Abstract
This thesis presents two polymer related projects: (1) synthesis and characterization of all-conjugated block copolymers for fundamental research, and (2) development of high gas resistance polybutylene terephthalate (PBT) for industrial research. In development of all-conjugated block copolymers, we present the synthesis, purification, and characterization of all-conjugated block copolymers comprising poly(3-hexylthiophene) (P3HT) and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th). A narrow-distributed, monobrominated P3HT (Mn = 7000, Mw/Mn = 1.31) is synthesized by Grignard metathesis polymerization. This is further reacted with distannyl and dibromo monomers of PTB7-Th by Stille step-growth polycondensation to provide the block copolymers of P3HT-b-PTB7-Th. In these reactions, block ratios are adjusted to 1 to 2 and 1 to 10 based on the numbers of the repeating units of the monomers (i.e. 3-hexylthiophene unit : two monomers of PTB7-Th = 1:2 and 1:10). A preparative gel permeation chromatography (GPC) is used to obtain low polydisperse polymer fractions using chloroform as eluent, leading to the block copolymers P3HT-b-PTB7-Th (namely, BCP10-1, BCP10-2, and BCP2-1) with various molecular weights. These fractions are analyzed by analytical GPC, yielding BCP10-1 with Mn = 53600 (Mw/Mn = 1.71), BCP10-2 with Mn = 28200 (Mw/Mn = 1.56), and BCP2-1 with Mn = 25800 (Mw/Mn = 1.59). In addition, these polymers are analyzed by 1H NMR and UV-vis absorption spectroscopies, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) to investigate their structural, optical, and thermal properties. In development of high gas resistance polymer, we attempt to improv gas barrier ability of PBT for use as food packaging material. We try to blend high moisture barrier material of PBT and high gas barrier material of ethylene vinyl alcohol (EVOH). To improve compatibility and morphology of the polymer blends, various compatibilizers, AX8900, A560, PTW, organoclay, and Surlyn, are used to prevent phase separation. Thin films of the polymer blends (size: 12 cm x 12 cm x 0.3 mm) are prepared using hot press molding machine. Thermal statbility of these films is investigated by thermogravimetric analysis. The blend films composed of the compatibilizers maintain relatively high stability with five weight percent loss temperature above 350 °C, which is slightly lower than original PBT (371.6 °C) due to addition of thermally less stable EVOH and compatibilizers. In addition, morphology of the films are observed using a scanning electron microscope and an optical microscope. The blend film shows very rough surface, where as pure PBT film shows smooth surface. Finally, oxygen permeation test of the thin films is conducted using the oxygen gas transmission apparatus. Original PBT shows gass transimission rate of 6.4 mL m-2 day-1, which is significantly improved to be 2.8 mL m-2 day-1 for the film composition of EVOH 5% and Surlyn 3%.