Pi‐conjugated chain extenders for the synthesis of optoelectronic segmented polyurethanes

The optical properties of mechanochromic materials change under mechanical stress. Segmented polyurethanes are elastomers composed of amorphous, saturated chain soft segments, and rigid pi‐conjugated hard domains. Within aggregates of hard domains pi–pi interactions may form and result in perturbation of the optoelectronic properties of the system. Disruption and restoration of these electronic interactions within the material may lead to observable mechanochromic response. A series of oligothiophene diols and diamines, as well as a naphthalene diimide diol, have been synthesized for incorporation into the hard domains of segmented polyurethanes and polyureas using long poly(tetramethylene oxide) chains as soft segments. The resulting polymers were evaluated to determine their extent of polymerization and their thermal stability. The optical properties of the materials were studied in solution and as thin films. Where possible the electrochemical properties of the polymers were also explored. The length of the soft segment chains in the segmented polyurethanes hindered electronic coupling of hard domains. Future work involving smaller, more solubilizing soft segments may allow for easier material characterization and mechanochromic response. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Synthesis and properties of polyurethanes bearing urethane moieties in the side chain

Polyurethanes bearing urethane groups in the side chains were prepared by the addition of isocyanates to the hydroxyl groups in poly(hydroxyurethane) prepared by the polyaddition of a bifunctional cyclic carbonate with 1,12‐diaminododecane. The urethanization proceeded quantitatively in the presence of a catalytic amount of di‐n‐butyltin dilaurate. The resulting polyurethane had a higher glass transition temperature than the original poly(hydroxyurethane), although its esterified product had a lower glass transition temperature. The urethanization with 3‐(triethoxysilyl)propyl isocyanate also proceeded effectively to afford both soluble and insoluble polymers, depending on the reaction conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3408–3414, 2007     

Phase morphology of hydrolysable polyurethanes derived from aqueous dispersions

Biodegradable polyurethanes are an interesting alternative to many applications that involve plastics since they can minimize environmental problems caused by the low rates of natural degradation of synthetic polymers. In addition, since waterborne polyurethanes are based on aqueous dispersions, they restrict the use of organic solvents during processing and application of the polymer, thus contributing furthermore to reduce environmental damage. In this work, aqueous anionic polyurethane dispersions (PUD) with tailorable susceptibility for hydrolysis were synthesized by progressively replacing polypropylene glycol (PPG) with a biodegradable polycaprolactone diol (PCL) as soft segments. The hard segments were formed by extending isophorone diisocyanate (IPDI) with hydrazine (HZ). Dimethylol propionic acid (DMPA) was used as ionic center and triethyl amine (TEA) as neutralizer. The degree of phase separation was evaluated mainly by infrared spectroscopy (FTIR) and small angle X-ray scattering (SAXS). The results indicated that phase separation between hard and soft segments of poly(ester-urethane) is more significant than that of poly(ether-urethane). Data obtained from SAXS experiments indicated that phase separation within soft domains can also be present in samples containing both polyester and polyether soft segments. Hydrolytic degradation of the polymers in buffer solution of pH 7.4 and alkaline solution was performed as an initial test. The results showed that the fraction of polyester soft segments in the polyurethanes can be used to tailor the susceptibility of the materials to hydrolytic attack. Polyurethanes having higher contents of polyester were more promptly hydrolytically degraded than polyurethanes containing only polyether segments.     

Synthesis and properties of liquid crystalline polyurethanes

Liquid crystalline polyurethanes were prepared from 4,4′-bis(2-hydroxyethoxy)biphenyl (BHBP) and 2,4-tolylene diisocyanate (TDI). The effect of partial replacement of BHBP by 25–75 mol % poly(oxytetramethylene) diol (PTMO, M _n = 250) on the liquid crystalline properties was studied. The BHBP/TDI/PTMO polyurethanes were obtained by one- and two-step polyaddition. The polyurethanes were investigated by DSC, polarizing microscopy, x-ray, and IR spectroscopy. The molecular weight distribution was determined by GPC. The morphology of the polymers was investigated by the SALS method. Thermogravimetric investigations of the polyurethanes were also performed. All polyurethanes containing BHBP units have liquid crystalline properties. Partial replacement of BHBP by PTMO-250 considerably changes the phase transition temperatures and the range of mesophase occurrence. More homogeneous polyurethanes were obtained, if the two-step polyaddition method was applied. The polyaddition method affects the phase transition temperatures. © 1993 John Wiley & Sons, Inc.     

