Synthesis and characterization of novel photoisomerizable liquid crystalline polymers containing cinnamoyl groups

A series of novel liquid crystalline monomers and polymers incorporating phenylbenzoate or phenylcinnamate segments as mesogenic cores have been synthesized to investigate the sensitivity of the photochromic cinnamoyl derivatives and to overcome the defects of the thermal instability of azobenzene. Their liquid crystalline, thermal, and photoinduced properties of all monomers and polymers were characterized. The polymers showed excellent solubility in common organic solvents such as CHCl₃, toluene, and DMF and exhibited good thermal stability with decomposition temperatures (T_d) at 5% weight loss greater than 340 °C and about 50% weight loss occurred beyond 430 °C under nitrogen atmosphere. The pitch length (about 574 nm) of the synthesized cholesteric polymeric film ( CP2 ) was estimated using scanning electron microscopy. These photochromic polymers exhibited strong UV–vis absorption maxima at about 264 or 320 nm. Moreover, photo induced configurational E/Z isomerization further changed the π‐electron conjugation systems leading to a decrease at the π‐π* transition and an increase in the range of 300 nm to 400 nm for photochromic copolymers. The thermal stability of the Z‐structural segment was confirmed by heating the polymer at 50 °C for over 5 h. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1289–1304, 2008     

Thermal and spectral stability of electroluminescent hyperbranched copolymers containing tetraphenylthiophene‐quinoline‐triphenylamine moieties

Fluorescent hyperbranched copolymers (HB‐x, x = 1–4) with inherent tetraphenylthiophene, triphenylamine (TPA) and quinoline (Qu) moieties were prepared to study the influence of the TPA branching point on the thermal and the spectral stability. All the HB‐x copolymers exhibited high glass transition temperatures (T_gs = 245–315 °C) with the detected values increasing with the increasing branching TPA content in the HB‐x. The solid HB‐x films possess high emission efficiency with the resulting quantum yields (?_Fs) in the ranges of 0.72–0.74. More importantly, the HB‐x copolymers and the derived light‐emitting devices exhibit high photoluminescence (PL) and electroluminescence (EL) stability towards thermal annealing at temperatures higher than 200 °C. After annealing at 200 °C (or 300 °C), no change was observed in the respective PL and EL spectra of HB‐1 (or HB‐4) copolymers. The spectral stability was found to correlate with T_g and with the highest branching density, HB‐4 copolymer possesses the highest thermal stability among all HB‐xs and show no EL spectral change after annealing at 300 °C for 4 h. The results indicate that all the branched HB‐x copolymers are promising candidates for the polymer light‐emitting diodes due to their high quantum yield and spectral stability. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Influence of composition on properties of nylon 6/EVOH blends

In this work, the relationships between composition and properties of Ny6/EVOH system were examined by means of several techniques and the results were interpreted in terms of level of compatibility. Blends of different ratio of Ny6 and EVOH have been processed in a laboratory‐based film blowing extrusion apparatus. Rheological measurements, FTIR and morphological analysis, and thermal and mechanical properties were carried out. Peculiar rheological, thermal, and mechanical behaviors were observed for the blend containing 25% by weight of EVOH. At this composition, FTIR analysis has pointed out that a minimum in molecular motion is achieved as a consequence of a maximum interaction of the polar groups (amide groups of Ny6 and hydroxyl groups of EVOH) involved. Moreover, gas permeability measurements on the blown films have been performed at T = 30°C. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2445–2455, 1999     

Novel thermally latent self‐crosslinkable copolymers bearing oxetane and hemiacetal ester moieties: The synthesis,self‐crosslinking behavior,and thermal properties

