Hans Adam Schneider

Glass transition behaviour of compatible polymer blends

It is shown that compatible polymer blends exhibit specific glass transition-composition behaviour, reflected in deviations from the Gordon-Taylor equation for supposed volume additivity of the blend components. Besides the intensity of the interchain interaction, conformational redistributions in the neighbourhood of the hetero-contacts are mainly responsible for the Tg behaviour of compatible polymer blends. Chain orientation due to the hetero-contact interaction is responsible for interchain stiffening, accompanied by an increase in the Tg temperature. The stronger the hetero-interchain interaction, the more likely it is that there will be an orientation effect. Decrease of the molecular weight of the stiffer blend component acts in the same way. Since it is then more mobile, the accommodation with the mobile blend component will be improved, resulting also in a closer packing of the blend components. Compensation for hetero-interaction and chain orientation effects may be responsible for the apparent volume additivity behaviour reflected by the Gordon-Taylor equation.

Approach to the composition dependence of the glass transition temperature of compatible polymer blends: 1

Starting with the idea that, besides conformational energy barriers, surface contacts are responsible for both conformation and ‘free’ volume distribution, a new concept is developed to describe the glass transition in compatible polymer blends. An extended Gordon-Taylor equation results if both the effective contact probabilities of the blend components and the effect of molecular surroundings on the contact contribution to the glass transition of the blend are considered. Free volume redistribution due to surface contacts is included. The Gordon-Taylor constant K of the relation obtained is now not a fitting parameter, but is related to the ratio of the different expansion coefficients of the free volume. The relation introduces two fitting parameters, K1 and K2, which are related to the intensity of polymer-polymer interaction and to the effect of immediate molecular surroundings on the interaction. Data analysis suggests that these fitting parameters are not only polymer-specific, but also molecular-weight-dependent.

The glass temperature of polymer blends: comparison of both the free volume and the entropy predictions with data

Abstract Experimental glass temperatures for 30 compatible blends have been compared with an equation derived from the hypothesis that the glass temperature is determined by conformational entropy changes and with the well known glass transition temperature ( T g ) versus composition equation of Fox based on volume additivity. Since these equations neglect interactions, it is not surprising that they fail in predicting at least half the experimental T g data. Nevertheless the approximate equivalence of the predictions of these two equations suggests that the glass temperature of an infinite molecular weight polymer is proportional to the mass divided by the number of flexible bonds of the monomer unit. As the interactions are disregarded, the two equations are zero-order treatments and thus they can both be improved.

A new approach to PVC-plasticizer interaction by using a Tg concentration power equation

Abstract The concentration power equation recommended by Brekner, Schneider and Cantow for adapting the compositional dependence of the glass temperature, T g , of compatible binary polymer blends has been used to correlate the experimental T g data obtained for PVC-plasticizer systems. It is demonstrated that the T g vs composition data for such systems can be adapted with the condition that two different concentration power equations are applied separately to the two branches of the curves separated by the cusp typical for these systems. Accordingly, different values are obtained for the parameters of the concentration power equation for the two branches of the T g vs composition curves. A certain significance is attributed to the cusp, characterized by a critical composition of the system. Below the critical composition the plasticizer will be fixed by energetic driven hetero-interaction preferentially in the ‘interdomains’ within the amorphous PVC matrix, causing a stiffening of the blend. Above the critical concentration the plasticizer will still penetrate these domains, but this time due to plasticizer-plasticizer homocontacts which thus contribute to an increase of the mobility and consequently of the entropy of the blend. This different behaviour is characterized by means of the different parameters of the concentration power equations for the two branches of the T g vs composition curves. Additionally it is shown that the parameters can be correlated with the usual compatibility criteria of the plasticizer ranking.

Thermally reactive oligomers of aromatic poly(ether sulphone) containing poly(dimethylsiloxane): 1. Synthesis and characterization

