Function Of Polymerization Temperature Research Articles

Synthesis of pyrene‐capped polystyrene by free radical polymerization and its application in direct exfoliation of graphite into graphene nanosheets

ABSTRACTIt is of great practical significance to acquire pyrene‐capped polymer, which has proven an excellent dispersant of nanocarbons, in an accessible way. Taking synthesis of pyrene‐capped polystyrene (PyPS) as the example, free radical polymerization was demonstrated to be an attractive option to satisfactorily fulfill such mission. For this, a new azo‐based pyrenyl compound was designed, synthesized, and used as initiator. The molecular structure of PyPS was studied as a function of polymerization temperature and content of chain transfer agent of 1‐dodecanethiol. Following the successful synthesis, a PyPS polymer structured as 1.04 pyrene groups per chain was chosen as dispersant for preparation of graphene. The results showed that 0.2 mg/mL of PyPS in chloroform permits 67.4 μg/mL of graphene nanosheets to be prepared by liquid‐phase exfoliation of graphite. In contrast, only 8.5 μg/mL of graphene nanosheets could be obtained in pure chloroform. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2175–2185

Albumin molecularly imprinted polymer with high template affinity — Prepared by systematic optimization in mixed organic/aqueous media

An approach using systematic optimization for the formation of an albumin molecularly imprinted polymer (MIP), able to separate albumin from proteins in solution, has been prepared by imprinting albumin using a copolymer comprising 3-dimethylaminopropyl methacrylate and tetraethylene glycol dimethacrylate in a mole ratio of 1 to 8. Cytochrome c, lysozyme and myoglobin were used in competitive re-binding experiments to compete with the polymer's native template with all protein species present at 0.0004 g mL − 1 . The effects of: monomer to crosslinker mole ratio, polymerization temperature and time were investigated. It was found that the addition of water 6.04%, into the pre-polymerization albumin–monomer complex enhanced the adsorption capacity and selectivity of the resulting MIP from 2.18 × 10 − 3 to 6.02 × 10 − 3 g g-MIP − 1 and 83.5% to 98.7%, respectively. These results also showed that the MIP possessed high selectivity and adsorption capacity with respect to albumin in comparison with interfering species also present in solution. Polymerization temperature, time and the water content of the pre-polymerization mixture were all shown to have significant effects on the resulting albumin-MIP's performance. However, their influence on the polymer's affinity for the potentially interfering species was negligible. Additionally, higher polymerization temperatures (> 38 °C) and extended polymerization times (> 60 h) increased monomer conversion as determined by HPLC, but decreased the selectivity and adsorption capacity of the MIP. An optimized MIP, with very high selectivity and 6.37 × 10 − 3 g g-MIP − 1 template re-adsorption capacity was obtained using the following polymerization conditions: 0.125 mole ratio of monomer to crosslinker, 6.04 wt.% water content with respect to the mass of the monomer complex, 60 h polymerization time at 38 °C, and with 0.47% albumin in the pre-polymerization monomer complex. Finally, the functions of polymerization temperature, time and the significance of the water content in the albumin–monomer complex are also discussed.

Study of ammonia-gas-induced irreversibility in polypyrrole films

Polypyrrole’s conductivity as a function of polymerization temperature and its properties on treatment with ammonia gas are studied. Electronic structures of PF6 (hexafluorophosphate) doped polypyrrole (PPY) films grown at −40, 0, and 20 °C, before and after ammonia treatment, are compared using angle resolved photoemission spectroscopy, electron paramagnetic spectroscopy, and semiempirical calculations. The valence band electronic structures of these polypyrrole films largely depend on polymerization temperature, and ammonia treatment. The light-polarization-dependent valence band structures reflect ordering of polymer chains with decreasing polymerization temperature. The irreversibility properties of polypyrrole, which can be used as an ammonia gas senor, are shown to possibly arise from detachment of the dopant molecules under pumping.

Kinetics of the anionic polymerization of 2-(tertbutyldimethylsilyloxy) ethyl methacrylate

AbstractThe kinetics and the extent of side reactions of the anionic polymerization of silyl-protected 2-hydroxyethyl methacrylate, 2-(tert-butyldimethylsilyloxy)ethyl methacrylate (TBDMS-HEMA), in tetrahydrofuran (THF) were studied as a function of polymerization temperature. Lithium chloride was added in order to achieve a controlled polymerization. The results of polymerizations at various temperatures are compared with reported data for methyl methacrylate and tert-butyl methacrylate in THF. The activation energy for the studied monomer is lower compared to the other methacrylates. Gel permeation chromatography-viscosity studies show that poly(TBDMS-HEMA) exhibits a more wormlike structure in THF than other polymethacrylates, as indicated by a higher Mark-Houwink exponent, α = 1.025.

