Synthesis and Properties of Lyotropic para‐Linked Aromatic Poly(amic ethyl ester)s

The paper describes the synthesis and structure‐property relations of para‐linked aromatic poly(amic ethyl ester)s with the intention to realize lyotropic precursor solutions for rigid‐rod polyimides. As compared to the commonly used flexible precursors, these preorganized precusors should be superior to obtain perfectly oriented polyimide films, orientation layers, and fibers. The poly(amic ethyl ester)s were synthesized by polycondensation of 2,5‐diethylbis(ethoxycarbonyl)terephthaloyl acid dichloride and several para‐functionalized diamines bearing fluoro substituents, bulky side groups, or non‐coplanar structures. Certain introduced structural modifications improve the solubility in NMP to concentrations up to 50 wt.‐% and lyotropic nematic solutions could be obtained. Polymers without fluoro atoms in the ortho position to the polyamide bond have a strong tendency to form a birefringent gel at room temperature which turns into a shearable lyotropic phase above 50°C. This transformation was studied by temperature dependent FTIR spectroscopy and WAXS. However when the ortho position is fluorinated the precursors form a lyotropic phase at room temperature under shear. The macroscopic surface morphology of the dried gels of concentrated solutions is dramatically affected by the chain stiffness. para‐Poly(amic ester)s show a distinct wormlike morphology, indicating molecular order within the gel, whereas the corresponding flexible meta‐poly(amic ester)s show a structureless, smooth surface.     

Synthesis and Properties of a New Poly(arylene ethynylene) Containing 1,3,5‐Triazine Units

Summary: A new photoluminescent poly(arylene ethynylene) containing 1,3,5‐triazine units was prepared by polycondensation between 2,4‐diphenyl‐6‐N,N‐bis(4‐bromophenyl)amino‐1,3,5‐triazine and 1,4‐didodecyloxy‐2,5‐diethynylbenzene using Pd(PPh₃)₄ and CuI as the catalysts in the presence of triethylamine. The polymer showed good solubility in common organic solvents and had a number average molecular weight, , of 3 400, and a weight average molecular weight, , of 8 100. In toluene the polymer exhibited an intrinsic viscosity [η] of 0.11 dL · g^?1 at 30 °C. The polymer showed photoluminescence (PL) with emission peaks at 479 nm in CHCl₃ and at 509 nm in the solid state; quantum yield of the PL in CHCl₃ was 21%. Electrochemical reduction (or n‐doping) of the polymer started at about ?2.05 V versus Ag/AgNO₃ and gave a peak at ?2.30 V versus Ag/AgNO₃.

The 1,2,3‐triazine unit‐containing poly(arylene ethynylene) (PATZ) polymer synthesized and investigated here.     

A New Series of Conjugated Platinum‐co‐Poly(p‐phenylenebutadiynylene)s Polymers: Syntheses and Photophysical Properties

An efficient route is developed to synthesize a series of platinum‐co‐poly(p‐phenylenebutadiynylene)s (Pt‐co‐PPBs) polymers by stoichiometric mixing of poly(p‐phenylenebutadiynylene)s (PPBs) and platinum bis‐phosphine dichlorides. This synthetic route involves two steps; first, oxidative coupling of diterminal phenyleneethynylenes (PEs) gives low‐molecular‐weight PPBs oligomers H? C?C? (Ph(OR)₂ ? C?C? C?C)_n ? Ph(OR)₂ ? C?CH (R = C₄H₉ 1 , R = C₈H₁₇ 2 , R = C₁₂H₂₅ 3 ) (M_n = 1000–3000, degrees of polymerization, P_n(M_n) = 4–6 ), which have bifunctional alkynyl end groups, and in the second step, these organic oligomers are allowed to react with trans‐[(PⁿBu₃)₂PtCl₂] to form newly designed Pt‐co‐PPBs (R = C₄H₉ 4 , R = C₈H₁₇ 5 , R = C₁₂H₂₅ 6 ) polymers. The yield of 4–6 varies from good (63%) to high (76%) with high molecular weights (M_n) ranging from 52 738 to 74 212, and this methodology tolerates different alkoxy substituted PPBs. These new organometallic polymers contain platinum to phenylenebutadiynylene (PB) ratio of 1:4 to 1:6 and are solution processable. Polymer 4 displays fluorescence at room temperature and fluorescence and phosphorescence at low temperature in thin film, which would be useful for studying the triplet emission in these polymers.     

