Open-loop Polymerization Of Block Copolymer And The Michael Addition Of The Preparation Of Graft And Hyperbranched Polymers Research

Biopolymer becomes more and more important in biology and iatrology, because many difficult problems on medicine have been solved via its applications. Its performance is tightly related with its structure and composition. As we know, the relationship between its structure and properties is significant in designing and synthesizing biopolymers with different architectures. In this thesis, biocompatible polymers with different architectures, such as linear, grafting and hyperbranched have been prepared by ring-opening polymerization or Michael addition polymerization, and their structure were characterized and their properties were studied. These biopolymers have potential applications in drug delivery and gene transfection. The main results obtained in this thesis are listed as follows:1. Poly(styrene-b-isoprene-b-ε-caprolactone) (PS-b-PI-b-PCL) triblock copolymers have been successfully synthesized by combination of anionic polymerization and ring-opening polymerization. Diblock copolymer capped with hydroxyl group (PS-b-PIOH) was synthesized by sequential anionic polymerization of styrene and isoprene and following endcapping reaction of EO, and then it was used as macro-initiator in ring-opening polymerization of CL. The results of DSC and WAXD show big effect of amorphous PS-b-PI on the thermal behaviors of PCL block in triblock copolymers and the lower degree of PCL crystalline in the triblock copolymer with higher molecular weight of PS-b-PI was observed. The real-time observation on the polarized optical microscopy shows the spherulite growth rates of PCL₂₇, PCL₃₂₈ and PS-b-PI-b-PCL₃₄₄ were 0.71, 0.46 and 0.07μm·s^-1, respectively. AFM images of the samples formed by self-assembling of PS₉₀-b-PI₆₆-b-PCL₂₈ show the columns morphology.2. Linear poly(ethylenimine)-graft-poly(ethylene glycol)s (LPEI-g-PEG) with various degrees of grafting and molecular weights were synthesized by Michael addition reaction of LPEI with methoxy poly(ethylene glycol) acrylate. The graft copolymers display pH-sensitive behavior in water, and the micelles with different sizes were formed from the aggregation of graft copolymers, LPEI-g-PEG induced by pH variation of the copolymer solution. The dynamic light scattering method was used to study the effects of ionic strength, chain composition and pH on hydrodynamic radius. Versatile morphologies of micelles aggregates were observed during the evaporation of solvent of aqueous micelles' solution at different preparation conditions.3. Novel star-like hyperbranched polymers with amphiphilic arms were synthesized. Hyperbranched poly (amino amine)s containing secondary amines and hydroxyl groups were successfully synthesized via Michael addition polymerization of a triacrylamide (TT) and 3-amino-1,2-propanidiol (APD) when their feed molar ratio was 1:2. ¹H, ¹³C and HSQC NMR techniques were used to clarify the structures of hyperbranched polymers and polymerization mechanism. Methoxyl poly(ethylene oxide) acrylate (A-MPEG) and carboxyl terminated poly(e-caprolactone) (PCL) were sequentially reacted with secondary amine and hydroxyl group and thus core-shell structures with poly (1TT-2APD) as core and two distinguished polymer chains, PEG and PCL, as shell were constructed. The star-like hyperbranched polymers have different sizes in dimethyl sulfoxide (DMSO), chloroform and deionized water. DLS and ¹H NMR results were used to characterize the properties in different solvents.4. The Michael addition polymerization of APD (AA') and TT (B₃) yielded hyperbranched polymers with plenty of vinyl and hydroxyl groups when molar ratio was 1:1. ¹³C NMR measurements showed that the dimmer B₂A' intermediate were formed until its self-polymerization started. Further polymerization of intermediate B₂A' resulted in hyperbranched poly(amino amine)s, and no gelation occurred until the complete conversion of the monomers. Vinyl groups in poly(1TT-1APD)s could react with primary amine terminated poly(ε-benzyloxycarbonyl-L-lysine) (PZLL) by Michael addition reaction to form star-like hyperbranched polymers. After benzyloxycarbonyl (Z) groups in the PZLL were removed by treated with HBr, the polymers with poly(L-lysine)s as arm and PAMAM as core were prepared.5. Poly(2-ethyl-2-oxazoline)-b-poly(ε-caprolactone)-b-poly(L-glutamic acid) (PEOz-b-PCL-b-PLGlu) triblock copolymer with thermo-sensitive PEOz and pH-sensitive PLGIu was synthesized successfully in five steps: (1) preparation of PEOz capped with hydroxyl group via ring-opening polymerization of 2-ethyl-2-oxazoline with methyl-p-toluenesulfonate as initiator; (2) synthesis of PEOz-b-PCL via ring-opening polymerization ofε-caprolactone with PEOz-OH as macroinitiator; (3) conversion of terminal hydroxyl group to primary amine group of the diblock copolymer; (4) preparation of PEOz-b-PCL-b-PBLG triblcok copolymer via ring-opening polymerization of N-carboxyl anhydride ofγ-benzyl-L-glutamate (BLG-NCA) derived from benzyl glutamate using PEOz-b-PCL-NH₂ as macroinitiator; (5) removal of the protective benzyl groups by treatment of HBr. ¹H NMR, GPC and FT-IR were used to characterize the structure, molecular weight and molecular weight distribution of the polymers obtained in each step.