Synthesis and Morphology Characterization of Amphiphilic Block Copolymer, polystyrene-block-poly[3-(trimethoxysilyl propyl methacrylate] (PS-b-PMSMA)
Date Issued
2006
Date
2006
Author(s)
Lin, Tien-Ching
DOI
en-US
Abstract
Amphiphilic block copolymers have been extensively studied in recent years. They can not only be prepared by versatile synthetic approaches but also have multiple morphologies generated from its different chemical interaction between two blocks or environment. In this thesis, the synthesis and morphologies of amphiphilic block copolymer, polystyrene-block-poly[3-(trimethoxysilyl)propyl methacrylate] (PS-b-PMSMA), are reported. Two issues will be addressed in this thesis:： (1) Control of molecular weight and its distribution, chain length and its ratio by the reaction conditions of atom transfer radical polymerization (ATRP); (2) correlation of morphology of PS-b-PMSMA with PS/or PMSMA selective mixed solvent.
In this study, the homopolymers of polystyrene(PS), poly[3-(trimethoxysilyl)propyl methacrylate](PMSMA), and diblock copolymer of PS-b-PMSMA were prepared by ATRP using alkyl bromide (MBrP) and CuBr/N,N,N’,N”,N”-pentamethyldiethylene -triamine (PMDETA) as initiator and catalyst, respectively. Various reaction composition and reaction condition were used to optimize the molecular weight and its distribution, including catalyst/initiator ratio, temperature, monomer and ligand concentration, and solvent content. The experimental results suggested the following conclusions for controlling the molecular weight and its distribution : (1)Increasing the concentration of CuBr and monomer or decreasing the content of solvent enhanced the polymerization rate and maintained the narrow molecular weight distribution; (2) Enhancing the concentration of CuBr2 would decrease polymerization rate but also decrease the molecular weight distribution; (3) enhancing reaction temperature could not only increase the polymerization rate but also enhance the initiation efficiency and obviously decrease the molecular weight distribution. The polydispersity indexes (PDI) of the obtained PS macroinitiators were controlled less than 1.1, and the PDI of both PMSMA and PS-b-PMSMA were controlled lower than 1.4. However, when the polymer molecular weight higher than 30000, the propagation of PMSMA would become difficult due to the high viscosity of polymerization reaction and steric hindrance from the polymer chain. Thus, the PDI would be out of control at such high molecular weight polymer.
The morphology of PS-b-PMSMA in different solvent systems was studied by TEM. The experimental results suggested various kinds morphology from the following solvent systems: (1) The morphology observed at anisole /PMSMA selective solvent (1-Methoxy-2-propanol, MOPO) system are mainly spheres due to the strong repulsion between PMSMA corona blocks or the high Tg PS blocks at the core of micelle. (2) The morphology observed in anisole/PS selective solvent( ethyl acetate, EA) system is more versatile than PMSMA solvent/anisole system. The coexistence of sphere and rod-like micelles was observed at the anisole/EA mixed solvent with volume ratio of 50/50, and vesicles are observed at 25/75, respectively. At this system, surface energy between solvent and core is considered as the major driving force to determine size and shape of micelles. The χ increases as the selective solvent content increases and results in an enhancing the surface energy, which leads to decrease the unit surface area (a0). Hence, with the increase of packing parameter P(=v/a0l), the micelle change form sphere (P=1/3), rod-like micelle(P=1/3~1/2), to vesicle(P=1/2~1) were observed in the mixed solvent system. (3) The effect of block length on the morphology was found less significant than the effect of selective solvent. The only difference observed is the morphology size, e.g., PS123-b-PMSMA42 spheres (60nm) are larger than the PS95-b-PMSMA42 spheres size (40~50nm) due to the longer PS chain length. (4) PMSMA block was found hydrolyzed spontaneously. When a basic catalyst was added into PS-b-PMSMA solution, the vesicles formed from self-assembly of hydrolyzed polymers would be fixed, as observed by TEM. 1HNMR and FTIR analysis also suggested the crosslink of PMSMA chains. The present study suggests that the morphologies of PS-b-PMSMA could be tuned by different solvent polarity, block length or the addition of hydrolysis catalyst.
Subjects
嵌段共聚物
形態學
聚乙烯
聚矽氧烷壓克力
PS
PMSMA
styrene
morphology
block copolymer
PTMSPMA
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-95-R93549015-1.pdf
Size
23.53 KB
Format
Adobe PDF
Checksum
(MD5):1010ddd45fc19331452700bd3c41843f