Synthesis of phosphorus-containing polyurethanes without use of isocyanates

Phosphorus-containing polyurethanes were synthesized by reacting phosphonic acid diesters (RO)₂P(O)X (X = H, CH₃, Ph) with hydroxycarbamates. These phosphorus-containing polyurethanes were characterized by a combination of molecular-weight determination (GPC) and NMR spectroscopy. The thermal stability of the polymers was evaluated by a combination of TGA and DTA techniques. These polymers are readily soluble in highly polar solvents like DMF and DMSO. The phosphorus-containing polyurethanes are water soluble. © 1996 John Wiley & Sons, Inc.     

Thermal stability enhancement of polyurethanes by surface treatment

Both oxidation and methoxymethylation of the surfaces of a series of MDI (methylene diphenyl isocyanate) and TDI (toluene diisocyanate) polyether and polyester soft segment 1–4 butanediol polyurethanes result in increased thermal stability as measured by TG. Explosive loss of mass above the hard segment melting temperature suggests that the diffusion of the dissociated diisocyanate moiety is hindered at lower temperatures. Thus suppression of the depolycondensation reaction by chemical blockage of the surface may result in a material with an increased service life at use temperatures as thermal stability of a polyurethane may depend upon the low diffusivity of its diisocyanate comonomer. The effect of vacuum, oxygen and water vapor on the kinetics of mass-loss of several of the polyurethanes is presented. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Synthesis of narrow‐polydispersity degradable dendronized aliphatic polyesters

The divergent dendronization of an ?‐caprolactone‐based polymer has been performed to provide access to dendronized polymers with sufficient biocompatibility and degradability for use as drug‐delivery scaffolds. The synthesis was performed through the tin(II) 2‐ethylhexanoate‐catalyzed polymerization of a γ‐functionalized ?‐caprolactone monomer, followed by the divergent growth of pendant polyester dendrons at each repeat unit. The resulting dendronized polymers were obtained up to the fourth generation with molecular weights as high as 80,000 Da and with polydispersities between 1.11 and 1.22. The fourth‐generation hydroxyl‐terminated dendronized polymer was degradable under a variety of aqueous conditions. A comparison of the dendronization approach with a procedure involving the ring‐opening polymerization of a second‐generation dendritic macromonomer reveals that the former procedure is best suited for the preparation of this family of dendronized polyesters because it requires shorter reaction times and affords materials with higher degrees of polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3563–3578, 2004     

Evaluation of tg data of htpb-based polyurethanes

Thermogravimetry (TG) was used to provide some new information on some polybutadiene-based polyurethanes. The results showed two main mass decomposition stages, from 230 to 564°C. The first mass loss stages were used to quantify the hard segments of the polymers. The results correlated well with the ASTM methodology. In addition, two 2³ factorial design studies were applied to evaluate the importance of some selected factors on the TG results of the polyurethanes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of a new polymer surface bearing grafted azo polymer chains

Azobenzene, a photosensitive chromophore that undergoes photoinduced and thermal cis–trans isomerization, can be applied in a nonlinear optical field. {4′‐[(Hydroxy)ethyl]amino}‐4‐nitroazobenzene (disperse red 1) corresponds to one of these azo compounds, which can be grafted to a polymer chain as a part of the main chain, as a dangling group, or onto the polymer surface. In the last case, disperse red 1 is transformed into an acrylic monomer and then grafted onto a polypropylene surface modified with a cold carbon dioxide‐plasma treatment. A method is proposed for quantifying the radicals formed during the plasma treatment and, consequently, for optimizing the grafting reaction. The best conditions (the nature of the solvent, temperature, monomer concentration, and duration) are given. Both IR and Raman spectroscopies were used as efficient techniques for grafting characterization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3052–3061, 2001     

