Stereocomplex Crystallization of Star-Shaped Four-Armed Stereo Diblock Poly(lactide) from the Melt: Effects of Incorporated Linear One-Armed Poly(l-lactide) or Poly(d-lactide)

Abstract

Star-shaped four-armed stereo diblock poly(lactide) (4-LD) and linear one-armed PLLA or PDLA (1-L or 1-D) having a molecular weight similar to that of 4-LD [higher molecular weight 1-L(H) or 1-D(H)] and that of one block of 4-LD [lower molecular weight 1-L(L) or 1-D(L)] were synthesized, and the effects of incorporated 1-L or 1-D on the isothermal and nonisothermal crystallization of 4-LD blends from the melt were investigated. Solely stereocomplex crystallites were formed in unblended 4-LD and 4-LD blends incorporated with 1-L or 1-D during isothermal and nonisothermal crystallization. Incorporated 1-L or 1-D increased normalized stereocomplex crystallinity and accelerated cold nonisothermal crystallization and isothermal crystallization. The accelerating effect became higher with decreasing the molecular weight of 1-L or 1-D. The crystalline growth mechanism was not altered by the incorporation of 1-L and 1-D, whereas the crystalline growth geometry changed from line to sphere or circle, depending on the type of sample and T. The difference in crystallization half time and cold crystallization temperature between 4-LD/1-L(H) and 4-LD/1-D(H) blends or 4-LD/1-L(L) and 4-LD/1-D(L) blends was explained by the difference in radial growth rate and spherulite density, which was further discussed considering the non-interpenetrating and interpenetrating models.

Relationship between crystallization state and degradation behavior of poly(l‐lactide)/four‐armed poly(d,l‐lactide)‐block‐poly(d‐lactide) blends with different poly(d‐lactide) block lengths

“…In Eqns ) and (), 0.2 is the weight ratio of the 4‐DL‐D copolymer to the PLLA matrix in the blends, the factor 2 means PDLA of one unit mass can form stereocomplexation of two unit mass, theoretically, 21 and φ (D) is the mass fraction for PDLA in the blends, which was calculated using the following equation: where M n (D) and M n (DL) are the number‐average molecular weight of PDLA and PDLLA parts in the four‐armed copolymers, respectively. X hc and X sc were normalized by assuming equimolar units of PDLA and PLLA form SC crystals and the excess PLLA forms homocrystals 22 . The results obtained from those equations are listed in Table 2, and non‐normalized and normalized X hc and X sc were abbreviated as non‐ X hc , n‐ X hc , non‐ X sc and n‐ X sc , respectively.…”

“…X hc and X sc were normalized by assuming equimolar units of PDLA and PLLA form SC crystals and the excess PLLA forms homocrystals. 22 The results obtained from those equations are listed in Table 2, and non-normalized and normalized X hc and X sc were abbreviated as non-X hc , n-X hc , non-X sc and n-X sc , respectively. In Fig.…”

Stereocomplex crystallization, homocrystallization, and polymorphism of enantiomeric copolyesteramides poly(lactic acid‐ co ‐alanine)s from the melt

“…The wide‐angle X‐ray diffraction (WAXD) measurements were performed at 25°C using a Rigaku (Tokyo, Japan) RINT‐2500 equipped with a Cu‐Kα source ( λ = 1.5418 Å), which was operated at 40 kV and 200 mA. The procedure for estimating the crystallinity ( X c ) of SC crystallites and homocrystallites [ X c (S) and X c (H), respectively] is reported in the literatures . The isothermal spherulite growth of the samples was observed using an Olympus (Tokyo, Japan) polarized optical microscope (BX50) equipped with a heating‐cooling stage and a temperature controller (LK‐600 PM , Linkam Scientific Instruments, Surrey, UK) under a constant nitrogen gas flow .…”

“…The procedure for estimating the crystallinity ( X c ) of SC crystallites and homocrystallites [ X c (S) and X c (H), respectively] is reported in the literatures . The isothermal spherulite growth of the samples was observed using an Olympus (Tokyo, Japan) polarized optical microscope (BX50) equipped with a heating‐cooling stage and a temperature controller (LK‐600 PM , Linkam Scientific Instruments, Surrey, UK) under a constant nitrogen gas flow . The samples were heated from room temperature to 250°C (blend samples) or 200°C (unblended samples) at 100°C minutes −1 , held at this temperature for 1 minute, cooled at 100°C minutes −1 to an arbitrary T c , and then held at the same temperature (spherulite growth was observed here) .…”

“…The isothermal spherulite growth of the samples was observed using an Olympus (Tokyo, Japan) polarized optical microscope (BX50) equipped with a heating‐cooling stage and a temperature controller (LK‐600 PM , Linkam Scientific Instruments, Surrey, UK) under a constant nitrogen gas flow . The samples were heated from room temperature to 250°C (blend samples) or 200°C (unblended samples) at 100°C minutes −1 , held at this temperature for 1 minute, cooled at 100°C minutes −1 to an arbitrary T c , and then held at the same temperature (spherulite growth was observed here) . With the same heating and cooling program utilized for the observation of isothermal spherulite growth, the overall crystallization behavior of samples during isothermal crystallization at an arbitrary T c was monitored by measuring the light intensity transmitted through the samples using BX‐50 equipped with LK‐600 PM and an As One (Osaka, Japan) LM‐332 photometer …”