Showing papers in "Polymer Bulletin in 1996"
TL;DR: In this paper, a comparison was made of two poly(DL-lactide) initiated with Zn metal and Sn octoate respectively and selected to have almost similar characteristics.
Abstract: Zn lactate, 3H2O and dehydrated Zn lactate were used as initiator to polymerize DL-lactide under various conditions. It is shown that the latter does polymerize DL-lactide up to high molecular weight at a slower rate than Sn octoate. Zn lactate being formed when lactic acid is allowed to react with Zn metal, it is believed that the active species in Zn metal initiation is Zn lactate. Comparison was made of the two poly(DL-lactide) initiated with Zn metal and Sn octoate respectively and selected to have almost similar characteristics. It is shown that degradation characteristics of the two polymers are different, especially water uptake and rate of heterogeneous degradation. It is further shown that residual Sn concentrated within the matrix remnants whereas the content in Zn remained constant according to degradation controlled release.
82 citations
TL;DR: In this paper, the essential work of fracture (EWF) concept was used to determine the inherent fracture behavior of ductile polymers, and a tensile-loaded deeply double-edge notched (DDEN-T) specimens of amorphous copolyesters (aCOPs) were used to push forward the EWF concept.
Abstract: The essential work of fracture (EWF) concept seems to be a proper and easy way to determine the inherent fracture behavior of ductile polymers. Unfortunately, all experiments reported until now were performed on polymers which did not meet the basic requirement of this fracture mechanical approach, viz. full ligament yielding prior to onset of crack growth. This problem often resulted in wrong conclusions and useless discussions on the specimen preparation, including notching techniques. By using tensile-loaded deeply double-edge notched (DDEN-T) specimens of amorphous copolyesters (aCOP) it was demonstrated that they are, in fact, the optimum choice to push forward the EWF concept for ductile polymers. Full ligament yielding before crack growth was evidenced by infrared thermographic (IT) frames taken during the loading of the DDEN-T specimens. The yielding “marked” with a load-drop in the corresponding load-displacement curves, enabled to split both the specific essential and non-essential work of fracture into their contribution terms: yielding and necking incl. fracture, respectively. It was argued that this EWF approach is most straightforward for the toughness description of such amorphous polymers that undergo necking by (multiple) shear banding without considerable strain-hardening, as aCOPs do.
66 citations
TL;DR: In this paper, the function of far UV radiation was examined with low density polyethylene (LDPE) substrate, polyethyleneterephthalate (PET) film as filter, and an high pressure mercury (HPM 15) lamp as UV radiation source.
Abstract: With low density polyethylene (LDPE) film as substrate, polyethyleneterephthalate (PET) film as filter, and an high pressure mercury (HPM 15) lamp as UV radiation source, the function of far UV radiation was examined The results show that when the far UV (200–300 nm) was eliminated, the rate of polymerization of acrylic acid in the interlayer between two LDPE films initiated by benzophenone (BP) dramatically decreased, and the grafting efficiency became close to zero The decisive effect of the far UV is further confirmed in UV-VIS spectra measuring the hydrogen abstraction reaction of the excited BP For polymerization systems containing allylic hydrogens, this effect is smaller, while hydroxycyclohexyl phenyl ketone (HHPK) and benzoyldimethylketal (BDK), which are typical photocleaving initiators, show little sensitivity to the far UV Based on an energy graph of the excited states, the bond energies and the relevant photochemical reactions a tentative interpretation of the results has been made
48 citations
TL;DR: In this paper, transmission electron microscopical and rheological investigations have been performed on polymer blend systems of the type A/B, A/A-b-B-B/B and A/C-b, B-B, C-b and C-B copolymer with poly(cyclohexyl methacrylate) being thermodynamically miscible with A. The sphere-size distribution was estimated from the TEM data and found to be monomodal for all blends.
Abstract: Transmission electron microscopical and rheological investigations have been performed on polymer blend systems of the type A/B, A/A-b-B/B, and A/C-b-B/B, where B is poly(methyl methacrylate) as the continuous and A is polystyrene as the dispersed phase. A-b-B is the corresponding diblock copolymer, and C-b-B is a diblock copolymer with poly(cyclohexyl methacrylate) (C) being thermodynamically miscible with A. The sphere-size distribution was estimated from the TEM data and found to be monomodal for all blends. Smaller sphere sizes in the A/C-b-B/B blends compared with the A/A-b-B/B blends prove the efficiency of the enthalpic acting compatibilizer.