Graft copolymerization of end allenoxy polyoxyethylene macromonomer onto ethyl cellulose in a homogeneous system

The homogeneous grafting of end-allenoxy polyoxyethylene macromonomers (Mn=390; PEGA39) onto ethyl cellulose (EC) was carried out using α–α′-azobisisobutyronitrile (AIBN) as free radical initiator in benzene as solvent. The grafting percentage, grafting efficiency and weight conversion were determined as a function of polymerization temperature, and the concentration of PEGA39, EC and initiator. The graft copolymers were characterized by infrared spectroscopy and intrinsic viscosity measurements. The observed low grafting efficiency of PEGA39 macromonomer onto EC are attributed to steric or excluded volume effect, involving repulsion between the growing chain and that of macromonomer and EC chains. The mechanism of the grafting reaction was proposed.

Rubber‐modified epoxies. II. Influence of the cure schedule and rubber concentration on the generated morphology

AbstractThe morphology of a system consisting of a bisphenol A diglycidylether (DGEBA) based epoxy, cured with a cycloaliphatic diamine (4,4′‐diamino‐3,3′‐dimethyldicyclohexylmethane, 3DCM), in the presence of an epoxy‐terminated butadience‐acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration. Scanning (SEM) and transmission (TEM) electron microscopy, differential scanning calorimetry (DSC) and dynamic mechanical analysis were used to characterize the generated morphology. SEM results were not affected by the type of mechanical test and strain rate. Trends observed for the particle size distribution, the volume fraction of dispersed phase, the concentration of dispersed phase particles and the composition of both phases as a function of polymerization temperature and rubber concentration, were discussed. A correlation between the viscosity at the cloud point and the average size of dispersed phase particles was found for different systems, independently of the cure temperature and the initial rubber amount.

Melt Polymerization of Adipic Anhydride (Oxepane-2,7-Dione)

Abstract Oxepane-2,7-dione (1) was prepared by the reaction of adipic acid and acetic anhydride followed by catalytic depolymerization under vacuum. the ring-opening polymerization of (1) was investigated in the melt, and was studied as a function of polymerization temperature, time and concentration of catalyst (stannous 2-ethylhexanoate). from 1H-NMR and IR spectra it can be deduced that stannous 2-ethylhexanoate coordinates with the anhydride bond of the ring, and that the resulting species reacts with the monomer by ring-opening of the acyl-oxygen bond. These observations indicate a non-ionic insertion polymerization mechanism at the beginning of the reaction, but after 2 h at 80°C, anhydride exchange appears to be the dominating reaction. Ring-opening melt polymerization of (1) resulted in low molecular weight poly (adipic anhydride).

Synthesis of high‐molecular‐weight poly(L‐lactide) initiated with tin 2‐ethylhexanoate

AbstractThe bulk polymerization of L,L‐dilactide was studied as a function of polymerization temperature (Tp), time and concentration of catalyst (tin 2‐ethylhexanoate). Poly(L‐lactide) (PLLA), with the highest value of intrinsic viscosity ([η] = 13 dl · g−1; M̄v ≈ 1 · 106) and heat of fusion (ΔHm = 64,7 J · g−1), was synthesized at a low catalyst concentration (0,015 wt.‐%) and at the lowest Tp studied (100°C), just above the melting point of L,L‐dilactide (98°C). The ceiling temperature of PLLA was found to be 275°C, as deduced from an M̄v max. − Tp curve. The M̄w/M̄n ratios of as‐polymerized PLLA samples ranged from 2 to 3. Fractions of PLLA with M̄v max. were already present at 50% conversion. The experimental results support a proposed nonionic insertion polymerization mechanism. Polymerization at 100–140°C resulted in early crystallization of PLLA leading to a rather untangled polymer and microporous (pores up to 100 nm) sample texture.

