Amorphous bisphenol-A polycarbonate

Figure 23. Stress-relaxation curves of amorphous bisphenol A polycarbonate at the different temperatures shown by the curves. The numbers in brackets are the maximum deformations used in the tests. (From Ref. 217.)...

M. Hutnik, A. S. Argon, and U. W. Suter, Polym. Prepr. ACS, Polym. Div., 30f2j, 36 (1989). Molecular Structure of Amorphous Bisphenol-A Polycarbonate. 

The spectrum of amorphous bisphenol-A polycarbonate showing both longitudinal and transverse Brillouin peaks is shown in Figure 2. 

In the early literature it is suggested that polycarbonates can be easily plasticized with common plasticizers. Plasticization of polycarbonate has been investigated by Kozlov et al. (12). These authors described the influence of plasticization on softening points and mechanical properties of bisphenol A polycarbonates. They conclude that the behavior of plasticized polycarbonate is similar to that encountered for most amorphous polymers. The influence of crystallization effects promoted by the plasticizer was not taken into account. 

Bisphenol A polycarbonate, BPA-PC (Fig. 25), has an unusual toughness among the amorphous thermoplastics, which has led to considerable industrial development. As early as the 1960s studies [8] were performed to understand the molecular origin of such a behaviour and to relate it to the secondary transition occurring around - 100 °C. 

The approach developed in this paper, combining on the one side experimental techniques (dynamic mechanical analysis, dielectric relaxation, solid-state 1H, 2H and 13C NMR on nuclei at natural abundance or through specific labelling), and on the other side atomistic modelling, allows one to reach quite a detailed description of the motions involved in the solid-state transitions of amorphous polymers. Bisphenol A polycarbonate, poly(methyl methacrylate) and its maleimide and glutarimide copolymers give perfect illustrations of the level of detail that can be achieved. 

The purpose of this paper is to investigate the mechanical properties (plastic deformation, micromechanisms of deformation, fracture) of several amorphous polymers considered in [1], i.e. poly(methyl methacrylate) and its maleimide and glutarimide copolymers, bisphenol A polycarbonate, aryl-aliphatic copolyamides. Then to analyse, in each polymer series, the effect of chemical structure on mechanical properties and, finally, to relate the latter to the motions involved in the secondary transitions identified in [ 1] (in most cases, the p transition). 

The mechanical properties of poly(methyl methacrylate), PMMA, have been studied for quite a long time and, in addition to its industrial interest, PMMA constitutes a kind of reference material. Indeed, among the amorphous linear polymers it represents an intermediate between the very brittle polystyrene and the tough bisphenol A polycarbonate considered in Sect. 4. Furthermore, as shown in [1] (Sect. 8.1), the molecular motions responsible for its large p transition are precisely identified, as well as the nature of the cooperativity that develops in the high temperature range of the p transition. 

Bisphenol A polycarbonate (BPA-PC), whose the chemical structure is shown in Fig. 66a, has very interesting fracture properties, exhibiting quite a high toughness for a pure amorphous polymer. At a very low temperature (- 100 °C at 1 Hz) it presents a secondary fi transition, shown in Fig. 67, which has been analysed in detail in [1] (Sect. 5). 

Figure 30. Mobility, g, plotted linearly in In, as a function of electric field strength (E), plotted as for holes in tri-/ -tolylamine (TTA) (40 wt.%) in bisphenol-A polycarbonate. The range of field strengths is approximately 10 -10 V cm (1-100 V pm ). The mobility depends exponentially on With increasing temperature, the overall magnitude of/r increases while the dependence on E weakens. These dependences are observed in nearly all amorphous molecular solids. (Reprinted with permission from Ref. [73r].)...

There have been many efforts for combining the atomistic and continuum levels, as mentioned in Sect. 1. Recently, Santos et al. [11] proposed an atomistic-continuum model. In this model, the three-dimensional system is composed of a matrix, described as a continuum and an inclusion, embedded in the continuum, where the inclusion is described by an atomistic model. The model is validated for homogeneous materials (an fee argon crystal and an amorphous polymer). Yang et al. [96] have applied the atomistic-continuum model to the plastic deformation of Bisphenol-A polycarbonate where an inclusion deforms plastically in an elastic medium under uniaxial extension and pure shear. Here the atomistic-continuum model is validated for a heterogeneous material and elastic constant of semi crystalline poly( trimethylene terephthalate) (PTT) is predicted. 

In addition to Tg (amorphous phases) and the melting temperature Tm (crystalline phases), polymers also manifest secondary relaxations at temperatures below those of major relaxations (Tg or Tm, which will collectively be referred to as T. The main secondary relaxation temperature wil be designated generically as Tp, although it may be labeled differently in the literature on specific polymers. For example, it is commonly labeled as Ty for bisphenol-A polycarbonate where Ty is for a relaxation of higher intensity than Tp, and occurring at a lower temperature, which is the main secondary relaxation of this particular polymer. 

The stress-strain curves of ductile thermoplastics (including both glassy amorphous polymers such as bisphenol-A polycarbonate and semicrystalline polymers such as polyethylene at room temperature) have the general shapes shown in Figure 11.16(a), which can be compared with the shape of the stress-strain curve of a very brittle material shown in Figure 11.16(b). The stress-strain curves of polymers which are neither very ductile nor very brittle under the testing conditions being utilized have appearances which are intermediate between these. two extremes. 

Rotational jumps not involving translations are observed in many polymers, particularly important types being the rotational jumps of methyl groups, as considered above for isotactic polypropylene and observable for a wide variety of polymers, and the 180° flips of para-disubsti-tuted benzene rings (phenylene rings, — — ). These flips have been observed in many polymers, including amorphous polymers such as bisphenol-A polycarbonate (PC), —C(CH3)2— —O—CO O, ... 

Physical blends of bisphenol-A polycarbonate (PC) and a poly-arylate (PAr) exhibit by thermal analysis two amorphous phases a pure PC phase and a PAr-rIch miscible mixed phase. On controlled thermal treatment, transreaction between PC and PAr takes place mainly in the mixed phase, producing a new copolymer. Reaction progression from block to random copolymers has been traced by DSC, 13c NMR and CPC. The final product of transreaction is an amorphous copolymer showing a single T depending on the original binary composition. ... 

Bisphenol-A polycarbonate 15 is normally amorphous (and clear) but is subject to solvent-induced crystallisation in the presence of some low-molecular-weight solvents [125]. 

Isoharic (constant pressure) and isochoric (constant volume) glass transitions in polymers were first observed for bisphenol A polycarbonate (62). A molecular dynamics study of such transitions in a model amorphous polymer has also been reported (63). This study shows that the glass transition is primarily associated with the freezing of the torsional degrees of freedom of polymer chains (related to chain stiffness), which are strongly coupled to the degree of freedom associated with the nonbonded Lennard-Jones potential (related to interchain cohesive forces). 

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