Synthesis and photo-controllable thermosensitivity of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) terminated with dimethylaminochalcone unit

Poly(N-isopropylacrylamide) terminated with dimethylaminochalcone unit (DMAC-terminated PNIPAM) were prepared by reversible addition-fragmentation chain transfer polymerization using dimethylaminochalcone-functionalized trithiocarbonate (TTC-DMAC) as chain transfer agent. Photodimerization of DMAC-terminated PNIPAM was confirmed by UV-Vis, fluorescence and GPC measurements. The lower critical solution temperature (LCST) of DMAC-terminated PNIPAM first increases and then decreases with increasing molecular weight. When subjected to 365 nm UV irradiation, a large increase of the LCST of DMAC-terminated PNIPAM has been observed especially in the polymer with low molecular weight. Furthermore, the LCST increases with increasing time of 365 nm UV irradiation, which shows photo-controllable thermosensitivity of DMAC-terminated PNIPAM.     

The degradation of an azo dye in a batch slurry photocatalytic reactor

The photocatalytic degradation of a commercial azo-reactive textile dye, Remazol Red F-3B, has been investigated in a batch slurry reactor using semiconductor catalysts like, ZnO and TiO₂, and two UV sources emitting mainly at 254 and 365 nm. Non-irradiated catalysts and non-catalyzed UV irradiation have negligible effect on the dye degradation. Initial pH, dye concentration, light power and catalyst loading as well as the catalyst type and UV wavelength are considered as process variables. The results showed that decolorization and TOC removal efficiencies of ZnO are higher under 365 nm UV. On the other hand, when two photocatalysts are compared, the decolorization performance of ZnO is higher than TiO₂ under 365 nm UV_, while TiO₂ performs better under 254 nm UV. Furthermore, from the TOC removal point, TiO₂ performs better than ZnO irrespective of the UV wavelength. TiO₂ irradiated under 254 nm UV degrades successfully both benzene and naphthalene derivatives.     

New telechelic polymers and sequential copolymers by polyfunctional initiator transfer agents (inifers)

Summary The Kennedy-Smith plot routinely used for the characterization of end-reactive (telechelic) polyisobutylenes has been recast to increase its accuracy and thus to increase its diagnostic value for the compositional analysis of telechelic polymers containing chromophores. A detailed error estimation is given. The plotting method and error limits are shown for representative mono-, di-, and tri-ended telechelic polyisobutylenes.     

Photolysis of poly(benzyl methacrylate)s and poly(benzyl acrylate)s in solution and films

Methacrylate and acrylate copolymers containing benzyl or 1‐phenylethyl groups and their monomeric model compounds were irradiated with a 254‐nm light in CH₂Cl₂ and solid films. Low molecular weight and polymeric products were analyzed by gas chromatography (GC) and NMR spectroscopy, respectively, and main‐chain scission efficiencies were determined by gel permeation chromatography (GPC). The results indicate that the ester bond cleavage in the side chain produces alkyl radicals in the main chain, leading to main‐chain scission and crosslinking. The higher stability of tertiary alkyl radicals formed in methacrylate polymers lead to the predominant main‐chain scission in solution. On the other hand, acrylate polymers were less susceptible to photodegradation. The degradabilities of the polymer films reflected those of the polymer solutions, although crosslinking preferentially occurred. The distinct effect of oxygen on the degradation was also observed in solution and films. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2227–2236, 2001     

New telechelic polymers and sequential copolymers by polyfunctional initiator transfer agents (inifers)

Summary Three-arm star polyisobutylenes carrying tert.-chlorine end groups and a phenyl ring at the center of the star (see formula II in the Introduction) have been prepared by a continuous polymerization process. Thus into a stirred glass reactor were fed continuously a mixed feed of monomer plus trinifer (TCC) and a separate feed of BCl₃ coinitiator in methyl chloride solvent at –40°C, and the product plus unreacted ingredients were removed continuously. Stationary conditions were maintained by keeping the rates of input and output (i.e., volumes) equal and constant. After a short induction phase (2–3 residence times) telechelic polymers of essentially theoretical number average end functionalities (¯F_n=3.0+0.1), close to theoretical molecular weights (¯M_n) and molecular weight distributions were obtained. The polymerization kinetics are discussed and compared to that of an earlier semicontinuous process used for the routine synthesis of telechelic polyisobutylenes.     

