Showing papers on "Glass transition published in 1971"

Viscous Liquids and the Glass Transition. III. Secondary Relaxations in Aliphatic Alcohols and Other Nonrigid Molecules

Abstract: The dielectric permittivity and the dielectric loss factor of 5‐methyl‐3, 4‐methyl‐3 and 3‐methyl‐3‐heptanol, n‐ and iso‐butanol, 1,2‐propanediol, dimethyl and diethyl phthallate, and 3‐methylpentane have been measured from 50 to 105 Hz and from −196 to about 20°C above their respective glass transition temperatures. The glass transition temperature Tg of these substances, several more isomeric octanols, and 1‐phenyl‐1‐propanol have been measured by differential thermal analysis. All substances except for 3‐methylpentane and iso‐butanol show either a well‐defined secondary relaxation peak in tanδ, or a clear indication of the presence of a secondary relaxation below their Tg's. Arrhenius plots for the α‐relaxation process of the isomeric octanols are linear with an activation energy of 16–18 kcal/mole, while for other substances they are nonlinear with the activation energy changing from 30 to 70 kcal/mole. The Arrhenius plots for the secondary relaxations are linear and have an activation energy of 4–8 k...

Relation between apparent glass transition temperature and liquids temperature for inorganic glasses

Abstract: The ratio of the glass transition temperature T g to the liquidus temperature T l (or T m ) was calculated for a wide variety of inorganic glass forming systems including the elements, oxides and sulfides and technologically important systems such as borates and silicates. It was found that a simple empirical rule T g /T l = 2 3 which was suggested for organic polymers holds suprisingly well for inorganic systems.

Pressure‐Volume‐Temperature Properties and Transitions of Amorphous Polymers; Polystyrene and Poly (orthomethylstyrene)

Abstract: An apparatus based on Bridgman's bellows method, originally devised for fluids, has been constructed for use with solid samples. Mercury is employed as the confining liquid. The operating range is 0≤t≤200 °C and 1≤P≤2000 bar. Calibration with benzene and mercury shows an accuracy of ±2×10−4 cm3/g in the measurement of the specific volume change. A detailed investigation of two systems, polystyrene and poly(orthomethylstyrene) in the glassy and liquid states is undertaken. The P‐V‐T results in both states can be well represented by the Tait equation, with the single parameter B as an exponentially decreasing function of T. Similar to the earlier result for polystyrene, a β‐relaxation region is observed in terms of the isothermal compressibility of the methylated polymer with Tβ/Tg≃0.70 for both. The pressure coefficients for the two transition temperatures are discussed. For the glass transition, the Ehrenfest‐type equation appears to be obeyed by the low‐pressure glasses (formed by cooling the liquid at a...

Dynamic mechanical properties of polyurethane block polymers

Abstract: The dynamic mechanical properties of polyester and polyether urethane block polymers have been investigated at four frequencies (3.5, 11, 35 and 110 Hz) in the temperature range of — 150 to 200°C. The existence of a two phase structure was demonstrated in these systems by the observation of two major transition regions corresponding to (1) the glass transition temperature (Tg) of the ester or ether soft segments, and to (2) the softening temperature of the aromatic-urethane hard segments. Several secondary relaxations were observed in addition to the two major relaxations. It was possible to assign molecular mechanisms to each of these relaxations. All relaxation phenomena were greatly influenced by the molecular weight of the prepolymer, weight percent of hard segments, and thermal history. An increase in the molecular weight of the prepolymer above 1,000 at constant hard segment content resulted in a semi-crystalline material, which possessed a lower Tg for the macroglycol segments. Annealing to enhance crystallinity increased the Tg of the soft segments, consistent with the usual observation in semicrystalline homopolymers. These findings suggest that the relaxation mechanisms of polyurethane block polymers are not only influenced by the degree of crystallinity, but also by the nature of the domain structure.

