A thermomechanical investigation of highly cold-drawn polycarbonate

A new technique detecting molecular motions in drawn polymers was applied to highly cold-drawn polycarbonate of bisphenol A. It is shown that the sample exhibits thermal shrinkage in three steps with the temperature increase up to above the glass transition temperature. The molecular relaxation at the highest temperature is due to the glass transition. The other two molecular motions at the lower temperature are those of main chain in the glassy state and they correspond to the molecular motions as revealed in dielectric measurement by Sacher.¹ By using the general theory of the thermal analysis by Ozawa,² the apparent activation energies of these molecular motions were obtained: for the highest temperature 110 kcal/mole, and for the lowest temperature, 33.5 kcal/mole. The impact strength and the cold workability of this polymer are also discussed in relation to these molecular motions.     

Kinetics of thermal inactivation of peroxidases in turnips and peas

The heat inactivation of peroxidase in green peas and turnips grown in Venezuela was determined experimentally at temperatures ranging from 60 degrees C to 76 degrees C for turnips, and between 72 degrees C and 82 degrees C for green peas. The thermal destruction curves obtained were found to be biphasic, following first-order kinetics of inactivation, and with average times for the change of phase of 22.5 sec and 23.8 sec for the turnips and peas, respectively. The activation energies, as calculated by the Arrhenius equation for the first and second inactivation intervals, were 27.1 kcal/mole and 43.5 kcal/mole for turnips, and 34.5 kcal/mole and 28.9 kcal/mole for green peas.     

Synthesis of end-functionalized polymer by means of living anionic polymerization. 4. Synthesis of polyisoprene and polystyrene with epoxy termini by reaction of their anionic living polymers with 2-bromoethyloxirane

In order to synthesize ω-epoxy-functionalized 1,4-polyisoprene ω-epoxy- and α,ω-diepoxy-functionalized polystyrenes, anionic living polyisoprene and polystyrene were allowed to react with excess amounts of 2-bromoethyloxirane in THF at ?78°C. The resulting polymers were analysed by SEC, ¹H and ¹³C NMR spectroscopy, and thin layer chromatography with flame ionization detection (TLC–FID). Both mono- and di-epoxy terminated polymers of controlled molecular weights (2.5 × 10³?2.6 × 10⁴ g/mol) and of narrow molecular weight distributions were obtained quantitatively with high functionalities.     

Thermal analysis of styrene–alkyl methacrylate polymers. II. Thermogravimetric kinetics

The thermal stability and degradation kinetics of several polystyrenes and styrene–alkyl methacrylate copolymers and terpolymers with a number-average molecular weight (M?_n) of 6000–250,000 g/mole have been studied using dynamic thermogravimetry (TG). The degradation kinetics of each polymer sample have been successfully attributed to a sample first-order reaction expression. The results indicate that the thermal stability and degradation kinetics of the polymers are independent of the size of the molecules within the molecular weight range investigated. The steric hindrance effects of the pendent groups appear to be responsible for the improved thermal stability and resistance of C? C bond scission in the styrene–alkyl methacrylate copolymers and terpolymers.     

The mass loss mechanisms of polymers in a radio frequency induced atomic oxygen environment

The effects of atomic oxygen on several classes of polymers were investigated. Particular attention was directed to the determination of erosion or mass loss mechanisms in relation to the physical and chemical structures of polymers. Nineteen polymeric materials were exposed to a thermal atomic oxygen environment at fluxes of 10²² atoms/m²?sec. Bulk material temperatures were maintained at 10, 45, and 75°C During exposure. Mass loss rate, which was characteristic of the type of polymer, was proportional to the exposure area and was linear in time for most polymers except for Mylar, which produced a shielding high temperature ash. The mass loss rate for the atomic oxygen degradation of polymers was related to the bond strength of the polymer structure and to the shielding effect of pendant structures. This degradation process was strongly dependent on polymer temperature. Activation energies ranged from 1 to 48 KJ / mole and were found to be related to gaseous diffusion in polymers. Frequency factors were proportional to activation energies. Activation energies were found to increase with increased mol wt and crosslinking. An equation was developed relating exposure area, atomic oxygen flux, frequency factor, and activation energy to the rate of polymer mass loss. © 1993 John Wiley & Sons, Inc.     

