Crosslinking of epoxidized natural oils with diepoxy reactive diluents

The different natural oils epoxidized with 3‐chloroperbenzoic acid were crosslinked with diepoxy reactive diluents, bisphenol A propoxylate diglycidyl ether, and 3,4‐epoxycyclohexylmethyl‐3,4‐epoxyclohexane‐carboxylate, using cationic initiator at 60°C and photoinitiators at the room temperature. The insoluble fraction of the polymeric products was 59–90%. The Young modulus of the crosslinked polymer films ranged from 2 to 861 MPa. The 10% weight loss temperatures of the crosslinked polymers estimated by thermogravimetric analysis were in the range from 250 to 420°C. The water vapor transmission rate of the crosslinked biopolymer films ranged from 6 to 49 g/m²/24 h. Biochemical oxygen demand and biodegradation in soil of the crosslinked polymers were studied. The crosslinked polymers showed higher biodegradation rate than cellulose, starch, and polyvinylalcohol. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Hyperbranched poly(arylene ether phosphine oxide)s

Summary New AB₂ and A₂B monomers, bis(4-fluorophenyl)-4'-hydroxyphenylphosphine oxide and bis(4-hydroxyphenyl)-4'-fluorophenyl-phosphine oxide were prepared and converted to corresponding hyperbranched poly(arylene ether phosphineoxide)s with hydroxyphenyl and fluorophenyl end functional groups. While the dihydroxy monomer gave a low molecular weight polymer, the difluoro monomer produced a high molecular weight hyperbranched polymer. The glass transition temperature of the obtained polymers was 266°C and 230°C, and 5% weight loss temperature was 491 °C and 391 °C, respectively. The fluorophenyl-terminated hyperbranched polymer was soluble in CHCl₃, but the hydroxyphenyl-terminated polymer was not soluble in CHCl3 even though it has lower molecular weight than the fluorophenyl-terminated polymer, indicating that properties of the hyperbranched polymers markedly depend on end functional groups as well as their molecular weight. Received: 23 August 2000/Revised version: 19 October 2000/Accepted: 31 October 2000     

Relaxation Behavior of Poly(N-monosubstituted Methacrylamides)

Abstract

A free-oscillating torsional pendulum was used to investigate the effect of substituents R on the dynamic mechanical relaxation behavior of poly(N-monosubstituted methacrylamides) in the temperature interval from –196 to 130°C. A comparison with the corresponding polymethacrylates shows that the relaxation motion of the side groups R, which gives rise to the low temperature dispersion (below – 130°C), is virtually independent of whether R is attached to COO or CONH groups. On the other hand the obtained data give evidence that a strong intermolecular interaction and high steric hindrances suppress the onset of the motion of CONH–R side chains as a whole. For the same reason the glass transition temperature of the poly(N-monosubstituted methacrylamides) is about 100°C higher than that of the corresponding polymethacrylates. The incorporation of low molecular weight substances leads to reduction of the low-temperature dispersion and to formation of a new secondary dispersion at a temperature of about – 100°C (1 Hz); with increasing concentration of the diluent this new dispersion becomes more intensive and shifts toward lower temperatures. These and the earlier data indicate that the transformation of the secondary relaxation processes due to the effect of diluents is likely of more general character.     

Thermal analysis of poly(phenylene sulfide) polymers. I: Thermal characterization of PPS polymers of different molecular weights

Thermal properties of Fortron®

1 ®Registered trademark of Hoechst Celanese Corporation.

poly(phenylene sulfide) (PPS) polymers of different molecular weights were studied by DSC. Crystallization studies revealed that the ability of these polymers to crystallize decreases with increasing molecular weight. The Avrami equation poorly describes the isothermal crystallization of PPS. Lamellar crystallization was observed for the lowest molecular weight sample. For the other, higher molecular weight polymers the Avrami exponent is always between 2 and 3, suggesting development of distorted spherulites with heterogeneous nucleation. The temperature dependence of the solid and melt heat capacities have been determined. The solid specific heat capacity did not exhibit a molecular weight dependence. The heat capacity increase at the glass transition, T_g, has been calculated to be 28.1 J°C^?1 mole^?1. The equilibrium melting point of PPS has been estimated to be 348.5°C using the Hoffman–Weeks method. The T_g of PPS increases with molecular weight. The T_g of the highest molecular weight evaluated is 92.5°C. A DMA relaxation peak corresponding to the onset of the phenylene ring rotation occurs at ?92°C. Only the highest molecular weight could be quenched to a completely amorphous state.     