46 citations
TL;DR: In this paper, the availability of these materials was used to determine whether there was any difference in the particles' reinforcing ability between ordered and random arrangements, and it was found that having the filler particles regularly arranged had little effect on these properties, and there was no anisotropy in their mechanical behavior.
Abstract: In an earlier investigation, poly(methyl acrylate) nanocomposites containing silica particles were found to have novel optical properties when the particles were regularly spaced rather than randomly located. The availability of these materials was used to determine whether there was any difference in the particles' reinforcing ability between ordered and random arrangements. The two types of composites were compared using near-equilibrium mechanical property measurements in uniaxial or equi-biaxial deformation, and dynamic mechanical properties measurements. It was found that having the filler particles regularly arranged had little effect on these properties, and that there was no anisotropy in their mechanical behavior. Related experiments could possibly be used to clarify the long-standing question of the importance of particle aggregation in elastomer reinforcement.
43 citations
TL;DR: In this article, the free radical polymerization of chloromethylstyrene (CMS) with benzoyl peroxide (BPO) as initiator and 2,2,6,6 tetramethyl-1-piperidiniloxy (Tempo) as counter radical was studied.
Abstract: The free radical polymerization of chloromethylstyrene (CMS) with benzoyl peroxide (BPO) as initiator and 2,2,6,6 tetramethyl-1-piperidiniloxy (Tempo) as counter radical was studied. The living character was demonstrated by the linear dependence of \(\overline {M_n } \) versus conversion like that the control with polydispersity lower than 1,5. In a second step, styrene was introduced in polychloromethylstyrene capped with Tempo to produce PCMS-b-PS block copolymers (12,000/60,000) with and PCMS-Tempo macroinitiator efficiency closed to 85%.
43 citations
Abstract: The temperature dependence of the Fourier transform Raman spectrum of polycarbonate has been investigated. C−O−C stretching and C−H stretching modes were found to be temperature-sensitive. The changes noted indicate the presence of a cis-trans conformation for the crystalline polymer, while the cis-cis conformation predominates in amorphous polycarbonate.
43 citations
TL;DR: In this paper, the authors synthesize CdS nanoparticles with narrow size distribution in polymer networks, and they have a hexagonal structure, and the particles size can be controlled by varying the amount of H2S.
Abstract: CdS nanoparticles were synthesized in polymer networks. EDAX data show that the content of Cd2+ was about 3%wt. The particles size can be controlled by varying the amount of H2S, and the absorption spectra indicated that the band edge shifts toward blue with decreasing the particles size. TEM and diffraction data show that the CdS nanoparticles with narrow size distribution were well assembled in polymer networks, and it has a hexagonal structure.
42 citations
TL;DR: In this article, the synthesis of furanic polyesters was conducted according to a transesterification procedure, and regular linear macromolecular structures were obtained with molecular weights well above those previously reported for similar polyesters prepared by more conventional routes.
Abstract: This paper describes a preliminary set of results concerning novel systems in which the synthesis of furanic polyesters was conducted according to a transesterification procedure. Regular linear macromolecular structures were thus obtained with molecular weights well above those previously reported for similar polyesters prepared by more conventional routes.
42 citations
TL;DR: In this paper, phase transformation toughening (PTT), characterized by a transition from a metastable to a stable crystalline phase and associated with volume expansion, is used for toughness improvement of metals and ceramics.
Abstract: Phase transformation toughening (PTT), characterized by a transition from a metastable to a stable crystalline phase and associated with volume expansion, is widely used for toughness improvement of metals and ceramics. The essential prerequisites of this toughening concept are met also for semicrystalline polymers since they are polymorphous and capable to undergo transformation from one crystalline phase to an other under mechanical stresses. The transition is, however, mostly connected to volume contraction, i.e. just the opposite what is being exploited in toughened steels and ceramics. It was argued that an irreversible transformation from a less dense crystalline phase to a more dense one could also be beneficial for toughness upgrading in polymers. This transition is combined with changes in lamellar and molecular level resulting in a “strain-hardened” microstructure, that can be considered as the best possible response of the polymer upon mechanical loading (“adaptive” toughening). The main advantage of the PTT concept is that toughness improvement is achieved without incorporation of foreign materials which is the guarantee of easy recycling.