Structure and property relationships in ethylene–vinyl acetate copolymers

Abstract: The effects of vinyl acetate content on crystallinity of ethylene–vinyl acetate (E/VA) copolymers were investigated by x-ray diffraction and differential thermal analysis (DTA). The values of these parameters obtained from DTA were found to agree quantitatively with data calculated from x-ray, probability equations, and copolymer theory. The melting points of the crystalline copolymers, and the molar amounts of vinyl acetate to produce a completely amorphous rubber corresponds exactly to that predicted by the Flory theory. The random character expected in E/VA copolymers is thereby confirmed. The physical properties of E/VA copolymers of all ranges of compositions and crystallinity were determined. Depending directly upon vinyl acetate content, the copolymers changed progressively from highly crystalline polyethylene to semicrystalline polyethylene, a completely amorphous rubber, a soft plastic with a glass transition near room temperature. Properties which were correlated with copolymer composition include: crystallinity, melting point, density, modulus, tensile strength, glass transition, and solubility. Finally, the effect on crystallinity and physical properties of replacing the acetoxy group in E/VA with the smaller, highly polar hydroxyl group (ethylene—vinyl alcohol copolymer) was also investigated.

The effect of liquid anhydrous ammonia in the structure and morphology of cotton cellulose

Abstract: The effect of liquid ammonia on cotton fabric was studied using x-ray diffraction (XRD) and electron microscopy. A phase diagram is presented describing the relationship between disordered cellulose, cellulose I, and cellulose III. The transition from cellulose I to III proceeds through the liquid ammonia. Cellulose III is obtained upon drying the ammonia-cellulose without the presence of water. Treatment of the cellulose III or of the ammonia-cellulose with water brings about the formation of cellulose I. The degree of crystalline order achieved in water is enhanced by heating, which is consistent with a glass transition temperature between room temperature and 100°C. The cellulose III crystallites obtained are much smaller than those of cellulose I,16-23Aas against 50-80A The interaction of ammonia with cotton cellulose is faster than with other swelling agents, such as ethylamine. The penetration of ammonia into the secondary wall of the cotton fiber is not only along the concentrical rings, as is the case with water, but also radially across the rings. Prolonged soaking in water increases the crystallite size with simultaneous rejection of swelling water.

Powdered coating compositions containing glycidyl methacrylate copolymers with anhydride crosslinking agents and flow control agent

Abstract: POWDER COATING COMPOSITIONS ARE DISCLOSED. IN GENERAL, INDIVIDUAL POWDER COATING COMPOSITIONS OF THIS INVENTION ARE A MIXTURE OF SEVERAL MATERIALS. ONE OF THE IMPORTANT MATERIALS IS A COPOLYMER OF GLYCIDYL METHACRYLATE AND AN ETHYLENICALLY UNSATURATED COMPOUND FORMED TO OBTAIN A COPOLYMER WITH A GLASS TRANSITION TEMPERATURE IN THE RANGE OF 40*C. AND A MOLECULAR WEIGHT ($N) IN THE RANGE OF 2500 TO 8500. THE GLACIDYL METHACRYLATE IS PRESENT IN THE COPOLYMER FROM AT LEAST ABOUT 5% BY WEIGHT TO NO MORE THAN ABOUT 20% BY WEIGHT. ANOTHER IMPORTANT MATERIAL OF EACH COATING COMPOSITION IS A CROSSLINKING AGENT FORMED IN AN ANHYDRIDE OF A DICARBOXYLIC ACID PRESENT IN THE AMOUNT OF 0.4 TO 1.0 ANHYDRIDE GROUPS FOR EACH EPOXY GROUP IN THE COPOLYMER, A THIRD IMPORTANT MATERIAL USED IN FORMING EACH POWDER COATING COMPOSITION IS A FLOW CONTROL AGENT WHICH FORMS AT LEAST 0.05% BY WEIGHT OF THE MIXTURE. THE FLOW CONTROL AGENT IS A POLYMER HAVING A MOLECULAR WEIGHT ($N) OF AT LEAST 1000. THE FLOW CONTROL AGENT ALSO HAS A GLASS TRANSITION TEMPERATURE AT LEAST 50*C. BELOW THE GLASS TRANSITION TEMPERATURE OF THE COPOLYMER. OTHER MATERIALS SUCH AS PIGMENTS, CATALYSTS, ANTISTATIC AGENTS AND PLASTICIZERS MAY BE USED IN INDIVIDUAL COMPOSITIONS.

