Star/Linear Polymer Topology Transformation Facilitated by Mechanical Linking of Polymer Chains

Abstract

Topology transformation of as tar polymer to al inear polymer is demonstrated for the first time.Athreearmed star polymer possessing am echanical linking of two polymer chains was synthesized by the living ring-opening polymerization of d-valerolactone initiated by ap seudo [2]rotaxane having three hydroxy groups as the initiator sites on the wheel component and at both axle termini. The polymerization was followed by the propagation end-capping reaction with ab ulky isocyanate not only to prevent the wheel component deslippage but also to introduce the urethane moiety at the axle terminal. The resulting rotaxane-linked star polymer with afixedrotaxane linkage based on the ammonium/crown ether interaction was subjected to N-acetylation of the ammonium moiety,which liberated the components from the interaction to movet he wheel component to the urethane terminal as the interaction site,e ventually affording the linear polymer.T he physical property change caused by the present topology transformation was confirmed by the hydrodynamic volume and viscosity.Structure or topology transformation and the resulting property change often seen in molecular switches or machines have attracted much attention because of their potential applicability to the macroscopic change of appearance or properties.[1] Because such atransformation is mainly limited to small molecules,atopology-transformable polymer would be attractive for bulk property control. In comparison with linear polymers,c orresponding topological polymers, [2] such as star polymers, [3] cyclic polymers, [4] dendrimers, [5] and hyperbranched polymers, [6] generally provide smaller hydrodynamic volume,l ower solution viscosity,a nd less polymer entanglement in the bulk. These properties are useful in solid materials that can help not only in reducing solvent use as sustainable products but also making the molding process easy because of low melt viscosity.However,m ost topological polymers [7] reported to date are not transformable,b ecause they are constructed by covalent bonds.T here are af ew reports on topology reconstruction using weak and reversible interactions to change polymer properties.[8] Meanwhile,w eh ave recently reported [9] the synthesis of mechanically linked block/graft copolymers as as hape-transformable polymer in which the two polymer chains are tied by the rotaxane structure;o ne polymer chain is threaded into the crown ether wheel to which the other is connected. Because we have found that the urethane moiety placed in the rotaxane axle has some attractive interaction with the crown ether wheel, [9c] which is consistent with Gibsons reports, [10] crown ether based rotaxanes having both ammonium and urethane moieties can be regarded as two-station-type molecular switches.Namely,the rotaxane structure plays akey role as acontrollable movable linking unit, thereby being applicable to more sophisticated transformable systems.T his paper describes the synthesis of as tar polymer characterized by the rotaxane linking of the polymer ch...

Photo-triggered solvent-free metamorphosis of polymeric materials

“…In most cases, the star-shaped starting molecules in the liquid state are converted to the corresponding solid network material, but such network formation reactions are in general irreversible. To address this, we focused on a repeatable molecular architectural transformation (MAT) strategy 18 – 23 . Various repeatable MATs, for example, linear–star 18 , linear–cyclic 19 – 22 , three-armed star–network 23 architectures have appeared and, moreover, MAT of amphiphilic block copolymers into star and comb polymers has recently been achieved by Diels–Alder reaction 24 .…”

“…To address this, we focused on a repeatable molecular architectural transformation (MAT) strategy 18 – 23 . Various repeatable MATs, for example, linear–star 18 , linear–cyclic 19 – 22 , three-armed star–network 23 architectures have appeared and, moreover, MAT of amphiphilic block copolymers into star and comb polymers has recently been achieved by Diels–Alder reaction 24 . Of various candidates exhibiting repeatable cleavage and reformation of covalent bonds 25 utilized as self-healing materials 26 , we focused on hexaarylbiimidazole (HABI) 27 as the linking point.…”

Topology-transformable polymers: linear–branched polymer structural transformation via the mechanical linking of polymer chains

“…[77][78][79][80] We first describe our results for the topology-transformable 3-arm star polymer derived from a crown ether-based M2R with secammonium and urethane moieties on the polymer axle that can be regarded as a two-station-type molecular switch. 81 As shown in Scheme 10, the topology-transformable star polymer (3-PVL_A) was synthesized using the trifunctional pseudo [2]rotaxane initiator 3-OH, which contains three primary OH groups, to ensure the synthesis of the well-defined three-armed star polymer 3-PVL-OH in which the arm polymer chains have the same DP. Treatment of the three terminal OH groups of the polymer with a bulky isocyanate gave the corresponding star polymer 3-PVL_A, in which the polymer chain on the wheel component is fixed at the center of the axle polymer chain by the sec-ammonium/crown ether interaction.…”

“…The g′ value of Rot-Star 4 _A to Rot-Linear_U was calculated to be g′ = 0.82, and this is higher than that of the model polymer (g′ = 0.74) but lower than that of the rotaxane-linked 3-arm polymer composed of PVL (g′ = 0.89). 81 In general, the smaller the g′ value, the larger the number of arm chains with same molecular weight in the star polymer. Therefore, the results suggest the successful synthesis of the multi-armed star polymer Rot-Star 4 _A as well as its structural transformation to a linear-like polymer (Rot-Linear_U) whose polymer-dangling wheel component may be partially located on the urethane linkage at the axle end.…”

Multi-responsive rotaxane with tunable fluorescence under azobenzene-based benzoxazine structure

“…Various classes of host molecules, such as crown-ethers, cyclodextrins, calixarenes, were reported for rotaxane fabrication. The self-assembled pseudorotaxane can be applied for reversible chain extended, star and block copolymers so called polymer topology transformations [13][14][15][16][17]. Polyrotaxanes are potential advanced materials such as self-healing polymers, stimuli responsive materials, molecular machines, actuators, and sensors [18].…”