wide‐angle X‐ray scattering (WAXD), and small‐angle X‐ray scattering as a function of the extrusion draw ratio (EDR). The deformation mode in the solid‐state extrusion of semicrystalline PLLA was more variable and complex than that in the extensional deformation expected in tensile drawing, which generally gave a mixture of α and β crystals. The deformation profile was extensional at a low EDR and transformed to a parabolic shear pattern at a higher EDR. At a given EDR, the central portion of an extrudate showed extensional deformation and the shear component became progressively more significant, moving from the center to the surface region. The WAXD intensities of the (0010)_α and (003)_β reflections on the meridian as well as the DSC melting thermograms showed that the crystal transformation from the initial α form to the oriented β form proceeded rapidly with increasing EDR at an EDR greater than 4. Furthermore, WAXD showed that the crystal transformation proceeded slightly more rapidly at the sheath region than at the core region. This fact, combined with the deformation profiles (shear at the sheath and extensional at the core), indicated that the crystal transformation was promoted by shear deformation under a high pressure rather than by extensional deformation. Thus, a highly oriented rod consisting of only β crystals was obtained by solid‐state extrusion of melt‐crystallized, low molecular weight PLLA slightly below T_m. The structure and properties of the α‐ and β‐form crystals were also studied. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 95–104, 2002     

Effects of molecular characteristics and processing conditions on melt‐drawing behavior of ultrahigh molecular weight polyethylene

The effects of molecular characteristics and processing conditions on melt‐drawing behavior of ultrahigh molecular weight polyethylene (UHMW‐PE) are discussed, based on a combination of in situ X‐ray measurement and stress–strain behavior. The sample films of metallocene‐ and Ziegler‐catalyzed UHMW‐PEs with a similar viscosity average MW of ～10⁷ were prepared by compression molding at 180 °C. Stress profiles recorded at 160 °C above the melting temperature of 135 °C exhibited a plateau stress region for both films. The relative change in the intensities of the amorphous scattering recorded on the equator and on the meridian indicated the orientation of amorphous chains along the draw axis with increasing strain. However, there was a substantial difference in the subsequent crystallization into the hexagonal phase, reflecting the molecular characteristics, that is, MW distribution of each sample film. Rapid crystallization into the hexagonal phase occurred at the beginning point of the plateau stress region in melt‐drawing for metallocene‐catalyzed UHMW‐PE film. In contrast, gradual crystallization into the hexagonal phase occurred at the middle point of the plateau stress region for the Ziegler‐catalyzed film, suggesting an ease of chain slippage during drawing. These results demonstrate that the difference in the MW distribution due to the polymerization catalyst system dominates the phase development mechanism during melt‐drawing. The effect of the processing conditions, that is, the including strain rate and drawing temperature, on the melt‐drawing behavior is also discussed. The obtained results indicate that the traditional temperature–strain rate relationship is effective for transient crystallization in to the hexagonal phase during melt‐drawing, as well as for typically oriented crystallization during ultradrawing in the solid state. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2455–2467, 2006     

Enhanced electrical properties of highly oriented poly(vinylidene fluoride) films prepared by solid‐state coextrusion

Oriented poly(vinylidene fluoride) (PVDF) films with β‐form crystals have been commonly prepared by cold drawing of a melt‐quenched film consisting of α‐form crystals. In this study, we have successfully produced highly oriented PVDF thin films (20 µm thick) with β‐crystals and a high crystallinity (55–76%), by solid‐state coextrusion of a gel film to eight times the original length at an established optimum extrusion temperature of 160°C, some 10°C below the melting temperature. The resultant drawn films had a highly oriented (orientation function f_c = 0.993) fibrous structure, showing high mechanical properties of an extensional elastic modulus of 8.3 GPa and tensile strength of 0.84 GPa, along the draw direction. Such highly oriented and crystalline films exhibited excellent ferroelectric and piezoelectric properties. The square hysteresis loop was significantly sharper than that of a conventional sample. The sharp switching transient yielded the remnant polarization P_r of 90 mC/m², and the electromechanical coupling factor k_t was 0.24 at room temperature. These values are about 1.5 times greater than those of a conventional β‐PVDF film. Thus, solid‐state coextrusion near the melting point was found to be a useful technique for the preparation of highly oriented and highly crystalline β‐PVDF films with superior mechanical and electrical properties. The morphology of the extrudate relevant to such properties is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2549–2556, 1999     