Capillary extrusion of elastomeric emulsion crosslinked interpenetrating networks

The rheological properties of an elastomeric emulsion thermosetting (EMSET) interpenetrating network (IPN) of poly(ethyl acrylate) (70 percent) and polystyrene (30 percent) were studied using a capillary rheometer to test if the submicron thermoset particles, persumably the flow units, could flow as a thermoplastic matrix. The IPN exhibited power law behavior over a wide range of shear rates (0.05 to 500 s^?1), with a power law exponent of approximately 0.18 over a large range of temperatures (80 to 200°C), without a yield stress or a Newtonian plateau evident. The flow activation energies were found to be comparable with most processable thermoplastic materials at 4 kcal/mole for constant shear rates, and 20 kcal/ mole for constant shear stresses. The effect of a roll mill shear modification step prior to extrusion indicated stability of the flow units. The pervasive rippling melt fracture and the significant slip velocity at the wall emphasized the importance of slip in the flow mechanism of this elastomeric EMSET IPN.     

Effects of chain ends and molecular weight on specific volumes of anionic polystyrene melts

Specific volumes of anionic polystyrenes prepared by butyl lithium initiation have been measured at temperatures between 110° and 237°C. Molecular weights of the fractions studied ranged from 2500 to 700 000. Plots of isothermal specific volume against reciprocal molecular weight (M^?1) are fitted by two straight lines intersecting at a molecular weight near 10 000. This parallels the behaviour of thermally initiated polystyrene fractions, which have different end-groups. Volumes attributable to end-groups are greater for the anionic polymers. The specific volume-molecular weight-temperature relations in the M ≤ 10 000 region are explained quite well by the equation of Francois and coworkers, in terms of end-group volumes and a uniform volume contribution from internal repeating units. Restraints on the motion of the butyl end-groups in these polymers by the attached polystyrene chain appear to be temperature dependent in terms of this model. Specific volumes of polymers with M ≥ 10 000 are affected by chain ends and by variation of the volumes of non-end repeating units with molecular weight. The present results parallel those which have been reported for partial specific volumes of polystyrenes in dilute solution and suggest that the same factors operate in both cases.     

Kinetics of hydrolysis,acetylation, and deamination reactions on polyamide fibers in homogeneous medium

Chemical reactions on polymers in homogeneous medium were used to characterize the structure of the macromolecules. The polymer was in the form of polyamide fibers dissolved in m-cresol to give a fairly highly concentrated solution (approximately 6%). Kinetic studies of hydrolysis, acetylation, and deamination reactions on the polyamide fibers were carried out in homogeneous medium at different temperatures. All the three reactions studied followed first-order kinetics. Rate constants and apparent activation energies were determined for these reactions, which show two rates—an initial fast rate followed by a slow one. A new microfibrillar model of the polymer dissolved in m-cresol is proposed, and the existence of two rates is explained on the basis of the two-phase structure of the proposed microfibril. The fast rate is attributed to the free chain segments, and the slow rate is shown to correspond to the regions which are strongly hydrogen bonded and which hold the various chains together to give the microfibrillar structure of the polymer in the homogeneous phase. The apparent activation energy for hydrolysis was 3.20 and 0.18 kcal/mole for the fast and slow rates, respectively. The apparent activation energy values for acetylation were 1.50 and 0.80 kcal/mole, while those for the apparent deamination reaction were 6.90 and 4.60 kcal/mole, respectively. Lower values of apparent activation energies are attributed to the ease of reaction in the difficult-to-penetrate regions of the microfibril due to the role played by the solvent of the homogeneous phase in carrying the reacting species inside these regions while simultaneously breaking the hydrogen bonds between the polypeptide chains. The apparent deamination reaction is shown to be a resultant reaction of simultaneous deamination and “amination” through hydrolytic breakdown of the polypeptide chain.     

