Polyaldehydes: homopolymers,block copolymers and promising applications

This minireview gives a brief overview on the polymerization of higher aldehydes, discusses current applications of certain polyaldehydes, and points toward potential future applications of these interesting materials. Although it was discovered long ago that several aldehydes can be polymerized, the application potential of these polymers was largely overlooked. This is somewhat surprising as many polyaldehydes show interesting properties such as fast and complete depolymerization triggered by chemical or thermal stimuli. Such stimuli‐responsive polymers can be useful materials in many applications in for example nanotechnology or drug delivery. By incorporating polyaldehydes into functional block copolymers even more versatile materials can be created. The increasing number of recent research examples demonstrates the growing interest in polyaldehydes as smart materials and their potential for novel applications. Copyright © 2012 Society of Chemical Industry     

Molecular weight determinations on polymers by electron microscopy

A technique has been developed by which molecular weight averages and distributions may be obtained for polymer fractions of high molecular weight. For glassy amorphous polymers, very dilute solutions in solvent-precipitant mixtures are atomised on to a thin carbon substrate, shadowed with platinum-carbon mixture and examined in the electron microscope. A solvent is chosen which is more volatile than the precipitant, so that on the path from the atomiser system to the substrate, and on the substrate itself, preferential evaporation of the solvent takes place. Contacts between polymer segments become more favourable than polymer-solvent contacts, resulting in the progressive contraction of the molecular coils, and the deposition of single spherical self-supporting molecules, the diameters of which can be determined from the lengths of the shadows cast by them. Molecules of polymers having glass transition temperatures below room temperature, or even slightly above, show varying degrees of collapse when prepared at room temperature. A device has been constructed which allows such polymer molecules to be deposited and shadowed at temperatures down to ?100°, at which temperature molecular collapse is not apparent. Molecular diameters may then be measured as for glassy polymers. An atomiser-separator system was constructed, which produced small droplets containing, essentially, one or zero polymer molecules, when a fraction of high molecular weight was used. All the solvent was evaporated from the droplets on the path to the cooled substrate, allowing the deposition of solvent-free molecules. Molecular weight averages and distributions are presented for a series of high-molecular-weight polymer fractions, in the glass transition temperature range from 100° to —73°. The high precision of the results from this technique is demonstrated, together with the close agreement between molecular weight averages obtained by electron microscopy, and those obtained by light-scattering and viscometry.     

Solubility of isobutane in two high-density polyethylene polymer fluffs

Solubility and rate of desorption of isobutane vapor in high-density polyethylene (HDPE) polymer fluff and a HDPE-hexene-1 copolymer fluff for isotherms between 65.5 and 93.3°C are reported. The data were obtained for pressures to near the vapor pressure of isobutane. Solubilities were correlated using Henry's law, Flory–Huggins theory, and weight fraction activity coefficients. The last approach gave the best correlation of data over the entire temperature and pressure range. The estimated rate of sorption of isobutane is 1.5 × 10^?4 mol iC₄H_10/g fluff/bar/min over the range studied.     

Viscosity and retention of sulfonated polyacrylamide polymers at high temperature

The viscosity and retention of several copolymers of acrylamide (AM) with sodium salt of 2‐acrylamido‐2‐methylpropane sulfonic acid (PAMS), and also hydrolyzed polyacrylamide (HPAM) have been studied under aerobic condition with and without the sacrificial agent, isobutyl alcohol (IBA) added at a temperature of 80°C. Parallel experiments have been performed in synthetic seawater (SSW) and 5 wt % NaCl. The viscosity at high temperature has been studied as a function of aging time, shear rate, sulfonation degree, molecular weight, and concentration of IBA. The retention in porous medium for sulfonated polyacrylamide polymers was measured in core floods using outcrop Berea sandstone. For the studied polymer sacrificial agent may protect polymer structure at high temperature. Higher sacrificial agent concentration gives better thermal stability in both 5 wt % NaCl and SSW solvents. Sulfonation degree also has a direct effect on thermal stability, i.e., higher sulfonation degree lead to better thermal stability in terms of viscosity. By increasing temperature, less relative reduction in polymer solution viscosity was observed for the polymer with lower molecular weight. The presence of divalent ions at high temperature leads to strong reduction of HPAM polymer solution viscosity, but the viscosity is better maintained for PAMS copolymer solution at high temperature. The precipitation of HPAM first occurred after 3 months at 80°C and for PAMS copolymer with lowest sulfonation degree precipitation started after 7 months. For the studied polymers the retention was found to be relatively independent of temperature and compared to HPAM a much lower retention is observed for the sulfonated copolymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Creep and recovery of ultra high modulus polyethylene