Viscoelastic properties of linear polymers in the fluid state and their transition to the high-elastic state

The experimental results of the Viscoelastic properties of linear polymers of narrow molecular weight distribution (MWD) and of their mixtures have been analyzed and generalized. Based on the study of the properties of polymers of narrow MWD, we propose a classification of high molecular weight compounds. It specifies a distinct boundary between oligomers and polymers, assuming that the most important feature of polymers is the manifestation of large high-elastic recoverable deformations of entropy character. For polymers to be characterized, not the absolute molecular weight is essential, but the molecular weight referred to the boundary values. The corresponding state for polymers is attained at temperatures 100°C away from the glass temperature. The transition from the fluid to the high-elastic state with increasing deformation rate (or frequency for cyclic deformation) has been studied. Transition to the high-elastic state takes place over a narrow stress range (0.1-1.0 dynes/cm²), independent of molecular weight, whereas the critical deformation rates (frequencies), like viscosity, depend greatly on molecular weight. An increase in the amount of deformation shifts, to u certain extent, this transition to lower Kites of deformation (frequencies). In the region of deformation rates (frequencies) corresponding to the high-elastic state, the effect of large deformations during shear manifests itself largely in the tear-off of polymers Iron, the confining surfaces and in specimen rupture. Polydispersity has a strong effect on the properties of polymeric systems. As the rate of deformation is increased, the transition proceeds successively from the higher molecular weight components. This relaxational transition is tantamount to a change of the structure for polymeric systems. It is responsible for non-linear, particularly, non-Newtonian behavior of such systems. The transition to the high-elastic state and all the related phenomena are observed also in concentrated solutions of high molecular weight polymers. The long-term durability of un-cured rubbers in the high-elastic state is described by the same relationships.     

Characterization of modulus and glass transition phenomena in poly(L‐lactide)/hydroxyapatite composites

In order to study the dynamic‐mechanical properties of Poly(L‐lactide)/Hydroxyapatite (PLLA/HA) composites, two different molecular weight (inherent viscosity (η_inh): 4.0 (dL/g), and 7.8 (dL/g)) poly(L‐lactide) (PLLA) were synthesized by bulk polymerization and filled with 10%, 30%, and 50% (w/w) with medical grade HA (size range: 25–45 μm and Ca/P = 1.69). The plain PLLA polymers and PLLA/HA composites were compression molded and machined to yield 50 × 3 × 2 mm³ specimens. The composites were investigated by dynamic mechanical thermal analyzer (DMTA) of imposed bending load on rectangular specimens over a temperature range from 30 to 120°C using multiple frequencies (0.3–50 Hz). The results showed that the bending storage modulus (E′) of the composites increased linearly with the percentage of the filler, reaching at 37°C and 0.1 Hz about 2.5, 3.7 and 5.0 GPa with 10, 30 and 50% of HA respectively. The glass transition temperature, evaluated at the tan δ peaks, were in the range 70–80°C and 50–70°C for PLLA matrix and PLLA composites respectively. The activation energies at the glass transition temperature were calculated from the Arrhenius plot in the range of 102–111 Kcal/mol for the composites, whereas 132 and 148 Kcal/mol were found for low and high molecular weight of PLLA respectively. The content of amorphous phase was evaluated from the intensity of tan δ peak. Results showed that HA causes an amorphous phase with a greater mobility with respect to the pure PLLA.     

Characterization of poly(methyl methacrylate) from radiation-induced polymerization in the presence of a kaolin clay substrate

Two types of polymer are formed in the radiation-initiated polymerization of methyl methacrylate (MMA)–kaolin clay complexes. Homopolymer can be extracted from the complex by the use of organic solvents. Inserted polymer must be removed by dissolution of the polymer–clay complex with hydrofluoric acid. The polymers formed show no differences in structure (as determined by infrared analysis), had high molecular weights (1–5 × 10⁶), and had similar molecular weight distributions (as determined by GPC). The molecular weights of the homopolymer increased as temperature increased (25°–75°C), and dose rate decreased (24.9–7.35 rads/sec). The isotacticity of the polymers when compared to irradiated bulk polymer decreased as follows: inserted > homo > bulk. The compressive properties of the irradiated composite compared well with those of commercial bulk polymers. Degradation temperatures were 20° to 30°C higher for the composite than for the commercial chemically initiated bulk polymer.     