Thermally crosslinkable oligomers of aromatic poly(ether sulphone) (PSU) with incorporated poly(dimethylsiloxane) (PDMS) segments were produced via Pt-catalysed hydrosilylation of α,ω-di(silane)PDMS with α,ω-di(vinylbenzyl)PSU. A 21 molar ratio of PSU to PDMS was used to obtain statistically a ‘triblock’ copolymer with on average one PDMS segment incorporated between two PSU segments. Nuclear magnetic resonance analysis of prepared ‘triblocks’ revealed that the reaction could be performed without detectable side reactions of the hydrosilane end groups of the PDMS. Thermal characterization of the ‘triblocks’ showed the thermal transitions of both segments, both before and after curing, to be highly dependent on the molecular weight of the component segments, good phase separation being realized at relatively low molecular weights, ∼ 3000 for both segments. Manipulation of the thermal transitions of both segments especially after cure was shown to be possible through proper choice of precursor molecular weights, or by blending of prepared ‘triblocks’ with varying amounts of homo-α,ω-di(vinylbenzyl)PSU. By these methods, it was possible to obtain cured PSU-PDMS-PSU ‘triblocks’ with PSU hard segment Tg values near to 200°C and low-temperature PDMS Tg values at about − 120°C. Dynamic-mechanical/rheological studies were also performed on these ‘triblocks’, and this is the subject of the following paper.

Alternating block copolymers of aromatic poly(ether sulphone) and poly(dimethylsiloxane) by hydrosilylation

Abstract Alternating block copolymers of aromatic poly(ether sulphone) (PSU) and poly(dimethylsiloxane) (PDMS) were prepared via Pt-catalysed hydrosilylation of α,Ω-di(vinylbenzyl)PSU or α,Ω-di(allylether)PSU with α,Ω-di(silane)PDMS. The vinyl functionalized PSUs were prepared by Williamson phase transfer catalysed (PTC) etherification of α,Ω-di(hydroxyphenyl)PSU with p-chloromethylstyrene or allyl bromide (chloride), respectively. The block copolymers prepared were characterized by nuclear magnetic resonance (n.m.r.), gel permeation chromatography (g.p.c.), differential scanning calorimetry (d.s.c.) and membrane osmometry. These block copolymers showed good degrees of chain extension and phase separation into rubbery PDMS and glassy PSU domains.

DSC and p-V-T Study of PVC/PMMA Blends

Poly(vinyl chloride)/Poly(methyl methacrylate) — PVC/PMMA — blends were investigated by comparative p-V-T and differential scanning calorimetry (DSC) measurements. The study was concentrated on the glass transition range of the blends, and it was found that the blends are characterized by a single glass transition temperature suggesting miscibility of the blend components. It is shown that the glass temperature of the blends increases with both increasing heating rate and pressure. In parallel hereto one observes a decrease in the volume expansion coefficients, which is more accentuated for the polymeric melts than for the polymeric glasses. The dependence of the glass temperature on the composition of the polymer blends shows a sigmoidal behaviour which is due to the fact that positive deviations of the glass temperature from values predicted by additivity rules are observed in the high PVC concentration range, whereas in the high PMMA range negative deviations occur. This suggests a denser packing of the blends and thus a stronger interaction between the blend components in the high PVC concentration range. These packing differences increase with increasing pressure and decreasing heating rate and are generally more accentuated for the glass temperatures evaluated from p-V-T measurements.

ISOTHERMAL MElT CRYSTALLIZATION KINETICS OF POLY(L-LACTIC ACID)

A DSC study was carried out of the isothermal melt crystallization kinetics of poly(L-lactic acid), PLLA, at 110, 115, 120, 125 and 130‡C. The experimental data were evaluated within the framework of the well-known Avrami kinetic model and an extended model involving an additional third kinetic parameter [8]. In order to perform the necessary numerical calculations, a number of functions built into the Mathematica® software system were used. The results showed that the isothermal melt crystallization kinetics of PLLA can be described adequately by both these kinetic models. It should also be stressed that the kinetic model of Urbanovici and Segal offers a better description of the experimental melt crystallization data of PLLA than the classical Avrami model.

The quantitative evaluation of TG-curves of polymers

Abstract It is shown that any attempt of kinetic interpretation of TG-data of polymer degradation has to consider all peculiarities of polymer destruction processes. Besides the heterogeneous character of this process, mainly its radical chain reaction nature, the presenceof weak bonds and possible scission in chain fragments of different length will prevent stationary state of reaction. Therefore rather a variation of activation energy during non-isothermal degradation of polymers will be the consequence. Supplementary larger polymer chain fragments must not be volatile at temperature of formation.

Thermodynamic aspects of the glass-transition in the compatible blend poly(styrene)-poly(vinylmethylether)

SummaryIt is shown that composition dependence of glass-transition in the compatible poly(styrene)-poly(vinylmethylether) blend exhibits deviations from additivity rules derived in the supposition of continuity of the thermodynamic excess functions of mixing. Only the acceptance of an additional adjusting parameter which accounts for interaction, enables the interpretation of experimental Tg-data. This adjusting parameter is quite different for the blends of PVME with oligomeric and high moleculare PS, respectively.