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 n uclei on partial melting of beta phase spherulites are investigated by thermal analysis and optical and electron microscopy. Nuclei concentr ations are determined from recrystallization characteristics. Alpha ph ase nuclei are formed within beta spherulites via two different mechan isms: (1) a low temperature formation of latent alpha phase nuclei (al phabeta nuclei) linked with a hitherto unsuspected beta to alpha grow th transition at T = T approximately 105-degrees-C, and (2) a high te mperature alpha phase nucleation process (alphabeta nuclei), also link ed with a similar beta to alpha growth transition at 140-degrees-C fir st reported by Varga et al. The low temperature nucleation mechanism i s 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.