Studies On "Perfect" Hyperbranched Chains Free And Confined In Solution

In this Ph.D. thesis study, we first synthesized a set of "perfect" hyperbranched homopolymers with different uniform subchain lengths by using our newly designed seesaw-type B～～～A～～～B macromonomer and traditional fractionation, measured their reaction kinetics, obtained fractal characteristics of these novel hyperbranched chains, and studied how their translocation through a small cylindrical pore depends on the chain topology. Then, we prepared few "perfect" hyperbranched copolymers with amphiphilic subchains, and investigated their intrachain folding and interchain assocaition behaviors in dilute solution as well as the sol-gel transition of these copolymer chains in semi-dilute solutions. Further, we prepared novel hetero-subchain hyperbranched copolymer with two kinds of subchains which are not only independently adjustable but also uniform, and studied how the mass-size scaling and crystallization property depends on the lengths of the subchain and the whole chain. Moreover, we synthesized novel amphiphilic copolymers made of large hyperbranched poly(acrylic acid) cores and short polystyrene grafting chains, and studied their association, emulsifying and solubilization properties. Finally, we applied our seesaw-type macromonomer strategy to construct degradable model hyperbranched structure with both uniform subchains and controlled locations of cleavable disulfide linkage, and detailedly studied their degradation kinetics in various organic solvents. More specifically, we have:1. successfully synthesized azide-PS-alkyne-PS-azide macromonomers with a high end-group functionality; monitored the self-polycondensation by size-exclusion-chromatography equipped with a multi-angle-laser-light-scattering detector (SEC-MALLS) and stand-alone laser light scattering (LLS); and found that the reaction rate increases with the macromonomer’s initial concentration but decreases with its initial chain length, and the reaction follows the2nd-order kinetics with a time-dependent reaction rate constant; namely,kAB=kAB,0/[1+(βt)2], where kAB,o is the initial rate constant at t=0, and1/β is the time at which kAB decreases to50%of its initial value and related to the molar concentration ([C]) and molar mass (M) as1/β～[C]-0.35M0.55, implying that the the reaction is governed by the interchain distance and diffusion.2. systematically characterized a set of hyperbranched polystyrenes with different subchain lengths by using a combination of LLS and viscosity measurements. Our results reveal that both the polymerization degrees of the subchain (Nb) and the whole chain (Nt) are scaled to the average radius of gyration (<Rg>), average hydrodynamic radius (<Rh>) and the intrinsic viscosity ([η]) as:<Rg>-Nt0.46Nb0.11,<Rh> Nt0.48Nb0.09and [η]=KηMw0.39Mw.b0.31,respectively. These scaling laws clearly indicate that hyperbranched chains with uniform subchains are fractal objectives.3.directly balanced the confinement and hydrodynamic forces (fc=kBT/ζ and fh=3πηue) on each "blob" of a polymer chain entrapped inside a small cylindrical tube with a diameter of D under an elongation flow instead of considering the free energy (de Gennes’arguments) to obtain a unified description of how polymer chains with different topologies (linear, star and branched) crawl through such a tube. Namely, the critical flow rate (qc) is related to the blob size (ζ) and D as qc/qc,linear=(D/ζ)2. For a confined linear chain,ζlinear=D; for a star chain,ζstar=[2/(f+|f-2fin|)]1/2D, where f and fin represent the total arm number and the number of the forwarded arms inserted into the tube; for a hyperbranched chain, branch=(D/b)αNt,Kuhnβ’Nb,Kuhnγ’, where b is the size of one Kuhn segment, Nt,Kuhn and Nb,Kuhn are respectively the numbers of Kuhn segments of the entire branched chain and the subchain between two neighboring branching points; and the three constant exponents (a’,β’and γ’) are directly related to the well-known Flory’s scaling exponents between the chain size and Nt,Kuhn or Nt,Kuhn.4. quantitatively revealed that the critical flow rate (qc,branch) of hyperbranched chains passing through a small cylindrical pore is affected by both Nb and Nt as qc,branch～NtγNbφ with y=1.0±0.1and φ=-0.4±0.1. In addition, we also found that branch decreases as the pore size D increases. The deviation between our experimental results and previous theoretical predictions is attributed to some inappropriate assumptions used before. Using the difference between the critical flow rates of different chains, we are able to separate hyperbranched chains with a similar hydrodynamic size but different subchain lengths.5. further studied the intrachain folding and interchain association of amphiphilic hyperbranched copolymer chains in dilute and semidilute solutions and found that individual hyper-(PtBA36-PS55-PtBA36)600chains can undergo the intrachain folding in cyclohexane selectively poor for PS at lower temperatures; namely, each PS block collapses into a small globule stabilized by its three neighboring soluble PtBA blocks without any intrachain or intrachain association. For hyper-(PAA23-PS14-PAA23)n chains with different molar masses in water, our results indicate that the the average aggregation number (Nagg) increases as the weight average degree of polymerization [(DP)w] decreases, i.e., Nagg～(DP)W-0.7, revealing that smaller chains tend to associate more. Unlike their linear triblock precursors, hyper-(PAA23-PS14-PAA23)n chains are able to form a physical gel and its strength increases with the initial concentration and molar mass of hyperbranched chains.6. carefully prepared novel hyperbranched copolymer HB-(PS-b-PCL)n with two kinds of subchains which are not only independently adjustable but also uniform by interchain "clicking" of novel seesaw-type N3-PS-≡-PCL-N3macromonomer. Moreover, we found the prepared hetero-subchain hyperbranched structure is still fractal object, and the increase of the PS subchain and the whole chain will lead to a decrease of the intrinsic viscosity and the degree of crystallinity.7. successfully constructed amphiphilic hyperbranched copolymer chains made of large hyperbranched poly(acrylic acid) cores grafted with short polystyrene stickers (HB-PAAn-g-PSn+1) with different n values (n=1,10,47). The research results indicate both of the chain topology and styrene content can greatly affect the solution properties of HB-PAAn-g-PSn+1. Namely, the increase of n will lead to a weaker tendency of interchain associatin, a lower emulsifying ability, and a poorer solubilization efficiency.8. finely prepared degradable hyperbranched model structure with uniform subchains and controlled locations of cleavable disulfide linkages simultaneously, and studied how the prepared model structure was degraded by dithiothreitol (DTT) in various organic solvents. We found that the internal and external disifide bonds of hyperbranhced polystyrene chains conributed to the degradation kinetics in two different ways, which is due to the different local concentrations of DTT and PS segment around each disulfide bond.