Tensile strength of highly oriented polyethylene. II. Effect of molecular weight distribution

The tensile strength of oriented polyethylene filaments is discussed in relation to molecular weight. Short-term tensile properties at room temperature were obtained in our laboratory and from the literature for polymer samples covering the molecular weight (M _w) range from 54 × 10³ to 4 × 10⁶, and polydispersities ranging from 1.1 to 15.6, oriented by solid-state extrusion, melt spinning/drawing, solution spinning/drawing, and “surface growth.” It was found that both the molecular weight and its distribution markedly affected tensile strength. The breaking stress σ of highly oriented fibers varied with molecular weight roughly as σ ∝, M^0.4, at constant M _w/M _n over the entire range studied. Reduction of polydispersity from 8 to 1.1 by an increase of M _n with M _w approximately constant at 10⁵ increased tensile strength of oriented polyethylene filaments by a factor of nearly 2.     

Fracture Behaviour and Deformation Mechanisms of Polyimide/Silica Hybrids

Films of particulate polyimide-silica hybrids were produced by a sol-gel process and were examined in terms of morphological structure and fracture properties at different temperatures, varying from 20 to 250 °C. The fracture toughness characteristics were studied by the “Essential Work of Fracture” method using double edge-notched specimens of different ligament lengths. The results showed that the fracture toughness, expressed through the essential (w_e) and non-essential work of fracture (βw_p) parameters increased when submicron silica particles were dispersed in the polyimide matrix. In particular, it was found that both w_e and βw_p increased with temperature to a larger extent than the parent polyimide. This enhancement in the fracture toughness was attributed to extensive cavitations and shear yielding originating at the particle interface and within the matrix.     

Melt drawing of ultra‐high molecular weight polyethylene: Comparison of Ziegler‐ and metallocene‐catalyzed reactor powders

The drawing behavior of the ultra‐high molecular weight polyethylene (UHMW‐PE) melts has been studied by comparing the stress/strain curves for two types of samples as polymerized using conventional Ziegler and newer metallocene catalyst systems. Two UHMW‐PE samples, having the same viscosity average molecular weight of 3.3 × 10⁶, but different molecular weight distribution, have been drawn from melt at special conditions. The sample films for drawing were prepared by compression molding of reactor powders at 180°C in the melt. Differences in the structural changes during drawing and resultant properties, ascribable to their broad or narrow molecular weight distribution, were estimated from tensile tests, SEM observations, X‐ray measurements and thermal analyses. The metallocene‐catalyzed sample having narrower molecular weight distribution, could be effectively drawn from the melt up to a maximum draw ratio (DR) of 20, significantly lower than that obtained for the Ziegler‐catalyzed sample, ∼ 50. The stress/strain curves on drawing were remarkably influenced by draw conditions, including draw temperature and rate. However, the most effective draw for both was achieved at 150°C and a strain rate of 5 min⁻¹, independent of sample molecular weight distribution. The efficiency of drawing, as evaluated by the resultant tensile properties as a function of DR, was higher for the metallocene‐catalyzed sample having narrower molecular weight distribution. Nevertheless, the maximum achieved tensile modulus and strength for the Ziegler sample, 50–55 and 0.90 GPa, respectively, were significantly higher than those for the metallocene sample, 20 and 0.65 GPa, respectively, reflecting the markedly higher drawability for the former than the latter. The stress/strain behavior indicated that the origin of differences during drawing from the melt could be attributed to the ease of chain relaxation for the lower molecular weight chains in the melt. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1921–1930, 1999     

Branched poly(1,4‐butylene carbonate‐co‐terephthalate)s: LDPE‐like semicrystalline thermoplastics

