New simple method of measuring the surface glass transition temperature of polymers

A lap‐shear joint mechanical testing method has been probed to measure the surface glass transition temperature (T) of the thick bulk films of high‐molecular‐weight polymers. As T, the temperature transition “occurrence of autoadhesion–nonoccurrence of autoadhesion” has been proposed. The influence of chain flexibility, of molecular architecture, of polymer morphology, and of chain ends concentration on the T has been investigated. The correlation between the reduction in T with respect to the glass transition temperature of the bulk (T) and the intensity of the intermolecular interaction in the polymer bulk in amorphous polymers has been found. The effect of surface roughness on T has been discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2012–2021, 2010     

Correlation between glass transition temperature and chain structure for randomly crosslinked high polymers

The empirical form for the dependence, T_g(n) ≅ T_g(∞)·(1 + α/n), of the glass transition temperature T_g on the average number n of repeat units between crosslinks, is generalized for randomly crosslinked high polymers. The new form, T_g(n) ≅ T_g(∞) · [1 + c/(n·N_rot)], is based on a correlation study of data for 77 samples of 10 different sets of resins. The fitting parameter α is resolved into composition-dependent N_rot and composition-independent c terms. N_rot summarizes the average number of rotational degrees of freedom per repeat unit, and is estimated in a straightforward manner from the structure and mol fraction of each repeat unit. The value of c is found from data analysis to be 5 ± 2. The results of this work are consistent with expectations based on the entropy theory of glasses, and provide improved understanding and predictive ability for the properties of crosslinked polymers. © 1996 John Wiley & Sons, Inc.     

The abnormal behavior of polymers glass transition temperature increase and its mechanism

In terms of the classical theory in textbooks, the two components with phase separation in a binary polymer blend will, depending on their compatibility, have their respective Tg get closer or remain in their original values. According to the classical theory, the Tg of plastic component shall remain unchanged or move toward the lower Tg of rubber component in a rubber/plastic blend. However, ultra-fine full-vulcanized powdered rubber (UFPR) with a diameter of ca. 100 nm can simultaneously increase the toughness and the Tg of plastics, which is abnormal and is difficult to explain by classical theory. In this feature article, the abnormal behavior and its mechanism are discussed in detail.     

Elevation of the glass transition temperature in flexible‐chain semicrystalline polymers

In the idealized two‐phase model of a semicrystalline polymer, the amorphous intercrystalline layers are considered to have the same properties as the fully‐amorphous polymer. In reality, these thin intercrystalline layers can be substantially influenced by the presence of the crystals, as individual polymer molecules traverse both crystalline and amorphous phases. In polymers with rigid backbone units, such as poly(etheretherketone), PEEK, previous work has shown this coupling to be particularly severe; the glass transition temperature (T_g) can be elevated by tens of degrees celsius, with the magnitude of the elevation correlating directly with the thinness of the amorphous layer. However, this connection has not been explored for flexible‐chain polymers, such as those formed from vinyl‐type monomers. Here, we examine T_g in both isotactic polystyrene (iPS) and syndiotactic polystyrene (sPS), crystallized under conditions that produce a range of amorphous layer thicknesses. T_g is indeed shown to be elevated relative to fully‐amorphous iPS and sPS, by an amount that correlates with the thinness of the amorphous layer; the magnitude of the effect is severalfold less than that in PEEK, consistent with the minimum lengths of polymer chain required to make a fold in the different cases. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1198–1204, 2007     

On the correlation of the glass transition temperature of a copolymer with its comonomer sequences

The glass transition temperature of a copolymer depends not only on chemical composition but also on its comonomer sequences. This experimental fact is explained by Barton's and Johnston's equations. Their equations, though complicated, become simple, if a suitable parameter is used to describe the comonomer sequences. It is shown that with these new expressions, their equations can be used to understand glass transition temperatures of two additional types of copolymers, compatible multiblock copolymers and homopolymers with various tacticities treated as steric copolymers.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayWe wish to thank the reviewer for his/her kind linguistic improvement of this article.     