41 citations
TL;DR: In this article, a method to improve the accuracy of the interpretation of TGA data was proposed to predict blend composition with an error less than 3%, even when there is an appreciable superposition between the temperature degradation range of starch and poly(ethylene-co-vinyl alcohol).
Abstract: Thermogravimetric analysis (TGA) has been shown to be a useful technique to determine the content of starch and other components that are usually present in blends of starch with synthetic polymers. However, some of these blends are composed of elements with an important superposition in their temperature degradation range. In these cases interpretation of the TGA results becomes quite difficult and usually important errors are committed in the determination of blend composition. We present here a method to improve the accuracy of the interpretation of TGA data. The analysis was developed to study blends containing starch, an ethylene-vinyl alcohol copolymer, and water plus glycerin as plasticizers. Using this procedure it is possible to predict blend composition with an error less than 3%, even when there is an appreciable superposition between the temperature degradation range of starch and poly(ethylene-co-vinyl alcohol). As the proposed method of analysis is quite general it may be extended to be used with other types of blends that give thermograms with similar characteristics to those described in this paper.
TL;DR: A living free radical polymerization process was adopted to synthesize a narrow polydispersity fullerene-end-capped polystyrene(NPFECPS).
Abstract: A living free radical polymerization process was adopted to synthesize a narrow polydispersity fullerene-end-capped polystyrene(NPFECPS). The UV-Vis, DSC, GPC demonstrated that fullerene(C60) was chemically bonded to polystyrene successfully, and C60 was almost monosubstituted. The NPFECPS can be dissolved in a variety of solvents, such as THF, toluene, trichloromethane, and so on. The good photoconductivity is also found for NPFECPS.
TL;DR: In this paper, a simple theoretical model including different motions in polymer network was extended by the discussion of an anisotropy parameter of segmental motion not only for the intercrosslink chains but also for the dangling ends.
Abstract: Structure and dynamics of unfilled and carbon black filled natural rubber vulcanizates were investigated by means of transversal1H-NMR-relaxation. A simple theoretical model including different motions in polymer network was extended by the discussion of an anisotropy parameter of segmental motion not only for the intercrosslink chains but also for the dangling ends. It makes characterization of the filling state of the network possible to approximate. The effect of increasing correlation times τf of the fast anisotropic local motion with reduction of the molecular mass of intercrosslink chains which was observed, but not cleared up in previous investigation is evidently smaller by using this modified model in accordance with the expectation of a local motion. The determined values of Mc are in good agreement with the results of fits by using the unmodified relaxation function.13C-NMR-spectra and stress-strain-experiments are leading in most cases to similar results, especially for Mc.
TL;DR: In this article, the phase diagram of AB-diblock copolymers is calculated taking the homogeneously mixed system as a reference state, and the predicted value (χN)c = 10.385 for a symmetric AB-block copolymer compares very well to the result of the original Random Phase Approximation theory.
Abstract: Based on the description of AB-block copolymers as micellar structures given by Semenov, the phase diagram of AB-diblock copolymers is calculated taking the homogeneously mixed system as a reference state. The predicted value (χN)c = 10.385 for a symmetric AB-diblock copolymer compares very well to the result of the original Random Phase Approximation theory (10.495). The simplicity of the model allows its extension to predict order-order transitions in ABC-triblock copolymers.
TL;DR: Carboxymethyl cellulose (CMC) was treated in a dipolar-aprotic solvent like N,N-dimethylacetamide, or dimethylsulfoxide (DMSO) with p-toluenesulfonic acid yielding a high reactive gel-suspension of the polymer.
Abstract: Carboxymethyl cellulose (CMC) was treated in a dipolar-aprotic solvent like N,N-dimethylacetamide, or dimethylsulfoxide (DMSO) with p-toluenesulfonic acid yielding a high reactive gel-suspension of the polymer. This mixture allows a direct esterification of free hydroxyl groups of CMC as exemplified by acylation with carbonic acid chlorides, or anhydrides, and with isocyanates as well as by sulphation, phosphating and silylation. The products characterized by elemental analysis and FTIR spectroscopy possess a high degree of functionalization.
