Double crystalline block copolymers (BCPs), syndiotactic poly(4-methyl-1-pentene)-b-poly(L-lactide) (sPMP-PLLA) and syndiotactic poly(4-methylstyrene)-b-poly(L-lactide) (sPMS-PLLA), were synthesized to examine crystallization effect on the self-assembled morphologies in the double crystalline BCPs. Because of the stainable chemical structures, morphological observation can be carried out in these double crystalline BCPs. Also, different microphase-separated structures including lamellae and hexagonally packed cylinders were explored to study the shape effect for double crystallization.
Based on differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) results, both sPMP and PLLA blocks are able to crystallize in the sPMP-PLLA BCP (fsPMPv=0.52) at the crystallization temperature (Tc) from 80¢XC to 120¢XC. Notably, temperature-dependent phase transitions between the PLLA polymorphisms are obtained by WAXD. By using small-angle X-ray scattering (SAXS) and transmission electron microscope (TEM), the microphase-separated lamellar structures can be observed in the sPMP-PLLA BCP (fsPMPv=0.52). Also, the preservation of the lamellar morphology at all Tcs (80¢XC~120¢XC) indicates that the sPMP and PLLA crystallization can be strongly confined within the lamellar microstructures due to the strong segregation strength of the sPMP-PLLA (fsPMPv=0.52) BCP. This can be further demonstrated by the ambiguous birefringence under polarized light microscope (PLM). According to the time-resolved SAXS and WAXD profiles at 90oC and 110oC, the sPMP block crystallizes first and induces the enlargement of the BCP long period. Also, the leading sPMP crystallization gives rise to the robust lamellar microstructural template and result in strong confinement for the subsequent PLLA crystallization.
In the sPMS-PLLA BCP (fsPMSv=0.58), the microphase-separated lamellar nanostructures can be found by SAXS and TEM. DSC analysis shows that PLLA block is able to crystallize as Tc=90¢XC~100¢XC; the sPMS block is able to crystallize as Tc ≥120oC. By self-nucleation processes, both sPMS and PLLA blocks are able to crystallize. Therefore, by the manipulation of the respective crystallization, two-stage crystallization and coincident crystallization, systematic studies in the semi-crystallization, double crystallization and coincident double crystallization with the accompanying environmental Tg effect and BCP segregation strength can be carried out in the lamella-forming sPMS-PLLA (fsPMSv=0.58) BCP. By SAXS and TEM, the microphase-separated lamellar microstructures can be preserved in the self-assembly of the sPMS-PLLA (fsPMSv=0.58) BCP whatever the PLLA crystallization occurs under hard confinement (Tc,PLLA<Tg,sPMS) or soft confinement(Tc,PLLA˃Tg,sPMS). For the sPMS crystallization under soft confinement, the lamellar microstructures can be preserved as Tc,sPMS ≤140oC, whereas the breakout morphology by the sPMS crystallization is found as Tc,sPMS ≥150oC. As a result, the final morphologies is strongly dependent on the BCP segregation strength in the lamella-forming sPMS-PLLA (fsPMSv=0.58) BCP.
In sPMS-PLLA BCP (fsPMSv=0.7), hexagonally-packed PLLA cylinders in the sPMS matrix are obtained by SAXS and TEM. DSC analysis shows that the sPMS block is able to crystallize as Tc=130¢XC~180¢XC, whereas no PLLA crystallization can be found in the cylinder-forming sPMS-PLLA BCP (fsPMSv=0.7). This indicates that the 2-D cylindrical shape might give rise to the strong confined effect and result in non-crystallizable PLLA. According SAXS and TEM results, the intrinsic hexagonally-packed cylinders can be preserved after the sPMS crystallization at 130oC due to the strong BCP segregation strength. By contrast, the crystallization driving force may overwhelm the microphase separation so as to form breakout morphology in the sPMS-PLLA (fsPMSv=0.7) BCP as Tc≥150¢XC.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0806112-161640 |
| Date | 06 August 2012 |
| Creators | Huang, You-Wei |
| Contributors | Rong-Ming Ho, Yeo-Wan Chiang, Ching-I Huang, Jing-Cherng Tsai, Shiao-Wei Kuo |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0806112-161640 |
| Rights | user_define, Copyright information available at source archive |
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