Poly(2‐isopropyl‐2‐oxazoline) Bearing a Spiropyran Side‐Chain: Synthesis and Evaluation of Photo and Temperature‐Responsive Properties

Poly(2‐isopropyl‐2‐oxazoline)s with varied loading of the spiropyran side‐chain are synthesized, and their photochemical and thermosensitive properties are characterized in aqueous solution. The absorption spectrum of the sample aqueous solution (0.1 wt%) indicates that 7.8 mol% of the pendant groups are in the zwitterionic merocyanine form. The introduction of spiropyran groups causes a marked decrease in the cloud point of the aqueous solution even when the pendant groups contain the zwitterionic merocyanine form. The cloud point of the aqueous solution of the samples in the spiropyran form is slightly (less than 1 °C) lower than that bearing the merocyanine group. Moreover, the photoinduced phase transition is demonstrated at an optimum temperature for the spiropyran‐bearing poly(2‐isopropyl‐2‐oxazoline). This material can be made applicable to a light‐driven drug releasing system by introducing a hydrophobic group to form micelles and increasing the photoinduced change of the cloud point.     

Tailoring Linear and Nonlinear Optical Properties of a Side‐Chain Liquid Crystalline Azo‐Polymethacrylate

The molecular orientation in a side‐chain liquid crystalline azopolymer with push–pull chromophores ( Pol‐PZ‐CN ) is studied by UV‐vis spectroscopy, refractive index and second harmonic generation measurements. Fresh films show homeotropic arrangement, but irradiation with polarized light induces “in‐plane” birefringence, which is enhanced by subsequent thermal annealing up to values as high as 0.34. The nonlinear response of Corona poled films with “in‐plane” anisotropy is governed by three independent NLO d_ij coefficients, evidencing symmetry different from the usual (C_∞v). For irradiated films, stable values d₃₁ = 1.4, d₃₂ = 0.9 and d₃₃ = 11 pm·V^?1 are measured at 1.9 µm. A noticeable higher d₃₁/d₃₂ ratio is obtained for preirradiated and annealed films. The proposed two‐step method consisting of light irradiation and heating is an effective strategy to tailor the polar molecular orientation of nonlinear liquid crystalline azopolymers.

     

Heterostereocomplex‐ and Homocrystallization and Thermal Properties and Degradation of Substituted Poly(lactic acid)s,Poly(l‐2‐hydroxybutanoic acid) and Poly(d‐2‐hydroxy‐3‐methylbutanoic acid)

Heterostereocomplex‐ and homocrystallization behavior, thermal properties and degradation of neat poly(l ‐2‐hydroxybutanoic acid) [P(l ‐2HB)], poly(d ‐2‐hydroxy‐3‐methylbutanoic acid) [P(d ‐2H3MB)], and their equimolar blend are first investigated. Regime I and II kinetics are observed for neat P(l ‐2HB), whereas regime II and III kinetics are seen for the blend. The growth geometry of the neat P(l ‐2HB) is linear and circular while that of the blend is spherical, whereas that of the neat P(d ‐2H3MB) changes from linear to spherical, depending on crystallization temperature (T _c). The main crystalline species is heterostereocomplex (HTSC) in the blend for a wide T _c range of 0–180 °C and a very small amount of P(d ‐2H3MB) homocrystallites form for melt‐crystallization at T _c below 70 °C and solution‐crystallization. The equilibrium melting temperature of P(l ‐2HB)/P(d ‐2H3MB) HTSC crystallites (234.5 °C) is higher than those of P(l ‐2HB) and P(d ‐2H3MB) homocrystallites (114.9 and 208.6 °C, respectively). The activation energy values for thermal degradation of the P(l ‐2HB)/P(d ‐2H3MB) blend (190–219 kJ mol^?1) are between those of neat P(l ‐2HB) and P(d ‐2H3MB) (164–180 and 210–380 kJ mol^?1, respectively), reflecting that the interaction between the polymers with opposite configurations is similar to or lower than that between the polymers with the same configurations at a high temperature in the melt.

