Copolymer single crystals

The morphology of C2Ht—CO copolymer single crystals has been studied and a structural transition has been observed on annealing 51). The melting point of the copolymer has been found to decrease with decreasing CO content. The heat and entropy of fusion have been measured and found to be lower than those for polyethylene 52). 

Iwata and coworkers ° ° also investigated enzyme adsorption to copolymer single crystals, and reported that PHA depolymerase adsorbed randomly on the surfaces of single crystals. However, the concentrations of adsorbed enzjune on the surface of copolymer single crystals are lower than that for P(3HB) homopolymer single crystals. PHA depolymerase molecules cannot bind tighdy to the irregular surface of copolymer crystals since the copolymer chains with second monomer units have loose loop folds. 

Structure and enzymatic degradation of poly[(R)-3- hydroxy-butyrate] copolymer single crystals with extracellular PHB Depolymerase from Comamonas acidovorans YM1609 and Alcaligenes faecalis Tl, Macromolecules, 30 (1997), p. 5290-5296... 

Several studies have concerned the microstnicture of lamellae in materials such as the block copolymers polystyrene-h/oc/r-poly-l-vinylpyridine [139] and polystyrene-h/oc/r-polybutadiene [140], as well as single crystals of poly-para-xylylene [139], and reveal features (such as intersecting lamellae (figure Bl.19.29)) that had not been previously observed. 

Amines can also swell the polymer, lea ding to very rapid reactions. Pyridine, for example, would be a fairly good solvent for a VDC copolymer if it did not attack the polymer chemically. However, when pyridine is part of a solvent mixture that does not dissolve the polymer, pyridine does not penetrate into the polymer phase (108). Studies of single crystals indicate that pyridine removes hydrogen chloride only from the surface. Kinetic studies and product characterizations suggest that the reaction of two units in each chain-fold can easily take place further reaction is greatiy retarded either by the inabiUty of pyridine to diffuse into the crystal or by steric factors. 

Single crystals with a Tm of 423 K have been produced from low-density polyethylene (ldpe). Isotactic PP crystals have a Tm of 444 K and syndiotactic PP has a Tm of 411 K, whereas atactic PP is amorphous and has a Ts of 255 K. Isotactic polyolefins with pendant groups, such as polyhexene, have high Tm values. Random copolymers of ethylene and propylene are amorphous, but block copolymers of these monomers are crystalline. 

Polyoxybenzoate is a stiff chain, lyotropic liquid crystalline material, as was discussed on the basis of its copolymers with ethylene terephthalate (see Sect. 5.1.4). The crystal structure of the homopolymer polyoxybenzoate was shown by Lieser 157) to have a high temperature phase III, described as liquid crystalline. X-ray and electron diffraction data on single crystals suggested that reversible conformational disorder is introduced, i.e. a condis crystal exists. Phase III, which is stable above about 560 K, has hexagonal symmetry and shows an 11 % lower density than the low temperature phases I and II. It is also possible to find sometimes the rotational disorder at low temperature in crystals grown during polymerization (CD-glass). 

M. J. Folkes and A. Keller, The birefringence and mechanical properties of a single crystal from a tri-block copolymer, Polymer, 12,222 (1971) M. J. Folkes and A. Keller, Optical and swelling properties of macroscopic single crystals of an S-B-S copolymer. I. Samples possessing a lamellar morphology, J. Polym. Sci., Polym. Phys. Ed., 14, 833 (1976). 

Kim et al. [22] have used vibrational sum-frequency generation spectroscopy (SFG) to characterize the surfaces of (3-HMX single crystals, as well as the interface between HMX and the copolymer Estane. SFG is a nonlinear vibrational spectroscopic technique, related to optical parametric amplification that selectively probes vibrational transitions at surfaces and interfaces. Compared with bulk HMX, the surface vibrational features are blueshifted and observed splittings are larger. The technique may have application to detection of explosive residues on surfaces. 

More recently, ordered ultradense arrays in block copolymer films have been obtained over macroscopic distances using faceted surfaces of commercially available single-crystal sapphire substrates [152]. The self-assembly overrides substrate defects and uses the topography only as a guide to the orientation of the arrays. 

Hydrosilation chemistry is presently having, and will continue to have, an important impact on certain areas of materials chemistry. The rapidity and cleanliness of the reaction, and the stability of the resulting Si-C bonds, have been used to produce dendritic polymers and block copolymers with well-defined structures [21]. The reaction can also be employed to attach molecules to surface Si-H groups, notably the Si-H present on the surfaces of aqueous etched single crystal, or nanoparticular Si [22], or other siliceous substrates, with substantial modification to their physical and chemical properties [23]. 

Figure 7. Comparison of DSC Spectra a) HBA/HNA (50/50) Copolymer Annealed for 16 hrs at 250°C, b) Single Crystals of the Alternating (HBA-HNA) (50/50) Copolymer, c) Homopolymer of PHBA or PHNA.

Radiation-induced Degradation.—There have been several reports on radiation effects in polymers,288 including single crystals,287 fluoropolymers,288 polyamides,289 polysiloxanes,270 polyethylene and its copolymers,271 polypropylene,272 polyolefins,273 polystyrene and its copolymers,274 poly(vinyl chloride) and related polymers,275 rubbers,278 polysulphones and other sulphur-containing polymers,277 polycarbonate,278 nylon,279 poly(vinylpyridines),280 and wool.281... 

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