Novel thermally latent self‐crosslinkable copolymers ( 14 and 15 ) containing hemiacetal ester and oxetane moieties were synthesized by the radical copolymerizations of 1‐propoxyethyl methacrylate, 3‐ethyl‐3‐methacryloyloxymethyl oxetane, and/or n‐butyl methacrylate at 60 °C in the presence of 2,2′‐azoisobutylonitrile as an initiator. The obtained copolymers showed good solubility for common organic solvents such as tetrahydrofuran, chloroform, and dimethyl sulfoxide (DMSO). The thermal crosslinking behaviors were examined with several Lewis acid catalysts ( 6 ). In particular, the treatment with aluminum‐2‐ethylhexanate triethanolamine complex ( 6c ) at 160 °C was found to efficiently yield the corresponding self‐crosslinked polymers ( 14′ and 15′ ). Incidentally, the resulting products were hardly insoluble in various organic solvents, including DMSO. The thermal properties of the obtained self‐crosslinked polymers 14′ and 15′ were estimated by thermogravimetric analysis and differential scanning calorimetry. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4260–4270, 2005     

Two‐step thermal conversion from poly(amic acid) to polybenzoxazole via polyimide: Their thermal and mechanical properties

Poly(amic acid) was synthesized with a low‐temperature solution polymerization of 3,3′‐dihydroxybenzidine and pyromellitic dianhydride in N,N‐dimethylacetamide. The cast films were thermally treated at various temperatures. The polyimide containing the hydroxyl group was rearranged by decarboxylation, resulting in a fully aromatic polybenzoxazole at temperatures higher than 430 °C. These stepwise cyclizations were monitored with elemental analysis, Fourier transform infrared, and nuclear magnetic resonance. Microanalysis results confirmed the chemical compositions of poly(amic acid), polyimide, and polybenzoxazole, respectively. A cyclodehydration from poly(amic acid) to polyimide occurred between 150 and 250 °C in differential scanning calorimetry, and a cyclodecarboxylation to polybenzoxazole appeared at 400–500 °C. All the samples were stable up to 625 °C in nitrogen and displayed excellent thermal stability. Polybenzoxazole showed better thermal stability than polyimide, but polyimide exhibited better mechanical properties than polybenzoxazole. However, polyimide showed a crystalline pattern under a wide‐angle X‐ray, whereas polybenzoxazole was amorphous. The precursor poly(amic acid) was readily soluble in a variety of solvents, whereas the polyimide and polybenzoxazole were not soluble at all. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2537–2545, 2000     

Melt‐processable poly(oxyphenylalkanoate): Synthesis,properties, and in vitro degradation of poly(4‐oxyphenylacetate)

The homopolyester of 4‐hydroxyphenylacetic acid (HPAA) was synthesized by one‐pot, slurry‐melt, and acidolysis melt polymerization techniques and was characterized by its inherent viscosity and IR and NMR spectra. Differential scanning calorimetry (DSC), polarizing light microscopy (PLM), and wide‐angle X‐ray diffraction (WAXD) studies of the homopolymer were carried out for its thermal and phase behavior. The results indicated that the yield and molecular weight of the polymer depended on the method of preparation; moreover, the acidolysis melt polymerization of the pure acetoxy derivative of HPAA was the best method for the preparation of high molecular weight poly(4‐oxyphenylacetate) (polyHPAA) without side reactions. DSC and PLM studies also showed that the thermal and optical properties depended largely on the polymerization conditions and inherent viscosity values. PolyHPAA did not show a clear texture typical of liquid‐crystalline polymers, whereas after cooling from the melt, structures similar to spherulitic crystals were observed. WAXD patterns showed a crystalline nature. The in vitro degradability of the polymer was also studied via the water absorption in buffer solutions of pH 7 and 10 at 30 and 60 °C; this was followed by Fourier transform infrared, inherent viscosity, DSC, thermogravimetric analysis, WAXD, and scanning electron microscopy techniques. Unlike Vectra®, which showed no degradation, polyHPAA showed an increase in hydrolytic degradation from 5.0 and 6.0% at 30 °C to 12.5 and 15.0% at 60 °C after 350 h in buffer solutions of pH 7 and 10, respectively. The results indicated a possible biomedical prosthetic application of poly(oxyphenylalkanoate)s such as polyHPAA with better crystallinity coupled with degradability as a substitute for poly(hydroxyalkanoates). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2430–2443, 2001     

