As a kind of stimuli-responsive materials,the disulfide-containing material has received a tremendous amount of interest.A novel functional disulfide-containing waterborne polyurethane(DS-WPU)nanoemulsion was prepared via a one-step in situ phase inverse emulsification technique and its reducing-responsive prope rty was investigated using dithiothreitol as the reductant.Results showed that the DS-WPU nanoemulsion had a uniform particle size in nanoscale and a good film-forming characteristic,and the DS-WPU latex film exhibited great responsiveness along with a self-assembled behavior in the reducing environment to form WPU emulsion again,including a long-to-short process of the polymer chains.
He QinHong ZhangXiaoteng ZhouDanfei GuLingxiao LiChengyou Kan
The solid form of drugs plays a central role in optimizing the physicochemical properties of drugs,and new solid forms will provide more options to achieve the desirable pharmaceutical profiles of drugs.Recently,certain drugs have been found to form crystalline inclusion complexes（ICs） with multiple types of linear polymers,representing a new subcategory of pharmaceutical solids.In this study,we used diflunisal（DIF） as the model drug host and extended the guest of drug/polymer ICs from homopolymers to block copolymers of poly（ethylene glycol）（PEG） and poly（s-caprolactone）（PCL）.The block length in the guest copolymers showed a significant influence on the formation,thermal stability and dissolution behavior of the DIF ICs.Though the PEG block could hardly be included alone,it could indeed be included in the DIF ICs when the PCL block was long enough.The increase of the PCL block length produced IC crystals with improved thermal stability.The dissolution profiles of DIF/block copolymer ICs exhibited gradually decreased aqueous solubility and dissolution rate with the increasing PCL block length.These results demonstrate the possibility of using drug/polymer ICs to modulate the desired pharmaceutical profiles of drugs in a predictable and controllable manner.
Cationic poly（styrene-co-N,N-dimethylaminoethyl methacrylate） （P（St-co-DMAEMA）） latexes were prepared in the absence of surfactant by using 2,2＇-azobis （2-methylpropionamidine） dihydrochloride （AIBA） as the initiator. The effects of the AIBA concentration, HC1/DMAEMA molar ratio and DMAEMA amount on the emulsion polymerization and the latex properties were investigated. The particle morphology and size, the zeta potential and the amino distribution of the P（St- co-DMAEMA） latexes were characterized by transmission electron microscope （TEM）, dynamic light scattering （DLS） and conductometric titration, respectively. Results showed that the emulsion polymerization performed smoothly with high monomer conversion and narrow particle size distribution under the optimized conditions with AIBA concentration of1 wt%, HC1/DMAEMA molar ratio of 1.2 and DMAEMA content of 5 wt%. The diameter of the dried latex particles decreased and the density of amino groups on the particle surfaces increased with increasing the DMAEMA content. The zeta potential of the P（St-co-DMAEMA） latexes was pH-dependent and the zero point was around at pH 7.2. A facile method was developed to fabricate P（St-co-DMAEMA）/laponite hybrid nanoparticles via electrostatic adsorption, in which the loading capacity of laponite platelets reached 17.7 wt%, and the resultant hybrid nanoparticles showed good thermal stability.
Crosslinked x-P（St-MAA） seed latex was first prepared via soap-free emulsion copolymerization of styrene （St） and methyl methacrylic acid （MAA） with divinyl benzene as crosslinker and ammonium persulfate as initiator, and x-P（St-MAA）/x-P（St-NaSS） core/shell latex particles were then synthesized through a novel seeded emulsion copolymerization of St and sodium styrene sulphonate （NaSS） in the presence of water-soluble crosslinker N,N＇-methylene bisacrylamide （BAA） using oil-soluble 2,2-azobis isobutyronitrile as initiator. TEM observation indicated that narrow dispersed core/shell latex particles were obtained, and element analysis showed that NaSS unit content in the whole particle and in the shell reached 22.8 wt% and 51.2 wt%, respectively.
Differential scanning calorimetry（DSC） has been widely applied to study crystallization and melting of materials. However, for polymeric lamellar crystals, the melting thermogram during heating process usually exhibits a broad endothermic peak or even multiple endotherms, which may result from changes of metastability via recrystallization process. Sometimes, the recrystallization exotherm cannot be observed due to its overlapping with the melting endotherm. In this work, we employed a step heating procedure consisting of successive heating and temperature holding stages to measure the metastability of isothermally crystallized poly（butylene succinate）（PBS） crystals. With this approach we could gain the fraction of crystals melted at different temperature ranges and quantitatively detect the melting-recrystallization behavior. The melting-recrystallization behavior depends on the polymer chain structure and the crystallization temperature. For instance, PBS block copolymer hardly shows recrystallization behavior while PBS oligomer and high molecular weight PBS homopolymer demonstrate remarkable melting-recrystallization phenomenon. High molecular weight PBS isothermally crystallized in the low temperature range shows multiple melting-recrystallization while those isothermally crystallized at elevated temperatures do not exhibit observable recrystallization behavior. Furthermore, the melting endotherms were fitted via the melting kinetics equations. The original isothermally crystallized lamellae demonstrate quite different melting kinetics from the recrystallized lamellar crystals that melt at the highest temperature range, which is attributed to the different degrees of stabilization. Finally, the mechanism of melting-recrystallization is briefly discussed. We propose that apparent meltrecrystallization phenomenon be observed when melting of preformed lamellar crystals and recrystallization of thicker lamellae have similar free energy barrier.
Hexagonal boron nitride nanosheets （BNNSs） can work as a more efficient nucleating agent for two polyesters compared to graphene. Studies on the crystallization and dewetting processes of two polyesters, poly（butylene succinate） and poly（butylene adipate）, on the two substrate surfaces prove that the interaction between BNNSs and the polyesters is stronger than that between graphene and the polyesters. This strong interaction induces the pre-ordered conformation of molten PBA which has been identified by the in situ FTIR spectra. Thus BNNSs possess higher nucleation property than graphene. Finally, a new polymer-substrate interaction induced nucleation mechanism was proposed to explain the nucleation efficiency difference between graphene and BNNSs.