Hole Theory of Liquids and Glass Transition

Abstract: A recently elaborated theory of the p‐V‐T properties successfully describes the behavior of amorphous polymers above the glass temperature. The improvement over earlier results arises from the introduction of a vacancy fraction which is obtained as a function of volume and temperature by a maximization of the partition function. We now explore a possible application of this theory to the glassy state by introducing an assumption following a frequently used idea, namely, the freezing of one parameter, (or more), for example, an unoccupied volume ratio. The natural quantity to consider is the vacancy fraction and its effect on the thermal expansion coefficient at the glass temperature. Experimental data at atmospheric pressure on a series of polymers, encompassing a wide range of Tg's, are examined and compared with theoretical predictions. The computed expansivities αg at T=Tg are uniformly smaller than is observed. We suggest as the primary reason for this discrepancy the assumption of a complete freezing of the hole fraction at the glass temperature, which should be replaced by a decreased dependence on volume and temperature as compared with the liquid. Additional factors are discussed.

Time‐dependent heat capacity in the glass transition region

Abstract: Time-dependent, apparent heat capacities of glucose, poly(vinyl chloride), polystyrene, selenium, poly(methyl methacrylate), and poly(2,6-dimethyl-1,4-phenylene ether) in the glass transition region were determined by differential thermal analysis. The thermal history was set by linear cooling at rates between 0.007 and 160°C/min. Linear heating for analysis was carried out at rates between 0.3 and 600°C/min. Average activation energies of 52, 81, 90, 54, 77, and 108 kcal/mole, respectively, were evaluated by using the hole theory of glasses previously developed. Within experimental limitations all data could be described quantitatively by the theoretical expressions using only one parameter, the number of frozen-in holes, to described the thermal history. Experimental and theoretical limitations are discussed.

Ionic Jump Distance and Glass Transition of Polyvinyl Chloride

Abstract: The electrical conduction of polyvinyl chloride was measured from low electric field to high field near breakdown below, in, and above a glass transition region. Ionic conduction was found to hold up to the field near breakdown. The estimated jump distance of a charge carrier changes considerably in the glass transition region, while it remains constant (12 A) at a temperature fairly below the glass transition Tg(=87°C) and seems to reach a saturation value (30 A) above Tg. The elongation of substantial jump distance may be explained by the change in the shape and height of potential barriers against ionic migration due to the liberation of micro‐Brownian motion of main chains in the glass transition region.

Side‐chain crystallinity. III. Influence of side‐chain crystallinity on the glass transition temperatures of selected copolymers incorporating n‐octadecyl acrylate or vinyl stearate

Abstract: The influence of side-chain crystallinity on the glass transition temperatures of selected copolymers was investigated. The copolymers were selected, in part, from those whose crystallinity was treated in the preceding paper. These included the lower amorphous acrylate esters, such as methyl, ethyl, n-butyl, and 2-ethylhexyl acrylates, together with methyl methacrylate and acrylonitrile, each copolymerized with n-octadecyl acrylate over the range of composition. The decline in the glass transition temperature was linear with increasing weight fraction of n-octadecyl acrylate for all systems in the composition range where the copolymers were essentially amorphous. The extrapolated Tg for the amorphous state of poly(n-octadecyl acrylate), and for amorphous poly(oleyl acrylate), was close to −111°C. This coincided with a value previously obtained by an extrapolation of data on homologs. Beyond a critical fraction of octadecyl acrylate (0.3 to 0.5), developing side-chain crystallinity in n-octadecyl acrylate raised the glass temperature steadily for all systems, up to a value of 17-C, obtained for the crystalline homopolymer. Crystallinity did not develop in stiff copolymers until Tg was about 30°C below the melting point of the most perfect crystals. In compositionally heterogeneous copolymers incorporating vinyl stearate, blocks of crystalline units appeared to be dispersed in a glassy matrix of amorphous co-units. An empirical equation was derived which fitted the experimental data for random copolymers, over all composition ranges, with fair accuracy.

