Poly-n-alkyl methacrylates

Ti values may occur with such native biopolymers as ribonuclease A, deoxyribonucleic acid, and collagen, whose molecular motions are restricted, but, as yet, high values have not been observed for polysaccharides in solution, or for gels, in which these motional-restriction effects may be equivalent, or less marked. However, an extensive relaxation-study by Levy and coworkers68 on poly(n-alkyl methacrylates) may serve as a model for future experiments on polysaccharides, as this type of molecule has a main chain and side chains, albeit more mobile than those in polysaccharides. 

Rogers, S. S., and L. Mandelkern Glass formation in polymers. I. The glass transitions of the poly(n-alkyl methacrylates). J. Phys. Chem. 61, 985—990 (1957). 

Type B. This type of molecular motion involves the rotation of a whole side group, e.g. the n-alkyl ester group in poly (n-alkyl methacrylates) and poly (n-alkyl acrylates). It does not necessarily mean that a complete rotation is made. Moreover a cooperative motion of the backbone might be required for this partly rotation. 

It is apparent that our concepts of the relaxational processes in well studied systems such as the poly(n-alkyl acrylates) and poly(n-alkyl methacrylates) warrant further study and that... 

Figure 13.28 Shear modulus (a) and damping (b) at 1 Hz as a function of temperature for poly(n-alkyl methacrylate). (---) Polymethyl methacrylate (-) polyethyl methacrylate (----) poly(n-propyl meth-...

The dielectric strength. As, which is proportional to the area under the loss peak, is much lower for the secondary processes, relative to the a relaxation analysed in the next section. This is a common pattern foimd in both polymer materials and glass formers. The P secondary process is even more depleted in linear polymers that contain the dipole moment rigidly attached to the m chmn, such as polycarbonate [78-80] and poly(vinyl chloride) (the behaviour of this polymer was revisited in ref [81] where the secondary relaxation motions are considered as precursors of the a-relaxation motions). Polymers with flexible polar side-groups, like poly(n-alkyl methacrylate)s, constitute a special class where the P relaxation is rather intense due to some coupling vnth main chain motions. 

Among the poly(n-alkyl methacrylate)s, the most studied ones are PMMA (poly-(methyl methacrylate)) [40, 50-51,102-104], PEMA (poly(ediyl methacrylate)) [40, 50-51,103-108] and PnBMA (poly(n-butyl methacrylate)) [40, 51, 103-106, 109], mainly by DRS and NMR (studies previous to 1965 have been reviewed in [2]). The development of the NMR technique and the increase of the frequency window in DRS brought new insights into the molecular dynamics of these materials (see [110] for details and references therein). 

As the size of the ester alkyl group increases in a series of poly(n-alkyl methacrylate)s, the polymer molecules become spaced further apart and the intermolecular attraction is reduced. Thus, as the length of the side chain increases, the softening point decreases, and the polymers become rubbery at progressively lower temperatures (Figure 4.9). However, when the number of carbon atoms in the side chain exceeds 12, the polymers become less rubbery, and the softening point, brittle point, and other... 

R 624 M. Wind, R. Graf, A. Heuer and H. W. Spiess, Structural Relaxation of Polymers at the Glass Transition Conformational Memory in Poly(n-Alkyl Methacrylates) , Phys. Rev. Lett., 2003,91,155702 R 625 J. -L. Wolfender, K. Ndjoko and K. Hostettmann, Liquid Chromatography with Ultraviolet Absorbance-Mass Spectrometric Detection and with Nuclear Magnetic Resonance Spectrometry A Powerful Combination for the On-Line Structural Investigation of Plant Metabolites , J. Chromatogr., A, 2003,1000,437... 

Themodynamically induced shear degradation also has been investigated using solutions of anionically polymerized poly(n-alkyl methacrylate)s in poor solvents Three different lengths of the alkyl substituents (methyl PMMA n-butyl PBMA -decyl PDMA) were used in the course of the study. As an example for the thermodynamic characterization of these systems, Fig. 6 shows the cloud point curves of PDMA dissolved in -butanol... 

Hempel, E., Kahle, S., Unger, R and Donth, E. (1999) Systematic calorimetric study of glass transition in the homologous series of poly(n-alkyl methacrylate)s Narayanaswamy parameters in the crossover region. Ther-mochimica Acta, 329, 97-108. 

Fig. 12.2. Equivalent Bragg spacing dnpa as calculated from the maxima of the pre-peaks for lower amorphous poly(n-alkyl methacrylates) ( ) as well as amorphous ( ) and semicrystalline ( ) PODMA (cf. Fig. 12.1). The inset shows a schematic picture of the structure of amorphous poly(n-alkyl methacrylates)...

A schematic picture of the structure of semi-crystalline PODMA is shown in the insets of Fig. 12.1. Basic idea is that the alkyl groups belonging to different monomeric units form layer-like alkyl nanodomains which are separated by main chains. The periodicity dnps of this lamellar structure reflected by the prepeak in x-ray scattering data is indicated. We assume that the alkyl groups within the alkyl nanodomains are basically interdigitated and not to far away from an extended chain conformation. This can be concluded from the dependence of the d ps value on the number of alkyl carbons per side chain C for atactic poly(n-alkyl methacrylates) (Fig. 12.2). The dependence of dnps on (7 is nearly linear and the slope is about 0.13 nm [50] per additional CH2 unit in the side chain corresponding to the value reported for extended chain alkanes (0.127 nm/carbon). 