Thermal decomposition of a blackband ironstone. II. Kinetics

Blackband ironstone and siderite have been separately decomposed in a fluidised bed of sand in an atmosphere of nitrogen and the progress of reaction followed by a ‘volatile matter’ test. For the ironstone in the temperature range 370–570°, the residual volatile matter (V_R) after a time (t) between 10 sec and 60 min. was given by the expression V_R = A – B log t, where A and B are constants for a given temperature. The kinetics of decomposition of siderite at 455 and 485° were first-order with an activation energy of 51 kcal. /mole. It is concluded that blackband ironstone appears to decompose by a large number of independent first-order reactions having a range of activation energies showing a peak frequency near 50 kcal.     

Bestimmung des molekulargewichts von „mikrogelhaltigem”︁ polystyrol mit der ultrazentrifuge (methode archibald)

The weight average molecular weight M_w of a mixture of two polystyrenes with very high and relatively low molecular weights (M_w = 16.1 · 10⁶ and 98 · 10³ g/mole), as a model for polymers containing microgel, was determined by ultracentrifugation with the ARCHIBALD-methode. M_w decreases with increasing number of rotation N. The exact molecular weight can only be determined by extrapolation to N = 0. This value depends nearly completely on the molecular weight and weight percentage of the “microgel”. It is not suitable for the characterization of the whole sample.     

Kinetics of the reaction between urea and formaldehyde in the presence of sulfuric acid

The kinetics of the reaction between urea and formaldehyde were studied in the presence of various amounts of sulfuric acid (5–45% by weight) at different temperatures (5°, 15°, and 25°C). The reaction was shown to follow first-order kinetics. The activation energy for the reaction varies from 12.51 kcal/mole to 14.59 kcal/mole in the range of sulfuric acid concentration studied.     

The thermal decomposition of poly(vinylidene chloride) in the solid state

The rate of decomposition of PVDC is sensitive to differences in the method of preparation of the polymer. Polymers prepared by mass polymerization of very pure monomer were most stable. Emulsion polymerized PVDC degraded the fastest. The activation energy for the latter was 34.4 kcal/mole. Over the range of 130°–190°C, the rate of decomposition increases with reaction time to ～10% HCl evolved. Beyond this point, the reaction follows first-order kinetics. The first-order rate is independent of molecular weight. Lamellar crystals of PVDC degrade at a higher rate than “as polymerized” powders. This may be due in part to annealing of the crystals in the degradation temperature range; but it also results from a sensitization of the polymer to thermal degradation from exposure to the polar solvents used for recrystallization. A mechanism is proposed to account for these observations.     

Pyrolysis and combustion of nylon 6. I. Effect of selected brominated flame retardants

The pyrolysis of nylon 6 has been shown to proceed by a first-order process to yield ε-caprolactam as the primary product. This degradation has an energy of activation of approximately 46 kcal/mole which would seem to indicate the involvement of a homolytic process. Inclusion of organobromine compounds such as hexabromobiphenyl and dodecabromopentacyclo [5·3·0·0^2,6·0^3,9·0^4,8]decane catalyzed the pyrolysis but did not significantly alter the nature of the degradation products. Because of this, simple organobromine compounds are not good candidates for utilization as flame retardants for nylon 6.     

