Physical properties, polymer thermodynamics

This chapter covers the chemistry, physical properties, and thermodynamics of polymers. First are discussed various methods of macromolecule preparation. Next are discussed the physical properties of polymers in the bulk, with emphasis on the morphology and rheology of polymeric materials. Finally, several aspects of polymer solutions are discussed, including their thermodynamics and rheological properties, which will be related to molecular parameters such as chain conformation. Current theories that account for the properties of macromolecules in the bulk and in solution are presented briefly. The reader is encouraged to seek further information in specialized texts (2-7), dictionaries (8), and encyclopedia (9-11). 

In this chapter we have discussed the thermodynamic formation of blends and their behavior. Both miscible and immiscible blends can be created to provide a balance of physical properties based on the individual polymers. The appropriate choice of the blend components can create polymeric materials with excellent properties. On the down side, their manufacture can be rather tricky due to rheological and thermodynamic considerations. In addition, they can experience issues with stability after manufacture due to phase segregation and phase growth. Despite these complications, they offer polymer engineers and material scientists a broad array of materials to meet many demanding application needs. 

Balsara NP (1996) Thermodynamics of polymer blends. In Mark JE (ed) Physical properties of polymers handbook. AIP Press, New York, p 257... 

PVDF is mainly obtained by radical polymerisation of 1,1-difluoroethylene head to tail is the preferred mode of linking between the monomer units, but according to the polymerisation conditions, head to head or tail to tail links may appear. The inversion percentage, which depends upon the polymerisation temperature (3.5% at 20°C, around 6% at 140°C), can be quantified by F or C NMR spectroscopy [30] or FTIR spectroscopy [31], and affects the crystallinity of the polymer and its physical properties. The latter have been extensively summarised by Lovinger [30]. Upon recrystallisation from the melted state, PVDF features a spherulitic structure with a crystalline phase representing 50% of the whole material [32]. Four different crystalline phases (a, jS, y, S) may be identified, but the a phase is the most common as it is the most stable from a thermodynamic point of view. Its helical structure is composed of two antiparallel chains. The other phases may be obtained, as shown by the conversion diagram (Fig. 7), by applying a mechanical or thermal stress or an electrical polarisation. The / phase owns ferroelectric, piezoelectric and pyroelectric properties. 

Petrie, S. E. B. The effect of excess thermodynamic properties versus structure formation on the physical properties of glassy polymers. J. Macromol. Sci., Phys. 12, 225 (1976)... 

The systems selected for evaluation are the PDMS-C02 system studied by Gerhardt et al. (1997, 1998) and PS-gas systems studied by Kwag et al. (1999). Properties for these systems are listed in Table 11.1. The variation in physical properties between these systems provides a very broad basis for evaluating the rheological properties of polymer-gas systems. The PDMS C02 system exhibits a favorable thermodynamic affinity between the polymer and dissolved gas, and provides the opportunity to evaluate the rheology of melts with very high dissolved gas content (up to 21 wt %). Carbon dioxide is much less soluble in polystyrene than in PDMS, so the PS-C02... 

The process model is given in Leversund et al. (1993). As the polymer product forms a separate solid phase, this was not included in the process model. The model includes mass and energy balances, column holdup and phase equilibria and results in a set of DAEs. All thermodynamic, physical properties are calculated from library subroutines. The column description and data for the process are given in Table 9.6. 

The basic issue confronting the designer of polymer blend systems is how to guarantee good stress transfer between the components of the multicomponent system. Only in this way can the component s physical properties be efficiently used to give blends with the desired properties. One approach is to find blend systems that form miscible amorphous phases. In polyblends of this type, the various components have the thermodynamic potential for being mixed at the molecular level and the interactions between unlike components are quite strong. Since these systems form only one miscible amorphous phase, interphase stress transfer is not an issue and the physical properties of miscible blends approach and frequently exceed those expected for a random copolymer comprised of the same chemical constituents. 

Mandelkem L and Alamo RG, "Thermodynamic Quantities Governing Melting", in Mark, JE (Ed), "Physical Properties of Polymers Handbook", Chapter 11, AIP Press, Woodbury, NY, 1996. 

In 1988 the Design Institute for Physical Property Data of the American Institute of Chemical Engineers established Project 881 to develop a Handbook of Polymer Solution Thermodynamics. In the area of polymer solutions, the stated purposes were (1) provide an evaluated depository of data, (2) evaluate and extend current models for polymers in both organic and aqueous, solvents, (3) develop improved models, and (4) provide a standard source of these results in a computer data bank and a how-to handbook with accompanying computer software. During the four years of this project most of these objectives have been met and the results are presented in this Handbook. 

Other relationships between % and an observable physical property such as osmotic pressure [20, 43], freezing point depression of polymer [20, 52] or solvent [20, 53], and gas liquid chromatography [46-54], were established in like fashion. The relationship determined for swelling of cross-linked polymer to thermodynamic equilibrium in excess liquid has particular significance for the subject of this review. It is given here in the form of the Flory-Rehner equation. 

Unless the nature and number of the liaisons in the initial and final states are known with certainty, the reliability of the x-Parameter (based on Eq. 7 and relationships derived therefrom) suffers accordingly, even with the most accurate thermodynamic methods for measuring colligative physical properties of polymer-liquid systems. It would be well, therefore, to develop methods for defining the mode of complexation at the initial and final states on a molecular basis. Elucidation of the molecular nature of these complexations at gel-saturation (or in true solution) is an end-objective of the work described in Sect. 3 of this review. 

More specifically, conformational analysis can provide information on stable isomeric states, which are defined as minima on energy-deformation plots, and on the energy barriers between these minima. Through these minima, the population of each state at different temperatures at thermodynamic equilibrium can be determined, and a description of the kinetics of the transition from one isomeric state to another can be obtained. Therefore, conformational analysis can define chain flexibility completely. Thus, conformational analysis is the key element required to establish the conceptual bridge between polymer structure and physical properties. 

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