Branched poly[1,4‐butylene carbonate‐co‐terephthalate]s (PBCTs) have been synthesized by the addition of a small amount of glycerol propoxylate ( 1 ) or pentaerythritol ( 2 ) in the polycondensation of 1,4‐butanediol, dimethyl carbonate, and dimethyl terephthalate. To avoid gel formation, the feed amount of 1 or 2 was carefully controlled at below 0.5 mol % for 1 and below 0.3 mol % for 2 . When feed of 1 or 2 was used, a high‐molecular weight melt state (M_w ～180,000 g/mol) was reached in a total reaction time of 5.5 to 6.5 h with a yield higher than 90%. The generated PBCTs were a semicrystalline polymer (T_g ～5 °C and T_m ～120 °C) when the terephthalate content (F_[TPA]) was 45 to 50 mol %. The crystallization rate increased with increasing F_[TPA] and branch content (F_{[ 1 or 2 ]}); PBCT composed of F_[TPA] = 49 mol % and F_{[ 1 ]} = 0.44 mol % was crystallized completely in a short time, ～3 min, at a crystallization temperature of 50 °C. The branched PBCT exhibited more pronounced toughness in tensile test while providing the advantage of processibility at high shear rates due to the pronounced shear thinning in melt. It was also found that the branched PBCTs were biodegradable. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 914–923     

Aromatic homo‐ and copolyesters from naturally occurring monosaccharides: PET and PEI analogs derived from L‐arabinitol and xylitol

The synthesis and characterization of new aromatic homo‐ and copolyesters based on l‐arabinitol and xylitol are described. These polymers were obtained by polycondensation reaction of the 2,3,4‐tri‐O‐methyl‐l‐arabinitol or 2,3,4‐tri‐O‐methyl‐xylitol, or their mixtures with ethylene glycol, with terephthaloyl chloride or isophthaloyl chloride in o‐dichlorobenzene or in the melt phase from the corresponding methyl phthalates. All the polymers were characterized by GPC, IR, and NMR. Their M_w values ranged between 11,500 and 46,500, with polydispersities from 1.5 to 2.3. They were found to be soluble in chloroform, but insoluble in water. In contrast with the homopolymers completely made with EG, they showed a significant hygroscopicity. DSC and TGA studies showed that the melting temperature of polyethylene terephthalate is depressed by the presence of pentitol units, whereas the thermal stability is kept above 350 °C. Only copolyesters containing 10% or less of pentitol units showed melting and produced X‐ray diffraction patterns characteristic of crystalline material. d‐Arabinitol‐based homopolyesters appeared to be more crystalline than those derived from xylitol and also presented a higher thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6394–6410, 2005     

Solvent‐free and nonisocyanate melt transurethane reaction for aliphatic polyurethanes and mechanistic aspects

A novel melt transurethane polycondensation route for polyurethanes under solvent‐free and nonisocyanate condition was developed for soluble and thermally stable aliphatic or aromatic polyurethanes. The new transurethane process was investigated for A + B, A‐A + B, and A‐A + B‐B (A‐urethane and B‐hydroxyl) ‐type condensation reactions, and also monomers bearing primary and secondary urethane or hydroxyl functionalities. The transurethane process was confirmed by ¹H and ¹³C NMR, and molecular weight of the polymers were obtained as M_n = 10–15 × 10³ and M_w = 15–45 × 10³ g/mol. The mechanistic aspects of the melt transurethane process and role of the catalyst were investigated using model reactions, ¹H NMR, and MALDI‐TOF‐MS. The model reactions indicated the occurrence of 97% reaction in the presence of catalyst, whereas its absence gave only less than 2% of the product. The polymer samples were subjected for end‐group analysis using MALDI‐TOF‐MS, which confirms the Ti‐catalyst mediated nonisocyanate pathway in the melt transurethane process. Almost all the polyurethanes were stable up to 280 °C, and the T_g of the polyurethanes can be easily fine‐tuned from ?30 to 120 °C by using appropriate diols in the melt transurethane process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2445–2458, 2008     

Synthesis and properties of blue light‐emitting,silicon‐containing,regio‐ and stereoregular conjugated polymers

This article concerns the hydrosilylation polyaddition of 1,4‐bis(dimethylsilyl)benzene ( 1 ) with 4,4′‐diethynylbiphenyl, 2,7‐diethynylfluorene ( 2b ), and 2,6‐diethynylnaphthalene with RhI(PPh₃)₃ catalyst. Trans‐rich polymers with weight‐average molecular weights (M_w's) ranging from 19,000 to 25,000 were obtained by polyaddition in o‐Cl₂C₆H₄ at 150–180 °C, whereas cis‐rich polymers with M_w's from 4300 to 34,000 were obtained in toluene at 0 °C–r.t. These polymers emitted blue light in 4–81% quantum yields. The cis polymers isomerized into trans polymers upon UV irradiation, whereas the trans polymers did not. The device having a layer of polymer trans‐ 3b obtained from 1 and 2b demonstrated electroluminescence without any dopant. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2774–2783, 2004     