Facile synthesis of high refractive index thiophene‐containing polystyrenes

High refractive index polymer films have been extensively investigated because of their wide application potentials. We now designed thiophene‐containing polystyrene as colorless and transparent high‐refractive‐index thin film. The copolystyrenes were synthesized by general radical polymerization with controlled mole ratios 0 : 10, 1 : 9, 3 : 7, 5 : 5, 7 : 3, 9 : 1, 10 : 0 (styrene : p‐bromostyrene), respectively. Next, the thiophene‐containing polystyrenes were synthesized by Suzuki‐Miyaura coupling reaction. The chemical structures of synthesized thiophene‐containing polystyrene in accordance with ratios were confirmed by using ¹H‐NMR, ¹³C‐NMR, and FTIR. The effect of the thiophene units on refractive index according to copolymer ratios were confirmed by using prism coupler. The thiophene‐containing polystyrene showed improved refractive index ranging from 1.58 to 1.67 and birefringence in the range of 0.0001–0.0019. The thermal stability and thermal behaviors of thiophene‐containing polystyrene also can be confirmed by TGA and DSC. The polymers have high glass transition temperature in the range of 108°C–177°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Water sorption and hydrolytic stability of polycarbonates

The hydrolytic stability of a new commercial polycarbonate (Calibre 300, Dow Chemical USA) was investigated and compared with that of other commercial polycarbonates. The tests were conducted between 56% and 95% relative humidity (R. H.) at 100°C. Also performed were water immersion tests at 80 and 100°C. The water diffusivity was found to be 8.7 × 10^?7 cm²/s at 100°C with an activation energy of 7.9 kcal/mole. These values are similar to other glassy polymers. The equilibrium water sorption, C_∞, was found to increase with temperature and R.H. The isotherm at 100°C was determined to be: C_∞ = 0.005945 [R.H.]. When samples immersed in a water bath at 100°C were transferred into room-temperature water, visible aqueous microcavities were formed due to the condition of super-saturation, and under stress may become crack initiation sites. For the polycarbonate investigated here, it was found that the decrease in weight-average molecular weight (M?)_w was a first-order process under a constant R.H. and temperature, and that hydrolytic embrittlement, i. e., (M?)_w <34,000, was reached after ca. 188, 143, 99, and 66 days under 56%, 73%, 87%, and 95% R.H., respectively, at 100°C. A comparison with reported hydrolytic stability data for other polycarbonates showed large differences in their stability which are believed to be due to the extent of end-group capping (over 95% in Calibre 300) and resin purity: both phenolic end-groups and some additives (i.e., fire retardants, thermal stabilizers) are known to accelerate hydrolytic degradation.     

Effect of aerosil on the course of thiuram accelerated sulfur vulcanization

Tetramethylthiuram disulfide (TMTD)-accelerated sulfur vulcanization of natural rubber has been investigated at temperatures from 100°C to 145°C. Continuous measurements in a Vuremo curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. The cure curves as well as their linearized forms (dependences of the logarithm of the extent of vulcanization on the cure time) clearly show that at lower cure temperatures the course of the vulcanization differs significantly from the first-order rate law. These digressions have been removed by the addition of a highly dispersed silica gel, Aerosil, which simultaneously speeds up the course of the vulcanization up to the value corresponding to the rate of zinc dimethyldithiocarbamate (ZnDMDC)-accelerated sulfur vulcanization. These results are in accordance with our recent theory supposing that ZnDMDC is the actual accelerator in TMTD-accelerated sulfur systems. In the presence of Aerosil, the formation of ZnDMDC from TMTD is catalyzed via dispersed silica gel. Support for this view derives from the temperature dependences of vulcanization reactions. The activation energies of TMTD-accelerated sulfur vulcanizations in the absence (31 kcal/mole) and in the presence of Aerosil (23.5 kcal/mole) correspond exactly to the values calculated from the rate constants of the thiuram decrease in TMTD-accelerated vulcanization (30 kcal/mole) and from the rate constants of crosslinking in the dithiocarbamate-accelerated sulfur vulcanization (23 kcal/mole), respectively.     