Synthesis and thermal characterization of novel poly(tetramethyl‐1,3‐silphenylenesiloxane) derivative with phenol moiety in the main chain

Novel poly(tetramethyl‐1,3‐silphenylenesiloxane) derivative with phenol moiety in the main chain, that is, poly(tetramethyl‐5‐hydroxy‐1,3‐silphenylenesiloxane) ( P1 ), was synthesized and the thermal properties were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). P1 was obtained via deprotective hydrogenation of poly(tetramethyl‐5‐benzyloxy‐1,3‐silphenylenesiloxane) ( Pre‐P1 ) catalyzed by 10% palladium on charcoal as well as via direct polycondensation of 3,5‐bis(dimethylhydroxysilyl)phenol ( M2 ). Pre‐P1 was obtained by polycondensation of 1,3‐bis(dimethylhydroxysilyl)‐5‐benzyloxybenzene ( M1 ), catalyzed by 1,1,3,3‐tetramethylguanidinium 2‐ethylhexoate. M1 was prepared by the Grignard reaction using chlorodimethylsilane and 1,3‐dibromo‐5‐benzyloxybenzene followed by the hydrolysis catalyzed by 5% palladium on charcoal. M2 was prepared by deprotective hydrogenation of M1 catalyzed by 10% palladium on charcoal. The obtained P1 was soluble in common organic solvents such as tetrahydrofuran, chloroform, dichloromethane, toluene, and so forth as well as in highly polar solvents as ethanol and methanol in which poly(tetramethyl‐1,3‐silphenylenesiloxane) is insoluble. The glass transition temperature (T_g) of P1 was determined to be 40 °C from DSC, which was much higher than that of poly(tetramethyl‐1,3‐silphenylenesiloxane) (?52 °C), indicating that the intermolecular and/or intramolecular hydrogen bondings based on hydroxyl groups restricted the mobility of the main chain. The temperature at 5% weight loss (T_d5) of P1 (393 °C) determined by TG was lower than that of poly(tetramethyl‐1,3‐silphenylenesiloxane) (ca. 500 °C), indicating that the phenol moieties decline the thermal stability; however, the obtained P1 would promise to be a new reactive‐polymer with phenolic–hydroxyl moieties to develop new functional materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 692–701, 2008     

Synthesis and characterization of self‐catalyzed imide‐containing pthalonitrile resins

Some new amino‐ and imide‐containing phthalonitrile compounds with 1:1 molar ratio of amino group to pthalonitrile unit were successfully synthesized. The molecular structures were characterized by spectroscopic techniques. They were thermally polymerized under nitrogen/air, even in the absence of curing additives. The thermal properties of the cured products were characterized by thermogravimetric analysis and differential scanning calorimetry. The 5% weight loss temperatures ranged from 525 to 528 °C and 513 to 520 °C under nitrogen and air, respectively. Char yields (900 °C) were in the range of 62–70%. Rheometric measurements showed that the rate of the cure reaction differs for all the three monomers. The glass transition temperature advances with increasing extent of cure and disappears on postcure at 375 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Controlled/living radical polymerization of vinylcyclicsilazane by RAFT process and their block copolymers

High molecular weight poly(vinyl)silazane were synthesized successfully by reversible addition fragmentation chain transfer (RAFT) polymerization in toluene at 120 °C, using dithiocarbamate derivatives and 2,2′‐azobis‐isobutyrylnitrile (AIBN) as the RAFT agents and thermal initiator, respectively. The polymerization of a vinylcyclicsilazane oligomer with 82.5% conversion was readily controlled to increase the molecular weight from 1000 to 12,000 g/mol with a narrow polydispersity <1.5. The resulting polymer showed a high ceramic yield of 70 wt % at 1000 °C. Moreover, the approach was extended successfully to the synthesis of poly(vinyl)silazane‐block‐polystyrene as an inorganic–organic diblock copolymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4594–4601, 2008     