The creep and recovery behaviour of ultra high modulus polyethylene has been studied over the temperature range 20–70°C. Four types of material were examined; low molecular weight and intermediate molecular weight homopolymer, an ethylene hexene-1 copolymer, and a sample prepared by γ-irradiation of isotropic low molecular weight polymer prior to drawing. With the exception of the low molecular weight homopolymer, the materials showed an apparent critical stress below which there was no detectable permanent creep. It is proposed that the behaviour of all the materials can be described to a good approximation by a simple model, where two activated processes are coupled in parallel. Tentative structural explanations of the results are also given.     

Hydrolytic depolymerization of poly(ethylene terephthalate) under microwave irradiation

This article covers the depolymerization of poly(ethylene terephthalate) (PET) under microwave irradiation in neutral water. The reaction was carried out in a sealed reaction vessel in which the pressure (or temperature) was controlled. The hydrolytic product contained terephthalic acid, ethylene glycol, and diethylene glycol characterized by IR spectrometry and gas chromatography. The undepolymerized PET was identified by gel permeation chromatography. Both the yield of terephthalic acid and the degree of PET depolymerization were seriously influenced by pressure (or temperature), the weight ratio of water to PET, and the reaction time. The applied irradiation power had little influence on the degree of PET depolymerization. With a pressure of 20 bar (temperature = 220°C), a reaction time of 90–120 min, and a weight ratio of water to PET of 10:1, the PET resin was depolymerized completely. The molecular weight and the molecular weight distribution indicated that the hydrolytic depolymerization of PET obeyed the regular chain‐scission mechanism to some extent. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 719–723, 2005     

Radiation-induced emulsion polymerization of vinyl acetate and styrene

Studies have been made of the γ-induced emulsion polymerization of styrene and comparisons made with chemically initiated emulsion polymerization. The polymerization proceeded smoothly to high conversions at 0 and 60°C, the reaction showing a high G (monomer) value. Complete conversions were obtained with total doses of less than 0.05 Mrad. In accordance with the behavior expected of systems having a constant rate of initiation, the molecular weight was found to decrease with decreasing temperature. The molecular weight and particle size distributions were narrower than those obtained in chemically initiated emulsion polymerizations at the same temperature. The radiation-induced emulsion polymerization of vinyl acetate proceeded smoothly at temperatures in the range 0–50°C to give polymers of much higher molecular weight than these obtained from chemically initiated polymerizations at the same temperature. Complete conversion was attained after a dose of 0.02 Mrad for latices approaching 50% solids. The elimination of ionic endgroups in the poly(vinyl acetate) radicals tends to drive the polymerization from the aqueous phase, resulting in faster rates and higher molecular weights than are obtained from chemically initiated systems. Rates of polymerization were found to be independent of temperature and the molecular weight of the polymer to be independent of dose rate. Latices of poly(vinyl acetate) of high solids content were evaluated for latex and film properties and found to have improvements over commercially available samples in both areas, especially in clarity of film and scrub resistance. A number of acrylate and maleate esters were copolymerized with vinyl acetate in a radiation-initiated emulsion system. High molecular weight copolymers were produced after low dose.     

