Thermally stable polyureas and poly(urea‐imide)s containing zinc and nickel napthtrien complexes

Two new napthtrien metal complexes, MNapth₂trien; where M = Zn and Ni, were synthesized and used for the synthesis of metal‐containing polyureas and poly(urea‐imide)s. MNapth₂trien underwent polymerization reaction with two diisocyanates, namely, 4,4′‐diphenylmethane diisocyanate and isophorone diisocyanate to yield polyureas. Poly(urea‐imide)s were obtained by the synthesis of metal‐containing isocyanate‐terminated polyurea prepolymers from the reaction between MNapth₂trien and excess diisocyanates, which could then undergo further reaction with different dianhydrides. The dianhydrides used were pyromellitic dianhydride and benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride. The polymers were characterized by infrared, nuclear magnetic resonance, elemental analysis, X‐ray diffraction, solubility, and viscosity. Glass transition temperature of the polymers was obtained from differential scanning calorimetry and dynamic mechanical thermal analysis. Thermal stability of polymers was studied by thermogravimetric analysis in air. It was found that the resulting metal‐containing polymers exhibited good thermal stability. Initial decomposition temperatures of the polymers depend on the amount of MNapth₂trien in the polymer composition. Char yields of metal‐containing poly(urea‐imide)s are higher than those of metal‐containing polyureas. Most metal‐containing polymers show good solubility in organic solvents. Shore D hardness test indicates that metal‐containing poly(urea‐imide)s are hard materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Photochemistry and photophysics of poly(organophosphazenes) and related compounds: A review. I. Monomolecular processes

In this review we report an outline of the synthesis, UV-Vis spectral characterization, and light-induced reactivity in monomolecular processes of poly(organophosphazenes). The photoreactivity of phosphazene polymers, both in solution and in solid state, strongly depends on the nature of the chromophore attached to the phosphorus atoms of the inorganic –P=N – backbone. In fact, polyphosphazenes not bearing mobile hydrogen atoms in the side moieties undergo, in the first excited singlet state, homolytic eleavage of the bonds connecting the substituents to the inorganic backbone: free radicals of the substituents and phosphazene macroradicals are formed. Moreover, for polyphosphazenes containing labile hydrogens in the side groups, C–H bond scission takes place with the formation of free hydrogens and radicals located in the phosphazene substituents. From these species degradation or crosslinking of the macromolecules will follow according to the experimental conditions.This review is in three parts. Parts II and III will appear sequentially in the next two issues of this journal.     

A Synthetic Approach to Star‐Like Polymers of Styrene and Butyl Acrylate by Linking Reactions using Functionalized Methacrylates

Summary: Coupling reactions between terminal functionalized polymer chains were chosen for the synthesis of star‐like polymers consisting of polystyrene and polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] arms. For the preparation of terminal functionalized polymer chains a side reaction of the 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) mediated free radical polymerization of methacrylates could be used successfully to convert TEMPO terminated polymers into end functionalized polymers. The number of functionalized monomer units attached to the polymer chain is directly related to the TEMPO concentration during this reaction. Different polystyrenes and polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] block copolymers were functionalized with a variable number of epoxide and alcohol groups at the chain end. For the determination of the optimal reaction parameters for the coupling reactions between these polymer chains, epoxy functionalized polystyrenes were converted with hydroxy functionalized polystyrenes under basic and acidic conditions. By activation with sodium hydride or boron trifluoride star‐like polymers were synthesized under mild conditions. The transfer of the reaction conditions to coupling reactions between end functionalized polystyrene‐block‐poly[styrene‐co‐(butyl acrylate)] copolymers showed that star‐like polymers with more than 12 arms were formed using boron trifluoride as activating agent.

     

Metallo-Supramolecular Polymerization: A Route to Easy-To-Process Organic/Inorganic Hybrid Materials

The self-assembly polymerization of ditopic macromolecules via metal–ligand binding is a facile route for the preparation of metallo-supramolecular polymers (MSPs). We herein review our recent work focused on the synthesis and investigation of metallo-supramolecular polymers based on 2,6-bis(1′-methylbenzimidazolyl)pyridine endcapped poly(p-phenylene ethynylene) and poly(p-xylene) macromonomers. These materials are readily solution-processable and display appreciable mechanical properties as well as other attractive properties such as specific opto/electrical functions or high thermal stability. Our work illustrates that metallosupramolecular polymerization offers an attractive approach to assemble high-molecular-weight macromolecules from well-defined, easy to process precursors. Variation of the ditopic ligands and metal ions allows one to easily tailor the desired properties. This paper is dedicated to Professor Ian Manners and his scientific accomplishments.     

Review on polyphosphazenes-based materials for bone and skeleton tissue engineering

The skeleton performs motley of functions. Defected bones and metameric loss of bone are often resulted due to innate abnormalities and accidental injuries. An assessment is made on the diversity of chemistry of phosphazene with an inflection on new developments and their importance in tissue engineering. Tissue engineering mostly uses polymers that can biodegrade in porous/permeable scaffolds form for treating damaged tissues and skeleton. Demand of these polymers is increasing as timely substrates for tissue regeneration in contrast to the mostly used polyethylene terephalate, polyorthoesters, and poly(α-amino acids). Polyphosphazenes as biodegradable polymers have great potential for applications of tissue engineering. Due to biodegradability of P–N backbone, vast diversity of structure and high functional density polyphosphazenes provides many advantages for the formation of biologically compatible macromolecules. However, the nature of the side group determines the degradation ability of such polymers. These biodegradable polymers (polyphosphazenes) provide harmless and pH neutral substances because phosphates and ammonia have high buffer capacity. This review article focuses on the biocompatible polyphosphazenes and their utilization as regeneration of tissues, skeleton, and bones with a particular focus on materials that contains only polyphosphazenes, blends of polyphosphazene, and composites made from polyphosphazene.     