Synthesis and properties of new hydroxyl‐pendant aromatic polyimides derived from trimethylsilylated 4,4′‐diamino‐3,3′‐dihydroxybiphenyl and aromatic tetracarboxylic dianhydrides

New phenolic hydroxyl‐pendant aromatic polyimides were synthesized with the N‐silylated diamine method in two steps: the ring‐opening polyaddition of tetrakis(trimethylsilyl)‐substituted 4,4′‐diamino‐3,3′‐dihydroxybiphenyl to various aromatic tetracarboxylic dianhydrides, giving trimethylsiloxy‐pendant poly(amic acid) trimethylsilyl esters, and thermal imidization. The hydroxyl‐bearing polyimides were amorphous but insoluble in organic solvents. They had glass‐transition temperatures greater than 370 °C and temperatures of 10% weight loss greater than 415 °C in nitrogen. The hydroxyl‐pendant polypyromellitimide film had a high tensile strength and a high modulus of 310 MPa and 10 GPa, respectively. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1790–1795, 2002     

Study of a plasticized‐unoriented P(VF2/VF3) (73/27 mol%) copolymer. I. The effects of crystallization conditions on morphology,physical, and thermal properties

The results of a study on the effects of a plasticizer, tricresyl phosphate, on the mechanical and thermal properties of unoriented films of poly(vinylidene fluoride–trifluoroethylene) (VF₂/VF₃) copolymer (73/27 mol%) are presented. Films were prepared by both quenching and slow‐cooling from the melt with plasticizer concentrations of 0, 5, and 10% by weight. For the slow‐cooled films, a reduction in crystallinity by 25% was observed for the heavily plasticized films, together with a reduced dynamic mechanical modulus (≈ 58%) and an increased dielectric constant (≈ 200%). For the quenched films, a small increase in crystallinity was observed together with a reduced modulus and an increased dielectric constant. Measurements of the temperature dependence of the modulus and dielectric constant at 10 Hz. were also carried out from −100°C to 100°C. This data showed that for slow‐cooled films the glass transition temperature decreased from −28°C to ‐52°C at the highest doping level. DSC thermal analysis shows a decrease in the Curie transition (≈ 4°C) and melting temperatures (≈ 9°C) for the quenched films, while the slow‐cooled films only showed a decrease in melting temperature (≈ 10°C), while the Curie transition temperature was unaffected. In addition, evidence of a two‐phase system or a nonferroelectric crystal phase is noted by the presence of two Curie transition temperature peaks. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 19–28, 1999     

Synthesis and characterization of liquid crystalline copolyester of 4-hydroxy-2,3,5,6-tetrafluorobenzoic acid with 6-hydroxy-2-naphthoic acid

4-Hydroxy-2,3,5,6-tetrafluorobenzoic acid/6-hydroxy-2-naphthoic acid copolymers (FHBA/HNA copolymer) with different copolymer compositions were prepared and the influence of FHBA residue on the thermal properties and structures of the copolymers were investigated. Introduction of FHBA decreased the crystal/nematic phase transition temperatures(T_CNs) of the FHBA/HNA copolymers. T_CNs of the copolymers were in the temperature range between 200 and 250°C, depending on the copolymer composition. They are approximately 40°C lower than those of 4-hydroxybenzoic acid/HNA copolymers. FHBA/HNA copolymers exhibited low crystallinity, and annealing treatment hardly influenced the crystalline natures. FHBA residue possibly interferes with the recrystallization during annealing. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 413–419, 1998     

Dual-functional,aromatic, epoxy-methacrylate monomers from bio-based feedstocks and their respective epoxy-functional thermoplastics

