Synthesis and structural characterisation of hyperbranched poly(benzyl ether) analogs with 1,3,5‐s‐triazine moiety

Hyperbranched poly(benzyl ether) analogs with the 1,3,5‐s‐triazine moiety were prepared by direct polymerization of AB₂ type monomers, 2,4‐bis(4‐hydroxyphenyl)‐6‐(4‐bromomethylphenyl)‐1,3,5‐s‐triazine. The triazine rings influenced the structural and material characteristics of these hyperbranched polymers. In the hyperbranched poly(benzyl ether) analog, only the O‐alkylated structure, instead of the C‐alkylated branches, was observed, possibly due to the electron‐withdrawing nature of the triazine ring which restrains C‐alkylation on the phenyl group of the monomer. The triazine moieties play an important role in producing the structural regularity of hyperbranched poly(benzyl ether) analogs.     

Synthesis of Branched Polymers by Means of Living Anionic Polymerization, 9. Radical Coupling Reaction of 1,1‐Diphenylethylene‐Functionalized Polymers with Potassium Naphthalenide and Its Application to Syntheses of In‐Chain‐Functionalized Polymers and Star‐Branched Polymers

Radical coupling reactions of both 1,1‐diphenylethylene (DPE)‐chain‐end‐ and DPE‐in‐chain‐functionalized polymers with potassium naphthalenide have been studied under the conditions mainly in THF at –78°C. Chain‐end‐functionalized polymers having M̄_n values of less than 10 kg/mol were very efficiently coupled in more than 90% yield to afford the polymeric dianion that were dimeric coupled products with two 1,1‐diphenylalkyl anions in the middle of the chains. However, the dimer yield decreased with increasing the molecular weight. The dimer was obtained in 59% yield with use of the chain‐end‐functionalized polymer having M̄_n of 33.9 kg/mol. Well‐defined in‐chain‐functionalized polymers with two benzyl bromide and DPE moieties each have been successfully synthesized by the reaction of the polymeric dianion thus obtained with 1‐(4‐bromobutyl)‐4‐(tert‐butyldimethylsilyloxymethyl)benzene and 1‐[4‐(4‐bromobutyl)phenyl]‐1‐phenylethylene, respectively. The radical coupling reaction of in‐chain‐functionalized polymers with DPE (M̄_n ca. 20 kg/mol) with potassium naphthalenide also proceeded efficiently to afford the coupled products that were A₂A′₂ and A₂B₂ four‐arm star‐branched polymers with well‐defined structures (M̄_n ca. 40 kg/mol).     

Thieno[3,4‐c]pyrrole‐4,6‐dione‐Based Polymers for Optoelectronic Applications

Over the last decade, great progress has been made in the field of organic electronics. Advancements in organic syntheses as well as in device engineering enabled preparation of polymer solar cells with power conversion efficiency (PCE) exceeding 8%–9%. In search for new polymers suitable for photovoltaic applications, push–pull polymers containing thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) motif as an electron deficient (pull) unit emerged as very promising candidates. This Trend Article summarizes research on TPD‐based polymers with a special emphasis on the structure–property relationships.     

Thermally Cross‐Linkable Poly(p‐xylylene)s for Advanced Low‐Dielectric Applications

A novel series of poly(p‐xylylene) homopolymer and copolymers containing thermally cross‐linkable cyclohexenyl moiety are prepared via base‐catalyzed Gilch route to yield high‐molecular‐weight polymers. The resulting polymers are highly soluble in a wide range of organic solvents and could be solution cast into flexible and transparent films. The polymers are thermally stable up to 350 °C and the glass transition temperature (T_g) is in the range of 136 ? 250 °C. They undergo thermal cross‐linking via the cyclohexenyl moiety. The cross‐linked polymer exhibits a high T_g of 294 °C, a low coefficient of thermal expansion (CTE) of 45 ppm K^?1. A low dielectric constant of 2.5 and a very low dielectric loss tan δ of 0.0004 at 1 GHz are obtained, which are superior to conventional interconnect polymers.     

