Study On Chromophore Functionalized Linear-comb/Star-comb Dendrigraft Polybutadiene

Photosensitive dendritic polymers are a new class of smart polymer materials, the unique three-dimensional structure of polymer backbones have a big impact on the photosensitive material properties and have been drew more and more attention. Dendrigraft polymers are a new class of dendritic polymers after dendrimer and hyperbranched polymers. Due to their regular controllable structures and convenient synthesis, dendrigraft polymers have a great advantage of functional value, but the photosensitive dendrigraft polymers have been barely reported. In this paper, it combined the anionic polymerization techniques and "click" chemistry to synthesize two kinds of photosensitive dendrigraft polybutadiene and the effect of dendrigraft architecuture on photosensitive material properties were systematically investigated. The main conclusions were summarized as follows:(1) A series of multicoumarin-functionalized dendrigraft polybutadienes with linear-comb or star-comb architecture were synthesized from generation0to3(LGn and SGn, respectively, n=0-3) via anionic polymerization. LGn-PB and SGn-PB (n=0-3) were functionalized by17-22mol%azide groups through chemical modification, obtaining linear-comb and star-comb dendrigraft polybutadiene template LGn-N3and SGn-N3(n=0-3). From the results of the molecular branching parameters, it showed that:with increasing the generation from0to3, the polymer architecture converted from one-or two-dimensional structure to aflexible branched structure, then advanced into a compact structure; meanwhile, the LGn-PB exhibited a relatively looser structure than its SGn-PB analog did.(2) The alkynyl-modified coumarin and alkynyl-modified spiropyran were linked to LGn-N3and SGn-N3(n=0-3) via "click" chemistry, obtaining coumarin-functionalized dendrigraft polybutadiene LGn-C and SGn-C (n=0-3) and spiropyran-functionalized dendrigraft polybutadiene LGn-SP and SGn-SP (n=0-3), respectively.(3) For LGn-C and SGn-C (n=0-3), the effect of dendrigraft structure on the fluorescence properties were summarized as follows:the fluorescence quantum yield (φDF) grew from1.7%of coumarin small molecules to7.3%and5.4%of LG1-C and SG1-C, respectively. The φf of LGn-C and SGn-C (n=0-3) with different generation were exhibited in an order of φF(G1)> OF(G2)> OF(G3)>φF(G0), and the OF of LGn-C were always better than those of SGn-C due to its looser architecture. These resluts indicated that there are inter-macromolecules fluorescence quenching and intra-macromolecules fluorescence quenching at the same time, while the fluorescence properties of LGn-C and SGn-C (n=0-3) were affected by the "inter-/intra-macromolecules quenching" pattern.(4) For LGn-C and SGn-C (n=0-3), the effect of dendrigraft structure on the photo-crosslinking properties were summarized as follows:maximum crosslinking degree (Ed, max) and the maximum recovery degree (Er,max) of LGn-C and the SGn-C were increased with increasing generation. SGn-C with the more compact structure exnibited higher Ed. max and Er.max than its LGn-C analog did. SG3-C and LG3-C exhibited.Ed,max as high as94.0%and92.8%, respectively. These results indicated that there are inter-macromolecules crosslinking and intra-macromolecules crosslinking at the same time, while the photo-crosslinking properties were affected by the "inter-/intra-macromolecules photo-crosslinking" pattern.(5) For LGn-C and SGn-C (n=0-3), the effect of dendrigraft structure on the photochromic properties were summarized as follows:Compared with spiropyran, LGn-SP and SGn-SP exhibited a slower colored speed and a faster fade speed. For LGn-SP and SGn-SP, the colored speed is slower and the fade speed is faster with increasing the gerneration from0to3. LGn-SP exhibited a slower colored speed and fade speed than its its SGn-PB analog did.