Dual-functional monomers consist of two distinctly different functional groups that enable chemical versatility. The most readily available epoxy-methacrylate dual-functional monomer is glycidyl methacrylate (GMA). In an effort to produce bio-based, aromatic complements to GMA, asymmetric phenolic diols (vanillyl alcohol, syringyl alcohol, gastrodigenin, and tyrosol) were identified and selectively epoxidized at the aromatic hydroxyl followed by subsequent esterification at the aliphatic hydroxyl to prepare dual functional monomers, vanillyl alcohol epoxy-methacrylate (VAEM), syringyl alcohol epoxy-methacrylate (SAEM), gastrodigenin epoxy-methacrylate (GDEM), and tyrosol epoxy-methacrylate (TEM). These monomers are viable platforms for a multitude of applications due to their unique chemical functionalities. VAEM, SAEM, GDEM, and TEM were homopolymerized individually to produce aromatic, bio-based epoxy-functional thermoplastics analogous to poly(GMA). The molecular weight distributions and thermal properties of each polymer were evaluated, as were the surface characteristics of flow-coated thin films from these polymers. Most of the newly prepared epoxy-functional thermoplastics exhibited increased thermal stability (initial decomposition temperatures >260 °C in air) relative to poly(GMA), while retaining similar glass transition temperatures (~ 65 °C) and surface energies (~ 53 mJ m⁻²); thus, these materials could be substituted for poly(GMA) and enable use in higher-temperature applications. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 673–682     

Investigation of microwave energy to cure carbon fiber reinforced phenylethynyl-terminated polyimide composites,PETI-5/IM7

The application of microwave energy to the processing of carbon fiber reinforced phenylethynyl-terminated polyimide composites (PETI-5/IM7) was investigated and evaluated with a variable-frequency microwave furnace. The thermal and physical properties of the composites were measured by dynamic mechanical thermal analysis, thermogravimetric analysis, thermomechanical analysis, and density and composition tests. The mechanical properties were determined by 3-point-bending and short-beam-shear tests at both room temperature and 177 °C. The shear failure surfaces of both microwave- and thermally cured composites were detected with environmental scanning electron microscopy. A comparison of the thermal and microwave processes was conducted to evaluate the advantage of the microwave process. Microwave-cured composites, fabricated under various pressures at the fixed process temperatures, also were investigated. From these studies, it was concluded that microwave energy successfully was used to fabricate PETI-5/IM7 composites with higher glass-transition temperatures (by 11–16 °C) and higher retention in flexural strength, flexural modulus, and shear strength at 177 °C than those fabricated by the thermal process. Furthermore, the microwave processes required only half the time used for the standard thermal process. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4616–4628, 1999     

Synthesis and characterization of siloxane resins derived from silphenylene‐siloxane copolymers bearing benzocyclobutene pendant groups

Two bis(dimethylamimo)silanes with benzocyclobutene (BCB) groups, bis(dimethylamino)methyl(4′‐benzocyclobutenyl)silane ( 2 ) and bis(dimethylamino)methyl [2′‐(4′‐benzocyclobutenyl)vinyl]silane ( 4 ), were synthesized from different synthetic routes, which were then employed to prepare two novel silphenylene‐siloxane copolymers (SiBu and SiViBu) bearing latent reactive BCB groups by polycondensation procedure with 1,4‐bis(hydroxydimethylsilyl)benzene. At elevated temperatures these copolymers were readily converted to highly crosslinked films and molding disks with network structures by polymer chain crosslinking, which followed the first‐order kinetic reaction model. The final resins of SiBu and SiViBu demonstrated excellent thermal stability with high glass transition temperatures (218 and 256 °C) and high temperatures at 5% weight loss (553 and 526 °C in N₂, 530 and 508 °C in air). After aging at 300 °C in air for 100 h, the cured resins showed weight loss lower than 4%. The films of cured SiBu and SiViBu also exhibited relatively low dielectric constants of 2.66 and 2.64, low dissipation factors of 2.23 and 2.12 × 10^?3, low water absorptions (≤0.28%), and high transparence in the visible region with cutoff wavelengths of 321 and 314 nm. Moreover, the aged films exhibited good dielectric properties and low water absorptions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7868–7881, 2008     