     

Hydrophobically Modified Poly(acrylic acid) Using 3‐Pentadecylcyclohexylamine: Synthesis and Rheology

Summary: Hydrophobically modified poly(acrylic acid) was synthesized using 3‐pentadecylcyclohexylamine (3‐PDCA), which was in turn synthesized from 3‐pentadecylphenol, one of the components of cashew‐nut shell liquid (CNSL), a renewable resource material. ¹H NMR spectra confirmed the incorporation of 3‐PDCA onto PAA and a series of HMPs with three different molar concentrations, viz ? 3, 5 and 7 mol‐% of 3‐PDCA, were synthesized. An increase in viscosity with increasing hydrophobic content was observed by rheological measurements. The critical association concentrations were determined using an Ubbelohde viscometer and a controlled stress rheometer. The stability of HMPs towards temperature and shear was studied. Rheological measurements showed that there was a steady increase in viscosity with increase in hydrophobe content due to the formation of reversible networks. These polymers exhibited gel‐like behavior at low concentrations (≥2 wt.‐%) with an apparent yield stress (ca. 10 Pa) and showed shear thinning properties (non‐Newtonian). However, below a critical concentration, c [η], they showed Newtonian behavior.

η_sp of unmodified and modified PAA‐Na at various polymer concentrations.     

A Convenient Method for the Synthesis of the Amphiphilic Triblock Copolymer Poly(L‐lactic acid)‐block‐Poly(L‐lysine)‐block‐Poly(ethylene glycol) Monomethyl Ether

The amphiphilic triblock copolymer PLA‐b‐PLL‐b‐MPEG is prepared in three steps through acylation coupling between the terminal amino groups of PLA‐b‐PZLL‐NH₂ and carboxyl‐terminal MPEG, followed by the deprotection of amines. The block copolymers are characterized via FT‐IR, ¹H NMR, DSC, GPC, and TEM. TEM analysis shows that the triblock polymers can form polymeric micelles in aqueous solution with a homogeneous spherical morphology. The cytotoxicity assay indicates that the final triblock polymer micelles after deprotection show low cytotoxicity against Bel7402 human hepatoma cells. MPEG and PLL were introduced into the main chain of PLA affording a kind of ideal bioabsorbable polymer materials, which is expected to be useful in drug and gene delivery.

     

Synthesis of a Poly(vinyl alcohol)‐Based Graft Copolymer Having Poly(ε‐caprolactone) Side Chains by Solution Polymerization

Poly(vinyl alcohol)‐graft‐poly(ε‐caprolactone) (PVA‐g‐PCL) was synthesized by ring‐opening polymerization of ε‐caprolactone with poly(vinyl alcohol) in the presence of tin(II) 2‐ethylhexanoate as a catalyst in dimethyl sulfoxide. The relationship between the reaction conditions of the solution polymerization and the chemical structure of the graft copolymer was investigated. The degree of substitution (DS) and degree of polymerization (DP) of the PCL side chains were roughly controlled by varying the reaction periods and feed molar ratios of the monomer and the catalyst to the backbone. PVA‐g‐PCL with a PCL content of 97 wt.‐% (DP = 22.8, DS = 0.54) was obtained in 56 wt.‐% yield. The graft copolymer was soluble in a number of organic solvents, including toluene, tetrahydrofuran, chloroform, and acetonitrile, which are solvents of PCL. The molecular motion of the graft copolymer from ¹H NMR measurements appears to be restricted to some extent at 27–50°C, however the ¹H NMR signal intensities measured at temperatures higher than ca. 50°C reflect the actual chemical structure of the graft copolymer as determined by elemental analysis. The graft copolymer having a short PCL side chain (DP = 4.4, DS = 0.15) was amorphous. The melting temperature of a sample with relatively high PCL content (DP = 22.8, DS = 0.54) was observed at 39°C. Thermogravimetric analysis revealed that the thermal stability of PVA was improved by introducing PCL side chains. The surface free energies of the air‐side of a graft copolymer film, as calculated by Owens' equation using contact angles, were comparable to that of PCL homopolymer.     