Thermal decomposition of additive polymerization initiators. I. Azobisisobutyronitrile

We measured the rate of thermal decomposition of azobisisobutyronitrile (AIBN) from the rate of loss of 2,2-diphenylpicrylhydrazyl (DPPH) on reaction of the free radicals formed by thermal decomposition of azobisisobutyronitrile (AIBN) in organic solvents with DPPH. There has been some doubt about the quantitative relation between AIBN and DPPH required to get the rate constant of thermal decomposition of AIBN. In the past, AIBN has been used in excess, and the rate constants measured by using DPPH are smaller than they ought to be. In our experiments we used as little of AIBN relative to DPPH as possible and obtained a value of 3.8 × 10^?4 min.^?1 at 50°C. as the rate constant of the first-order reaction, which was shown satisfactorily by the linearity of the graph. We also obtained 32 kcal./mole as activation energy. We were also able to make clear the meaning of the result when a large quantity of AIBN was used.     

The effects of β-C2S/class H cement mixed fillers on the kinetics and mechanical properties of polymer concretes

The effects of the inclusion of a hydraulic cement-type filler prepared with a beta dicalcium silicate (β-C₂S) to Class H cement ratio of 1:1 on the hydrothermal stability of polymer concrete (PC) containing vinyl-type polymers having carboxylate groups in their molecules was evaluated. Studies were made of the mechanical properties, fracture energy, and kinetics of the cement-filled composites before and after exposure to a 25% simulated geothermal brine at 240°C. Excellent physical properties of the PC, developed by the appearance of a Ca-copolymer complex structure and hydration products formed during exposure to hot brine, were obtained. The results indicated 103.9 MPa compressive strength, 7.3 MPa tensile strength, 6.0 MPa shear bond strength, 4.40 × 10⁴ MPa modulus of elasticity, and 3.15 × 10³ erg/cm² fracture energy. In addition, the activation energy for the thermal decomposition of the Ca-copolymer complex was calculated using an Arrehenius plot method to be 44.0 kcal/mole.     

Differential scanning calorimetry investigation of curing of bisphenolfurfural resins

Bisphenolic resins have been prepared by alkali catalyzed condensation of bisphenol-F, bisphenol-A, and bisphenol-C, respectively, with furfural. The resin samples have been characterized by elemental analysis, dilute solution viscosity measurement, and measurement of number-average molecular weight. Curing reactions of these bisphenolic resins with hexamine have been investigated by differential scanning calorimetry. The overall apparent activation energies for the curing have been found to be 24 ± 2, 34.2 ± 1.9, and 36.8 ± 2.3 kcal/mole for bisphenol-F-furfural, bisphenol-A-furfural, and bisphenol-C-furfural resin, respectively. The curing reactions have been found to follow an overall first-order kinetics.     

Diffusion of stabilizers in polymers. II. 2-hydroxy-4-octoxybenzophenone in polyolefins

The migration of radioactively labeled 2-hydroxy-4-octoxybenzophenone in a number of polyolefins was investigated over the temperature range 36–75°C. The rates of diffusion in the polymers studied were found to decrease in the order low-density polyethylene > high-density polyethylene ～ isotactic polypropylene, the activation energies being approximately 17, 36, and 24 kcal/mole, respectively. The results of the present study were found to be in qualitative agreement with those previously determined for the same stabilizer/polymer systems, quantitative differences being attributed to the different methods of sample preparation and the resulting differences in the morphological structures of the test specimens. The calculated solubilities of the substituted 2-hydroxybenzophenone in the various polymers were substantially higher, at a particular temperature, than the corresponding values previously determined for 2,4-dihydroxybenzophenone, being 1.4, 0.4, and 0.8 wt-% for low-density polyethylene, high-density polyethylene, and polypropylene, respectively at 75°C. Studies to determine the rate of loss of the stabilizer from polymer samples immersed in water resulted in extremely low rates of extraction, in contrast to those found for 2,4-dihydroxybenzophenone, as a result of the octoxy substituent and the resulting increase in compatibility between the stabilizer and polymer.