Effect of degree of deacetylation on solubility of low‐molecular‐weight chitosan produced via enzymatic breakdown of chitosan

Chitosan has emerged as a unique biomaterial, possessing scope in diverse applications in the biomedical, food and chemical industries. However, its high molecular weight is a concern when handling the polymer. Various techniques have been explored for depolymerization of this polymer, wherein enzymes have emerged as the most economic method having minimum degrading effect on the polymer and resulting in formation of side products. Chitosan can be depolymerized using a broad range of enzymes. In this study, various enzymes like α‐amylase, papain, pepsin and bromelain were employed to depolymerize chitosan and convert it into its lower molecular weight counterpart. Further, attempts were made to elucidate the process of depolymerization of chitosan, primarily by determining the change in its viscosity and hence its molecular weight. The process of depolymerization was optimized using a one‐factor‐at‐a‐time approach. The molecular weight of the resultant chitosan was estimated using gel permeation chromatography and infrared spectroscopy. These studies revealed a considerable decrease in molecular weights of chitosan depolymerized by pepsin, papain, bromelain and α‐amylase, resulting in recovery of the low‐molecular‐weight chitosan of 76.09 ± 5, 74.18 ± 5, 55.75 ± 5 and 49.18 ± 5%, respectively. Maximum yield and depolymerization were obtained using pepsin and papain due to their enzymatic recognition pattern, which was also validated using studies involving molecular dynamics. © 2019 Society of Chemical Industry     

Preparation of copolymer of L‐aspartic acid and L‐glutamic acid

In this article, a new copolymer of L ‐aspartic acid and L ‐glutamic acid, which may be a biodegradable high molecular polymer and can be used more widely in many areas, was synthesized. The conditions of preparation, such as catalyst, reaction time, reaction temperature, the amount of catalyst, the times of adding catalyst, and the molar ratio of L ‐aspartic acid to L ‐glutamic acid, were optimized. The copolymer was characterized by ¹³C NMR, infrared spectroscopy, and X‐ray diffractometer. The molecular weight was determined by GPC. The result indicated that production yield, purity of product, and molecular weight of product increased with amount of catalyst and molar ratio of L ‐aspartic acid to L ‐glutamic acid increasing. The best condition of preparation was the following: reacting 2–4 h at the temperature of 180–200°C. The product yield with the molecular weight 13,000.00 reached 63.2% and the purity of product was 96.33% when the copolymerization was carried out at the temperature of 200°C under vacuum for 2 h. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3626–3633, 2006     

Catalytic synthesis and characterization of an alternating copolymer from carbon dioxide and propylene oxide using zinc pimelate

New zinc pimelate catalysts used for copolymerization of carbon dioxide and propylene oxide have been synthesized in high yield by a magnetic stirring method. The regular molecular structure of the zinc pimelate was confirmed by Fourier‐transform infrared spectroscopy and wide‐angle X‐ray diffraction techniques. Accordingly, poly(propylene carbonate) (PPC) can be synthesized from carbon dioxide and propylene oxide using these zinc pimelate catalysts. High catalytic efficiency (95.2 gram polymer per gram catalyst or 21 300 g of polymer per mole of zinc) was achieved by optimizing the PO/catalyst ratio. NMR measurement revealed that the PPC synthesized had an alternating copolymer structure. The thermal properties of PPC were determined by modulated differential scanning calorimetry and thermogravimetric analysis. The results demonstrated that the PPC copolymer exhibited an extremely high glass transition temperature of 44.27 °C and decomposition temperature of 257 °C, comparable with values reported in literature. Copyright © 2003 Society of Chemical Industry     

Synthesis of ethylene and butyl methacrylate-based copolymer by emulsion polymerization

The emulsion copolymerization of ethylene with butyl methacrylate (BMA) was carried out in an aqueous medium at 60 °C under moderate reaction conditions. The polymer system is well controlled with a linear increase in the molecular weight (M_n) versus ethylene feed pressure and narrow molecular weight distributions (>1.36) were observed throughout the copolymerization reaction. The spectroscopic analyses confirm the presence of acrylate functional as well as methylene group in the synthesized poly(ethylene-co-BMA) copolymer. Morphological behavior of poly(ethylene-co-BMA) has been studied using SEM and TEM analyses. Thermal stability of the copolymers was investigated by thermogravimetric analysis and it was observed that the copolymer is stable up to 380 °C. X-ray diffraction analysis confirmed the amorphous behavior of poly(ethylene-co-BMA). Dynamic light scattering measurement confirms the formation of poly(ethylene-co-BMA) nanoparticles. The particle size of copolymer nanoparticles were in the range of 85–108 nm with low polydispersity indexes (>0.2). The viscous and the elastic property of the copolymer were investigated and established that at high temperature elastic behavior predominant over viscous effect. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47994.     