Mechanical relaxations in polyamides

Abstract: Dynamic mechanical measurements were carried out as a function of temperature (−100 to + 180°C) and frequency (3.5 to 110 cps) for a series of aliphatic terpolyamides, nylon 6 and nylon 12. Effect of crosslinking with toluene diisocyanate, of absorbed water, and of frequency are used to estimate the statistical segment length associated with the α′ relaxation. The effects of variations in the aliphatic chain length in the repeating unit on the temperature of the α′ relaxation are examined by means of copolymer rules with a view to explaining the reported insensitivity of the glass transition temperature of these polymers to changes in (CH2)/(amide) group ratio. From the estimated length of the segmental motion associated with the α′ relaxation it is inferred that in a series of polyamides of the type nylon X or nylon X,Y (where X or Y = 3, 4, 5, 6, etc.) there should be a relatively small change in the temperature of the α′ transition for those polyamides having X or Y less than about 45. Experiments which are intended to establish the position of the crystalline α–γ transition are discussed.

Pressure-sensitive adhesives comprising a block copolymer and a tackifier

Abstract: NORMALLY TACKY PRESSURE-SENSITIVE ADHESIVES AND ADHESIVE TAPES HAVING EXCELLENT SHEAR STRENGTH AND CREEP RESISTANCE, PARTICULARLY AT ELEVATED TEMPERATURES, TOGETHER WITH GOOD PEEL STRENGTH AND TACK PROPERTIES, ARE OBTAINED BY COMBINING TACKIFYING RESIN WITH LOW MOLECULAR WEIGHT A-B BLOCK COPOLYMER. THE COPOLYMER A BLOCK IS NORMOLLY GLASSY AND HAS A GLASS TRANSITION TEMPERATURE ABOVE 75*C. WHILE THE COPOLYMER B BLOCK IS AMORPHOUS AND ELASTOMERIC AT TEMPERATURES ABOVE -20*C. SHEAR STRENGTH OF THE ADHESIVE MAY BE INCREASED BY ADDITION OF BLOCK COPOLYMERS CONTAINING THREE OR MORE BLOCKS.

Glass forming region and DTA survey in the Ge-As-te memory switching glass system

Abstract: The glass forming region for 2.0 gm melts in the Ge-As-Te system is reported together with a comparison of glass transition temperatures and metastable glass melt crystallisation temperatures for bulk glass pieces of different compositions, heated at 20° C/ min under standardised conditions in a nitrogen atmosphere. The crystallisation characteristics of certain compositions are correlated with published compositional data on device quality memory switches.

Shapable fiber-reinforced low molecular weight polyethylene terephthalate

Abstract: Glass fiber-reinforced thermoplastic polymer composite sheets are formed using semicrystalline polymers that have their glass transition temperature above room temperature and may be cold formed, i.e., shaped in a cold mold when preheated outside the mold. Glass-reinforced low molecular weight polyethylene terephthalate, or blends thereof, may be shaped in a cold mold, and exhibit excellent performance.