TL;DR: In this article, a functional copolymers consisting of ethene and 4-vinylcyclohexene (4-VCH) were synthesized by a stereorigid metallocene/methylalumoxane catalyst.
Abstract: New functional copolymers consisting of ethene and 4-vinylcyclohexene (4-VCH) were synthesized by a stereorigid metallocene/methylalumoxane catalyst. The content of 4-VCH depends on the polymerization temperature, thus influencing the polymeric properties. Investigations of the microstructure were made using 13C NMR spectroscopy, thus revealing that 4-VCH is inserted regioselectively into the growing polymer chain. Hydroboration of selected copolymers followed by an oxidative workup yielded polyacohols which display different polymeric properties than the precursor
TL;DR: In this article, the swelling ratio dependence on temperature was found to be significantly more prominent for block terpolymers than for the corresponding random ter polymers, even at concentrations as low as 10 mol%.
Abstract: Hydrogels prepared by block terpolymerization of N-isopropylacrylamide (NIPAAm), acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA) exhibit significant temperature sensitivity due to the block structure of the NIPAAm moiety, even at concentrations as low as 10 mol%. pH-Sensitivity was also observed due to the ionizable AA component. The swelling ratio dependence on temperature is significantly more prominent for block terpolymers than for the corresponding random terpolymers.
TL;DR: In this paper, the enzyme-catalyzed synthesis of poly(1,6-hexanediyl terephthalate) and poly( 1, 6-hexaneediyl isophthalate) is described.
Abstract: The enzyme-catalyzed synthesis of poly(1,6-hexanediyl terephthalate) and poly(1,6-hexanediyl isophthalate) is described. An unsuccessfull attempt to synthesize poly(1,6-hexanediyl o-phthalate) is also presented and the reactivity of those three monomers is discussed according to the enzymatic nature of the catalyst. The crude polyesters are characterized by 1H and 13C NMR spectroscopy and by differential scanning calorimetry. Macrocycles are isolated from poly(1,6-hexanediyl isophthalate) and characterized by steric exclusion chromatography and by mass spectrometry. The number-average molar masses and the thermal properties of the crude, linear and cyclic polyesters are also reported.
TL;DR: In this article, the authors investigated the influence of scanning rate on the shape of DSC melting curves in semicrystalline polymers in which the melting point varies spatially within the sample.
Abstract: We have investigated the influence of scanning rate on the form of DSC melting curves in semicrystalline polymers in which the melting point varies spatially within the sample. A numerical solution for the heat balance in the sample cell was used, taking into account heat absorbed during the melting transition for a given sample mass. The simulation accounted well for the effects of scanning rate on the shape of the DSC peak for polyoxymethylene samples crystallized above 150°C, which were assumed to be free from effects arising from lamellar thickening during the scan.
TL;DR: In this article, an initiator for living free radical polymerization may be prepared by trapping the benzylic ethylbenzene radical with the stable 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) radical.
Abstract: An initiator for living free radical polymerization may be prepared by trapping the benzylic ethylbenzene radical with the stable 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) radical. The adduct, 2,2,6,6-tetramethyl-1-(1-phenethyloxy)piperidine (TMPEP), smoothly undergoes thermal fragmentation at temperatures approaching 140° C to afford an active carbon radical capable of initiating polymerization and a passive mediating nitroxyl radical to reversibly cap and preserve the propagating polymer chain.
TL;DR: In this article, a new β-substituted-β-lactone (malolactonic acid), which was considered as totally unstable due to the presence of a carboxyl group, has been isolated, characterized and prepared in large quantities.
