Synthesis, characterization, effect of architecture on crystallization, and spherulitic growth of poly(L‐lactide)‐b‐poly(ethylene oxide) copolymers with different branch arms

Abstract

Well‐defined poly(L‐lactide)‐b‐poly(ethylene oxide) (PLLA‐b‐PEO) copolymers with different branch arms were synthesized via the controlled ring‐opening polymerization of L‐lactide followed by a coupling reaction with carboxyl‐terminated poly(ethylene oxide) (PEO); these copolymers included both star‐shaped copolymers having four arms (4sPLLA‐b‐PEO) and six arms (6sPLLA‐b‐PEO) and linear analogues having one arm (LPLLA‐b‐PEO) and two arms (2LPLLA‐b‐PEO). The maximal melting point, cold‐crystallization temperature, and degree of crystallinity (Xc) of the poly(L‐lactide) (PLLA) block within PLLA‐b‐PEO decreased as the branch arm number increased, whereas Xc of the PEO block within the copolymers inversely increased. This was mainly attributed to the relatively decreasing arm length ratio of PLLA to PEO, which resulted in various PLLA crystallization effects restricting the PEO block. These results indicated that both the PLLA and PEO blocks within the block copolymers mutually influenced each other, and the crystallization of both the PLLA and PEO blocks within the PLLA‐b‐PEO copolymers could be adjusted through both the branch arm number and the arm length of each block. Moreover, the spherulitic growth rate (G) decreased as the branch arm number increased: G6sPLLA‐b‐PEO < G4sPLLA‐b‐PEO < G2LPLLA‐b‐PEO < GLPLLA‐b‐PEO. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2034–2044, 2006

CHAPTER 3. Crystallization of PLA-based Materials

“…109,[120][121][122][123][124][125][126][127][128][129] These block copolymers are usually miscible or weakly segregated in the melt (depending on their segregation strength, a function of the average molecular weight of each block time the Flory-Huggins interaction parameter). 40,121,122,125,126,[130][131][132][133][134][135][136][137] Microphase separation takes place during crystallization. 120,122,125,130 Miscibility in the melt has also been reported for some high-molecular-weight blends of PLLA and PEO.…”

Preparation of drug‐loaded microspheres of linear and star‐shaped poly(D,L‐lactide)s and their drug release behaviors

“…Pentaerythritol, dipentaerythritol, and Boltorn H20 have been used as hydroxyl end-group initiators for synthesizing the biodegradable starshaped polyesters containing 4, 6, and 16 arms, respectively. 8,18 However, comparison of these starshaped and linear polyester microspheres as drug delivery carriers has been scarcely published.…”

Sequential crystallization and morphology of triple crystalline biodegradable PEO-b-PCL-b-PLLA triblock terpolymers

“…29 On the other hand, the decrease in the crystallization temperature of PEO or PCL is a consequence of the restriction imposed by the previously crystallized PLLA that confines their crystallization. 14,29 In fact, a fractioned crystallization 4,6 phenomenon has been reported on PEO in some PEO-b-PLLA diblock copolymers when PEO content was 29 % or lower. 7,29 If the PEO content is below 20 %, this block is not able to crystallize.…”

“…7,29 If the PEO content is below 20 %, this block is not able to crystallize. 14,23,[30][31][32] In the case of PEO-b-PCL diblock copolymers, their crystallization and melting behaviour is well documented [33][34] but not easy to elucidate, due to the closeness of both crystallization and melting temperatures of the blocks. As in the aforementioned diblocks copolymers, these temperatures are highly influenced by composition and M w of each component.…”