Tearing energy study of “oriented and relaxed” polystyrene in the glassy state

To study the effect of processing history, molecular weight/molecular weight distribution, and thermal history on solid state properties (in particular fracture properties and orientation), carefully characterized polydisperse and monodisperse polystyrene samples were drawn above T_g and the orientation frozen in. The objective was to simulate the incidental orientation of polymer chains after processing, molding, and so forth (e.g., injection or compression, blow molding) as a result of melt flow. A series of polystyrene samples was produced by hot drawing at temperatures of 113 and 148 °C, followed by a relaxation period, and then a quench to below T_g. The level of segmental orientation imposed in the samples was determined by birefringence measurements. The tear energy of the sheets was measured at 20 °C by tearing along the draw direction, ultimately giving a value for the fracture energy, G_3C. Samples of high draw ratio and low segmental orientation were unexpectedly found to have highly anisotropic fracture properties despite the low level of optical anisotropy. The fracture properties also depended significantly on whether the samples were drawn with or without lateral constraint. The results are compared with measurements of isotropic samples and the findings of a previous investigation utilizing SANS and birefringence. Modeling the drawing conditions at the chain level using a recent nonlinear tube theory explains how birefringence alone is an inadequate measure of molecular orientation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 377–394, 2007     

Oriented crystallization of poly(L‐lactic acid) in uniaxially oriented blends with poly(vinylidene fluoride)

This article describes the oriented crystallization of poly(L ‐lactic acid) (PLLA) in uniaxially oriented blends with poly(vinylidene fluoride) (PVDF). Uniaxially drawn films of PLLA/PVDF blend with fixed ends were heat‐treated in two ways to crystallize PLLA in oriented blend films. The crystal orientation of PLLA depended upon the heat‐treatment process. The crystal c‐axis of the α form crystal of PLLA was highly oriented in the drawing direction in a sample cold‐crystallized at T_c = 120 °C, whereas the tilt‐orientation of the [200]/ [110] axes of PLLA was induced in the sample crystallized at T_c = 120 °C after preheating at T_p = 164.5–168.5 °C. Detailed analysis of the wide‐angle X‐ray diffraction (WAXD) indicated that the [020]/ [310] crystal axes were oriented parallel to the drawing direction, which causes the tilt‐orientation of the [200]/ [110] axes and other crystal axes. Scanning electron microscopy (SEM) suggested that oriented crystallization occurs in the stretched domains of PLLA with diameters of 0.5–2.0 μm in the uniaxially drawn films of PVDF/PLLA = 90/10 blend. Although the mechanism for the oriented crystallization of PLLA was not clear, a possibility was heteroepitaxy of the [200]/[110] axes of the α form crystal of PLLA along the [201]/[111] axes of the β form crystal of PVDF that is induced by lattice matching of d₁₀₀(PLLA) ≈ 5d₂₀₁(PVDF). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1376–1389, 2008     

Construction of PIB‐b‐PDEAEMA well‐defined amphiphilic diblock copolymers via sequential living carbocationic and RAFT polymerization

A series of well‐defined amphiphilic diblock copolymers consisting of hydrophobic polyisobutylene (PIB) and hydrophilic poly(2‐(diethylamino)ethyl methacrylate) (PDEAEMA) segments was synthesized via the combination of living carbocationic polymerization and reversible addition fragmentation chain transfer (RAFT) polymerization. Living carbocationic polymerization of isobutylene followed by end‐capping with 1,3‐butadiene was first performed at ?70 °C to give a well‐defined allyl‐Cl‐terminated PIB with a low polydispersity (M_w/M_n =1.29). This end‐functionalized PIB was further converted to a macromolecular chain transfer agent for mediating RAFT block copolymerization of 2‐(diethylamino)ethyl methacrylate at 60 °C in tetrahydrofuran to afford the target well‐defined PIB‐b‐PDEAEMA diblock copolymers with narrow molecular weight distributions (M_w/M_n ≤1.22). The self‐assembly behavior of these amphiphilic diblock copolymers in aqueous media was investigated by fluorescence spectroscopy and transmission electron microscope, and furthermore, their pH‐responsive behavior was studied by UV‐vis and dynamic light scattering. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1478–1486     

Development of oriented structure and properties on drawing of poly(vinylidene fluoride) by solid‐state coextrusion

