Quenched polymer density

Density, mechanical, and thermal properties are significantly affected by the degree of crystallinity. These properties can be used to experimentally estimate the percent crystallinity, although no measure is completely adequate (48). The crystalline density of PET can be calculated theoretically from the crystalline stmcture to be 1.455 g/cm. The density of amorphous PET is estimated to be 1.33 g/cm as determined experimentally using rapidly quenched polymer. Assuming the fiber is composed of only perfect crystals or amorphous material, the percent crystallinity can be estimated and correlated to other properties. 

In Fig. 5.1, the densities of the annealed and of the quenched polymers are plotted against Mh the inverse molecular mass of the network strands. All the annealed samples were denser by about 0.15% than the quenched ones. Bero and Plazek [52] observed an effect of similar magnitude between quenched samples and samples cooled at 0.2 K/h. 

Apparently, annealing was not impeded by crosslinks (Fig. 5.1). The density effects observed agree with the results of the glass transition temperature measurements (Sect. 4.2). There, the Tg of the annealed (and therefore denser) sample was consistently higher by about 2 K than the Tg of the quenched polymer. 

Fig. 5.1. Densities of annealed and of quenched polymers are plotted against 1/MC, that is the inverse molecular mass between crosslinks. Test temperature 23 °C. The density of the thermoplastic Phenoxy is indicated. The diamond represents polymer E.

Another feature observed in these simulations of deep quenches with many vacancies was a segregation of vacancies, if one chooses a model with attractive interactions between monomers (eAA = eBb = — e, eAB = 0). This phase separation between polymers and solvent shows up via the growth of the structure factor Sp(q, t) measuring the polymer density fluctuations, Fig. 37,... 

Structural rearrangements in a micelle with quenched PE corona can be investigated using the mean-field approach (described in Sect. 5) in combination with the local electroneutrality approximation (LEA). As before, we neglect here the radial gradients in the polymer density and mobile ion distributions (i.e., implement the boxlike model). Moreover, we omit the contribution due to nonelectrostatic... 

The mean-field approach combined with the local electroneutrality approximation (LEA) can be extended beyond the boxlike model. To calculate the free energy of a micellar corona with the radial gradients in polymer density, we assume that all the free ends of blocks A are located at the corona periphery and are equally stretched. Within this model, the free energy of a micelle of morphology i (t = 1,2,3), can be explicitly calculated for both quenched and annealing PE coronae. We outline here only a general scheme of the approach, whereas the details can be found in [22, 32]. 

The role of disorder in the photophysics of conjugated polymers has been extensively described by the work carried out in Marburg by H. Bassler and coworkers. Based on ultrafast photoluminescence (PL) (15], field-induced luminescence quenching [16J and site-selective PL excitation [17], a model for excited state thermalizalion was proposed, which considers interchain exciton migration within the inhomogenously broadened density of states. We will base part of the interpretation of our results in m-LPPP on this model, which will be discussed in some detail in Sections 8.4 and 8.6. 

Fig. 5.3. Young s moduli Efle, as determined by flexural tests on small samples after thermal treatment are plotted against the densities of those samples. The dots are situated along a single line since the annealed samples are denser and more rigid than the quenched samples prepared from the same polymer...

Fig. 6.3. Yield strengths from flexural tests are plotted against the densities of the polymers. The annealed samples were noticeably stronger than the quenched ones of similar density. Rigidity (Fig. 5.3.) was governed by the density of the polymer whereas yield strength seemed to depend mostly on molecular conformations...

Model Deyelopment. Rachow and Timm (] ) derived working relationships for the kinetic mechanism described. Degree of polymerization is considered to be a continuous variable. For quenched samples a relationship correlating population density of associated polymer molecules as a function of time, degree of polymerization and environmental factors is... 

Vc crystalline Va, amorphous). The densities of the pure crystalline (pc) and pure amorphous (pa) polymer must be known at the temperature and pressure used to measure p. The value of pc can be obtained from the unit cell dimensions when the crystal structure is known. The value of pa can be obtained directly for polymers that can be quenched without crystallization, polyfethylene terephtha-late) is one example. However, for most semi-crystalline polymers the value of pa is extrapolated from the variation of the specific volume of the melt with temperature [16,63]. 

Pre-crystalline order in PET has been investigated by a number of different groups and in the present volume the issue is reviewed under different perspectives in two other contributions [25,26]. Nodular structures measuring ca. 7.5 nm and ca 15 nm apart in PET quenched from the melt close to Tg were first described by Geil [27,28]. Such structures are essentially amorphous, albeit characterized by some degree of orientational order and by a significantly higher density as compared to the fully isotropic polymer. They are indeed qualitatively compatible with the bundle model we propose [29]. Apparently... 

Annealing can reduce the creep of crystalline polymers in the same manner as for glassy polymers (89,94,102). For example, the properties of a quenched specimen of low-density polyethylene will still be changing a month after it is made. The creep decreases with time, while the density and modulus increase with time of aging at room temperature. However, for crystalline polymers such as polyethylene and polypropylene, both the annealing temperature and the test temperatures are generally between... 

Water-soluble QDs now are available from a number of manufacturers (Invitrogen, Evident Technologies, and Crystalplex). Each supplier uses their own proprietary methods of surface pacification to create biocompatible particles. Even coated QD clusters are available that contain hundreds of particles bound together in a polymer matrix (Crystalplex). These form intensely bright labels for biomolecules, because the nanocrystals do not quench when clustered together at high density. 

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