Radical high pressure polymerization of ethylene with stable initiators

In order to assess the suitability of stable initiators for the high pressure polymerization of ethylene, polymerization tests were carried out in a stirred autoclave in continuous operation. The pressure used was 1700 bar, the average residence time 30 seconds and the temperature was adjusted to between 200 and 360°C. The initiator concentration in the ethylene feed varied between 4 and 40 mol ppm. Di-tert-butyl peroxide, di-tert-amyl peroxide, tert-butyl hydroperoxide, and 3,4-di-methyl-3,4-di-phenyl hexane, a C? C labile compound, were chosen for use as stable initiators. The level of conversion and the specific initiator consumption were determined. The polymers obtained were characterized by measuring their density, average molecular weight, and melt flow index. The stable initiators used were all characterized by a very low level of consumption. In the case of dialkyl peroxides and alkyl hydroperoxide, the optimum application temperature is substantially above 200°C and above 300°C in the case of the C? C labile initiator. Under these conditions, polymers with a low density, a low molecular weight, a narrow molecular weight distribution and a high melt flow index were obtained.     

Synthesis and thermal,optical and morphological characterization of oligomeric polyamides based on thiophene and alkyl/phenyl‐silane moieties. Study of the electrospun deposition process

Polyamides were synthesized from a thiophene‐containing diamine by direct polycondensation with organosilane acyl dichlorides. The obtained polymers had good solubility in common organic solvents and THF, with TDT_10% values upper than 400 °C and T_g between 150 and 180 °C. Combination of these properties reveals that the processability of the polymers was increased with respect to traditional aromatic polyamides. Inherent viscosity values and SEC analysis indicated low molecular weight species. Samples showed high visible transparency and bandgap values associated to insulating materials. Polymer solutions were deposited using electrospun technique and their surface properties were studied by SEM. Spheres were created according to electric field applied during deposition process. Low molecular weight and conductivity prevent charge accumulation in the surface hindering fibers generation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43702.     

Viscoelastic properties and stability of BBL ladder polymers

Viscoelastic properties of the BBL ladder polymer were determined by a dynamic mechanical technique for the temperature range ?150°C to 250°C and at frequencies of 3.5, 11, and 110 Hz. A secondary loss dispersion centered at ?50°C (at 110 Hz) was discovered which probably arises from an in-chain relaxation mechanism. The loss dispersion resembles β-transitions found in more conventional polymers in intensity (maximum tan δ = 0.035), activation energy( E = 19,000 cal/mole), and in its close relation to the high-temperature mechanical properties of the polymers. Only slight changes in the low-temperature loss peak cause significant increases in brittleness. It is proposed that such changes, produced by a variety of environments, result from random chain scission at imperfection points in the ladder structure. For this reason we conclude that improving the environmental stability of BBL is of prime importance in its further development for specific applications.     

External Effects on the Structure and Dynamics of Molecules in Oriented Polyolefins

Abstract

Oriented polyethylene samples are investigated mechanically, thermally and by oxidation. A complicated character of changes in mobility of molecules on static loading of oriented polyolefins is studied. The influence of deformation, stretching, molecular mass and its distribution on the value and sign of this change is found. The regularities of structural changes in the course of ozone oxidation are revealed. It is shown that the initial stage of oxidation is followed by a considerable improvement of mechanical properties. At a greater extent of oxidation the dependence of molecular mobility on reversible deformation of highly oriented samples of medium molecular weight (MW) and narrow molecular weight distribution (MWD) is reversed. A relaxational transition is observed over the temperature range of from 40°C to 60°C for polyethylene and from 60°C to 70°C for polypropylene. After ozone oxidation at a temperature above 90°C and oxidation under load and subsequent annealing (at the temperature of relaxational) transition the latter is not observed.     

Effect of molecular weight distribution on polymer diffusion during film formation of two-component high-/low-molecular weight latex particles

We describe fluorescence resonance energy transfer (FRET) studies of film formation by a new type of two-component latex particles. These particles consist of a miscible blend of two components that have a similar composition but very different molecular weights. In our approach, we used sequential seeded emulsion polymerization to generate (in situ) a fraction of oligomer in poly(butyl acrylate-co-methyl methacrylate) P(BA-MMA) seed particles that contained a relatively high molecular weight (high-M) dye-labeled polymer. In this way we could systematically change the molecular weight distribution of polymer inside the particles. We varied the amount and the molecular weight of the oligomers. For latex films cast from these two-component particles, we studied the diffusion rate of the high molecular weight polymer by FRET. These measurements revealed that oligomers promoted diffusion rate during latex film formation (oligoplasticization). We analyzed our diffusion data in terms of the Fujita–Doolittle free-volume model and showed that higher molecular weight oligomers are less efficient as plasticizers. In separate experiments, oligomers with similar molecular weights as those in the two-component particles were introduced via latex blending. We compared oligoplasticization in latex blends films with that in the two-component particles films. Finally, we investigated the rheological behavior of the two-component polymers with compositions adjusted to have a common T_g (2 °C). The higher the molecular weight of the oligomer, the more that had to be added to achieve T_g = 2 °C. All of the oligomers were much shorter than the entanglement length and act as diluents of the entanglements in the high-M polymer. We found that incorporating larger amounts of oligomers with a higher molecular weight resulted in a more pronounced drop in polymer viscosity, associated with the decrease in the entanglement density.     