Living carbocationic polymerization of isobutylene by tert-amyl alcohol/BCl3/1-methyl-2-pyrrolidinone initiating system

1-Methyl-2-pyrrolidinone has been investigated, for the first time, as an efficient electronpair donor in conjunction with tert-amyl alcohol and BCl₃ in CH₂Cl₂ diluent at ?40°C for the living polymerization of isobutylene. The use of this new monofunctional initiator -trans fer (minifer) system has led to the synthesis of low molecular weight, living (near-monodisperse) polyisobutylenes carrying “ethyl” head group and “tert-chloro” end group (asymmetric telechelic polyisobutylenes). The nature of these groups was confirmed by ¹H-NMR spectroscopy. The living nature of the α-ethyl-ω-(tert-chloro)polyisobutylenes has been demonstrated by a linear plot, passing through the origin, of number-average molecular weight (M?_n) vs. the amount of polymer formed (W_p) and a horizontal N (number of polyisobutylene molecules) vs. W_p plot. These results are further substantiated by gel permeation chromatography data of these polymers, and the molecular weight distributions of these polymers are narrow (low M?_w/M?_n = 1.1–1.2). The initiating efficiencies (I_eff) are close to 100% with this system. Dehydrochlorination of the prepolymer has yielded an isopropylidene (exo-olefin) end group. Structure of the end group in the resulting polymer, α-ethyl-ω-(isopropenyl)polyisobutylene, was confirmed by FTIR spectroscopy.     

Application of a new unimolecular initiator in the synthesis of (α,ω) ketone functionalized polystyrene in nitroxide mediated polymerization

The ketone functionalized N‐alkoxyamine, a derivative of 4‐oxo‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl (4‐oxo‐TEMPO) was synthesized and applied as an initiator in the nitroxide mediated polymerization of styrene in bulk at 120°C. In the presence of the prepared initiator: 1‐phenyl‐1‐(4‐oxo‐2,2,6,6‐tetramethylpiperidinoxy)propanone polymers with well‐defined molecular weight were obtained. By contrast, when an accelerator such as acetic anhydride (10%) was added to the system, lower control of polymerization was observed. Additionally, the functionality of polymers was evaluated on the basis of a quantitative investigation of UV–visible spectra of 2,4‐dinitrophenylhydrazone formed from the polymers and the synthesized initiator. The UV–vis spectra of the hydrazone derivatives obtained from polymers by means of 2,4‐dinitrophenylhydrazone made it possible to confirm that the polymers prepared in the presence of the ketone functionalized N‐alkoxyamine retain the ketone functionality on the polymer chain. The functionality for the obtained polymers exceeded 1 significantly. The obtained (α, ω) telechelic polymers are of great importance in the synthesis of new biohybrid materials such as bioconjugates with proteins or peptides as well as new polymer nanostructures. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Molecular weight distribution and rheological properties of polyisobutylene solutions

The molecular weight distribution of a series of polyisobutylenes was determined using osmotic pressure measurements, gel permeation chromatography, and intrinsic viscosity. All of the polymers except for one, a blend of the highest and lowest molecular weight constituents, had similar moderate molecular weight distributions. The “extended chain length” method of calibrating the gel permeation chromatograph for polyisobutylenes was found to be effective. Steady state and transient shear stresses and normal stresses were measured on 5% decalin solutions of these polymers. The zero shear viscosity increased with the 3.3 power of molecular weight, and the zero shear normal stress coefficient (σ₁₁ ? σ₂₂)/Γ² varied with the 7.5 power. Relative elastic memory as measured by (σ₁₁ ? σ₂₂)/σ₁₂ or stress relaxation increased with increasing molecular weight (and at constant number- or weight-average molecular weight) with breadth of distribution. Stress overshoot also correlated with this tendency.     

