Study Of Crystallization And Self-assembly Behavior Of Nonlinear Block Copolymers

In this paper, two class of non-linear copolymers were synthesized via thecombination of enzyme catalyzed ring-opening polymerization （e-ROP） and atomtransfer radical polymerization （ATRP）, including Y-typed block copolymerPCL-b-（PS）₂and H-typed block copolymer （PS）₂-b-PCL-PEO-b-PCL-b-（PS）₂,followed by the study of the former’s crystallization behavior and later’s aqueoussolution properties, respectively.In the second chapter, three polymer samples, ranked as PCL-b-（PS）₂-1PCL-b-（PS）₂-2and PCL-b-（PS）₂-3according to their descending PCL weight percent,were chosen for the investigation of the dependence of their crystallinity on their PCLcontent from a series of Y-typed copolymers PCL-b-（PS）₂with different molecularweight. Crystallization process of those copolymers from melt was detected by POM,and we observed that initial crystal nuclei were grown into spherulite in the scope.DSC technique was utilized to study the isothermal crystallization kinetics andnon-isothermal crystallization kinetics of those copolymers. Specifically, for theisotheral crystallization process of those specimens, Avrami equation was exploited todescribe it, giving a declining Avrami exponent n for PCL-b-（PS）₂-1PCL-b-（PS）₂-2and PCL-b-（PS）₂-3, and PCL-b-（PS）₂-1showed the largest crystallization rate whenthe inverse of semi-crystallization time for each copolymer sample was used as ameasure to evaluate the crystallization rate of copolymers, both evidence indicating adefinite restrict on the mobility of molecular chain by PS in glassy state. However, forthe non-isotheral crystallization process of those specimens, Mo method was proven amore successful equation to fit them, rather than Jeziorny equation and Ozawaequation. F（T）, parameter derived from Mo equation, represents the cooling ratenecessary to reach a predetermined crystallization degree. For sample with highweight percent of PS block, a larger F（T） value suggested that it needed larger coolingrate than those with lower weight percent of PS block, when crystallization process developed to the same extent, indicating that in the non-isothermal crystallizationprocess of the three copolymers, its molecular chain could rearrange into orderly stateless easily than the others, caused by a gradual increasing hindrance on thecrystallization of PCL, in consistency with the phenomenal involved in isothermalcrystallization process of them. Moreover, the activation energy, ΔE, released in thenon-isothermal crystallization process of those Y-typed copolymers, were calculatedthrough Kissinger method, and of all these copolymers, the absolute value of ΔE forPCL-b-（PS）₂-1is the most largest, due to the lowest weight percent of amorphous PSblock.In the third chapter, polymeric micelles in aqueous environment were prepared bydialysis of the THF solution of H-typed copolymers against twice distilled water,followed by dilution with a given amount of water, to introduce a series of its aqueoussolution with different concentration. The value of critical micelle concentration ofthose copolymers were determined by the ratio of fluorescence intensity at374nm andthat at385nm in the fluorescence emission spectra, obtained through fluorescencespectroscopy using pyrene as florescence probe, and the CMC value for（PS）₂-b-PCL-PEO-b-PCL-b-（PS）₂-1,（PS）₂-b-PCL-PEO-b-PCL-b-（PS）₂-2and（PS）₂-b-PCL-PEO-b-PCL-b-（PS）₂-3was0.005,8.71×10-4and2.24×10-4mg/mlrespectively, indicating that as the hydrophobic block of the copolymer increased, thepolymeric micelles formed in the water surroundings would be much more stable thanthose formed by less hydrophobic units-containing copolymers. The hydrodynamicdiameters of those polymeric micelles were recorded by dynamic light scatterinstrument, and the result showed that the hydrodynamic diameter of those polymericmicelles with the largest length of hydrophobic block was smaller than the ones withshorter hydrophobic block, due to largely that the interaction between hydrophiliccomponent PEO and water molecules contributed considerably to an increase in thesize of polymeric micelles. The characterization of the morphology of polymericaggregates in a water-free state was performed on atomatic force microscopy, offeringheight images with spherical micelles spread on it.