Homogeneous Graft Copolymerization of Vinyl Monomers onto Cellulose in a Dimethyl Sulfoxide–Paraformaldehyde Solvent System III. Methyl Acrylate

Homogeneous graft copolymerization of methyl acrylate (MA) onto cellulose was carried out in a dimethyl sulfoxide–paraformaldehyde solvent system. Ammonium persulfate (APS), benzoyl peroxide (BPO), and azobisisobutyronitrile (AIBN) were used as radical initiators. The optimum grafting condition and the number of grafts per cellulose chain for each monomer–initiator system were determined as functions of polymerization temperature and concentrations of monomer, initiator, and cellulose. Grafting onto cellulose proceeded in the MA–APS system, but hardly at all in the MA–BPO and MA–AIBN systems. The number of grafts was found to be 1.5 at most in the MA–APS system. BPO was found unsuitable as a grafting initiator due to the degradation of the cellulose chains.

Homogeneous Graft Copolymerization of Vinyl Monomers onto Cellulose in a Dimethyl Sulfoxide–Paraformaldehyde Solvent System II. Characterization of Graft Copolymers

Homogeneous graft copolymerization of acrylonitrile and of methyl methacrylate onto cellulose using radical initiators was carried out in a dimethyl sulfoxide–paraformaldehyde solvent system. The graft copolymers obtained under various grafting conditions were hydrolyzed to isolate the graft polymers. The molecular weight of graft polymer and the number of grafts per cellulose chain were determined as functions of polymerization temperature and concentrations of monomer and initiator. The molecular weight of graft polymer increased with increasing monomer concentration but decreased with raising temperature and with increasing initiator concentration. The number of grafts increased with raising temperature and with increasing initiator concentration but decreased with increasing monomer concentration.

ESR and electrical conductivity of carbon black doped polyester resin

AbstractThe dependence between paramagnetic centre concentration, as well as ESR spectral line width and electrical conductivity of a polyester resin doped with various admixtures of acetyelene carbon black has been investigated. Distinct correlations have been found between ESR spectrum and electrical conductivity of the resin as a function of polymerization temperature and accelerant concentration. The correlations confirm the mechanism of the electrical conductivity of the composition which is based on formation of conducting bonds between the carbon black particles and the polyester macromolecules in process of the free radical polymerization.

Radiation‐induced solid‐state polymerization of trioxane under high pressure

AbstractThe in‐source polymerization of trioxane in the solid state was investigated over a wide range of temperature and pressure, i.e., from 30 to 140°C and up to 7000 kg/cm2, respectively. In the polymerization that was carried out slightly below the melting point under pressure, the higher the pressure, the higher the rate of polymerization. It was confirmed that the maximum rate of solid‐state polymerization of trioxane occurs near the melting points, even under elevated pressure. The rate of polymerization decreased with increasing pressure at constant temperature. The shape of the time–conversion curves may be classified into two types, i.e., one which is typical of high pressure and low temperature, and the other which is typical of low pressure and high temperature. Changes in the shape of the conversion—intrinsic viscosity curves occurred coincidentally. Thus, three regions for the different “polymerization characteristic” were determined as functions of polymerization temperature and pressure. Explanations are given for the above‐mentioned polymerization characteristic.

Polymerization Mechanism in Methyl Methacrylate–Grignard Reagent System. I. Phenylmagnesium Bromide

The mechanism of stereospecific polymerization in a methyl methacrylate–Grignard reagent (C6H5MgBr) system is studied as a function of polymerization temperature with high-resolution nuclear magnetic resonance (NMR) spectroscopy for obtained polymers. It is found that the maximum temperature during the reaction in our experiments is appropriate for adoption as the polymerization temperature rather than the commonly used setting temperature.As a result it is found that the mechanism is different at temperatures higher and lower than about 266°K. Also, the NMR spectra of C6H5MgBr in a deuterated toluene-d8 are measured over a wide range of temperatures and remarkable change is observed in the vicinity of about 266°K. It may reflect the above difference in polymerization mechanisms on both sides of about 266°K.

