Solid-State Morphology

In addition to counit concentration, the size of the branches also affects the degree of spherulite organization. It was observed that as the alkyl side chains become longer, they exert a greater influence on the interfacial structure of the crystallites. This in turn lowers the organization of the lamellar stacks and leads to less well-developed spherulitic superstructures [21]. 

5 [28]. They indicate that as the short-chain branching content increases from 2.9 to 28.2 branches per 1000 C atoms, the crystal core thickness decreases from 97 to 18 A and the transition layer thickness increases from 8 to 21 A. These results are in qualitative agreement with Flory s prediction that crystal core thickness 

The two most widely accepted mechanisms for this phenomenon are defect inclusion in the crystalline phase and surface stresses related to reduced lamellar thickness [13,31,33]. In the second mechanism, defects are mostly rejected from the crystals, but preferentially reside in the interfacial layer, thereby exerting stress on the crystal surface [31,34,35]. As the counit concentration increases, the lamellar crystal becomes thinner. This leads to an increase in the crystal s surface-to-volume ratio, which in turn amplifies the magnitude of this stress-induced unit cell deformation. 

Partial inclusion of small branches in the polyethylene unit cell was confirmed by solid-state nuclear magnetic resonance ( C NMR) [38-40]. It was observed that while methyl groups partitioned into the polyethylene unit cell on an equilibrium basis, the composition of the crystalline phase in copolymers containing longer side groups was dependent on crystallization history. Slow-cooled copolymer samples showed lower degrees of defect incorporation because the crystallite was allowed more time to perfect its order [38]. 

Partitioning of branches in both polyethylene and isotactic polypropylene copolymers was also investigated by Hosoda et al. [41, 42]. Ethylene-alkene and propylene-alkene statistical copolymers were degraded by fuming nitric acid to selectively remove their amorphous phase. The degree of branch inclusion in the residual crystalline phase was then determined by solid- 

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Alward DB, Kinning DJ et al (1986) Effect of arm number and arm molecular weight on the solid-state morphology of poly(styrene-isoprene) star block copolymers. Macromolecules 19 215-224... 

Polyethylene and polystyrene are two of the most commercially important and ubiquitous polymers, primarily because of their commercial value. Since the early days of polymer research there has been considerable interest to produce copolymers from ethylene (E) and styrene (S) because of both academic and business interests. Depending on the nature and type of polymerization chemistry, a variety of different molecular architectures can be produced. In addition to the different monomer distributions (random, alternating or blocky nature), there are possibilities for chain branching and tacticity in the chain microstructure. These molecular architectures have a profound influence on the melt and solid-state morphology and hence on the processability and material properties of the copolymers. 

Perrut M, Jung J, Leboeuf F. Solid state morphology of particles prepared by a supercritical fluid process. In Bertucco A ed. High Pressure in Venice. Chemical Engineering Transactions. Vol 2. Milan AIDIC, 2002 711-716. 

Fig. 1.7 Polystyrene-b-polyisoprene (PS-b-PI) solid-state morphologies as a function of increasing volume fraction of the polystyrene block (Adapted from [56]).

Proton spin-temperature equilibration between the hard- and soft-segment-rich domains of the polyurethane elastomer on the order of 10-100 ms might be considered fast relative to a macroscopically phase-separated blend [26] or copolymer, but slow relative to a strongly interacting mixture [25]. This is reasonable for a microphase-separated material whose solid state morphology has been the subject of considerable theoretical and experimental research. Under fortuitous circumstances, intimate (near-neighbor) contact between dissimilar molecules in a mixture can be studied via direct measurement of proton spin diffusion in a two-dimensional application of the 1H-CRAM PS experiment (Combined Rotation And Multiple Pulse Spectroscopy). Belfiore et al. [17,25,31] have detected intermolecular dipolar communication in a hydrogen-bonded cocrystallized solid solution of poly(ethylene oxide) and resorcinol on the f00-/xs time scale, whereas Ernst and coworkers [26] report the absence of proton spin diffusion on the 100-ms time scale for an immiscible blend of polystyrene and poly(vinyl methyl ether), cast from chloroform. 

Block copolymers, particularly of the A-B-A type, can exhibit properties that are quite different from those of random copolymers and even from mixtures of homopolymers. The physical behavior of block copolymers is related to their solid state morphology. Phase separation occurs often in such copolymers. This can result in dispersed phases consisting of one block dispersed in a continuous matrix from a second block. Such dispersed phases can be hard domains, either crystalline or glassy, while the matrices are soft and rubber-like. 

Mullins, W. W., Solid state morphologies governed by capillarity, in Metal Surfaces Structure, Energetics and Kinetics, ASM, Metals Park, Ohio, 17-66, 1963. 

The crystallization kinetics and thermodynamics must be fully understood, in order to control the solid-state morphology that ultimately provides the desired... 

Besides the aforementioned block copolymers 6-7 reported by Stupp and co-workers, the solid-state morphologies of a number of representative rod-coil oligomers composed of perfectly monodisperse rod segments, in particular 42, 48, and 49, have been studied in great detail using scattering and/or microscopic techniques. ... 

Solubility, Miscibility, and the Impact on Solid-State Morphology... 

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