The effect of the molecular weight on thermal degradation of fractionated PVC

A commercial PVC and another one prepared in bulk at 40°C were fractionated by means of fractional solution method using cyclohexanone-methanol mixtures. Both fractionations resulted in two sets of fractions. Their thermal degradation at 175, 180 and 185°C was followed by means of a conductivity cell which allows a continuous titration of the evolved HCl. The results showed that the lower the molecular weight the higher the degradation rate was; nevertheless, this relationship is only valid up to molecular weights of 60 000 to 90 000, from which the degradation rate appeared to be independent on the molecular weight. The UV-visible spectra of the degraded polymers suggest a similar polyene sequence distribution for all the fractions which accounts for a similar mechanism of degradation in contrast to what happens to fractions with different tacticity.     

Highly active peroxides in the radical polymerization of ethylene under high pressure. Properties of the polymers

Using highly active peroxide initiators, a number of polyethylene samples were prepared at low temperatures of 70–140°C and a pressure of 1900 bar. The average molecular weight and the melt flow index were adjusted by adding propionaldehyde as modifier. The characteristic properties of the samples as regards the molecular weight distribution, the average molecular weight, the frequency of long chain branching, the crystallinity and the density were determined. As expected, the polymers are characterized by density values of more than 0.955 g/ml and crystallinity values of 65–80% which are characteristic of PE-HD. The molecular weight distribution, too, remains within narrow limits. On the other hand, rather surprisingly, a relatively high frequency of long chain branching typical of PE-LD is obtained. The investigation of the phase behaviour has shown that polymerization under high pressure at temperatures above 115–118°C takes place in the homogeneous range. The samples polymerized in the transition zone between the single and the two phase area exhibit maximum crystallinity and melt enthalpy. The frequency of long chain branching passed through a minimum.     

A new method for producing optically active polybutadiene

The anionic polymerization of butadiene monomer in cyclohexane at 20°C gave polybutadiene (PB50) with a narrow molecular weight distribution. This polymer was allowed to react with 4-phenyl-1,2,4-triazoline-3,5-dione via the ‘ene’ reaction to the extent of 5, 10 and 15%. These functionalized polymers were reacted with N-phthaloyl-L -leucine acid chloride in the presence of pyridine at room temperature. These reactions lead to the replacement of N-H by an optically active group, and the resulting polymers became optically active. Some structural characterization and physical properties of these optically active polybutadienes are reported. © 1998 Society of Chemical Industry     

Fluoroalkylene ether silicate/Viton GLT blends: An approach toward improved low temperature flexibility

Low molecular weight fluoroalkylene ether silicate (FES) polymers demonstrating glass transition temperatures of ?82°C to ?91°C were obtained from the condensation polymerization of fluoroether bisdimethyl carbinols and bis(dimethylamino)methyl vinyl and dimethyl silane derivatives. Peroxide cure reactivity through the pendant vinyl moieties was demonstrated. In an effort to improve the low temperature flexibility of a peroxide curable fluorocarbon elastomer (Viton GLT from Du-Pont), blends were prepared using the FES material as an additive cocuring plasticizer. Temperature retraction tests demonstrated an optimum 5°C (9°F) improvement in low temperature flexibility. The optimum blend formulation employed FES polymers with vinyl cure site concentrations ranging from 2.35 to 2.70 mol %. The optimum blend formulation maintained the strength and low compression set properties of the Viton GLT standard. These properties reflect sufficient cocuring between the FES and Viton GLT components to provide physical properties adequate for o-ring seal application. o-Ring seal evaluations in Freon E6.5 fluid (rod and piston seal tests) demonstrated some seal enhancement and comparable durability to standard Viton GLT o-rings.     