Synthesis of functional π-conjugated polymers from aromatic acetylenes

Because of their unique structures and properties, π-conjugated polymers have attracted the attention of scientists and engineers. The authors have studied the synthesis of two kinds of π-conjugated poly(aromatic acetylene)s, i.e. poly(arylacetylene)s and poly(aryleneethynylene)s with the aim of obtaining new polymers having novel functions or higher performances. This review mainly concerns the authors' results, as follows: first, we describe the synthesis and properties of achiral poly(arylacetylene)s, containing trimethylsilyl groups, oligodimethylsiloxanyl groups, dendritic groups, and glavinoxyl groups, for application as oxygen permselective membrane materials. Their self-membrane-forming abilities and high oxygen permeabilities are presented. Second, the synthesis by asymmetric-induced polymerization of chiral poly(arylacetylene)s having both a main-chain chirality and chiral pendant groups and their application as optical resolution membranes are described. Third, two new synthetic methods for preparing chiral helical poly(phenylacetylene)s without the coexistence of any other chiral moieties are presented. One is helix-sense-selective addition polymerization and the other is in situ removal of chiral pendant groups from membranes of poly(arylacetylene)s that also contain a main-chain chirality. The chiral helical poly(arylacetylene)s were tested as optical resolution membranes. The chiral and achiral poly(arylacetylene)s were synthesized by addition polymerization using metathesis catalysts or rhodium complexes. Finally, the synthesis of regiospecific poly(aryleneethynylene)s bearing stable radicals by the polycondensation of bromoethynylanthracene derivatives using a Pd(0) complex is described. The magnetization and the static magnetic susceptibility of the polyradicals are explained.     

Novel poly(arylene ethynylene) derivatives containing main chain triphenylamine and pendent quinoxaline moieties: synthesis and elementary characterization

BACKGROUND: Various poly(arylene ethynylene)s (PAEs) have been prepared and applied as molecular wires, in sensors, in nonlinear optics and as electroluminescent materials. But, to our knowledge, there has been no attention paid to the investigation of conjugated PAEs containing both triarylamine and quinoxaline groups. The influence imparted by the introduction of triarylamine and quinoxaline on the photophysical and electrochemical properties of PAEs is of interest. RESULTS: Two kinds of novel PAE derivatives, with electron‐donating triphenylamine groups in the backbone and electron‐accepting pendent quinoxaline moieties and bearing side chains of different lengths, were successfully synthesized with the Sonogashira coupling reaction. These polymers are soluble in common organic solvents and exhibit good film‐forming ability and thermal stability. UV‐visible investigations indicate that the ground states of these materials are unaffected by the polarity of their medium. An efficient intramolecular charge transfer effect is observed from an investigation of their photoluminescence properties in different solvents. Cyclic voltammetry study reveals that these polymers possess relatively high highest occupied molecular orbital levels due to the incorporation of triphenylamine segments into the polymer backbones. CONCLUSION: Primary characterization of these novel PAE derivatives shows that they might serve as potential active materials in optoelectronic devices. Copyright © 2009 Society of Chemical Industry     

From Rings to Polymers

A short review of the origins and development of my research program at the University of Vermont in the area of inorganic polymers is presented. The topics include the discovery of a class of hybrid polymers and copolymers in which an inorganic ring such as a cyclophosphazene or cycloborazine system is a substituent on a carbon polymer chain. The subsequent elucidation of the electronic and chemical reactivity factors which control the formation of these materials allowed for design of successive generations of improved materials. Additional topic includes work in polyphosphazenes which have substituents with exploitable organic functionality.     

Preparation and Performance of Poly(Lactic Acid)-γ-Cyclodextrin Inclusion Complex-Poly(Lactic Acid) Multibranched Polymers by the Reactive Extrusion Process

The poly(lactic acid)-γ-cyclodextrin inclusion complex-poly(lactic acid) multibranched polymers were prepared by reactive extrusion process with L-lactide as raw material, stannous octoate as catalyst and the carboxyl poly(lactic acid)-γ-cyclodextrin inclusion compound as cores prepared by ultrasonic coprecipitation and carboxylation reaction. It was shown that the comprehensive performance of poly(lactic acid)-γ-cyclodextrin inclusion complex-poly(lactic acid) had been significantly improved compared with liner poly(lactic acid) by the study of structure and properties. Thus, the novel poly(lactic acid)-γ-cyclodextrin inclusion complex-poly(lactic acid) multibranched polymers have a potential use in biomedical materials. This study provided a simple and feasible preparation method for improving the performance of poly(lactic acid).     

Origin of the methylene bonds in poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene] prepared according to Gilch's method: novel applications

Impurities containing methylene bridges between 2‐((2′‐ethylhexyl)oxy)‐5‐methoxy‐benzene molecules are inevitably formed during the synthesis of 1,4‐bis(chloromethyl)‐2‐((2′‐ethylhexyl)oxy)‐5‐methoxy‐benzene, the monomer used in the preparation of poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV), but they can be removed by double recrystallization of the monomer prior to polymerization. When impurities containing methylene bridges participate in a Gilch polymerization, the methylene bonds formed in the main chains are prone to break at 200 °C, that is, at least 150 °C below the major degradation temperature of defect‐free MEH‐PPV. Interestingly, the thermal treatment used to break the methylene bonds present reduces the chain aggregation of MEH‐PPV during film formation and induces its blends with poly(2,3‐diphenyl‐5‐octyl‐p‐phenylene‐vinylene) (DPO‐PPV) to form a morphology similar to that of block copolymers. Both significantly enhance the luminescence properties. Copyright © 2006 Society of Chemical Industry