A-B-A-Triblock and multiblock copolyesters prepared from ε-caprolactone, glycolide and l-lactide by means of bismuth subsalicylate

Ring-opening copolymerization of (R,S)-β-butyrolactone and ε-caprolactone using sodium hydride as initiator

“…Linear aliphatic polyesters such as poly(glycolide) (PGL), poly(lactide) (PLA), poly(β-butyrolactone) (PBL) and poly(ε-caprolactone) (PCL) and their co-and terpolymers are the most popular bioabsorbable polymers. Because of the wide range of applications in biomedicine, it is necessary for the polyesters to present different mechanical and physical properties to adjust the adequate time of their degradation; in this sense copolymerization constitutes an attractive mean for modulating the basic properties of each homopolymer [4][5][6]. In particular, block copolymerization may offer a broader spectrum of mechanical and degradation properties in order to meet the demands of a larger number of applications.…”

“…Blocks with different physical properties, for example, a soft, amorphous segment together with a hard semicrystalline one, can be used to modulate the thermal and mechanical material behaviour [4,[7][8][9]. The mechanical properties can be controlled by the hard/soft segment ratio [7] and copolymers with various morphologies such as solid, pasty and waxy states, can be obtained according to the monomer composition [6,10]. The soft phase provides elasticity and the degradation behaviour, whereas the rigid phase gives mechanical strength and also acts as a physical crosslinker [6].…”

“…The mechanical properties can be controlled by the hard/soft segment ratio [7] and copolymers with various morphologies such as solid, pasty and waxy states, can be obtained according to the monomer composition [6,10]. The soft phase provides elasticity and the degradation behaviour, whereas the rigid phase gives mechanical strength and also acts as a physical crosslinker [6]. Polymerization of racemic monomer (R,S)-β-butyrolactone ((R,S)-BL) has given an atactic poly (R,S)-(β-butyrolactone) ((R,S)-PBL) with elastomeric properties because of its low crystallinity [7,11,12].…”

“…Many effective catalysts based on tincompounds, have been employed for this purpose [4,7,8,[13][14][15][16][17][18][19][20][21]. However, many are relatively toxic and impossible to remove completely from the synthesized material, this being undesirable for pharmaceutical or biomedical applications [2,6]. Therefore, several attempts to use a catalyst based on much less toxic metal compounds are being undertaken [2,6,11,[22][23][24][25][26][27].…”

“…However, many are relatively toxic and impossible to remove completely from the synthesized material, this being undesirable for pharmaceutical or biomedical applications [2,6]. Therefore, several attempts to use a catalyst based on much less toxic metal compounds are being undertaken [2,6,11,[22][23][24][25][26][27]. The anionic polymerization of β-butyrolactone had been widely studied [27][28][29][30][31][32][33][34][35][36][37][38][39][40], and in general polymers with low molecular weight were obtained.…”