Viscous behavior of some liquid rubber resins

The flow behavior of several low molecular weight polymers has been studied as a function of shear rate and temperature. These polymers, which had terminating hydroxyl or bromine groups, included homopolymers of polybutadiene and acrylonitrile–butadiene and styrene–butadiene copolymers. Viscosity was measured as a function of shear rate for the temperature range 25°–35°C, and the limiting zero shear viscosities were obtained for the range 25°–60°C. A cone plate viscometer was employed to measure the effect of shear rate on viscosity, and a Brookfield viscometer was used to verify the zero-shear rate values. A tendency of the fluid to flow out of the cone-plate gap was observed for some of the materials studied. From the viscosity data, characteristic times were estimated, and the data were compared with two constitutive equations. A modified Arrhenius equation was fitted to the zero-shear viscosity data. In the case of one material, it was possible to test the Nakajima relationship between viscosity and molecular weight distribution. The dependence of material parameters on temperature is discussed in detail.     

Influence of rheological properties on the sagging of polypropylene and abs sheet for thermoforming applications

The isothermal sagging resistance of different grades of conventional and a high melt strength (HMS) PP has been correlated with the rheological characteristics of the polymers, such as dynamic shear properties, melt strength, and zero shear viscosity. A thermoforming grade of acrylonitrile‐butadiene‐styrene (ABS) was used as a reference material. At 190°C, ABS had the highest viscosity and elastic modulus in the frequency range measured, showing that this polymer is highly elastic. HMS PP had a greater shear thinning behavior than conventional PP because of its broader molecular weight distribution. The tan δ of the polymers showed that conventional PP had a higher tendency to flow than HMS PP and ABS when heated above 172°C. This was confirmed with sagging experiments performed in an air circulating oven, where the rate of sagging decreased as the melt strength and the zero shear viscosity of the polymer increased.     

Mechanical Relaxation in Solid-state Polymerized Poly(ethylene terephthalate)

Abstract

The dynamic mechanical tensile properties, storage modulus E′ and loss modulus E″, of the amorphous and semi-crystalline PET samples, ranging in molecular weight from 15,000 to 300,000 g/mol, were measured over temperature T range from 150°C to +250°C at four frequencies v=3.5, 11, 35 and 110 Hz. The samples with molecular weight larger than 15,000 were produced by solid-state polymerization in high vacuum. An increase in the height of loss β-peak, at T= ?60… -30°C, with an increase in molecular weight was found both in the amorphous and semi-crystalline PET. On the other band, the height of loss β-peak for the amorphous samples appeared to be smaller in comparison with that for the semi-crystalline samples. By contrast, the height of loss δ-peak, at T= + 90. +110°C, for the amorphous samples was larger than for the semicrystalline samples. An increase in the E value with an increase in the molecular weight of the amorphous polymer was accompanied by an increase in the E″ value. This behavior was explained by the effective interpenetrated network of the high-molecular-weight polymer and better short-range ordering in the low-molecular-weight polymer. The intensity of the β-process was found to weaken with an increase in the chain ends concentration in both the amorphous and semi-crystalline samples. This result indicates that there is no contribution of the chain ends to the process of β-relaxation in PET.     

Reverse iodine transfer polymerization of vinyl acetate and vinyl benzoate: synthesis and characterization of homo‐ and copolymers

Homo‐ and copolymers of vinyl esters including vinyl acetate (VAc) and vinyl benzoate (VBz) were synthesized via the reverse iodine transfer radical polymerization technique. Polymerization was carried out in the presence of iodine as the in situ generator of the transfer agent and 2,2′‐azobis(isobutyronitrile) as the initiator at 70 °C. Reverse iodine transfer radical homopolymerization of VAc and VBz led to conversions of 76 and 57%, number‐average molecular weights of 8266 and 9814 g mol^?1 and molecular weight distributions of 1.58 and 1.49, respectively. The microstructure of the synthesized polymers was investigated in detail using gel permeation chromatography, ¹H NMR, ¹³C NMR and distortionless enhancement of polarization transfer (135° decoupler pulse) techniques. Relatively narrow molecular weight distribution and controlled and predictable trend of molecular weight versus conversion were observed for the synthesized polymers, showing that reverse iodine transfer radical homo‐ and copolymerization of VAc and VBz proceeded with controlled characteristics. Results of molecular weight and its distribution along with the ¹H NMR spectra recorded for homo‐ and copolymers indicated that side reactions can occur during the course of polymerization with a significant contribution when VAc, even in a small amount, was present in the reaction mixture. This can result in polymer chains with aldehyde dead end and broadening of the molecular weight distribution. © 2015 Society of Chemical Industry