Thermal and X‐ray powder diffraction studies of aliphatic polyester dendrimers

The syntheses and thermal and X‐ray powder diffraction analyses of three sets of aliphatic polyester dendrimers based on 2,2‐bis(hydroxymethyl)propionic acid as a repeating unit and 2,2‐dimethyl‐1,3‐propanediol, 1,5‐pentanediol, and 1,1,1‐tris(hydroxymethyl)ethane as core molecules are reported. These dendritic polyesters were prepared in high yields with the divergent method. The thermal properties of these biodendrimers were evaluated with thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the compounds occurred around 250 °C for the hydroxyl‐ended dendrimers and around 150 °C for the acetonide‐protected dendrimers. In addition, the crystallinity of the lower generation dendrimers was evaluated with X‐ray powder diffraction. The highest crystallinity and the highest melting points were observed for the first‐generation dendritic compounds. The higher generation dendrimers showed weaker melting transitions during the first heating scan. Only the glass‐transition temperatures were observed in subsequent heating scans. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5574–5586, 2004     

Linear and A2+B3‐type hyperbranched polyesters comprising phenylbenzothiazole unit: Preparation,liquid crystalline,and optical properties

Novel liquid crystalline (LC) hyperbranched (HB) polyesters comprising phenylbenzothiazole (PBT) unit as mesogen in the interiors were prepared at various feed mole ratios (A₂/B₃) by solution polycondensation of a dioxydiundecanol derivative of PBT (A₂ monomer) with trimesic acid trimethyl ester (B₃ monomer) via A₂+B₃ approach and their LC and optical properties were investigated. Analogous linear polyesters containing the PBT unit in the main chains were also prepared by the solution polycondensation of A₂ monomer with aromatic or aliphatic dimethyl esters. FTIR and ¹H‐NMR spectroscopies indicated that the HB polyesters are produced without gelation during the polycondensation and have degree of branching (DB) of 7–46%. The structures of HB polymers changed depending on the feed mole ratios and the polymer prepared in the mole ratio of A₂/B₃ = 3/2 had the highest inherent viscosity and DB. Acetylation of terminal OH group‐having HB polyesters prepared in excess mole ratios of A₂/B₃ afforded ones bearing acetoxy groups in the terminals. DSC measurements, polarizing microscope observations of textures, and X‐ray analyses suggested that only the terminal OH group‐having HB polymer prepared in the mole ratio of A₂/B₃ = 3/1 form smectic C phase. In the linear polymers, the polymers derived by using the aromatic dimethyl esters had no LC melt, but those from the aliphatic dimethyl esters formed LC smectic C phase. The acetoxy group‐bearing HB polymers showed more stable smectic A or C phase than those with the OH terminals. Solution UV‐vis and photoluminescent (PL) spectra indicated that the linear and the HB polymers have analogous optical properties and display maximum absorbances and blue‐light emission on the basis of the PBT unit, where the Stokes shifts were observed because of intermolecular aggregation effects, but there is a large difference between the optical behaviors of the linear and the HB polymers in film, whose E_g values of the linear polymers decreased and those of the HB polymers vice versa. Quantum efficiencies (Φ) had a tendency of increase in the linear polymers and the HB polymers forming LC phases. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6688–6702, 2008     

Effects of thermal stability on the crystallization behavior of poly(vinylidene chloride)

