Precise Synthesis of ABCDE Star Quintopolymers by Combination of Controlled Polymerization and Azide–Alkyne Cycloaddition Reaction

A facile approach based on integrated utilization of ring-opening polymerization (ROP), reversible addition–fragmentation chain transfer (RAFT) process, and azide–alkyne cycloaddition reaction was efficiently used to construct amphiphilic 5-arm ABCDE star quintopolymers. The miktoarm stars are composed of poly­(ethylene glycol) (A), poly­(ε-caprolactone) (B), polystyrene (C), poly­(l-lactide) (D), poly­(<i><i>N,N</i></i>-dimethylaminoethyl methacrylate) (E₁), poly­(methyl methacrylate) (E₂), and poly­(methyl acrylate) (E₃). Alkyne-in-chain-functionalized BC and DE diblock copolymers were synthesized by successive ROP and RAFT process. Selective [3 + 2] click reaction between two-azide-end-functionalized PEG and BC copolymer gave azide-core-functionalized ABC star terpolymer, and a subsequent click reaction with DE copolymer afforded well-defined ABCDE stars with well-controlled molecular weight, low polydispersity, and precise composition, as evidenced from ¹H NMR, GPC, and GPC-MALLS analyses. DSC analyses revealed part of polymer segments in ABCDE stars were compatible. This general methodology has some advantages such as straightforward synthesis, mild reaction conditions, versatile polymerizable monomers, and high yields, which is promising for the construction of numerous functional star copolymers with multiple compositions and precise microstructures

Versatile Synthesis of Multiarm and Miktoarm Star Polymers with a Branched Core by Combination of Menschutkin Reaction and Controlled Polymerization

Menschutkin reaction and controlled polymerization were combined to construct three types of star polymers with a branched core. Branched PVD was synthesized by reversible addition–fragmentation chain transfer (RAFT) copolymerization and used as a core reagent to synthesize multiarm and miktoarm stars with poly­(ε-caprolactone) (PCL), polystyrene, poly­(methyl methacrylate), poly­(<i>tert</i>-butyl acrylate), and poly­(<i>N</i>-isopropylacrylamide) segments. Effects of reaction time, feed ratio, and arm length on coupling reaction between PVD and bromide-functionalized polymer were investigated, and a variety of A_<i>m</i>-type stars (<i>m</i> ≈ 7.0–35.1) were obtained. Meanwhile, A_<i>m</i>B_<i>n</i> stars (<i>m</i> ≈ 9.0, <i>n</i> ≈ 6.1–11.3) were achieved by successive Menschutkin reactions, and A_<i>m</i>C_<i>o</i> stars (<i>m</i> ≈ 8.8–9.0, <i>o</i> ≈ 5.0) were generated by tandem quaternization and RAFT processes. Molecular weights of various stars usually agreed well with the theoretical values, and their polydispersity indices were in the range of 1.06–1.24. The arm number, chain length, and chemical composition of star polymers could be roughly adjusted by control over reaction conditions and utilization of alternative methods, revealing the generality and versatility of these approaches. These ion-bearing stars were liable to exhibit solubility different from normal covalently bonded polymers, and the chain relaxation and melting behaviors of polymer segments were strongly dependent on the macromolecular architecture

Synthesis and Properties of Multicleavable Amphiphilic Dendritic Comblike and Toothbrushlike Copolymers Comprising Alternating PEG and PCL Grafts

Facile construction of novel functional dendritic copolymers by combination of self-condensing vinyl polymerization, sequence-controlled copolymerization and RAFT process was presented. RAFT copolymerization of a disulfide-linked polymerizable RAFT agent and equimolar feed ratio of styrenic and maleimidic macromonomers afforded multicleavable A_<i>m</i>B_<i>n</i> dendritic comblike copolymers with alternating PEG (A) and PCL (B) grafts, and a subsequent chain extension polymerization of styrene, <i>tert</i>-butyl acrylate, methyl methacrylate, and <i>N</i>-isopropylacrylamide gave A_<i>m</i>B_<i>n</i>C_<i>o</i> dendritic toothbrushlike copolymers. (PEG)_<i>m</i>(PCL)_<i>n</i> copolymers obtained were of adjustable molecular weight, relatively low polydispersity (PDI = 1.10–1.32), variable CTA functionality (<i>f</i>_CTA = 4.3–7.5), and similar segment numbers of PEG and PCL grafts, evident from ¹H NMR and GPC-MALLS analyses. Their branched architecture was confirmed by (a) reduction-triggered degradation, (b) decreased intrinsic viscosities and Mark–Houwink–Sakurada exponent than their “linear” analogue, and (c) lowered glass transition and melting temperatures and broadened melting range as compared with normal A_<i>m</i>B_<i>n</i> comblike copolymer. In vitro drug release results revealed that the drug release kinetics of the disulfide-linked A_<i>m</i>B_<i>n</i> copolymer aggregates was significantly affected by macromolecular architecture, end group and reductive stimulus. These stimuli-responsive and biodegradable dendritic copolymer aggregates had a great potential as controlled delivery vehicles

