Design And Synthesis Of Novel Polymers Based On Helical Polyisocyanates

Polyisocyanates have recently received much attention because of their unique features such as the ability to form helical and liquid crystalline structures. Due to the helical structure, they have a stiff polymer backbone with large persistence length. Chiral initiators, solvents or monomers can lead to helical isocyanate polymers with a predominant helicity. Because of the unique rod-like, helical structures and appealing properties, polyisocyanates are recognized as good candidate materials for developing liquid crystals, optical switches, recognition devices and so forth. In this dissertation, helical polyisocyanates with a variety of topological structures, such as linear, star, comb-like and core/shell, were prepared. On one hand, we prepared amphiphilic triblock terpolymers to improve the hydrophilicity of polyisocyanates. However, the triblock terpolymers became inaccessible when the molecular weight of the coil block increased up to 6000. In order to overcome this limitation, we prepared star-shaped block coporymers consisting of pory(n-hexyl isocyanate) (PHIC) and pory(ε-caprolactone). On the other hand, we prepared comb-like polymers based on polyisocyanates and demonstrated that the comb-like coporymers could recognize (S)-(-)-1-phenylethylamine in the two enantiomers. In the meantime, we also prepared a novel type of magnetic materials based on polyisocyanates. They judiciously combined the advantages of both Fe3O4 nanoparticles (rapid magnetic responsivity) and helical PHIC. These materials will not nory enrich the structure of materials based on polyisocyanates, but also expand the application fields of polyisocyanates.The major research contents are shown as follows:1. Amphiphilic triblock terporymers, pory(n-hexy1 isocyanate)-b-pory(ethylene glycol)-b-pofy(n-hexyl isocyanate) (defined as PHIC-b-PEG-b-PHIC) was synthesized by using CpTiCl2-PEG-CpTiCl2 as macromolecular initiator. GPC, FT-IR,1H NMR and DSC analyses confirmed the formation of amphiphilic block terporymers. UV-vis spectra demonstrated that the PHIC block in the triblock terporymers adopted helical structures. Increasing temperature is not favorable to maintain the helical structures. In toluene, tetrahydrofuran and chloroform, the PHIC-b-PEG-b-PHIC triblock terporymers formed liquid-crystalline. At a concentration of 20 and 30 wt%in toluene, the triblock terporymer crystalline structures exhibited rod-like and spheric shapes, respectively. A further increase of the concentration of the triblock terpolymer to 45 wt% led to oriented liquid crystalline structures. Contact angle measurements demonstrated that the hydrophilicity of the triblock terpolymers was improved with increasing the content of PEG. Comparing with traditional rod-coil-rod triblock terpolymers, this novel type of triblock terpolymers has rod blocks with dynamic helical structures. Also notably, the present investigation would open a new approach for improving the hydrophilicity of polyisocyanates.2. Star poly(ε-caprolactone)s (defined as s-PCLs), star poly(n-hexy1 isocyanate)s (s-PHICs) and in particular the star block copolymers consisting of poly(ε-caprolactone)-b-poly(n-hexyl isocyanate)s [s-(PCL-b-PHIC)s] were synthesized via coordination polymerization by using organotitanium catalysts. The purpose of the study is to develop polymers with novel structures and interesting properties. The three types of star-shaped (co)polymers were characterized by size exclusion chromatography, FT-IR and 1H NMR techniques. UV-vis spectra demonstrated that the PHIC chains in the s-PHICs and s-(PCL-b-PHIC)s adopted helical structures in both solution and solid states. Increasing temperature was not favorable to maintain the PHIC helical structures. Polarized optical microscopy (POM) and wide angle X-ray diffraction measurements showed that the rod PHIC segments in the block copolymers changed not only the spherulitic morphology but also the crystal structure of PCL blocks. POM also demonstrated that s-PHICs and s-(PCL-b-PHIC)s