Preparation of Microporous Polymers Based on 1,3,5‐Triazine Units Showing High CO2 Adsorption Capacity

Microporous polymers based on 1,3,5‐triazine units are prepared by Friedel‐Crafts reaction of 2,4,6‐trichloro‐1,3,5‐triazine with aromatic compounds. 2,4,6‐Trichloro‐1,3,5‐triazine is polymerized with benzene, biphenyl, and terphenyl in dichloromethane in the presence of aluminum chloride. The surface areas of the polymers are in the range of 558 to 1266 m² g^?1, depending on the aromatic linker length. At ambient pressure and temperature, the polymers exhibit high CO₂ uptakes of 38–51 cm³ g^?1. The CO₂ uptake is significantly enhanced by 70–90% for the polymers carbonized at 400 °C for 1 h and at 800 °C for an additional 1 h under nitrogen. This result suggests that rigid microporous polymers can be used as precursor polymers for the synthesis of advanced porous carbon materials without the activation process.     

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(ε‐caprolactone) and Poly(ω‐pentadecalactone)‐Based Networks with Two‐Way Shape‐Memory Effect through [2+2] Cycloaddition Reactions

In this work, the synthesis and characterization of triple‐shape and two‐way shape‐memory effect of novel poly(ester‐urethane)s (PURs) made of a poly(ε‐caprolactone) (PCL) and poly(ω‐pentadecalactone) (PPDL) segments and N,N‐bis(2‐hydroxyethyl)cinnamide (BHECA) monomer by reactive extrusion (REx) is reported. PCL and PPDL are chosen as semicrystalline segments because of their inherent ability to undergo tensile elongation upon cooling, as prerequisite for the two‐way shape‐memory effect. BHECA is used as the “cross‐linker” due to its ability to participate in reversible [2+2] cycloaddition reaction and to mainly maintain the crystalline features of semicrystalline precursors within these PURs. This novel simple strategy is considered extremely versatile and adaptive because of the possibility to vary crystallizable segments and coupling agents, thus paving the way to the design of a multitude of triple (or more) shape‐memory polymers with two‐way behavior. Feasibility with PURs containing PCL, PPDL, and BHECA is demonstrated by adjusting the shape‐memory behavior (one and two‐way effects), and studying the structure–property relationships of the resulting PURs by DSC, DMTA, and 2D wide angle X‐ray scattering analyses while varying the weight composition of the two semicrystalline segments.     

Crystallization of the polyethylene block in polystyrene‐b‐polyethylene‐b‐polycaprolactone triblock copolymers, 1. Self‐nucleation behavior

The self‐nucleation of branched polyethylene chains of different degrees of chain mobility was studied. The polyethylene block (PE block) within poly(styrene‐b‐ethylene‐b‐caprolactone) triblock copolymers (SEC) of varying compositions was studied. Differential scanning calorimetry was used to determine the self‐nucleation domains as a function of the self‐nucleation temperature (T_s). The self‐nucleation behavior of PE chains within SEC block copolymers was found to be anomalous in comparison to the classical self‐nucleation behavior exhibited by homopolymers. When the degree of chain constraint is high, as in the case where the SEC copolymer only contains 15% of PE, domain II (only self‐nucleation domain) completely disappears and annealing can take place before self‐nucleation occurs. This means that chain constraint complicates the self‐nucleation process and this situation persists until, upon decreasing the self‐nucleation temperature (T_s), annealing has generated crystals that are big enough to act as self‐nuclei for the less restricted portions of the chain. If the PE content in the copolymer is very low (15%), two crystal populations can be distinguished. This may reflect the differences in diffusion of the PE chain segments close to the interfaces with the other two blocks and those segments that are close to the middle of the PE block. The influence of chain constraint on determining the difficulty of the chains to self‐nucleate was further explored using a crosslinked low‐density polyethylene (XLDPE). In this case, crosslinking junctions instead of covalent links with other blocks restrict chain mobility. Nevertheless, a similar difficulty in self‐nucleation was found as in the case of the PE block within SEC triblock copolymers in contrast to neat LDPE, a polymer that exhibited the classical self‐nucleation behavior with the usual three domains.     

