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Hydrolytic degradation and crystallization behavior of linear 2‐armed and star‐shaped 4‐armed poly( l ‐lactide)s: Effects of branching architecture and crystallinity
Author(s) -
Tsuji Hideto,
Hayashi Toshiki
Publication year - 2015
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.41983
Subject(s) - crystallinity , hydrolysis , crystallization , amorphous solid , polymer , polymer chemistry , pentaerythritol , materials science , branching (polymer chemistry) , degradation (telecommunications) , polymer degradation , polyester , lactide , crystallite , chemical engineering , chemistry , organic chemistry , copolymer , composite material , telecommunications , fire retardant , computer science , engineering , metallurgy
“Linear” aliphatic polyesters composed of two poly( l ‐lactide) arms attached to 1,3‐propanediol and “star‐shaped” ones composed of four poly( l ‐lactide) arms attached to pentaerythritol (2‐L and 4‐L polymers, respectively) with number‐average molecular weight ( M n ) = 1.4–8.4 × 10 4 g/mol were hydrolytically degraded at 37°C and pH = 7.4. The effects of the branching architecture and crystallinity on the hydrolytic degradation and crystalline morphology change were investigated. The degradation mechanism of initially amorphous and crystallized 2‐L polymers changed from bulk degradation to surface degradation with decreasing initial M n ; in contrast, initially crystallized higher molecular weight 4‐L polymer degraded via bulk degradation, while the degradation mechanism of other 4‐L polymers could not be determined. The hydrolytic‐degradation rates monitored by molecular‐weight decreases decreased significantly with increasing branch architecture and/or higher number of hydroxyl groups per unit mass. The hydrolytic degradation rate determined from the molecular weight decrease was higher for initially crystallized samples than for initially amorphous samples; however, that of 2‐L polymers monitored by weight loss was larger for initially amorphous samples than for initially crystallized samples. Initially amorphous 2‐L polymers with an M n below 3.5 × 10 4 g/mol crystallized during hydrolytic degradation. In contrast, the branching architecture disturbed crystallization of initially amorphous 4‐L polymers during hydrolytic degradation. All initially crystallized 2‐L and 4‐L polymers had δ‐form crystallites before hydrolytic degradation, which did not change during hydrolytic degradation. During hydrolytic degradation, the glass transition temperatures of initially amorphous and crystallized 2‐L and 4‐L polymers and the cold crystallization temperatures of initially amorphous 2‐L and 4‐L polymers showed similar changes to those reported for 1‐armed poly( l ‐lactide). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132 , 41983.