Atom Transfer Radical Polymerization and Third‐Order Nonlinear Optical Properties of New Azobenzene‐Containing Side‐Chain Polymers

The atom transfer radical polymerization (ATRP) technique has been successfully applied to synthesize a series of nonlinear optically (NLO) active homopolymers, 4‐(4‐nitrophenyl‐diazenyl) phenyl acrylate ( P ‐ NPAPA ) and 4‐(4‐methoxyphenyl‐diazenyl) phenyl acrylate ( P ‐ MPAPA ), containing azobenzene groups on the side chain. The third‐order NLO properties of the polymer films were measured by the degenerated four‐wave mixing (DFWM) technique. A dependence of the χ⁽³⁾ values and response times of polymers on their number‐average molecular weight and the electronic effect of the substituent (nitro‐ or methoxy‐) on the azobenzene group have been evidenced. The increasing χ⁽³⁾ value of the polymer films at the magnitude of about 10^?10 was displayed with increasing molecular weight and the presence of the push‐pull electronic system contributes much in enhancing the third‐order NLO susceptibility of polymers.

     

Immiscible Poly(L‐lactide)/Poly(ε‐caprolactone) Blends: Influence of the Addition of a Poly(L‐lactide)‐Poly(oxyethylene) Block Copolymer on Thermal Behavior and Morphology

Summary: A binary blend of poly (L ‐lactide) (PLLA) and poly(ε‐caprolactone) (PCL) of composition 70:30 by weight was prepared using a twin screw miniextruder and investigated by differential scanning calorimetry (DSC), optical microscopy and scanning electron microscopy (SEM). Ternary 70:30:2 blends were also obtained by adding either a diblock copolymer of PLLA and poly(oxyethylene) (PEO) or a triblock PLLA‐PCL‐PLLA copolymer as a third component. Optical microscopy revealed that the domain size of dispersed PCL domains is reduced by one order of magnitude in the presence of both copolymers. SEM confirmed the strong reduction in particle size upon the addition of the copolymers, with an indication of an enhanced emulsifying effect in the case of the PLLA‐PEO copolymer. These results are analyzed on the basis of solubility parameters of the blend components.

Optical micrograph of M3EG2 blend melt quenched at 125 °C.     

Self‐Assembly Behavior and Optical Properties of Poly(3‐thiopheneacetate)/Dialkyldimethylammonium Complexes

Poly(3‐thiopheneacetate)/dialkyldimethylammonium complexes (PTA‐Cn) were prepared by mixing regiorandom poly(3‐thiopheneacetic acid) with dialkyldimethylammonium bromide to study the effect of their self‐assembled structures on the optical properties. The lengths of the alkyl groups in the ammonium salts were varied from decyl (C10) to octadecyl (C18) groups. These complexes showed fully developed layer structures with ordered mesophases. PTA‐C16 and PTA‐C18 with longer alkyl groups showed side‐chain crystalline phases, and PTA‐C10, PTA‐C12, and PTA‐C14 with shorter alkyl groups showed side‐chain crystalline and liquid crystalline phases at room temperature. When PTA‐C18 was heated, a melting transition from side‐chain crystalline to smectic liquid crystalline phase was observed at 41.5 °C. The maximum absorption and emission wavelengths of these complexes increased with increasing alkyl chain length indicating that the π‐conjugated structure of the regiorandom thiophene backbone changes according to the alkyl groups.