Abstract: Racemic and optically active 4-carboxy-2-oxetanones have been prepared, starting from racemic, (R)-4-benzyloxycarbonyl-2-oxetanone, by catalytic hydrogenolysis of the lateral benzyl protecting group. This new β-substituted-β-lactone (malolactonic acid), which was considered as totally unstable due to the presence of a carboxyl group, has been isolated, characterized and prepared in large quantities. The liberated carboxylic acid function can be used for coupling reactions with different types of molecules in the goal to tailor make functionalized multimeric macromolecules (reactive polymers, supported catalysts, liquid crystals polymers, macromolecular prodrugs). This possibility has been examplified by using 2, 4, 5-trichlorophenol as activating agent and chloramphenicol as bioactive molecule, which have been bound to malolactonic acid and then copolymerized by anionic ring opening polymerization in the presence of 4-benzyloxycarbonyl-2-oxetanone. It has been shown that this new route conducts to activated derivatives of poly (malic acid) and polymeric drug carriers patterns.
Abstract: Poly(glycidyl azide), PGA, was grafted onto Hydroxyl Terminated Poly(butadiene), HTPB, via free radical mechanism. PGA-macro azoinitator and HTPB polymer mixture was casted from solution and the polymer film was kept at 90°C for 4 hours. The grafted polymer was isolated from the product by fractional precipitation and characterized by NMR and FT-IR spectroscopy. Graft copolymer structure was also confirmed that volume ratio of nonsolvent to the solution of the graft copolymer was between those of corresponding homopolymers. TGA traces of the block polymers were containing two different maxima at 253°C (for PGA units) and 469°C (for HTPB units). Because of the incompatibility of the blocks, DSC curve showed two Tg's which belong to the related segments.
TL;DR: In this article, the adsorption of some cationic dyes such as basic red 9 (BR 9), basic green 4 (BG 4), cresyl violet (CV), and basic blue 20 (BB 20) on AAm/IA hydrogels is studied by batch adsorization technique.
Abstract: Acrylamide/itaconic acid (AAm/IA) hydrogels prepared by irradiating with γ radiation were used in experiments on the adsorption of some cationic dyes such as basic red 9 (BR 9), basic green 4 (BG 4), cresyl violet (CV), and basic blue 20 (BB 20). Adsorption of the cationic dyes onto AAm/IA hydrogels is studied by batch adsorption technique. In the experiments of the adsorption, Langmiur type adsorption in the Giles classification system was found. Monolayer coverages for AAm/IA hydrogel-dye systems were calculated by using B point method. Adsorption studies indicated that monolayer coverages of AAm/IA hydrogel by these dyes were increased with following order; BB 20>CV>BR9>BG 4.
TL;DR: In this article, the effect of the comonomer chain length and amount on density, melting temperature, and heat of fusion was studied for copolymers of ethylene and 1-octene.
Abstract: Copolymers of ethylene and 1-octene, 1-tetradecene and 1-octadecene were synthetized in order to study the effect of the comonomer chain length and amount on density, melting temperature and heat of fusion. They were also compared with the properties of the copolymers obtained with the heterogeneous titanium catalyst. It could be seen that the density/melting-area of the copolymers obtained with the zirconocene catalyst was much broader than with the titanium catalyst. It could also be seen that with the same comonomer content 1-tetradecene gave lower density of the copolymers than 1-octene. However, no difference were seen between the densities of the copolymers obtained with 1-tetradecene and 1-octadecene. The melting temperature of the copolymers was seen to be the lower the longer the comonomer was. In the area of the high branching amount the linear correlation was not in work. It was also shown that the differences in the heat of fusions could only be seen at high amount of branches (>15 branches/1000C): the longer the comonomer the lower amount of heat was needed to melt the copolymer.
TL;DR: In this article, the degree of conversion (θ), the complex stability constant, K, and the thermodynamic parameters of these reactions were evaluated, and values of θ near unity were obtained for the higher molecular weight samples.
Abstract: Interpolymer complexing of poly(acrylic acid) (PAA) with poly(N-vinyl-2-pyrrolidone) (PVP) as well as with chitosans (CHI) of various chain lengths was studied at different temperatures by pH measurements. The degree of conversion (θ), the complex stability constant, K, and the thermodynamic parameters of these reactions were evaluated. Complexing proceeds cooperatively in both systems and values of θ near unity are obtained for the higher molecular weight samples. The variation of K with θ for the PAA-CHI system indicates that this complex comprises long sequences of bound pairs of monomer units.
TL;DR: In this article, the shrinking behavior of the bulk materials obtained by this combination of the sol-gel process with the thiol-ene polymerization were investigated, which can be crosslinked by the photoinitiated reaction with multifunctional thiols.
