Kricheldorf HR, Weidner SM, Meyer A. High
T m linear poly(l-lactide)s prepared
via alcohol-initiated ROPs of l-lactide.
RSC Adv 2021;
11:14093-14102. [PMID:
35423910 PMCID:
PMC8697697 DOI:
10.1039/d1ra01990b]
[Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Accepted: 04/06/2021] [Indexed: 11/21/2022] Open
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.
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