     

Mechanical Properties of Blends of Double‐Fullerene End‐Capped Poly(ethylene oxide) and Poly(L‐lactic acid)

Summary: The crystallization behavior and mechanical properties of composites of PLLA and FPEOF were studied using DSC, DMA and tensile strength measurements. For PLLA/FPEOF composites aged at room temperature, when PLLA was amorphous, an astonishing around 100 times increase in the fracture strain with a high modulus was observed. For PLLA/FPEOF composites aged at 90 °C, the mechanical performance of the composites was greatly decreased and the fracture strain did not show much of an increase compared with pure PLLA. A mechanism for the large changes in the mechanical properties of PLLA/FPEOF blends aged at different temperatures was proposed.

Strain‐stress curves of the PLLA/FPEO20F6 composite aged at 90 °C and room temperature.     

A Unique Meta‐Form Structure in the Stereocomplex of Poly(D‐lactic acid) with Low‐Molecular‐Weight Poly(L‐lactic acid)

The crystalline structure and crystallization behavior of PLLA crystals in a 1:1 w/w mixture of low‐MW PLLA with high‐MW PDLA were analyzed using WAXD, DSC, and SAXS. Under cold crystallization, homopolymeric PLLA, appearing as a meta crystal, was discovered in the PDLA/LMW‐PLLA blend. The meta‐ and α′ crystal forms of PLLA were found to form on crystallization at a T_cc of 85–95 °C and the α crystal PLLA formed at 100 ≤ T_cc < 120 °C. The meta‐crystal PLLA may be incorporated in the stereocomplexed PDLA/LMW‐PLLA lamellar region. During heating, the meta‐crystal PLLA first partially melted and then repacked directly into the α crystal PLLA without going through the less‐stable α′ form.

     

Synthesis and Characterisation of Poly[oligo(ε‐caprolactone)L‐malate‐graft‐poly(L‐lactide)]

Graft copolyesters with a PCL backbone and PLLA side chains were successfully prepared in three steps avoiding transesterification. First ε‐caprolactone was polymerised with 1,6‐hexane diol as initiator to obtain hydroxytelechelic oligo(ε‐caprolactone)s. These diols were then subjected—in the second step—to polycondensation with L ‐malic acid yielding in linear poly[oligo(ε‐caprolactone)L ‐malate] having secondary hydroxyl functions in the side chain. For both reactions scandium triflate Sc(OTf)₃ was used as a catalyst. In the third step various amounts of L ‐lactide were grafted from the polymer backbone using Zn(oct)₂ as catalyst. The successful reaction was confirmed by NMR and SEC (size exclusion chromatography) analysis. Further the thermal properties of the graft copolymers with different graft lengths were determined via differential scanning calorimetry.

     

Synthesis and Characterization of Comb‐Like Copolymers Based on Poly(ε‐caprolactone) and Poly(α‐olefin)

Comb‐like copolymers based on a polyolefin backbone of poly(10‐undecene‐1‐ol) (PUol) with poly(ε‐caprolactone) (PCL) side chains are synthesized in two steps. After synthesis of PUol by metallocene‐catalyzed polymerization, the side‐chain hydroxyl functionalities of this polar polyolefin are used as an initiator for the ring‐opening polymerization (ROP) of ε‐caprolactone (CL). In this context, copolymers with different lengths of PCL grafts are prepared. The chemical structure and the composition of the synthesized copolymers are characterized by ¹H and ¹³C NMR spectroscopy. It is shown that the hydroxyl end groups of PUol act effectively as initiating sites for the CL ROP. Size‐exclusion chromatography (SEC) measurements confirm the absence of non‐attached PCL and the expected increase in molar mass after grafting. The thermal and decomposition behaviors are investigated by DSC and thermogravimetric analysis (TGA). The effect of the length of the PCL grafts on the crystallization behavior of the comb‐like copolymers is investigated by DSC and wide‐angle X‐ray scattering (WAXS).