Abstract: Bicyclo[2.2.1]hept-2-ene-5-yl (norborn-2-ene-5-yl) derivatives of silic acid were synthesized by the Diels-Alder reaction, of the corresponding (meth)acryloxypropyl silanes with cyclopentadiene monomer. The norbornenyl silanes were characterized by elemental analyses, IR, 1H NMR, 13C NMR and 29Si NMR spectroscopy. The hydrolysis and condensation of norbornene-funktionalized silic acid esters yield polysiloxanes which can be crosslinked by the photoinitiated reaction with multifunctional thiols. The shrinking behaviour of the bulk materials which are obtained by this combination of the sol-gel process with the thiol-ene polymerization were investigated.
TL;DR: In this article, the authors investigated the structural properties of polyphenylene sulfide (PPS)/glass fiber composites according to the glass fiber content and testing temperature change and found that the fracture surface became more rugged as the glass fibre content increased.
Abstract: Mechanical properties and corresponding microstructures of polyphenylene sulfide(PPS)/glass fiber composites were investigated according to the glass fiber content and testing temperature change. Tensile test results showed that maximum stress and elastic modulus increased markedly with increasing glass fiber content at below the glass transition temperature(Tg) of PPS matrix. Notched Izod impact strength showed a maximum value at the glass fiber content of 40 wt% regardless of testing temperatures. Scanning electron microscope (SEM) observation of tensile and impact fractured specimens showed that, at the same testing temperature condition, the fracture surface became more rugged as the glass fiber content increased. Polarized optical microscope(POM) observation showed the crack tip bifurcation at the glass fiber surface in tensile fractured specimens, whereas glass fiber breakdown in impact fractured specimens at higher glass fiber content.
TL;DR: Gelation of polyvinyl alcohol (PVA) in dimethyl sulfoxide (DMSO)/water was observed at 23°C with viscometry, spectrophotometry, wide angle X-ray scattering and light scattering as discussed by the authors.
Abstract: Gelation of poly(vinyl alcohol) (PVA) in dimethyl sulfoxide (DMSO)/water was observed at 23°C with viscometry, spectrophotometry, wide angle X-ray scattering and light scattering. Here transparent gel formation was found to take place prior to being turbid in some cases, whereas the solution became turbid prior to gelation in other cases. Whether transparent gel is formed at first or solution becomes turbid, depends on DMSO composition. PVA solution forms gel in the DMSO composition range from 20 to 80 wt.%. Below the boundary DMSO composition of 60–70 wt.%, gelation takes place at first (i.e. transparent gel is formed) and then becomes turbid eventually, while beyond this DMSO composition the solution becomes turbid and then opaque gel is formed.
TL;DR: In this paper, the surface modification of low-density polyethylene (PE) by liquid phase photograft polymerization with acrylic acid(AA), acrylamide(AM), and glycidyl methacrylate(GMA) was described.
Abstract: The surface modification of low-density polyethylene(PE) by liquid phase photograft polymerization with acrylic acid(AA), acrylamide(AM) and glycidyl methacrylate(GMA) was described. The grafting of AA and AM was proved and characterized by electron spectroscopy for chemical analysis(ESCA). It was found that fully hydrophilic surface can be obtained in very short irradiation time. With ESCA and attenuated total reflection infrared spectroscopy(ATR-IR), it can be confirmed that bifunctional monomer GMA was grafted onto the PE film surface. Through further reaction with GMA grafted film, heparin and protamine were immobilized onto the grafted film surface.
TL;DR: In this article, the authors explored the effect of a cross-linking agent on the drag reduction capability of hydroxypropyl guar and guar gum solutions in turbulent flow through horizontal pipes.
Abstract: In this work we explore the effect of a cross-linking agent on the drag reduction capability of hydroxypropyl guar and guar gum solutions in turbulent flow through horizontal pipes. The results show that the addition of a cross-linking agent (borax) to solutions with concentrations below those required for gel formation enhances drag reduction due to the increased dimensions of the macromolecules in the presence of intermolecular cross links. The flow-induced degradation of the polymers is not appreciably affected by the addition of cross-linking agent.