Cyclic distribution in dimethylsiloxanes

AbstractGas–liquid chromatography was used to determine the amounts of cyclic molecules present in an equilibrium polymerization mixture of high polymer and cyclic dimethylsiloxane molecules. The study was carried out as a function of polymerization temperature. For [(CH3)2SiO]4–10 the equilibrium concentration is shown to be independent of temperature. The change in cyclic concentration as a function of n for [(CH3)2SiO]4–10 does not follow the theoretical Stockmayer‐Jacobson distribution. The concentrations of [(CH3)2SiO]3,4 are qualitatively predictable by the Stockmayer‐Jacobson theory and by the model proposed by Carmichael and Kinsinger. For [(CH3)2SiO]4, Kexp = 0.74 mole SiO/l. The model calculations yield 0.12 (Stockmayer‐Jacobson) and 0.36 Carmichael‐Kinsinger. For [(CH3)2SiO]3, Kexp = 0.024 mole SiO/l. Model calculations yield 0.017–0.16 (Stockmayer‐Jacobson) and 0.056–0.52 (Carmichael‐Kinsinger). The range of values rises because of uncertainty in the cyclic strain energy.

Crystallization in Butadiene-Styrene Copolymers

Butadiene-styrene copolymers contain the following units: trans-1,4-polybutadiene, cis-1,4-polybutadiene, 1,2-polybutadiene, and bound styrene. Of these the first is the only type which has been shown to form crystals. By the use of published data on volume change arising from crystallization (largely due to Meyer) and on structure as a function of polymerization temperature (largely due to Hampton) it is found that crystallization in emulsion polymers has been observed only when the trans-1,4-polybutadiene content has been greater than about 58 percent, becoming more complete the more this value is exceeded. From this observation one can then draw the following conclusions, all of which are in accordance with direct experimentation: (1) Crystallization is not observed if the polymerization temperature is above 60°C. (2) For polymerizations at 50°C a small amount (2 to 6 percent) of bound styrene inhibits crystallization completely. (3) For polymerizations at 5°C the limit is at about 15 to 18 percent bound styrene content. (4) At −40°C (the lowest polymerization temperature normally utilized) this limit is at about 30 percent bound styrene.

Viscometric Detection of Branching in Polymers. II. Branching in Poly(Butadiene-Co-Styrene) as a Function of Polymerization Temperature

Abstract Previous experience with polystyrene, normal and cross-linked, and with GR-S, gave strong support to our belief that, in careful viscosity measurement and evaluation of either of the slope constants β and k′, a useful and convenient means is available for the detection and measurement of branching in soluble high polymers. Moreover, since the measurements are made on separate fractions, information can be obtained regarding the relation between the size of polymer molecules and the degree to which they are branched. In the work reported here, this method was applied in a study of the effect of the temperature of polymerization on branching. It is now well known, of course, that, by reducing the temperature of polymerization, desirable changes of the physical behavior of emulsion polymers may be effected. This observation led to the development of “cold rubber” as an improvement over GR-S for use in tire tread stocks. Many efforts have been made to explain this superiority on the basis of changes in molecular structure. Several effects of lowering the temperature of polymerization have been noted : a narrowing of the molecular-weight distribution, a slight decrease of the proportion of the 1,2-isomer, a more marked increase of the proportion of the trans-form of the 1,4-isomer, and a decrease of the extent of chain branching. Of these various effects, the one most difficult to detect and to measure quantitatively is chain branching.

Viscometric detection of branching in polymers. II. Branching in poly(butadiene‐co‐styrene) as a function of polymerization temperature

AbstractSamples of poly(butadiene‐co‐styrene)—all of charge ratio butadiene:styrene 72:28—were prepared in emulsion at 15, 30, 40, and 50°C. Essentially the same redox recipe was used for each, with slight modifications to produce in about the same time polymers of similar intrinsic vistex (1.9 to 2.0) at similar conversions (about 65%) well below the gel point. Each sample was fractionated by precipitation from 1% benzene solution with methanol, special pains being taken to obtain fractions of equal size (each around 5% of the original rubber in the sample fractionated). Careful measurements of the viscosity functions [η], β, and k′ for each fraction were made; with every sample except that prepared at the lowest temperature, the values of β and k′ were observed to deviate in the high molecular weight region from the “base value” common to lower fractions, the deviation starting at a lower molecular weight, and being greater at a given high molecular weight, the higher the temperature of polymerization. It is concluded that branching in a diene polymer of this type is repressed as the temperature of polymerization is decreased: the lower the temperature the higher is the molecular weight at which branching is detectable and the lower is the degree of branching at a given molecular weight. In the 15°C. rubber no branching was detectable at any molecular weight.