Stereocomplexes of star-shaped poly[(R)-lactide]s and poly[(S)-lactide]s bearing various
number of arms. Synthesis and thermal properties (in English)
Polimery 2007, No 2, 106
Stereocomplexes composed of 6, ~13, 24 and 32 arm star-shaped poly(lactide)s (ss-sc-PLAs) and of the mixed star-shaped - linear PLAs (sl-sc-PLAs) were prepared in a controlled way. Their thermal properties were characterized by DSC and compared to their linear counterparts properties. It was observed that the equimolar mixtures of star-shaped (R)-PLA and (S)-PLA crystallize during precipitation into methanol from the methylene chloride solution preferentially in the form of the highly crystalline (up to 70%) stereocomplexes. The star-shaped PLA stereocomplexes with the number of arms higher than six (i.e. ~13, 24 and 32) survived melting and after slow cooling during the second heating run crystallized once again showing exclusive stereocomplex formation. After melting and annealing at high temperature and then fast cooling to the room temperature, in the second heating run also only two peaks in thermograms appeared exothermic cold crystallization peak (Tccsc) and endothermic melting peak (Tmsc) for star-shaped sc-PLAs with ~13, 24 and 32 arms. For high molar mass linear, mixed star-shaped - linear and six arm star-shaped stereocomplexes additional (R)-PLA and (S)-PLA homo-crystallites melting peaks appeared. These results show that thermal stability of stereocomplexes is strongly influenced by the topology and the number of arms in the star-shaped components.
Key words: star-shaped polylactides, stereocomplexes, differential scanning calorimetry, thermal properties
Stereocomplexes of star-shaped poly[(R)-lactide]s and poly[(S)-lactide]s bearing various number of arms. Synthesis and thermal properties (in English)