High Tm linear poly(l-lactide)s prepared via alcohol-initiated ROPs of l-lactide. Issue 23 (14th April 2021)

• Record Type: Journal Article
• Authors: Kricheldorf, Hans R.; Weidner, Steffen M.; Meyer, Andreas
• Is Part Of: RSC advances. Volume 11:Issue 23(2021)
• Page Start: 14093
• Page End: 14102
• Publication Date: 2021-04-14
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d1ra01990b
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : By variation of reaction conditions and catalysts a cyclic tin(ii ) compound was found, which enables synthesis of high melting (>190 °C) poly(l -lactide) via ROP of l -lactide, whereas the technically used catalyst SnOct2 does not show such a performance. Abstract : Alcohol-initiated ROPs of l -lactide were performed in bulk at 160 °C for 72 h with variation of the catalyst or with variation of the initiator (aliphatic alcohols). Spontaneous crystallization was only observed when cyclic Sn(ii ) compounds were used as a catalyst. Regardless of initiator, high melting crystallites with melting temperatures ( T m ) of 189–193 °C were obtained in almost all experiments with Sn(ii ) 2, 2′-dioxybiphenyl (SnBiph) as catalyst, even when the time was shortened to 24 h. These HTm poly(lactide)s represent the thermodynamically most stable form of poly(l -lactide). Regardless of the reaction conditions, such high melting crystallites were never obtained when Sn(ii ) 2-ethylhexanoate (SnOct2 ) was used as catalyst. SAXS measurements evidenced that formation of HTm poly(l -lactide) involves growth of the crystallite thickness, but chemical modification of the crystallite surface (smoothing) seems to be of greater importance. A hypothesis, why the "surface smoothing" is more effective for crystallites of linear chains than for crystallites composed of cycles is discussed.