Thermal analysis based on TGA (thermal gravimetric analysis) and DSC (differential scanning calorimeter) shows no significant degradation for PVDC which has been annealed at 210°C for less than 2 min. And the following recrystallization behavior at lower temperature (120°C) is also independent of the thermal treatment and is not affected by the difference of molecular weight. The degradation which includes dehydrochlorination at lower temperature and intramolecular cyclization or intermolecular crosslinking of the polyenes at higher temperature starts when the melting time at 210°C is more than 2 min, which also causes weight loss and heat exchange in the TGA and DSC thermograms. The recrystallization behavior of the degraded PVDC (staying at 210°C for more than 2 min) shows a strong dependence on the molecular weight. The crystallinity is decreased with the melting time at 210°C due to the increase of the degree of crosslinking. However, the POM (polarized optical microscopy) pictures and IR spectra show a favorable nucleation effect is present due to the formation of trichlorobenzene from the cyclization of the polyenes as nuclei. The crystallinity of the PVDC recrystallized at 120°C after staying at 210°C for more than 2 min is actually dependent on the molecular weight, melting time at 210°C, and cyclized or crosslinking types of degradation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3269–3276, 1999     

Hydroxyl‐terminated hyperbranched aromatic poly(ether‐ester)s: Synthesis,characterization, end‐group modification,and optical properties

Novel AB₂‐type monomers such as 3,5‐bis(4‐methylolphenoxy)benzoic acid ( monomer 1 ), methyl 3,5‐bis(4‐methylolphenoxy) benzoate ( monomer 2 ), and 3,5‐bis(4‐methylolphenoxy)benzoyl chloride ( monomer 3 ) were synthesized. Solution polymerization and melt self‐polycondensation of these monomers yielded hydroxyl‐terminated hyperbranched aromatic poly(ether‐ester)s. The structure of these polymers was established using FTIR and ¹H NMR spectroscopy. The molecular weights (M_w) of the polymers were found to vary from 2.0 × 10³ to 1.49 × 10⁴ depending on the polymerization techniques and the experimental conditions used. Suitable model compounds that mimic exactly the dendritic, linear, and terminal units present in the hyperbranched polymer were synthesized for the calculation of degree of branching (DB) and the values ranged from 52 to 93%. The thermal stability of the polymers was evaluated by thermogravimetric analysis, which showed no virtual weight loss up to 200 °C. The inherent viscosities of the polymers in DMF ranged from 0.010 to 0.120 dL/g. End‐group modification of the hyperbranched polymer was carried out with phenyl isocyanate, 4‐(decyloxy)benzoic acid and methyl red dye. The end‐capping groups were found to change the thermal properties of the polymers such as T_g. The optical properties of hyperbranched polymer and the dye‐capped hyperbranched polymer were investigated using ultraviolet‐absorption and fluorescence spectroscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5414–5430, 2008     

New insights into the multiple melting behaviors of the semicrystalline ethylene‐hexene copolymer: Origins of quintuple melting peaks

A semicrystalline ethylene‐hexene copolymer (PEH) was subjected to a simple thermal treatment procedure as follows: the sample was isothermally crystallized at a certain isothermal crystallization temperature from melt, and then was quenched in liquid nitrogen. Quintuple melting peaks could be observed in heating scan of the sample by using differential scanning calorimeter (DSC). Particularly, an intriguing endothermic peak (termed as Peak 0) was found to locate at about 45 °C. The multiple melting behaviors for this semicrystalline ethylene‐hexene copolymer were investigated in details by using DSC. Wide‐angle X‐ray diffraction (WAXD) technique was applied to examine the crystal forms to provide complementary information for interpreting the multiple melting behaviors. Convincing results indicated that Peak 0 was due to the melting of crystals formed at room temperature from the much highly branched ethylene sequences. Direct heating scans from isothermal crystallization temperature (T_c, 104–118 °C) were examined for comparison, which indicated that the multiple melting behaviors depended on isothermal crystallization temperature and time. A triple melting behavior could be observed after a relatively short isothermal crystallization time at a low T_c (104–112 °C), which could be attributed to a combination of melting of two coexistent lamellar stack populations with different lamellar thicknesses and the melting‐recrystallization‐remelting (mrr) event. A dual melting behavior could be observed for isothermal crystallization with both a long enough time at a low T_c and a short or long time at an intermediate T_c (114 °C), which was ascribed to two different crystal populations. At a high T_c (116–118 °C), crystallizable ethylene sequences were so few that only one single broad melting peak could be observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2100–2115, 2008