Synthesis of iron-containing polymers with azo dyes in the backbones or side chains

The synthesis of cationic cyclopentadienyliron-containing polymers with pendent azobenzene chromophores was accomplished via metal-mediated nucleophilic aromatic substitution reactions. All of the desired polymers were isolated as vibrantly coloured materials and displayed excellent solubility in polar aprotic solvents. Cationic and neutral cyclopentadienyliron polymers incorporating azo dyes in the backbone were also prepared. Reactions of azo dyes with dichlorobenzene complexes allowed for the isolation of cationic cyclopentdienyliron (CpFe₊) complexes with azo dye chromophores. These complexes were then reacted with 1,1′-ferrocenedicarbonyl chloride to produce the trimetallic monomers with terminal chloro groups. These monomers contained two pendent CpFe₊ cations and a neutral iron moiety in the backbone. Nucleophilic substitution reactions of these monomers with oxygen and sulfur containing dinucleophiles gave rise to a new class of polymeric materials. The pendent CpFe₊ moieties could also be cleaved from the polymer backbones using photolysis to afford novel ferrocene based polymers. The UV-vis spectra of the organoiron monomers and polymers display similar wavelength maxima however incorporating azobenzene chromophores with electron-withdrawing substituent into the polymer chains resulted in bathochromic shifts of the λ_max values.     

TGA/FTIR studies of segmented aliphatic polyurethanes and their nanocomposites prepared with commercial montmorillonites

Nanocomposites prepared with segmented polyurethane (SPU) and commercially available nanoclays (Cloisite™ Na⁺, Cloisite™ 15A, Cloisite™ 30B) were studied using thermogravimetric analysis coupled with Fourier Transform Infrared Spectroscopy (TGA/FTIR). The results showed that the thermal degradation of unfilled SPU and the 4, 6 and 10 wt% hand mixed nanocomposites occurred in two stages being the first due to degradation of hard segments and the second due to the degradation of soft segments. It was also found that the thermal stability of these nanocomposites was not improved by increasing nanoclay concentration except for SPU/Cloisite™ 15A nanocomposites were a 40 °C increase was observed. In a similar manner, FTIR spectra of the evolved gases obtained after the thermal degradation of these nanocomposites were qualitatively similar to the unfilled polymer except in those containing Cloisite™ 30B where isocyanate absorptions were detected. In contrast, SPU/Cloisite™ 30B nanocomposites prepared by in-situ polymerization, exhibited higher thermal stability than the corresponding hand mixed nanocomposites. In addition, these nanocomposites exhibited the presence of carbon dioxide in the evolved gases during its second degradation stage which was not observed in the hand mixed nanocomposites. In this case, it can be said that the presence of clays in the nanocomposites has a significant effect on the thermal degradation pathways.     

Synthesis and characterization of water-soluble PEGylated lignin-based polymers by macromolecular azo coupling reaction

Water-soluble PEGylated lignin polymers were efficiently synthesized by macromolecular azo coupling reaction between alkali lignin and PEG based macromolecular diazonium salts in alkaline water.     

Synthesis and properties of bio‐based polyurethanes bearing hydroxy groups derived from alditols

Four kinds of bio‐based polyurethanes bearing hydroxy groups in the pendants were synthesized by the polyaddition of D ‐mannitol‐ and D,L ‐erythritol‐derived diols (1,2:5,6‐di‐O‐isopropylidene‐D ‐mannitol and 1,2‐O‐isopropylidene‐D,L ‐erythritol) with hexamethylene diisocyanate and methyl (S)‐2,6‐diisocyanatohexanoate and the subsequent deprotection of the isopropylidene groups. They were hydrolyzed much more quickly than the corresponding protected polyurethanes at 50 °C and pH 7.0, although their hydrolytic degradation rate was lower than that of polyurethanes with saccharic and glucuronic lactone groups, which had been reported in our previous articles. The introduction of D ‐mannitol units to the polyether‐polyurethanes containing poly(oxytetramethylene) glycol units also enhanced their hydrolyzibility. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Divergent synthesis and self‐assembly of amphiphilic polymeric dendrons with selective degradable linkages