Mass transfer and depolymerization of styrene in polystyrene

This work shows how laboratory experiments may provide parameters which are useful in modeling a commercial process of polystyrene devolatilization. Such processes often occur at temperatures where depolymerization of polystyrene to monomer may be significant. Polystyrene devolatilizers function by forming thin films of the polymer, with styrene loss by flashing and diffusion and styrene generation by depolymerization. The modeling parameters of importance are: depolymerization rate constant, monomer diffusivity, and thermodynamic equilibrium polymer-vapor partition coefficient. Typical levels of styrene in polystyrene in the last stage of devolatilization are 100 to 1000 ppm. Pressures and temperatures in the devolatilizer are often less than 10 torr and greater than 200°C. For styrene-polystyrene the desired parameters have not been reported, nor apparently measured, at the concentration, pressure and temperature levels of interest.     

Synthesis and characterization of acrylonitrile methyl acrylate statistical copolymers as melt processable carbon fiber precursors

Statistical (random) copolymers of acrylonitrile (AN) and methyl acrylate (MA) have been synthesized by free radical homogeneous (solution) and heterogeneous (suspension) methods. Selected compositions can be fabricated by environment friendly, solvent-free melt spinning and are of interest as precursors for carbon fibers. The dynamic and steady state melt viscosities of these copolymers were studied as a function of molecular weight and copolymer composition. Melt processability at 200–220 °C depends on the copolymer composition, and also on the molecular weight, which was controlled by chain transfer agent concentration and reaction temperature. Copolymers of controlled molecular weight containing 10 or more mol[percnt] of methyl acrylate show good melt processability, which can be further enhanced by stabilizers. This thermoplastic behavior is supported by a significant increase in temperature by the cyclization exotherm. Thermal analysis (differential scanning calorimetry, dynamic mechanical analysis) further illustrates that the comonomers retarded the cyclization, which permits thermoplastic processing.     

Melt processable and biodegradable aliphatic polycarbonate derived from carbon dioxide and propylene oxide

Alternating poly(propylene carbonate)s (PPC)s were successfully synthesized from carbon dioxide and propylene oxide in higher yield than previously reported. Such thermally stable and high molecular weight copolymers were achieved by optimizing the reaction conditions. The molecular structural change and mechanical properties of the alternating copolymer subjected to melt extrusion were examined by means of modulated differential scanning calorimetry (MDSC), thermogravimetric analysis (TGA), NMR, and tensile tests. The MDSC and TGA results showed that the alternating copolymer generally exhibits a high glass‐transition temperature of above 40°C and a decomposition temperature of above 250°C. These PPCs can be readily melt processed under conditions similar to those for commercial polyolefins. For instance, they can be melt extruded in a temperature range from 150 to 170°C under varying extrusion pressures. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3301–3308, 2003     

Synthesis and Characterization of Poly (phenylene oxide)-Based Block Copolymers via Cobalt Mediated Radical Polymerization (CMRP)

Novel well-defined poly(phenylene oxide) (PPO) based block copolymers were polymerized from 4-bromo-2,6-dimethylphenol (BDMP) in the presence of a cobalt acetylacetonate (Co(acac)₂) catalyst with dimethyl formamide (DMF) as a ligand and initiated with benzoyl peroxide (BPO) at 60 °C. The monomer copolymerized with vinyl acetate (VAc), polymethyl(meth)acrylate-b-poly(dimethyl siloxane)-b-polymethyl(meth)acrylate (PMMA-b-PDMS-b-PMMA) and polystyrene-b-poly(dimethyl siloxane)-b-polystyrene (PSt-b-PDMS-b-PSt) triblock copolymers in good yield. Characterization indicated a very narrow molecular weight distribution. The solid polymer obtained is a stable polymer with high thermal stability at 220 °C. The block copolymer indicated a new microstructure of phenylene oxide which was analyzed by proton-nuclear magnetic resonance (¹H-NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetriy (DSC) and gel permeation chromatography (GPC). Meanwhile, the number average molecular weights calculated from the ¹H-NMR spectra were in very good agreement with the theoretically calculated values. The DSC results also indicated the successful formation of these new block copolymers.     