Zhang Weibang, Feng Ke and Li Zhuomei, Synthesis of Poly(n-alkyl methacrylates) auid Their Effects on the Pour-point Depression of Oil. Polymeric Materials Science and Engineer... 

Fig. 13. (a) Waxs spectra of a series of poly(n-alkyl methacrylates) shown at 293 K. Notice the development of the LVDW peak which shifts to lower Q values with increasing alkyl side chain, (b) Waxs spectra for PnDMA shown at two temperatures as indicated. Arrows show the positions of the three main peaks in the spectra, o T = 293 K —— T = 223 K. 

Other poly(n-alkyl methacrylate)s give a mixture of depoljmerization and side-group rearrangement, depending on the number of -hydrogens and the temperature. 

Besides polybutadiene, a similar behavior of the static stmeture factor is found for instance for polyethylene in the molten state, poly(ethylene propylene), poly(ethylene oxide), polyisobutylene,or poly(vinyl chloride). For these polymers, S(Q) in the intermolecular region displays one well-defined diffraction peak. For other cases, a peak with a shoulder or even two well-sepatated peaks can be observed in the Q-range characteristic for the intermolecular correlations. Examples for that are polyisoprene (Pl), polycarbonate, polystyrene (PS), 1,2-polybutadiene, poly (vinyl acetate), and poly(n-alkyl methacrylates). " In some cases, the existence of a multipeak stmrture in the intramolecular range of the momentum transfer does not correlate with the existence of bulky or longer side groups. 

Fig. 1 (a) Extended chain conformation of syndiotactic poly(n-alkyl methacrylates), (b) Anisotropic chain motion during glass process, (c) NMR spectra indicating anisotropic motion... 

Molecular dynamics of a macromolecular chain involves both cOTiformational and rotational motions. Along these lines, the backbone dynamics of poly(n-alkyl methacrylates) has been elucidated by advanced solid state NMR, which enables conformational and rotational dynamics to be probed separately [41], The former is encoded in the isotropic chemical shift. The latter is probed via the anisotropic chemical shift [14] of the carboxyl group with unique axis along the local chain direction. Randomization of conformations and isotropization of backbone orientation occur on the same time scale, yet they are both much slower than the slowest relaxation process of the polymer identified previously by other methods [40]. This effect is attributed to extended backbone conformations, which retain conformational memory over many steps of restricted locally axial chain motion (Fig. lb, c). These findings were rationalized in terms of a locally structured polymer melt, in... 

For long-chain molecules there are different geometric possibilities for the orientation of molecular dipole vectors with respect to the backbone. Following the notation of Stockmayer (1967), polymers are classified as type A (with dipoles fixed parallel to the mainchain, e.g., ds-l,4-polyisoprene and polyethers), type B [with dipole moments rigidly attached perpendicular to the mainchain e.g., poly (vinyl acetate) and most synthetic polymers], or type C [with a more-or-less flexible polar sidechain e.g.,poly(n-alkyl methacrylate)s]. However, a polymer possessing only one type of dipole moment is an exceptional case. The timescale (speed) of each polarization (and subsequent relaxation) process will determine whether this process will be monitored by a particular dielectric technique. Characteristics and fundamental peculiarities of relaxations generally found in polymers are discussed hereafter. Note that cases where finite polarization is present even in the absence of an external field (e.g., the permanent polarization in ferroelectrics) are not considered. 

For the majority of amorphous polymers Ae Ae e.g., for poly(ethylene terephthalate), which contains dipoles rigidly attached to the main-chain, and poly-(vinyl acetate), which has dipole moment components rigidly attached to the main-chain and attached to the flexible side-group (see McCrum et al., 1967). For certain amorphous polymers, notably the conventional poly(n-alkyl methacrylates)... 

Fig. 3. C,.o as a function of the number of carbons in the alcohol used to make the ester for poly(n-alkyl methacrylates) and poly (cycloalkyl methacrylates). C increases with increasing side group size in each family. For small rings is larger for cycloalkyl versus n-alkyl materials. Reprinted with permission from J. Macromol. Sd., Rev. Macromol. Cbem. Phys., C28(3 4) 393 (1988). Copyright 1988 Marcel Dekker, Inc.

K12 Kilbum, D., Dlubek, G., Pionteck, J., and Alam, M.A., Free volume in poly(n-alkyl methacrylate)s from positron lifetime and PVT experiments and its relation to the stmctural relaxation (experimental data by G. Dlubek), Polymer, 47, 7774, 2006. 

The determination of the experimental variables for apphcation of this approach is based on analysis of FTIR data on the blends and is covered in the references noted above. The application of the association model to determine or predict the phase behavior of interacting polymer systems include poly(2,6-dialkyl-4-vinyl phenol) blends with poly(n-alkyl methacrylates) and ethylene-vinyl acetate copolymers [217], poly(4-vinyl phenol)/poly(hydroxybutyrate) blends [218] and poly(4-vinyl phenol) in ternary blends with PEMA and PMMA [219] as weU as a number of examples in [92]. The determination of the equihbrium constants Ka and Kb) from FTIR data has been reported for ethylene-methacryhc add copolymers with polyethers [118] and ethylene-methacrylic add copolymers with poly(2-vinyl pyridine) [220]. 

FIGURE 1.9 Brittle points of poly(n-alkyl acrylate)s and poly(n-alkyl methacrylate)s. (After Rehberg, C. E. and Fisher, C. H. 1948. Ind. Eng. Chem., 40, 1431.)... 

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