Gel films of poly(vinylidene fluoride) (PVDF) consisting of α‐form crystals were drawn uniaxially by solid‐state coextrusion to extrusion draw ratios (EDR) up to 9 at an optimum extrusion temperature of 160 °C, about 10°C below the melting temperature (T_m). The development of an oriented structure and mechanical and electrical properties on coextrusion drawing were studied as a function of EDR. Wide‐angle X‐ray diffraction patterns showed that the α crystals in the original gel films were progressively transformed into oriented β‐form crystals with increasing EDR. At the highest EDR of 9 achieved, the drawn product consisted of a highly oriented fibrous morphology with only β crystals even for the draw near the T_m. The dynamic Young's modulus along the draw direction also increased with EDR up to 10.5 GPa at the maximum EDR of 9. The electrical properties of ferroelectricity and piezoelectricity were also markedly enhanced on solid‐state coextrusion. The D–E square hysteresis loop became significantly sharper with EDR, and a remanent polarization P_r of 100 mC/m² and electromechanical coupling factor along the thickness direction k_t of 0.27 were achieved at the maximum EDR of 9. The crystallinity value of 73–80% for the EDR 9 film, estimated from these electrical properties, compares well with that calculated by the ratio of the crystallite size along the chain axis to the meridional small‐angle X‐ray scattering (SAXS) long period, showing the average thickness of the lamellae within the drawn β film. These results, as well as the appearance of a strong SAXS maximum, suggest that the oriented structure and properties of the β‐PVDF are better explained in terms of a crystal/amorphous series arrangement along the draw axis. Further, the mechanical and electrical properties obtained in this work are the highest among those ever reported for a β‐PVDF, and the latter approaches those observed for the vinylidene fluoride and trifluoroethylene copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1371–1380, 2001     

A novel silk‐based segmented block copolymer containing GlyAlaGlyAla β‐sheets templated by phenoxathiin

A novel segmented block copolymer, containing polyethylene glycol segment and GlyAlaGlyAla sequence derived from B. mori silk, has been prepared as a model for silk‐based materials using both solution and interfacial techniques. Inherent viscosity, size exclusion chromatography, and light‐scattering measurements gave molecular weight between M_w 34,000–39,000. Evidence for phase separation was provided by differential scanning calorimetry, which gave two T_g's at −57 °C and 111 °C, and transmission electron microscopy, which showed a morphology in which the peptide domain, estimated to be about 20–50 nm, was dispersed in the continuous polyether phase. Solid‐state FTIR spectroscopic results showed that the polymer contained both parallel and antiparallel β‐sheet stacks, and that the solution‐polymerized material has the higher β‐sheet content. This was further confirmed by ¹³C NMR, which gave about 80% total β‐sheet content for the solution‐polymerized product and about 40% for the polymer obtained by interfacial polymerization. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 352–366, 2000     

Microstructure and fracture behavior of semicrystalline polymer–clay nanocomposites

The relationships between the microstructure and the fracture behavior of three polymer/clay nanocomposites were studied. Two different polymer matrices were chosen, namely polyamide‐6 and polyethylene (compatibilized with PE‐g‐MA or PE‐g‐PEo), to reach very different clay dispersion states. The microstructure was characterized in terms of polymer crystallinity, orientation of the polymer crystalline lamellae, clay dispersion state, and orientation of the clay tactoids. The mechanical behavior was characterized by tensile tests. The essential work of fracture (EWF) concept was used to determine the fracture behavior of the nanocomposites. Both tensile and EWF tests were performed in two perpendicular directions, namely longitudinal and transversal. It is shown that the fracture behaviors of the matrices mainly depend on the polymer crystalline lamellae orientation. For the nanocomposites, the relationships between the matrix orientation, the clay dispersion states, the values of the EWF parameters (w_e and βw_p), and their anisotropy are discussed. The results show that the lower the average clay tactoid thickness, the lower is the decrease of fracture performance for the nanocomposite and the more consumed energy as longer the path of the crack. Besides, a linear dependence of the anisotropy of the EWF parameters of the nanocomposites on the average clay aspect ratio is found. The more exfoliated the structure is, the less pronounced the anisotropy of the EWF parameters. Interestingly, it is thought that the average clay aspect ratio is the parameter representing the clay dispersion state that governs the fracture anisotropy of the nanocomposites (as the elastic properties determined by tensile tests). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1820–1836, 2008     

