Morphological Evolution during Isothermal Crystallization Observed in a Crystalline-Crystalline Diblock Copolymer

Abstract

Morphological evolution during isothermal crystallization over a long time ($3 d) in a crystalline-crystalline diblock copolymer, poly("-caprolactone)-block-polyethylene (PCL-b-PE), has been investigated at various temperatures T c by SAXS, DSC, and FT/IR techniques. The crystallization temperature of PE blocks was sufficiently higher than that of PCL blocks, so that PE blocks crystallized first by quenching PCL-b-PE from a microphase-separated melt into T c followed by the crystallization of PCL blocks, and eventually PCL+PE-crystallized morphology was formed in the system. The long period L, an alternating distance of the morphology, did not change at all during isothermal crystallization after an initial increase in L by the crystallization of both blocks, indicating no apparent change in the morphology at the late stage crystallization. However, DSC and FT/IR results revealed that the crystallinity of PCL blocks significantly increased and simultaneously that of PE blocks decreased moderately with increasing crystallization time at the late stage. These results suggest the partial melting of PE crystals facilitated by further crystallization of PCL blocks in order to compensate the space previously occupied by amorphous PCL blocks.KEY WORDS: Crystalline-crystalline Diblock Copolymer / Isothermal Crystallization / Morphological Evolution / Crystalline-crystalline diblock copolymers show an interesting morphology formation by the interplay between two kinds of crystallization starting from the microdomain structure formed in the melt.1 There are many studies on the crystallization behavior and resulting morphology of double crystalline diblock copolymers, such as poly("-caprolactone)-blockpoly(ethylene oxide) (PCL-b-PEO), 2-11 poly(p-dioxanone)-15-17 poly(L-lactide)-block-PCL (PLLA-b-PCL), [18][19][20][21][22] and PCL-b-PE. [23][24][25][26][27] In PCL-b-PEO, both blocks have a close melting temperature T m and eventually two kinds of crystallization occur simultaneously to result in a characteristic morphology in the system. In other block copolymers, T m of one block is enough higher than that of the other, and consequently the higher-T m blocks crystallize first by quenching the copolymer from a microphase-separated melt into low temperatures, followed by the crystallization of lower-T m blocks starting from the crystallized solid morphology already formed in the system. In dynamic studies on the morphology formation in such systems, the early stage crystallization of higher-T m blocks and/or lower-T m blocks was mainly investigated by time-resolved small-angle X-ray scattering with synchrotron radiation (SR-SAXS), where the SAXS curves show a drastic change by the crystallization of each block.We have recently investigated the melting behavior of PCLb-PE diblocks by SR-SAXS, and found that the long period L, an alternating distance of the morphology, changed complicatedly during heating. 26 In particular, L decreased discontinuously at T m of PCL blocks (lower-T m blocks) for all PCL-b-PE copolymers investi...

Dynamic Mechanical Study of Block Copolymer Crystallization Confined within Spherical Nanodomains

“…In the crystallization of hPCL, both 1ðt c Þ and T m increase steadily with increasing t c at the late stage (t c > 5 min). The increase of these values is known to be linear in a semi-logarithmic plot for usual crystalline homopolymers, 30,31 which is attributed to the lamella thickening during the late stage crystallization. 32 In addition, the well-known Avrami plot at the early stage gave the Avrami index of ca.…”

Crystallization of polymer chains confined in nanodomains

“…The sequential crystallization has been examined using several crystalline-crystalline diblock copolymers with sufficiently separate crystallizable temperatures [56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72]. We examined the crystallization behavior and crystal orientation of PCL blocks in PCL-block-polyethylene (PCL-b-PE) diblock copolymers [56,58,[61][62][63]65,69], where the PCL blocks (with T c,2 $ 40°C) were accommodated between the crystalline lamellar morphology provided by the advance crystallization of PE blocks (with T c,1 $ 100°C), and started to crystallize there.…”

“…We examined the crystallization behavior and crystal orientation of PCL blocks in PCL-block-polyethylene (PCL-b-PE) diblock copolymers [56,58,[61][62][63]65,69], where the PCL blocks (with T c,2 $ 40°C) were accommodated between the crystalline lamellar morphology provided by the advance crystallization of PE blocks (with T c,1 $ 100°C), and started to crystallize there. It was found from dynamic studies on crystallization that the crystallinity of PCL blocks increased sigmoidally during crystallization irrespective of T c and PCL layer thickness d PCL , though the crystallization mechanism of PCL blocks was slightly affected by the existing crystalline lamellar morphology, judging from the moderately reduced Avrami exponent n as compared with the crystallization of bulk PCL homopolymers.…”

Significant increase in the melting temperature of poly(ɛ-caprolactone) blocks confined in the crystallized lamellar morphology of poly(ɛ-caprolactone)-block-polyethylene copolymers

“…[16][17][18][19][20][21] We prepare several asymmetric PCL-b-PE copolymers with PE blocks (higher-T m blocks) as a minor component, so that PCL blocks will deform in the preexisting lamellar morphology formed by the crystallization of PE blocks (PE lamellar morphology). As a result, DS m of PCL blocks (that is, DS 2 in Figure 1) will be smaller than that in crystalline-amorphous diblocks (DS 1 ), yielding a significant increase in T m .…”