More insight into tandem ROMP and ADMET polymerization for yielding reactive long-chain highly branched polymers and their transformation to functional polymer nanoparticles

Tandem chain transfer ring-opening metathesis polymerization (ROMP-CT) and acyclic diene metathesis (ADMET) polymerization were carried out in a controlled one-pot procedure, and behaved noticeable differences in polymerization of monomers by different ruthenium catalysts, whereas there indeed had been two distinctly polymerization stages. In the first one, ROMP-CT of functional monomers was conducted in the presence of a symmetrical multi-olefin as chain transfer agent within various reaction time scales, yielding linear telechelic polymers. Next, ADMET polymerization of telechelic polymers was performed and generated a series of reactive long-chain highly branched polymers (LCHBPs) with acrylate and/or azobenzene groups having molecular weights of 8.5–47.9 kDa under varied conditions. LCHBPs were fully characterized by several techniques, and interestingly, UV–vis analysis displayed the specific peak at 278 nm, which offered a new evidence for the existence of internal acrylate structure on the LCHBP backbone, and supported the highly branched architecture of polymers. LCHBP containing a number of pendent acrylate groups was readily converted, by thiol-Michael addition click reaction, to novel thiol-functionalized intra-molecular crosslinked unimolecular polymer nanoparticles with diameter of 40–60 nm, which provided a facile method for post-functionalization of branched polymers.     

Eugenol-based non-isocyanate polyurethane and polythiourethane

Global resource crisis and severe environmental problems have compelled world scientists to develop sustainable and green chemical materials. In this work, eugenol, a cheap and renewable phenol derivative found in cloves, is successfully utilized to prepare hydroxyl non-isocyanate polyurethanes (HNIPU), with number-average molecular weights (M _n) from several to dozens of kilodaltons. First, a diepoxide intermediate is synthesized through three steps in 43.9% total yield. Second, this diepoxide reacts with CO₂ at atmospheric pressure to form an intermediate possessing two cyclic carbonate groups in moderate yield. Third, the cyclic carbonate-containing intermediate further reacts, with compounds such as 4,4′-diaminodiphenyl methane, 1,6-hexanediamine and p-xylene diamine by nucleophilic ring-opening to obtain the desired HNIPUs. Furthermore, the diepoxide intermediate and CS₂ undergo addition reaction to form cyclic dithiocarbonate intermediate that further reacts with 4,4′-diaminodiphenyl methane to afford polythiourethane (PTU). The resulting PTU contains mercapto groups in its each unit. Number-average molecular weight of PTU is Mn 2800 Da. Finally, crosslinking reactions occur between the mercapto groups of PTU and crosslinkers (1,6-hexanediol acrylate and/or cardanol) by thiol-ene reactions under UV (λ = 365 nm) irradiation conditions, leading to their corresponding crosslinked polymers. The optimized conditions for preparing crosslinked polymers include: PTU/cardanol/1,6-hexanediol acrylate = 1:1:0.05 (mass ratio), and UV irradiation time for 30 min. This work is expected to expand applications of eugenol and to provide a new route to NIPUs and PTUs using various diamines.     

Preparation of partially fluorinated aryl/alkyl vinylene ether polymers

A new class of partially fluorinated alternating aryl/alkyl vinylene ether (FAVE) polymers were prepared from addition polymerization of aryl trifluorovinyl ethers (TFVEs) with 1,4‐butanediol or 4‐hydroxybenzyl alcohol. Monodisperse FAVE telechelic polymers were also prepared possessing latent thermal reactivity which afforded chain‐extended perfluorocyclobutyl (PFCB) aryl ethers via step‐growth [2 + 2] cyclodimerization of the aryl TFVEs. Both linear and PFCB chain‐extended FAVE polymers produced thermally robust, optically transparent, flexible spin‐cast films. The FAVE polymers and their telechelic polymers were characterized using ¹⁹F NMR and ¹H NMR complemented with molecular weight analysis using gel permeation chromatography and thermal analysis employing differential scanning calorimetry and thermogravimetry. © 2013 Society of Chemical Industry     

Reversible addition-fragmentation chain transfer polymerization of 7-(4-(acryloyloxy)butoxy)coumarin