Polyisobutylene‐b‐Poly(N,N‐diethylacrylamide) well‐defined amphiphilic diblock copolymer: Synthesis and thermo‐responsive phase behavior

Polyisobutylene‐b‐poly(N,N‐diethylacrylamide) (PIB‐b‐PDEAAm) well‐defined amphiphilic diblock copolymers were synthesized by sequential living carbocationic polymerization and reversible addition‐fragmentation chain transfer (RAFT) polymerization. The hydrophobic polyisobutylene segment was first built by living carbocationic polymerization of isobutylene at ?70 ° C followed by multistep transformations to give a well‐defined (M_w/M_n = 1.22) macromolecular chain transfer agent, PIB‐CTA. The hydrophilic poly(N,N‐diethylacrylamide) block was constructed by PIB‐CTA mediated RAFT polymerization of N,N‐diethylacrylamide at 60 ° C to afford the desired well‐defined PIB‐b‐PDEAAm diblock copolymers with narrow molecular weight distributions (M_w/M_n ≤1.26). Fluorescence spectroscopy, transmission electron microscope, and dynamic light scattering (DLS) were employed to investigate the self‐assembly behavior of PIB‐b‐PDEAAm amphiphilic diblock copolymers in aqueous media. These diblock copolymers also exhibited thermo‐responsive phase behavior, which was confirmed by UV‐Vis and DLS measurements. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1143–1150     

Flexibilized styrene‐N‐substituted maleimide copolymers. I. Multiblock copolymers prepared from styrene‐maleimide telechelics and polytetrahydrofuran

Telechelic copolymers of styrene and different N‐substituted‐maleimides (SMIs) with a molecular weight of 2000–8000 g/mol were synthesized using the starved‐feed‐reactor technique and were nearly bifunctional when the monomer feed had a high styrene concentration. The COOH‐terminated rigid SMI blocks were polycondensated with OH‐terminated poly(tetrahydrofuran) (PTHF) blocks, with a molecular weight of 250–1000 g/mol, which are the flexible parts in the generated homogeneous multiblock copolymer. The entanglement density, which is closely related to the toughness of materials, increased in these flexible SMI copolymers (ν_e = 5.2 · 10²⁵ m⁻³) compared to the unflexibilized ones (ν_e = 2.4 · 10²⁵ m⁻³). The glass transition temperature of these flexibilized, single‐phase multiblock copolymers was still high enough to qualify them as engineering plastics. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3550–3557, 2000     

Interplay between solid state microstructure and photophysics for poly(9,9‐dioctylfluorene) within oriented polyethylene hosts

We present a study of isotropic and uniaxially oriented binary blend films comprising ≤1 wt % of the conjugated polymer poly(9,9‐dioctylfluorene) (PFO) dispersed in both ultra‐high molecular weight (UHMW) and linear‐low‐density (LLD) polyethylene (PE). Polarized absorption, fluorescence and Raman spectroscopy, scanning electron microscopy, and X‐ray diffraction are used to characterize the samples before and after tensile deformation. Results show that blend films can be prepared with PFO chains adopting a combination of several distinct molecular conformations, namely glassy, crystalline, and the so‐called β‐phase, which directly influences the resulting optical properties. Both PFO concentration and drawing temperature strongly affect the alignment of PFO chains during the tensile drawing of the blend films. In both PE hosts, crystallization of PFO takes place during drawing; the resulting ordered chains show optimal optical anisotropy. Our results clarify the PFO microstructure in oriented blends with PE and the processing conditions required for achieving the maximal optical anisotropy. © 2014 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 22–38     

Microwave‐assisted ring‐opening polymerization of ϵ‐caprolactone

Ring‐opening polymerization of ?‐caprolactone was carried out smoothly and effectively with constant microwave powers of 170, 340, 510, and 680 W, respectively, with a microwave oven at a frequency of 2.45 GHz. The temperature of the polymerization ranged from 80 to 210 °C. Poly(?‐caprolactone) (PCL) with a weight‐average molar mass (M_w) of 124,000 g/mol and yield of 90% was obtained at 680 W for 30 min using 0.1% (mol/mol) stannous octanoate as a catalyst. When the polymerization was catalyzed by 1% (w/w) zinc powder, the M_w of PCL was 92,300 g/mol after the reaction mixture was irradiated at 680 W for 270 min. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1749–1755, 2002