Thermally Sensitive N‐Type Thermoelectric Aniline Oligomer‐Block‐Polyethylene Glycol‐Block‐Aniline Oligomer ABA Triblock Copolymers

High‐performance n‐type thermoelectric polymers are vital in the development of polymer thermoelectric generators (PTEGs). However, the progress is very slow due to their low stability and low thermoelectric properties. Here, aniline oligomer‐block‐polyethylene glycol‐block‐aniline oligomer (ANI)_n‐b‐PEO‐b‐(ANI)_n) (n = 4, 8, 16) are prepared and studied. The results indicate that the (ANI)_n‐b‐PEO‐b‐(ANI)_n show unique temperature sensitivity and switch from p‐type to n‐type when the temperature is above 300 K. Differential scanning calorimetry curves show that the T_g of the (ANI)_n‐b‐PEO‐b‐(ANI)_n is lower than 300 K, indicating that PEO segments of the (ANI)_n‐b‐PEO‐b‐(ANI)_n easily move above 300 K and have high flexibility. Temperature‐dependent Raman spectra confirm that there are strong interactions between PEO segments and aniline oligomers during the raising temperature, and PEO chains might provide plenty of negative charge at high temperature, which can convert the (ANI)_n‐b‐PEO‐b‐(ANI)_n into n‐type thermoelectric materials. To adjust the number of aniline unit, (ANI)₈‐b‐PEO‐b‐(ANI)₈ shows excellent n‐type characteristics with Seebeck coefficient as large as ?1171 µV K^?1 at 381 K. The strong interaction between PEO and aniline oligomers plays a dominant role in the n‐type thermoelectric performance of the triblock copolymers, which have potential application in the field of PTEGs and temperature sensors.     

Controlled/Living Free‐Radical Polymerization in the Presence of Benzyl 9H‐Carbazole‐9‐Carbodithioate under 60Co γ‐Ray Irradiation

Summary: Free‐radical polymerizations of vinyl monomers under ⁶⁰Co γ‐ray irradiation in the presence of benzyl 9H‐carbazole‐9‐carbodithioate (BCCDT) have been studied. The polymers obtained were characterized by gel permeation chromatography (GPC) and ¹H nuclear magnetic resonance (¹H NMR) spectroscopy. The results for the polymerization of methyl acrylate show that the molecular weight increases linearly with monomer conversion, that the molecular weight distribution is fairly narrow (even equal to 1.01) and that a linear relationship exists between ln([M]₀/[M]) and polymerization time. All the evidence suggests that BCCDT is a good control agent and that the polymerization has excellent living characteristics. For styrene, the polymerization is a controlled process, although it is very slow, whereas the polymerization of methyl methacrylate is uncontrolled. To the best of our knowledge, this is the first time that dithiocarbamate has been used in γ‐ray initiated living free radical polymerization.

GPC curve of PMA from the polymerization under ⁶⁰Co γ‐ray irradiation, in the presence of BCCDT.     

Ultrastructural triple localization of laminin‐1, nidogen‐1, and collagen type IV helps elucidate basement membrane structure in vivo

The basement membrane models which have been proposed to date are generally based on biochemical data, mainly binding studies and artificially synthesized polymers in vitro. Basically these have led to models proposing two three‐dimensional laminin‐1 and collagen type IV networks interconnected by nidogen‐1. Whether they reflect the in vivo basement membrane structure is still not clear. We localized laminin‐1, nidogen‐1, and collagen type IV ultrastructurally in adult and fetal mouse kidney basement membranes with the help of immunogold‐histochemistry performing double and triple localization to try to elucidate the molecular organization of basement membranes in vivo. We found laminin‐1, nidogen‐1, and collagen type IV distributed over the entire basement membranes in adult and fetal kidneys. This contradicts earlier studies ascribing laminin‐1 to the lamina lucida and collagen type IV to the lamina densa. In addition, various basement membrane segments exhibited an organized labeling pattern for the BM components. Double‐labeling revealed co‐localization of laminin‐1 and nidogen‐1. We conclude that the combination of laminin‐1 with collagen type IV as double‐network basement membrane partially interconnected by nidogen‐1 is found already in the early fetal kidney in vivo. However, our data cannot exclude the possibility of other variants of basement membrane assemblages. This is also indicated by a changing structure even in individual segments of one basement membrane type which renders a more flexible basement membrane architecture plausible. Anat Rec 254:382–388, 1999. © 1999 Wiley‐Liss, Inc.     

Helix‐Sense‐Selective Polymerization of Achiral Bis(hydroxymethyl)phenylacetylenes Bearing Alkyl Groups of Different Lengths

4‐Alkyloxy‐3,5‐bis(hydroxymethyl)phenylacetylenes with eight types of alkyl groups were synthesized and polymerized with a chiral catalytic system. We found that the length of the alkyl groups played a very important role in achieving helix‐sense‐selective polymerization. Five helix‐sense‐selective polymerizations were achieved resulting in polymers with alkyl groups whose chain length was longer than six. We think that the longer ‐ chain alkyl groups prevented the polymers from becoming insoluble by forming intermolecular hydrogen bonds between the hydroxyl groups, and stabilized their one‐handed helical structure by promoting the formation of intramolecular hydrogen bonds.