Glass-forming composition regions and glass transition temperature in nonaqueous electrolyte solutions

With an interest in assessing the suitability of various nonaqueous solutions for electrolyte studies in the viscous region of the liquid state, the glass-forming properties of solutions of calcium nitrate dissolved in various nonaqueous solvents have been determined and compared with the corresponding aqueous solution properties. Solutions in dimethyl formamide prove of particular interest. The composition dependence of the glass temperature is similar in all solvents at high salt contents. Ideal glass temperatures, estimated from thermodynamic data for the pure solvents, are compared with experimental or extrapolated values.     

Free volume microstructure of amorphous polymers at glass transition temperatures from positron annihilation spectroscopy data

The analysis of annihilation characteristics of ortho-positronium at conventional calorimetric glass transition temperatures for a series of amorphous polymers reveals empirical correlations of average lifetime of o-Ps , and of its product with a relative intensityI _3g with appropriateT _g ^DSC values. These trends in terms of free volume mean that both the average size of free volume hole entityv _hg and the fractional free volume grow with increasingT _g ^DSC . The results are discussed considering the chemical microstructure as well as possible mechanisms acting in glass transition. A relation is indicated between geometric and flexibility characteristics of chains and thev _hg andf _g parameters of free volume microstructure on the one side and potential motional processes responsible for solidification of the amorphous system on the other side.     

In situ measurement of the glass transition temperature of polymers with compressed fluid diluents

In situ measurement of the creep compliance of poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA), equilibrated with a pressurized CO₂ phase, is used to determine the glass transition temperature. Corrections due to dilation of the polymer by CO₂ as well as the buoyancy are assessed. Both polymer systems exhibit a recently discovered phenomenon, retrograde vitrification, in which a liquid polymer becomes a glass with an increase in temperature. The experimental results are predicted semi-quantitatively in terms of the temperature and pressure effects on the solubility of the compressed fluid in the polymer. © 1994 John Wiley & Sons, Inc.     

Crystallization and glass transition of chlorobenzene/toluene binary amorphous systems

Crystallization and glass-transition phenomena were studied for amorphous chlorobenzene (CB)/toluene (TL) binary systems as the function of composition. Samples were prepared by vapor-deposition onto cold substrates, and their structural changes due to temperature elevation were monitored with Raman scattering and light transmission. It was found that the crystallization temperature (T _c) of CB-rich amorphous samples increases as the TL concentration is increased. This is similar to the linear dependence of glass-transition temperatures (T _g) of many organic compounds on the concentration of additive. Also found was that T _c of TL-rich supercooled-liquids decrease as the CB concentration is increased. Issues related to the two kinds of T _c are discussed briefly. This revised version was published online in August 2006 with corrections to the Cover Date.     

The glass temperature of dendritic polymers

A theoretical treatment of the glass temperature of dendritic polymers is presented. The influences of polymer backbone, end group, initiator core, branching unit, composition and functionality are discussed. In dendritic polymers the glass temperature is dependent only on the generation number of dendritic growth and thus only on the molecular weight of a dendron, but not on the molecular weight of the whole molecule. It is governed primarily by the backbone glass temperature and depends little on branching functionality. Only minor differences between linear polymer and dendrite are obtained, since the influences of end groups and branching compensate each other to a large extent. © 1995 John Wiley & Sons, Inc.     

Moisture effects on the glass transition and the low temperature relaxations in semiaromatic polyamides

The influence of moisture absorption on the primary (glass) transition (T_a or T_g) and the low temperature relaxations of semiaromatic amorphous polyamides synthesized by isomeric aliphatic diamine and metha or para oriented phthalicdiacids has been investigated by means of differential scanning calorimeter (DSC) and dynamic mechanical thermal analyser (DMTA). The glass transition of semiaromatic polyamides was lowered due to the water absorption, and the β and the γ relaxations were as well. From the observed T_g and the difference in the heat capacity, the calculated T_g depression per 1 wt % water content was 12.3 K and the result was in good agreement with the experimental data. The depression of the glass transition may be expressed by the same manner as the plasticization of nylon 6 by water. The depressed β relaxation observed in the specimen containing a few percent of moisture was splitted into two transitions due to the reduction of water content, of which one was the elevation of the T_β and another was the simultaneous appearance of the T_γ, and then the single T_γ solely was observed for the completely dried specimen. The T_γ seemed to be merged into or not to be observed by the large and broad T_β transition when the sample was governed by a few percent of water, then it was emerged from the T_β due to water desorption. Thus, the T_β is believed to arise from the intermolecular hydrogen bonding between water molecules or between water and amide groups in wet polyamides. In addition, the γ relaxation originated from the peptide groups is attributable to the inter- and intramolecular hydrogen bonding between amide groups. © 1997 John Wiley & Sons, Inc. J Polyn Sci B: Polym Phys 35: 807–815, 1997     