Insight into the Role of Hydrogen Bonding in the Molecular Self-Assembly Process of Sulfamethazine Solvates

The new solid forms screening of sulfamethazine was conducted in 16 kinds of different pure solvents. Four new sulfamethazine solvates were reported for the first time, and three crystal structures of solvates were successfully determined from single-crystal X-ray diffraction data. The results showed that sulfamethazine solvate formation directly depended on the solvents used in the experiments. The solvent properties were used to evaluate the effects of solvent on solvate formation. It was found that the H-bond acceptor ability of the solvent was the main factor that governed the solvate formation. The H-bonded motifs in the structures of solvates have been fully characterized. The results revealed that sulfamethazine solvate formation was mainly driven by molecular self-assembly through hydrogen bonding between solvent and solute molecules. Meanwhile, the crystal structures results also showed that the sulfamethazine molecule had flexible conformation. Furthermore, the principles of different sulfamethazine molecules packing in different crystal structures were discussed from the view of molecular intermolecular interactions and the molecular conformation

Phase Transformation between Anhydrate and Monohydrate of Sodium Dehydroacetate

The crystal structures of monohydrate and anhydrous substance were determined from the single crystals for the first time. The phase transformation between anhydrate and monohydrate of sodium dehydroacetate was in situ investigated by using Raman spectroscopy. The mechanism of the phase transformation was proposed. The results showed that the monohydrate crystalline phase of sodium dehydroacetate can transform to anhydrous phase through solid–solid transformation upon heating or solution-mediated phase transformation. From powder X-ray diffraction (PXRD) patterns and thermal gravimetric analysis (TGA) data, it was found that the anhydrous crystals obtained by these two methods are the same in structure. However, the scanning electron microscopy (SEM) results revealed that the surface of the anhydrous sodium dehydroacetate crystals obtained by high-temperature dehydration was much rougher than that obtained by solution-mediated phase transformation. Furthermore, the dynamic vapor sorption (DVS) results showed that the anhydrous crystals with rough surface had faster hydration rate than the anhydrous crystals with smooth surface when increasing humidity. The reasons behind these phenomena were discussed

Phase Transformation between Anhydrate and Monohydrate of Sodium Dehydroacetate

The crystal structures of monohydrate and anhydrous substance were determined from the single crystals for the first time. The phase transformation between anhydrate and monohydrate of sodium dehydroacetate was in situ investigated by using Raman spectroscopy. The mechanism of the phase transformation was proposed. The results showed that the monohydrate crystalline phase of sodium dehydroacetate can transform to anhydrous phase through solid–solid transformation upon heating or solution-mediated phase transformation. From powder X-ray diffraction (PXRD) patterns and thermal gravimetric analysis (TGA) data, it was found that the anhydrous crystals obtained by these two methods are the same in structure. However, the scanning electron microscopy (SEM) results revealed that the surface of the anhydrous sodium dehydroacetate crystals obtained by high-temperature dehydration was much rougher than that obtained by solution-mediated phase transformation. Furthermore, the dynamic vapor sorption (DVS) results showed that the anhydrous crystals with rough surface had faster hydration rate than the anhydrous crystals with smooth surface when increasing humidity. The reasons behind these phenomena were discussed

Simultaneous Effects of Multiple Factors on Solution-Mediated Phase Transformation: A Case of Spironolactone Forms

In this work, the single-crystal structure of the ethanol solvate of spironolactone was determined for the first time. The thermodynamic stabilities of the ethanol solvate, form II, and the hydrate of spironolactone were determined from the water–ethanol–spironolactone ternary phase diagram. Meanwhile, the solution-mediated phase transformation of spironolactone forms was investigated using in situ Raman and ATR-FTIR spectroscopy. The transformation processes were controlled by nucleation and growth of the stable form and/or dissolution of the metastable form in different situations. Then the simultaneous effects of temperature and solvent composition on phase transformation were investigated in detail. The desired spironolactone form could be obtained by adjusting the temperature and the water content in the solvent mixture. Furthermore, the phase transformation was examined in relation to the intermolecular interactions. It appeared that the conformational flexibility of spironolactone and the hydrogen-bond donor propensity of the solvent played critical roles in the formation of the final forms

Solid–Liquid Phase Equilibria of Ternary Mixtures Containing 1,2‑Dihydroacenaphthylene and Dibenzofuran

Ternary phase diagram data of 1,2-dihydroacenaphthylene-dibenzofuran mixtures in a series of alcohols, including methanol, ethanol, propan-2-ol, propan-1-ol, butan-1-ol, and pentan-1-ol were measured using a dynamic method at 308.15 and 313.15 K. The experimental data were correlated with the Wilson model (including pseudobinary systems), UNIQUAC model, and NRTL model. The results indicate that pseudobinary systems with the Wilson equation give a better description of the solubility of the ternary system. The eutectic point shifts toward dibenzofuran when the more polar methanol and ethanol are used. This shift may help achieve a more efficient separation of 1,2-dihydroacenaphthylene and dibenzofuran