formed liquid-crystalline in toluene, tetrahydrofuran and chloroform solutions. Increasing the concentration of star copolymers resulted in different liquid-crystalline forms. The presence of coil PCL blocks slightly influenced the liquid crystal behavior of PHIC segments. Scanning electron microscopy demonstrated the wrinkled surface of s-(PCL-b-PHIC)s, and the wrinkling degree increased with increasing the molecular weight of the blocks. Atomic force microscopy observations also revealed phase separation in s-(PCL-b-PHIC)s. In PHIC-b-PEG-b-PHIC section, we found that the triblock terpolymers became inaccessible when the molecular weight of coil block was increased up to 6000. The synthesis of s-(PCL-b-PHIC) has overcome this limitation. Comparing with traditional rod-coil star block copolymers, this novel type of star block copolymers has rod blocks with dynamic helical structures. The present study provides a versatile platform for preparing novel star-shaped block copolymers consisting of PCL, PHIC, and even other varieties of polymers, from which intriguing properties and significant potential applications are expected.3.4-Ethynylbenzyloxy-containing poly(n-hexyl isocyanate)s (defined as PHIC-C(?)Cs) were synthesized via coordination polymerization by using organotitanium catalyst. The PHIC-C(?)Cs were characterized by GPC, FT-IR, NMR, mass spectrometry (MALDI-TOF MS) and elemental analysis techniques. UV-vis spectra demonstrated that the PHIC-C(?)Cs adopted reversible helical structures in solution. The obtained PHIC-C(?)Cs were then used as macromonomers and subjected to Rh-catalyzed coordination polymerization to form comb-like double helical polymers composed of helical polyacetylene backbones and meanwhile helical PHIC pendants. Additionally, the PHIC-C(?)Cs underwent catalytic copolymerizations with chiral N-propargyl-(S)-camphanamide (M1), to form comb-like coporymers consisting of polyacetylene backbones and PHIC pendants. GPC, FT-IR and NMR confirmed the formation of the two types of comb-like double helical polymers. UV-vis spectra indicated that both the polyacetylene backbones and the PHIC pendants in the comb-like (co)polymers adopted dynamic helical structures. Circular dichroism effects demonstrated that the presence of chiral Ml units led to preferred-handed helical conformations in the polyacetylene backbones in the comb-like coporymers. The comb-like coporymers recognized (S)-(-)-1-phenylethylamine in the two enantiomers, demonstrating the potentials of such comb-like coporymers in chiral recognition and chiral resolution. The present study not onry provides an opportunity for preparing novel poryisocyanates with comb-like structures, but also expands the application fields of poryisocyanates.4. A novel type of magnetic composite particles was constructed using helical PHIC and Fe3O4. For this purpose, oleic acid-coated magnetic Fe3O4 nanoparticles (Fe3O4@OA NPs) were prepared through coprecipitation method. Then, azide-modified magnetic Fe3O4 nanoparticles (Fe3O4@N3 NPs) were prepared through the reaction between 3-azidopropyltrimethoxysilane (APTMS) and Fe3O4@OA NPs. The obtained clickable PC-C(?)C and Fe3O4@N3 NPs were subjected to the Cu-catalyzed azide/alkyne cycloaddition for synthesizing the anticipated Fe3O4@PHIC composite NPs. FT-IR, TGA and TEM techniques confirmed the formation of the magnetic composite nanoparticles. UV-vis absorption spectra demonstrated that the PHIC chains coated on the magnetic Fe3O4 NPs adopted dynamic helical structures. XRD measurements revealed that coating PHIC chains on Fe3O4 nanoparticles did not change the phase property of Fe3O4 nanoparticles. The Fe3O4@PHIC composite NPs showed a saturation magnetization of 17.8 emu·g-1 and the expected rapid magnetic responsivity. This novel type of magnetic composite nanoparticles possessed the advantages of both Fe3O4 nanoparticles and helical PHIC. We are convinced that the present study will be useful for preparing novel magnetic pohyisocyanates and will be helpful for expanding the application fields of polyisocyanates.