The light sensitive vinyl monomer with coumarin unit, 7-(4-(acryloyloxy)butoxy)coumarin (7AC), was synthesized. The reversible addition-fragmentation chain transfer (RAFT) polymerization of 7AC, initiated by 2,2′-azobisisobutyronitrile (AIBN), was carried out using 2-cyanoprop-2-yl dithiobenzoate (CPDB) as a RAFT agent in N,N-dimethylformamide (DMF) solution. The kinetics exhibited first-order relationship with respect to the monomer concentration. The molecular weight of the polymer increased linearly with the monomer conversion. The chain extension of poly(7-(4-(acryloyloxy)butoxy)coumarin) (P7AC) using styrene (St) as the second monomer demonstrated that the obtained polymers were almost “living”. The fluorescence intensity of P7AC increased with the molecular weight of P7AC and was stronger than that of the monomer. The obtained polymer had strong ultraviolet (UV) absorption at 322 nm. The molecular weights of the polymer had no effect on its ultraviolet absorption intensity. The coumarin structure existing in P7AC underwent [2 + 2] cycloaddition reaction (photodimerization) under UV irradiation in tetrahydrofuran (THF) solution, which can be further used to prepare small particles from the single polymer.     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (inifers)

Summary The synthesis and quantitative end group characterization of anisole-terminated polyisobutylenes are described. These new telechelic prepolymers consist of a linear or a three-arm star polyisobutylene (PIB) carrying exactly two or three anisole termini, respectively. The synthesis was accomplished by quantitative Friedel-Crafts alkylation of anisole by olefin-and/ortert.-chloro-telechelic PIB's, and characterization involved¹H NMR and UV spectroscopy, GPC and osmometry. According to charcterization research the linear and three-arm star anisole-terminated polyisobutylenes have the following structures:     

Preparation and reactions of polymers having 1-aroyl-2-(3-pyridyl)ethylenes as photosensitive groups

The reactions of 1-aroyl-2-(3-pyridyl)ethylenes (APE) with polychloromethylstyrene (PCMS) yield polymeric systems which undergo rapid crosslinking upon short exposure to ultraviolet (UV) light. The photochemical reaction of polymers as well as model compounds was followed by the measurement of UV absorption of APE and the analysis of extinction coefficient difference (ED) diagrams.¹     

Photodegradation of Natural Organic Matter in Water with UV Irradiation at 185 and 254 nm: Importance of Hydrodynamic Conditions on the Decomposition Rate

Abstract

The kinetic investigation of photodegradation of the natural organic matter (NOM) in natural lake water was conducted using two low‐pressure mercury lamps of the same nominal power: a) with suprasil quartz envelope emitting at both wavelengths ?254 nm and 185 nm (hereafter VUV); b) with standard quartz envelope emitting only at 254 nm (hereafter UV). In comparison to the UV process, the addition of 185 nm irradiation (VUV process) increased the degradation rate ten‐fold overall at lower and seventeen‐fold at higher Reynolds numbers, respectively. The hydrodynamic characteristics of the photoreactor are of crucial importance for total energy efficiency for VUV processes.     

Ferrocene-Decorated Hyperbranched Poly(aroxycarbonylphenylene)s: Synthesis, Light Refraction, Photopatterning and Precursor to Magnetic Ceramics

Ferrocene-decorated hyperbranched poly[1,3,5-tri(aroycarbonyl)phenylene]s (hb-PTACPs) are prepared in moderate yields with high molecular weights by one-pot polycyclotrimerization of 4,4′-isopropylidenediphenyl bipropiolate with 4-(ferrocenylmethyl)phenyl propiolate in reflux dimethylformamide. All the polymers are soluble and film-forming. They enjoy high thermal stability and lost little of their weight when heated to 300 °C under nitrogen. Thin solid films of the organometallic polymers shows high refractive indices (RI = 1.7038–1.6295) in the wavelength region of 400–1,700 nm. Ceramization of the organometallic hb-PTACPs at high temperature under inert atmosphere gives iron nanoparticles with high magnetizabilities. The organometallic polymers are readily crosslinked under UV irradiation and pyrolysis of the patterned polymer films produces magnetic ceramic patterns with good shape retention.     

