Type-II spherulites

Fig. 10.17 Illustration of lamellar stacking structure (from left to right are axialites, type-I spherulites and type-II spherulites)...

Both have fibrillar structures but the structure of Type I is coarser than that of Type II. Occasionally rings are observed in Type II spherulites. Sonnetimes as shown in Figure 2 both types of texture are observed in a single spherulite. 

Figure 4. Melting of spherulites of 164A. At 80°C both Type I and Type U spherulites are visible. By 115°C Type I spherulites are melted. Type II spherulites disappear by 117°C (83x),...

If either type grows faster, the data in Figure 6 suggests that Type II spherulites grow faster. 

These polymers have the highest melting temperatures we have observed so far and a broad maximum in rate versus temperature curve that suggests a broad processing range. The "fast crystallizing" polymers also have the highest optical rotations that we observed. They crystallize in the form of Type II spherulites. We have studied many examples of each type of polymer. 

Overall crystallization rate of blends of "fast" and "slow" crystallizing polymers. We obtained further evidence that the greater ease of nucleation of optically active polymer into Type II spherulites is responsible for the observed increase in crystallization rate by studying solution blends of 2413 and a nonopt-ically active polyepichlorohydrin. We found that addition of only 6% of 2413 reduced the ti at 50"C of the blow" polymer from 32 min to less than 10 min. 

The results of this study further reveal that the crystalline polyepichlorohydrin we have studied consists of isotactic sequences that can crystallize in the form of two different kinds of spherulites. We have shown that the two kinds of spherulites can cocrystallize- At present our educated guess is that all the polymers we have examined contain either Type I or a mixture of Type I and Type II spherulites in varying proportions. The polymers that crystallize most rapidly and that have the highest melting temperatures have some optical activity and their films contain predominantly Type II spherulites. We conclude that the Type II spherulites are obtained from optically active polymer sequences. We do not mean to imply that all sequences in these... 

The purposes of this study were to determine what chemical and physical structures are present in polyepichlorohydrin and to correlate these structures with the crystallization rates observed microscopically and dilatometrically. Crystallization rates were shown to be an extremely sensitive way of characterizing these polymers. For example, the study revealed that the crystalline polyepichlorohydrins examined consisted of isotactic sequences that can crystallize as two different kinds of spheru-lites, arbitrarily called Type I and Type II. The two types can cocrystallize. The polymers that crystallize most rapidly and that have the highest melting temperature have some optical activity. Their films contain predominantly Type II spherulites. Polymers that contain Type I spherulites melt lower and show little or no optical activity. These polymers are racemic mixtures. 

Figure 1, PolyepicMorohydrin spherulites. Left Type 1 spherulites from 329C after melting at 170°C and crystallizing at 50°C for 185 min. (ISSx). Right Type II spherulites from 39A after melting at 150 C and crystallizing at 50°C for 222 min. (128x).

Fig. 15.5. Schematic models of supramolecular fibrillar assemblies of Afi(l-40) fibrils. Variation in morphology can arise at the level of oligomeric species, protofilaments, or initial short fibrils. They associate together on the quartz surface, creating three types of supramolecular fibrillar assemblies Straight fibrils (Type I), spherulitic assemblies (Type II), and worm-like fibrils (Type III). A mixed architecture of type I and fibrils (Type I/II) was also observed when the internal density is coarse. It is to be noted that the different precursors are represented together in a box and that the relationships between amyloid precursors and final products remain unclear. Reproduced from [18] with permission...

Fig. 11.1 Examples of initial crystallization hits from a single on-chip screening experiment of a type II topoisomerase ATPase do-main/ADP, 12mgmL b (A) Irregular spherulite. (B) Phase separation and spherulites with nucleating microcrystals. (C) Thin plate clusters. (D) Thick plate stacks. (E) Well-formed microcrystals. (F) Large single crystals. All scale bars are 100 pm.

When the spherulites were observed between crossed pola-roids using a 1st order red plate in the usual 45 orientation, it was found that both types of spherulites are negatively birefring-ent. This is not surprising since negative spherulites have also been observed in polypropyleneoxide films (10). Nevertheless, the spherulites are not identical when viewed with the 1st order red plate. Type I is blue in the second and fourth quadrants and orange in the first and third. Type II is similar but the quadrants are separated by a red cross. 

Figure 2. Type I and II spherulites both seen in the same smerulite, from 164A melted at 150 C and crystaUiTxd at S0 C for 168 min. (128x)...

Figure 6. Comparison of spherulite growth rates at 50°C after melting at 150°C. O = Type I spherulites from 329C. = Type II spher-ulites from 39A.

Studies have been conducted on poly (tetramethylene oxide )-poly-(tetramethylene terephthalate) -segmented copolymers that are identical in all respects except for their crystalline superstructure (66,67,68). Four types of structures—type I, II, and III spherulites (with their major optical axis at an angle of 45°, 90°, and 0° to the radial direction, respectively), and no spherulitic structure—were produced in one segmented polymer by varying the sample-preparation method. Figures 10 and 11 show the stress-strain and IR dichroism results for these samples, respec-... 

Three types of blend crystallization are distinguished (1) simultaneous of both components (2) in the presence of molten second component and (3) in the presence of solid second component. The case (1) takes place when ranges of the crystallization temperatures, T, of the two polymers overlap and their crystallization rates are similar their mixed spherulites usually have additive physical properties. For the case (2), Paul and Barlow predicted five crystallization patterns (i) no effect (ii) retardation (iii) delay (iv) acceleration and (v) crystallization of a... 

Figure II - 12. Schematic drawing of two types of crystallites (a) firinged micelles and (b) spherulites.

In some cases, the enzymatic polymerization afforded spherulites of artificial cellulose II, composed of single crystals with the molecular axis orientated perpendicular to the plane (29). Both positive- and negative-type spherulites were observed by polarization optical microscopy. By changing the reaction parameters. 

The PLOM technique has several limitations (i) the presence of additives with high refractive indices hinder the observation of polymer samples under light transmission microscopes [4] and (ii) if spherulites with different growth rates are present in various concentrations during transformation (as for polymorphs and polymer blends), the measure of growth rates may not be easy, especially for less abundant spherulite types. 

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