Evaluation of poly(allyl methacrylate)-co-(hydroxyethyl methacrylate) as negative electron-beam resist

Poly(allyl methacrylate)-co-(hydroxyethyl methacrylate) has been evaluated as a high-sensitivity, high-resolution, high temperature-resistant negative electron resist. The effects of molecular weight and polydispersity of the copolymer on its lithographic performance as an E-beam resist were studied. The sensitivity of the copolymer is nearly constant in the weight-average-molecular-weight range of 50,000 to 75,000, and it gradually decreases with a decrease in molecular weight. As expected for a negative resist, the resist contrast increases as the polydispersity is decreased. The sensitivity curve shape of the polymer was independent of the prebake temperature, which varied from 70 to 110°C, and of the various developers used. The exposed coating requires vacuum curing for image optimization. Resolution of 0.5 μm line/space pairs was obtained from a 0.6 μm thick resist by exposing the resist to 10 keV electrons with either a raster-scan-type or vector-scan-type electron-beam exposure machine. After postbaking at 170°C, the resist had good resistance to both chemical etching and dry etching. The plasma-etch resistance was about twice that of PMMA.     

The forced gas sweeping process for semibatch melt polycondensation of poly(ethylene terephthalate)

The experimental and modeling studies are presented on the melt polycondensation of poly(ethylene terephthalate) by a gas sweeping process. In this process, low molecular weight prepolymer is polymerized to a higher molecular weight polymer in a molten state at ambient pressure as ethylene glycol is removed by nitrogen gas bubbles injected directly to the polymer melt through a metal tube. In the temperature range of 260–280°C, the rate of polymerization by the gas sweeping process is quite comparable to that of conventional high vacuum process. The effects of nitrogen gas flow rate and reaction temperature on polymerization rate and polymer molecular weight were investigated. Polymer molecular weight increases with an increase in gas flow rate up to certain limits. A dynamic mass transfer–reaction model has been developed, and the agreement between experimental data and model simulations was quite satisfactory. The effect of ethylene glycol bubble nucleation on the polymerization has also been investigated. It was observed that the presence of nucleated ethylene glycol bubbles induced by the bulk motion of polymer melt has negligible impact on the polymerization rate and polymer molecular weight. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1388–1400, 2001     

Spherulite crystallization in bisphenol-A-polycarbonate of varying molecular weight distribution

The spherulitic structure of films of fractionated bisphenol-A-polycarbonate having a range of different average molecular weight and molecular weight distribution has been studied using the polarization microscope. Spherulitic crystallization was induced in specimens by the action of solvent or solvent vapor at room temperature or by isothermal heat treatment at 180°C. These phenomena were all shown to be a function of the average molecular weight and polydispersity of the material. The glassy amorphous and spherulite polymer phases were investigated using a microscopic etching technique and gel permeation chromatography (GPC). Results of this investigation have established that considerable segregation by molecular weight occurs during the crystallization process. Spherulites produced have been shown to exhibit variation in morphologic texture depending on conditions of induction and polydispersity of the polymer. Examples of unusual and previously unreported spherulites have been observed.     

Structure and properties of polyethylene produced by γ-radiation polymerization in flow system

The radiation-induced polymerization of ethylene was carried out by use of a benchscale plant with a flow-type reactor of 1 liter capacity under the following conditions: pressure, 200–400 kg/cm²; temperature, 30–90°C; irradiation intensity, 3.8 × 10⁵ rad/hr; and ethylene flow rate, 300–3000 nl/hr. The molecular weight of polymer formed was shown to decrease with increasing reaction temperature and to increase with increasing pressure. When the ethylene flow rate increases, the molecular weight decreases in the polymerization at 30–60°C, but it does not change in the polymerization at 75–90°C. Methyl group content, which is a measure of short-chain branching of the polymer, increases with increasing reaction temperature, i.e., ca. 1 CH₃/1000 CH₂ at 30°C and ca. 9 CH₃/1000 CH₂ at 90°C. Methyl content is independent of the ethylene flow rate. The changes in the melt index of polymer with reaction conditions corresponds to the change of the molecular weight. The density, crystallinity, and melting point of polymer decrease with the reaction temperature as the short-chain branching increases, and they are almost independent of ethylene flow rate and pressure.