Novel chalcone-based aromatic polyamides: synthesis,characterization, and properties

Two novel diacid-based monomers have been synthesized by anchoring a benzylideneacetophenone (chalcone) moiety through an amide or ester bridge at the fifth position of the isophthalic acid ring. Two series of new polyamides bearing chalcone side chains were prepared by direct polycondensation reaction of the aforementioned dicarboxylic acids and various aromatic diamines in N-methyl-2-pyrrolidinone, using triphenyl phosphite and pyridine as condensing agents. Their molecular structure and the basic properties were investigated by nuclear magnetic resonance, Fourier-transform IR and UV–vis spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and wide-angle X-ray diffraction. The inherent viscosity, molecular weights measurements (by gel permeation chromatography), water uptake, and solubility tests completed the research study. Introduction of the rigid and bulky chalcone units into the polymer side chains improved remarkably the solubility of the aromatic polyamides, endowed them with an amorphous nature, good thermal stability, and photosensitivity. The resulting polymers were obtained in good yields, inherent viscosities varied between 0.49 and 0.86 dL/g, and their relative high molecular weights conferred them film-forming properties. They were soluble in amide-type polar solvents, such as N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone. These polyamides had glass transition temperatures between 219 and 264 °C, and 10% weight loss temperatures in the range of 394–436 °C and around 50% residue at 700 °C in nitrogen atmosphere. The polyamides underwent a [2 + 2] photocycloaddition reaction upon UV light irradiation both in solution and film state in the absence of a photoinitiator or photosensitizer. The polymer films became insoluble in solvents as a result of the crosslinking .     

Imide-modified polyurethanes,syntheses, thermal,and mechanical characteristics

Polyurethanes based on polyethylene glycol and hydroxy-terminated polybutadiene, bearing pyromellitimide groups in the backbone, were synthesised via a sequential method. The diisocyanate and diamine telechelic precursor polymers, the polyamic acid intermediate and the polyimides were characterized by physicochemical and thermoanalytical techniques. The imide content could be varied in the chain through selection of the polyol of desired molecular weight or by a chain extension process of the diisocyanate precursor. The thermal and mechanical properties of the imide-modified polyurethane increased proportionate to the hard segment content, constituted by the imide and the urea groups. The presence of the imide group resulted in better thermomechanical profile and caused enhancement in glass transition temperature of the modified polyurethane vis-à-vis the unmodified resin. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1483–1491, 1998     

Characterization of UV-irradiated Lexan polycarbonate films

Lexan polycarbonate films were irradiated by UV radiation at wavelength $ \lambda $  = 250 nm under different time exposures of 1, 2, 4, 6 and 7 h. Structural, optical and mechanical modifications were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), UV–Visible spectroscopy, impedance analysis, tensile testing and rheometry methods. The crystallite size and percentage of crystallinity were found to decrease upon irradiation as was studied by XRD. It indicated that polymer was moving towards more disordered state after irradiation corroborating DSC results. FTIR Study showed the carbonate linkage is the radiation-sensitive linkage and benzene ring does not undergo any change after irradiation. SEM results showed the formation of pores after irradiation. The atomic force microscopy measurements revealed that the average roughness of the film increased after being irradiated. The glass transition temperature was observed to decrease after irradiation as revealed by DSC measurement. UV–Visible spectra showed decrease in optical band gap after irradiation due to chain scission in the Lexan polycarbonate. Plot of AC conductivity versus log (f) displayed a sharp increase in conductivity at higher frequencies and dielectric constant/loss was observed to change with the irradiation time. The mechanical properties and average molecular weight of Lexan polycarbonate decreased after irradiation, while the average number of chain scissions per original polymer molecule increased with increase in time of exposure.     

Molecular weight (M n) and functionality effects on CUP formation and stability

The formation of colloidal unimolecular polymer (CUP) particles from single polymer strands was investigated as a function of molecular weight. The CUP particle size was correlated with the absolute molecular weight and its distribution. The characteristics of the particles were evaluated with respect to viscosity, acid number, size distribution, and stability. The particle size varied from less than 3 nm to above 8 nm representing polymers with molecular weight in the range of 3000–153,000. Lower molecular weight polymers were found to be unstable. Particle size measurements using dynamic light scattering technique indicated a normal distribution which corresponded to the molecular weight distribution of the copolymer. The statistical distribution of the acid groups in the polymer chains played a significant role in the stability of low molecular weight polymers.