     

Visible Light‐Induced Atom Transfer Radical Polymerization

Visible light‐induced reverse and simultaneous reverse and normal initiation (SR&NI) atom transfer radical polymerizations of vinyl monomers are examined using various dyes and type I photoinitiators. The effect of photoinitiator types on the control of molecular weight and distribution is described. In both dye and type I photoinitiator sensitized SR&NI ATRP systems, the molecular weights increase linearly with conversion. However, the experimental molecular weights are considerably higher than the theoretical values and the polymers show broad‐molecular‐weight distributions ranging from 1.28 to 1.60 in the dye‐sensitized SR&NI ATRP. However, the polymers obtained by SR&NI ATRP using type I photoinitiator system had molecular weight values close to the theoretical ones and very narrow‐molecular‐weight distributions ranging from 1.11–1.18.     

Synthesis of New Side‐Chain Liquid‐Crystalline Polyoxetanes with Two Mesogenic Groups Connected by a Flexible Spacer in the Side Chain

The synthesis of a different geometry of side‐chain liquid‐crystalline polymers is reported where two mesogenic units connected by a flexible spacer are attached as pendent groups of a polymeric chain. The resulting structure is the following, where R₁, R₂ and R₃ are methylenic or oxymethylenic segments: The monomers were obtained by linking the dimer structure to an oxetane ring. These substituted oxetanes were polymerised by a boron trifluoride‐initiated cationic ring‐opening reaction to obtain the corresponding polymers. The polymerisation proceeds with high yields, in spite of the steric hindrance derived from the bulkiness of the side chain, and the presence of some functional groups in the molecule that compete against the cyclic ether for the nucleophilic attack at the propagating centre. A fraction of cyclic oligomer is obtained together with high molecular‐weight polyoxetane, as a result of back‐biting reactions during the polymerisation. Several systems with spacers of different length and parity were synthesised in order to analyse the influence of the nature of the spacer on the phase behaviour. The formation of mesophases was proved by means of differential scanning calorimetry, X‐ray diffraction and microscopic analysis. Most of the monomers form smectic structures at subambient temperatures. The polymers display a similar phase behaviour, although shifted to higher temperatures.     

Preparation of Block Copolymers with a Single Tg Based on Segments of Poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) and Polycarbonate of Bisphenol A

Summary: The synthesis and the properties of block copolymers based on PPO and PC segments are reported. Copolymers that have a multi‐block structure are synthesized by a polycondensation reaction that employs oligomeric PPO and PC diol terminated with phosgene or bischloroformate of bisphenol A. In the reaction scheme two steps are involved: first, the reaction of one of the oligomeric diols (PPO or PC) with the bischloroformate or phosgene; second, the oligomeric bischloroformate is reacted with the other diol. The molecular characteristics of the prepared samples are studied by SEC, ¹H and ¹³C NMR, and FT‐IR spectroscopy. The thermal and rheological properties and the thermal stability have also been investigated by means of DSC, rotational rheometry, and TGA, respectively. Polymers that have a single glass transition temperature are obtained if low‐molecular‐weight segments are used. From a rheological point of view, these materials show a remarkably lower melt viscosity compared with a PPO homopolymer that has a comparable average molecular weight.

Rheometric curves of PPO‐b‐PC (3) compared with a commercial PPO.     

Alpha‐Helix Self‐Assembly of Oligopeptides Originated From Beta‐Sheet Keratin

The structure and characterization of the oligopeptide crystals formed from the feather keratin solution obtained by superheated water treatment are reported. The FTIR spectra and ¹H and ¹³C solid‐state NMR results indicate that the peptides, arranged mostly in a beta‐sheet structure in feather, reorganize into a mainly alpha‐helix and less beta‐sheet mixed secondary structure, when self‐assemble from the solution at room temperature. MALDI‐ToF‐ToF spectra confirm that the most primary sequence with the mass 1884 come from the feather keratin 4, KRFA_CHICK of Gallus gallus. The largely preservation of all but cystine amino acid species and the increase of hydrophobic amino acids content in the oligopeptide crystals are proved by the amino acid analysis.     