Interactions in a blend of two polymers greatly differing in glass transition temperature

Blends of poly(N‐methyldodecano‐12‐lactam) PMDL with poly(4‐vinyphenol) PVPh have been studied by the DSC and ATR FTIR methods. The difference in glass transition temperature T_g between the components is 206 °C. A single composition‐dependent T_g suggests miscibility of the system, that is, homogeneity on the scale of about 10 nm. Fitting of the equation of Brostow et al. to the T_g data indicates relatively strong specific interactions and high complexity of the system. The Schneider's equation applied separately to low‐ and high‐PVPh regions provides good agreement with experiment; the calculated curves cross at the point of PVPh weight fraction 0.27. In the low‐PVPh region, the analysis indicates weak interactions with predominance of segment homocontacts and strong involvement of conformational entropy. In the high‐PVPh region, strong specific interactions predominate and entropic effects are suppressed. Composition dependences of the heat capacity difference at T_g and the width of glass transition indicate strong interactions in the system and existence of certain heterogeneities on segmental level, respectively. According to ATR FTIR, hydrogen bonds between PVPh as proton donor and PMDL as proton acceptor induce miscibility in blends of higher PVPh content (above about 0.28 weight fraction). In low‐PVPh blends, it is conformational entropy that enables intimate intermolecular mixing. Hydrogen bonds adopt several (distorted) geometries and are on average stronger than average hydrogen bonds formed in self‐associating PVPh. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Influence of matrix glass transition temperature on the memory effect of polymer‐dispersed liquid crystals

In this article, macroinitiators with different glass transition temperature (T_g) were synthesized by reversible additional‐fragmental chain transfer polymerization, and used to prepare polymer‐dispersed liquid crystals (PDLCs) with methyl acrylate. The memory effect of these PDLCs was investigated. The results showed that remarkable memory effect exhibit only in PDLCs with high and low T_g block chain. The possible mechanism responsible for the behavior is sketched. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 729–732, 2010     

Investigation of the relationship of the glass‐transition temperature and the polymer structure by fuzzy set theory

Fuzzy set theory can be used to study the relationship between the glass‐transition temperature (T_g) and structure of polymers. We used the method to map this relationship and obtained T_g's for 241 polymers with a standard deviation of 20 K (the confidence bound was 90%). We also used the method to predict T_g's for 15 polymers with a standard deviation of 67 K (the confidence bound was 90%). This study demonstrates that fuzzy set theory can be effectively used for determining the quantitative structure–property relationship of polymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 454–459, 2002; DOI 10.1002/polb.10105     

On the glass transition temperature of styrene-n-butyl methacrylate copolymers in dependence on chemical composition,molecular weight,and mixtures

For statistic copolymers of styrene and n-butyl methacrylate, the relation between the glass transition temperature and the chemical composition or molecular weight of the copolymers has been determined. Further, the dependence of the glass transition temperature on the composition of binary and ternary blends from statistical poly (styrene-co-n-butyl methacrylates) of a nearly equal chemical composition but a very different molecular weight has been studied. Among several equations considered for the correlation between glass transition temperature and composition of the mentioned copolymers with relatively low molecular weights, the Gordon/Taylor and Couchman equations gave the best agreement with the experimental results. For the glass transition temperature of poly(styrene-co-n-butyl methacrylate) with an n-butyl methacrylate content of about 30 wt % in dependence on the molecular weight, the Kanig-Ueberreiter and Fox-Flory equations proved to be useful for the examined molecular weight range. The glass transition temperatures of the polymer blends have been studied for a low/high-molecular component system, a system of two low-molecular components, as well as for systems with a third component. The glass transition temperatures of the mixtures frequently exceeded those of their individual components. © 1994 John Wiley & Sons, Inc.