SELF-NUCLEATION AND RECRYSTALLIZATION OF POLYMERS - ISOTACTIC POLYPROPYLENE, BETA-PHASE - BETA-ALPHA-CONVERSION AND BETA-ALPHA-GROWTH TRANSITIONS

The mechanisms which, in isotactic polypropylene, create alpha phase nuclei on partial melting of beta phase spherulites are investigated by thermal analysis and optical and electron microscopy. Nuclei concentrations are determined from recrystallization characteristics. Alpha phase nuclei are formed within beta spherulites via two different mechanisms: (1) a low temperature formation of latent alpha phase nuclei (alphabeta* nuclei) linked with a hitherto unsuspected beta to alpha growth transition at T = T* approximately 105-degrees-C, and (2) a high temperature alpha phase nucleation process (alphabeta nuclei), also linked with a similar beta to alpha growth transition at 140-degrees-C first reported by Varga et al. The low temperature nucleation mechanism is the more efficient one: it significantly affects the melting of beta phase, and results in samples with over 10(13) alpha nuclei . cm-3. (C) 1993 John Wiley & Sons, Inc.