Small angle x-ray scattering studies of phase transitions in polymeric and oligomeric systems

Abstract: Small angle x-ray scattering (SAXS) is a valuable method for studying structure changes which take place during phase transitions in polymeric and oligomeric systems. Measurements of the dependence of SAXS on temperature yield information on the changes in morphology or of the structure on a supermolecular level. The technique can be applied to various problems: glass transition in highly crystalline polymers, solid state phase transitions in crystalline polymers, rotational transition in n-paraffins, premelting phenomena in crystals of chain molecules, and partial melting of homoand co-polymers. The glass transition temperature of the amorphous regions in highly crystalline polymers can be measured by SAXS since the scattered intensity depends on the thermal expansion coefficient of the two phases. This technique was applied to so-called single crystals grown from solution of polybutene-1, branched and linear polyethylene. The amorphous surface layer of linear polyethylene single crystals exhibits a 7, of — 125° ± 4°C. Solid state phase transitions of polymer crystals are often accompanied by characteristic changes in morphology. As examples, the annealing behaviour of trans-1,4-polybutadiene and isotactic polybutene-1 is described. The rotationa1' transition in paraffins studied with n-tritriacontane as an example also leads to a pronounced structure change of the surface of the paraffin lamellae, speaking in favour of a transition theory which is based on the assumption of a sudden change in the concentration of kinks within the crystals. With increasing temperature an increase of the roughness and depth of the surface region of paraffin crystals is observed. This phenomenon can be described as 'surface premelting of chain molecular crystals' and SAXS yields quantities suitable for a thermodynamic explanation of that process. In homoand co-polymer crystals partial melting during heating is observed. The SAXS studies show that this effect can be due to a 'boundary premelting of polymer crystals' which manifests itself by a reversible increase of the thickness of the intercrystalline layers. This phenomenon can be observed in many polymers, it can be described quantitatively by analysis either of the scattering curves or of the correlation functions y(x) obtained from the intensity distribution.

Polysulfone–polydimethylsiloxane block copolymers

Abstract: Alternating block copolymers have been synthesized from dihydroxyl-terminated polysulfone and bis(dimethylamine)-terminated polydimethylsiloxane oligomers. The products are soluble, amorphous, and transparent, and display excellent thermal and hydrolytic stability. Elastomeric and rigid compositions can be prepared by varying oligomer molecular weight. Copolymers made with oligomers of ≥ 5000 molecular weight are two-microphase systems which display glass transition temperatures at −120°C and at +160°C, and therefore have a wide useful temperature range.

Direct observation of the double glass transition in a phase-separated glass

Abstract: Heat capacity measurements have been performed for the phase-separated pseudobinary chalcogenide glass system X PbSe-(1− X )Ge 1.5 As 0.5 Se 3 in the composition range X = 0.0 to 0.6. The heat capacity versus temperature plots for the phase-separated glasses exhibit two glass transition breaks. The composition dependences of the heat capacity changes, ifΔC p , at the two transitions are shown to be in accord with the behavior predictable from the phase diagram of a glass-forming system exhibiting liquid-liquid immiscibility and with the structure of these glasses as determined by electron microscopy. The two composition points on the immiscibility dome at which the temperature is equal to the higher glass transition temperature have been determined from the composition dependence of the ΔC p 's and indicate that the dome spans almost the entire composition range for this system.

Thermodynamic Studies on the Glass Transition and the Glassy State of Polymers. I. Pressure Dependence of the Glass Transition Temperature and Its Relation to Other Thermodynamic Properties of Polystyrene

Abstract: The pressure dependence of the glass transition temperature, Tg, and the coefficients of thermal expansion, α, and the compressibility, β, of polystyrene were measured. For the same sample, DSC measurement was also carried out, to obtain specific heat, Cp. From the results, it was confirmed that the relation (∂Tg/∂P)≅TVΔα/ΔCp<Δβ/Δα was valid, in accordance with our theory based on a hole model for polymer liquids and glasses with an assumption of iso-configurational entropy at Tg. Changes of specific heats at Tg associated with intrasegmental interactions and inter-segmental ones were calculated separately by the use of the theory, and ΔCpintra=0.041 and ΔCpintra=0.036 cal/gK were obatined.

