Gelation‐crystallization in isotactic polystyrene solutions and its implications to crystal morphology, to the origin and structure of gels, and to the chemical homogeneity of polyolefins

摘要: As part of a wider study on the crystallization isotactic polystyrene solutions it was observed that at sufficient concentrations (> 3–5%) gelation sets in below certain (very high) supercooling competition with usual single crystal formation which itself produces turbid suspensions. It established is form (mode A) must be fringed micellar type to provide connectedness as opposed chain folded lamellae B) gives rise discrete particles. The gel crystals (A) display sharp melt endotherms and produce distinct x-ray diffraction patterns both which, however, differ decisively from those provided by B, distinction can preserved even after removal solvent. melting points A are significantly lower than B incompatible recognized structure (31 helix) possessed B; they point broadly planar zig-zag arrangement chain. This strongly suggests we have blocks chemically sequences could syndiotactic or head-to-head tail-to-tail (presently substantial support for latter) responsible forming crystallization. However, so far C13 nuclear magnetic resonance (NMR) results do not evidence these species but explanations our observations any other basis seem lead unsuperable difficulties view. Consequently, paper left open ended possibilities discussed. Amongst existence very few long, seems most attractive. implications facts stand morphology (fringed micelles versus lamellae), origin gels general, block copolymers issues relating chemical homogeneity (tacticity, tail-to-tail) discussed preliminary effects quoted indicate may also relevant atactic polymers.