Topological Analysis And Control On Intramolecular Cyclization In Hyperbranched Polymers

Hyperbranched polymers are special polymers with highly branched frameworks and numerous terminal groups. In comparison to linear polymers, they possessed characteristics including much more terminal functional groups, lower solution or melt viscosity, and better solubility. Normally, they are prepared by one-pot fabrication which is much faile than dendrimers. Therefore, hyperbranched polymers have wide applications in various functional materials. In principle, the unique properties of hyperbranched polymers are due to their special topological structures. In this dissertation, the systematic investigations were implemented on the topological analysis and control of hyperbranched polymers. From the perspective of topology, the macromolecular structures of hyperbranched polymers were analysized, and the quantitative relationship of structural units and cyclic structures in hyperbranched polymers was deduced. Furthermore, several novel indexes and methods were defined to describe the topological features of highly branched polymers. And the control on intramolecular cyclization was also presented. In summary, the main contents and results are described as follows: 1. Topological analysis on macromolecular structure of Am+Bn type hyperbranched polymers At first, macromolecular structures of general Am+Bn type hyperbranched polymers were divided into a series of structural units according the types and numbers of terminal groups on structural units, then the quantitative relationship of structural units and cyclic structures were deduced respectively by step-construction method and functional groups-covalent bonds balance method under the consideration of chain-growth and intramolecular cyclization. The average number of intramolecular cyclic structures per macromolecule(ANC) and cyclic-average molecular weight(MC) were defined to characterize the cyclic feature of Am+Bn type hyperbranched polymers. Subsequently, the analysis results were verified by various Am+Bn type structural models. The ANC and MC values of model polymers of Am+Bn type polycarbosilanes and polyesters were determined successfully. ANC and MC values of different samples were analyzed, and it was found that intramolecular cyclic structures existed in all samples, furthermore, the high feed ratio of 2:1 was much more result in intramolecular cyclization than that of 1:1. 2. Quantitative characterization of topological structure of A2+B3 type hyperbranched polymers Based on the analysis results of general Am+Bn type hyperbranched polymers, the A2+B3 type hyperbranched polymers were analyzed specifically. A2+B3 type hyperbranched polymers possessed dual topological features of branching and cyclizing, and DB cannot reflect the cyclic feature. Therefore, the cyclic index(CI) was defined to determine the extent of intramolecular cyclization in polymers and the terminal index(TI) was defined to characterize the composite features of branching and cyclizing. With the model of A2+B3 type hyperbranched polycarbosilanes and polyesters, their CI and TI values were determined by 29 Si NMR and 13 C NMR. The CI and TI values of different samples were analyzed, and it was found that CI could reflect the cyclic feature of A2+B3 type hyperbranched polymers and TI could characterize the real topological structure of A2+B3 type hyperbranched polymers more accurately than DB. Furthermore, the degree of cycling in hyperbranched polymers containing rigid interval units was lower than that in hypbranched polymers containing flexible interval units. 3. Topological analysis of ABn type hyperbranched polymers With the aid of topological analysis, it was found the intramolecular cyclic structures in ABn type hyperbranched polymers were negligible, and the content of terminal groups only depended on the number of B functional groups in ABn monomers(n) and the total degree of polymerization regardless of the degree of branching. The quantitative expression of CT was found and could be facile determined by the known values of n and molar mass of linear unit of A0B(n-1). For the model of AB2 type hyperbranched polyesters, the content of terminal hydroxyl groups were determined by formula method, traditional NMR method, and titration method respectively. Through comparing these methods, it was formula method was much more facile than other two methods. 4. The control on intramolecular cyclization in A2+B3 type hyperbranched polymers According to the result that hyperbranched polymers containing rigid interval units had a lower degree of cylizing, we proposed to introduce rigid interval units into framework of hyperbranched polymers to limit intramolecular cylization. By designing disulfide containing A2 monomers and synthesizing A2+B3 type hyperbranched polymers by Cu(I)-catalyzed azide–alkyne cycloaddition(CuAAC), disulfide bonds and rigid triazole units were introduced into hyperbranched polymers together and endowed the product poly(ester triazole)s with reduction-cleavable and limited their intramolecular features. With the assistant of topological analysis and 1H NMR, it was found tha the introduction of triazole units can limit intramolecular cyclization effectively and conduce to prepare regular hyperbranched polymers. In addition, the monitor of GPC and 13 C NMR showed that the obtained A2+B3 type hyperbranched poly(ester triazole)s possessed a good reduction-responsibility that were degradated completely in 10-14 h.