Enhancing the structural complexity and functionality of the building blocks allows the construction of supramolecular assemblies. In this work, we demonstrate a strategy for the design and synthesis of complex macromolecular architectures. We use atom transfer radical polymerization to produce well‐defined polymers with telechelic end‐group functionality, and “click” them together to form functional 3rd generation dendrons, and incorporated degradable linkages and certain functionality at the polymer chain‐ends of each generation. The 3rd generation polymeric dendrons consisted of homopolymer polystyrene (PSTY) with either four solketals or eight alcohols, diblock PSTY and poly(t‐butyl acrylate), and amphiphilic diblock. The peripheral ends consisting of alcohols create functionalization points for further chemical modification or chemical coupling and the cleavable linkages between the 2nd and 3rd generations all provide the first steps toward smart nanostructures. Importantly, we can synthesize these dendrons in pure form. The self‐assembly of the amphiphilic dendrons (the inner and outer generations consisting of PSTY and polyacrylic acid, respectively) in water produced micelles of uniform size with an aggregation number of 43 dendrons per micelle. The size of the micelles was small (D_H =20.7 nm) and comparable to the size found by transmission electron microscopy (14–18 nm). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1533–1547, 2008     

Effect of crosslinking on the photoinduced orientation of azo groups in thin polymer films

A series of amorphous copolymers containing disperse red 1 and crosslinkable acrylic groups were prepared. The crosslinked polymers were prepared in thin films by thermal polymerization of the acrylic groups in the copolymers. The orientation induced by irradiation with a linearly polarized laser was measured as birefringence at several temperatures, and the effect of crosslinking on the photoinduced orientation was investigated. Crosslinking enhanced the stability of the photoinduced birefringence. In particular, crosslinking helped to maintain the birefringence both at high temperatures and after the linearly polarized laser was turned off. The birefringence dynamics was analyzed with biexponential curve fitting. Crosslinking influenced not only the birefringence levels but also its rate of growth. The growth rate of the photoinduced birefringence decreased by crosslinking, whereas the relaxation was not significantly affected. Although crosslinking restrained the mobility of the azo chromophores, a certain fraction could orient or move randomly even in highly crosslinked polymer networks. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1686–1696, 2001     

Synthesis of novel moisture‐curable polyurethanes end‐capped with trialkoxysilane and their application to one‐component adhesives

Novel silane endcappers and novel polyurethanes end‐capped with trimethoxysilane (silylated polyurethanes) were developed as water‐curable materials in which the curing reaction occurred under humid conditions in the presence of dioctyltin diversatate as a curing catalyst. A variety of amine‐terminated trimethoxysilane compounds were synthesized by the Michael addition reaction of commercially available 3‐aminopropyltrimethoxysilane with acrylates, and the resulting silane endcappers were used to react with isocyanate‐terminated polyurethanes, providing the silylated polyurethanes. The moisture‐curable silylated polyurethanes were used for the preparation of novel one‐component and solvent‐free adhesives. The evaluated properties were the curing speed, the tensile shear bond strength, and the adherence to some substrates. The longer alkyl chains of the silane endcappers derived from various acrylates led to a slower curing speed, lower tensile strength at break, and longer elongation at break of the silylated polyurethanes. The tensile shear bond strength of the silylated polyurethane‐based adhesive decreased with decreasing the trimethoxysilane end‐capping ratio, whereas an increase in the adherence was observed. The adherence to the acrylic substrate was improved by changes in the main‐chain structure of the polyurethane based on the composition of poly(propylene oxide) and poly(ethylene oxide). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2689–2704, 2007