Proton‐Conducting Properties of Acid‐Doped Poly(glycidyl methacrylate)‐1,2,4‐Triazole Systems

1,2,4‐triazole‐functional PGMA polymers have been synthesized and their anhydrous proton‐conducting properties were investigated after doping with phosphoric acid and triflic acid. PGMA was prepared by solution polymerization and then modified with 1H‐1,2,4‐triazole (Tri) and 3‐amino‐1,2,4‐triazole (ATri). FT‐IR, ¹³C NMR and elemental analysis verify the high immobilization of the triazoles in the polymer chain. Phosphoric‐acid‐doped polymers showed lower T_g and higher proton conductivities. PGMA‐Tri 4 H₃PO₄ showed a maximum water‐free proton conductivity of approximately 10^?2 S · cm^?1 while that of PGMA‐ATri 2 H₃PO₄ was 10^?3 S · cm^?1. The structure and dynamics of the polymers were explored by ¹H MAS and ¹³C CP‐MAS solid‐state NMR.

     

Ruthenium Ring‐Opening Metathesis Polymerization Catalysts Bearing o‐ Aryloxide‐N‐Heterocyclic Carbenes

A series of o‐aryloxide‐N‐heterocyclic carbene ruthenium complexes 2–4 is synthesized via sequential reactions of the o‐hydroxyaryl imidazolium proligands (2‐OH‐3,5‐^tBu₂C₆H₂)(R)(C₃H₃N₂)⁺Br^? (R = Me ( 1a ), ⁱPr ( 1b ), Mes ( 1c )) with Ag₂O and [(C₆H₆)RuCl₂]₂. All of the complexes are characterized by ¹H and ¹³C NMR spectroscopy, high‐resolution mass spectrometry (HRMS), and elemental analysis. The molecular structure of 2 is determined by single‐crystal X‐ray diffraction analysis. The ring‐opening metathesis polymerization (ROMP) of norbornene (NBE) with 2 – 4 is studied. Among them, complex 4 exhibits the highest activity and efficiency toward ROMP of NBE at 85 °C without any cocatalyst, and the resultant polymers have very high molecular weight (>10⁶ Da) and narrow molecular weight distributions. This complex can also efficiently catalyze the alternating copolymerization of NBE and cyclooctene.     

Star Polymers from Single‐Chain Cyclized/Knotted Nanoparticles as a Core

Star polymers are comprised of a spatially defined “core‐shell‐periphery” structure. Their unique properties render them for diverse applications. One of the central challenges in the synthesis of star polymers is the design of a multifunctional core with many reaction sites for the conjugation with presynthesized arms or the initiation of the growth of arms. In this paper, it is demonstrated that the single‐chain cyclized/knotted nanoparticles (SCKPs) with multiple vinyl functional groups can be synthesized by Cu⁰&Cu^II‐mediated homopolymerization of bisphenol A ethoxylate diacrylate. Furthermore, the SCKPs with multiple pendant vinyl groups are used as the core and uniform amphiphilic star poly(β‐amino ester)s with 17 high‐molecular‐weight arms are synthesized via a grafting‐onto approach. This facile approach opens new avenues for the design and preparation of novel star polymers.     

Enhanced Mechanical Properties of PET‐Based Thermoplastic Elastomers: Brittle–Ductile Transition via Micro Cross‐linking Technology

A novel micro cross‐linking technology is proposed to enhance the mechanical properties of poly(ethylene terephthalate) (PET)‐based thermoplasctic elastomers (TPEEs) whose molecular weights are difficultly increased via traditional synthetic technologies. It is found that the brittle fractures of TPEEs, usually observed in polymers with low molecular weights, can be converted into ductile form with the introduction of a certain fraction of 1,2,3,4‐butane tetracarboxylic acid as a cross‐linking agent. Unlike the traditional cross‐linking technologies, which usually cause the elastomers to suffer the deficiencies of extremely high stiffness, inherent weakness, and the inability to be efficiently reused, TPEEs still maintain their elastomeric characteristics well with the incorporation of micro cross‐linking structure and are endowed with a well‐defined microphase‐separated structure, excellent tensile properties, and the abilities to be melt‐processed and reused. This work offers a new guideline to improve the mechanical properties for polymers with relatively low molecular weights.