     

Ni‐Catalyzed Polymerization of Poly(3‐alkoxythiophene)s

The Ni‐catalyzed polymerization of P3AOTs was studied and compared with the controlled chain‐growth polymerization of P3ATs. By varying the ratio of the initial monomer concentration to the initiator concentration, no linear dependence of the molar mass was observed, revealing that the polymerization does not proceed via a controlled mechanism. This was also confirmed by analyzing the end‐groups of the polymer with MALDI‐TOF mass spectrometry. To acquire more information on the polymerization mechanism, the formation of the actual monomer and the polymerization reaction were studied into more detail. These experiments proved that the polymerization proceeds via a chain‐growth mechanism, although not in a controlled way.

     

Synthesis of High‐Molecular‐Weight Poly(L‐lactic acid) by Direct Polycondensation

To prepare poly(lactic acid) (PLA) with improved mechanical properties, high‐molecular‐weight poly(L ‐lactic acid) (PLLA) was synthesized by the direct polycondensation of lactic acid in solution phase. During polymerization, the molecular weight of PLA was influenced by the water content present in the solution; thus, the experimental apparatus was designed to remove the water efficiently and this study was focused on the optimization of the polymerization conditions such as polymerization time, solvent, and kinds of catalyst, etc. Additionally, to search for a good catalyst in the polymerization, the mixed oxide catalysts were synthesized by sol–gel method and it was characterized by XRD and BET. The results show that the M _v of PLA obtained was about 33 000, when 0.2 wt.‐% of SnCl₂ · 2H₂O was used as a catalyst in the polymerization. The DSC study shows that the thermal properties of PLA such as T_g and T_m were influenced by the kind of solvent as well as the molecular weight of PLA.

The effect of various kinds of stannous compounds on the molecular weight of PLA synthesized in solution polymerization with molecular sieve.     

Synthesis and Characterization of Poly(glycolic acid‐alt‐6‐aminohexanoic acid) and Poly(glycolic acid‐alt‐11‐aminoundecanoic acid)

Summary: Poly(ester amide)s derived from glycolic acid and ω‐amino acid units, such as aminohexanoic or aminoundecanoic acids, are synthesized by a thermal polycondensation reaction that involves the formation of metal halide salts. Polymerization kinetics of different metal salts are studied by isothermal and nonisothermal methods and the corresponding parameters compared. The condensation reaction begins in the solid state for the aminohexanoic derivatives, although a rapid liquefaction is observed. On the other hand, the melting temperatures of the sodium and the potassium chloroacetylaminoundecanoate salts are lower than the reaction temperatures, and consequently polycondensation proceeds fully in the liquefied state. These polymers are characterized by an alternate disposition of ester and amide groups and can be obtained with high molecular weights and short polymerization times. Thermal properties (glass transition and melting temperatures) of the two new polymers are determined and compared. Thermal stability is also investigated; the results indicated that decomposition temperatures were always far from both reaction and polymer fusion temperatures.

DSC heating scans performed at different rates for potassium chloroacetylaminoundecanote.     

Melting of Conformationally Disordered Crystals (α′‐Phase) of Poly(l‐lactic acid)

Melting and reorganization of conformationally disordered crystals (α′‐phase) of poly(l ‐lactic acid) (PLLA) are analyzed as a function of the rate of heating in a wide range between about 10^?1 and 10³ K s^?1. It is found for the first time that the reorganization of conformationally disordered α′‐crystals into stable α‐crystals can be suppressed by fast heating. Heating of α′‐crystals of PLLA at a constant rate, faster than 30 K s^?1, leads to its complete melting between 150 and 160 °C and suppression of formation of α‐crystals on continuation of heating. Non‐isothermal reorganization of α′‐crystals into α‐crystals only occurs when heating at a rate slower than 30 K s^?1. It is evidenced that isothermal reorganization of α′‐crystals into α‐crystals at 150–160 °C proceeds via melting followed by recrystallization rather than a solid–solid phase transition.