Heat capacities and thermal behavior of alkali borate glasses

Abstract: The heat capacities of selected glasses in the five alkali borate systems have been measured over a range of high temperatures which includes the respective glass transition regions. The heat capacities per gram atom at 350°K show little variation with composition while those at the low temperature ends of the glass transition, Tg-, show some systematic variations. When compared with the respective 3R values, the heat capacities at Tg- range from about 0.75 for B2O3 to values in excess of unity for various alkali borate compositions. The present data on heat capacity have been combined with previous data on the elastic moduli, densities and thermal expansion coefficients to evaluate the Gruneisen constant, γ, for each composition for temperatures around ambient. For B2O3, γ has a low value of about 0.25. It decreases with additions of Li2O and increases with additions of the other alkali oxides.

Single crystals of poly(2,6-dimethyl-1,4-phenylene)oxide

Abstract: Poly(2,6-dimethyl-1,4-phenylene)oxide crystals obtained from 0.1%α-pinene solutions by isothermal growth at temperatures from 80–90 as well as 100 °C, were investigated by optical and X-ray diffraction techniques. A study has been made by differential scanning calorimetry in order to measure the melting point, glass transition and melting point depression temperatures of mixtures of the polymer withα-chloro-naphthalene. The densities of the dry mats of single crystals were measured by a flotation method.

Sequentially produced alkyl acrylate polymers blended with poly(vinyl halides)

Abstract: PROCESSING AIDS OF IMPROVED DISPERSIBILITY IN LOW MOLECULAR WEIGHT POLY(VINYL CHLORIDE) COMPOSITIONS COMPRISE A SEQUENTIALLY PRODUCED POLYMER CHARACTERIZED BY 1 TO 30 WEIGHT PERCENT OF (A) A FIRST RELATIVELY SOFT STAGE CHARACTERIZED BY A GLASS TRANSITION TEMPERATURE OF 60*C. OR LESS; AND 99 TO 70 WEIGHT PERCENT OF (B) A FINAL SUBSTANTIALLY THERMOPLASTIC STAGE POLYMERIZED IN THE PRESENCE OF A PRODUCT CONTAINING THE FIRST STAGE, AND IN INITIAMATE CONTACT WITH THE FIRST STAGE AND FURTHER CHARACTERIZED IN THAT IF THE MONOMER OR MONOMERS WERE POLYMERIZED IN THE ABSENCE OF THE PRODUCT OF THE FIRST STAGE, A POLYMER WOULD BE FORMED HAVING A GLASS TRANSITION TEMPERATURE OF 25*C. OR GREATER.

Rheology and plasticization of polyvinyl chloride

Abstract: The behaviour of polyvinyl chloride in the range of temperatures from 77°C to 230°C is characterized by the persistence of a slight amount of crystallinity, which gives rise to very peculiar rheological properties. In particular flow takes place partially through particle slippage, which predominates, with respect to molecular deformation, the lower the temperature and the higher the molecular weight and the crystallinity. The flow behaviour may change appreciably with shearing time and with thermal history. Viscous heat generation must be taken into account, even at relatively low shears. The molecular weight dependence of viscosity and relaxation time is anomalous for both rigid and plasticized samples. For the latter, the composition dependence of the glass transition temperature appears to be in line with predictions based on free volume concepts.

Steady flow and dynamic viscosity of branched butadiene–styrene block copolymers

Abstract: Steady flow and dynamic viscosities were determined for symmetrical linear and starbranched block copolymers of butadiene and styrene above their upper (polystyrene) glass transition. Block structures examined were B-S-B, (B-S-)3, S-B-S, (S-B-)3 and (S-B-)4. At constant molecular weight and total styrene content viscosities were greater for polymers terminating in styrene blocks, irrespective of branching. Branching decreased the viscosity of either polybutadiene-terminated or polystyrene-terminated block polymers, compared at equal Mw. However, comparisons at equal block lengths showed that the length of the terminal blocks, not the total molecular weight, governs the viscoelastic behavior of these polymers to a surprisingly good approximation. This unusual result is rationalized in terms of the two-phase domain structure of these polymers, which persists to a significant degree in the melt. Below the glass transition of the polystyrene blocks the effects of branching were masked by differences in the morphology of the domain structure unrelated to branching.