Rational Design of Waterborne Polyurethane Pressure Sensitive Adhesives for Different Working Temperatures.

The appropriate pressure sensitive adhesion performances at working temperature are vital for the applications of waterborne polyurethane (WPU). Understanding the relationship among rheological behaviors, macromolecular structures and adhesive performances can be very useful to the rational design of waterborne polyurethane pressure sensitive adhesives (WPU-PSAs) for different operating temperatures, as well as other kinds of adhesives. In this study, four kinds of WPU-PSAs were prepared by reacting polypropylene glycol (PPG), hydrogenated hydroxyl-terminated polybutadiene (HHTPB), dimethyl alcohol propionic acid (DMPA), 1,6-hexamethylene diisocyanate (HDI) and four kinds of chain extenders. Gel permeation chromatography (GPC), swelling and rheology tests were used in parallel with an analysis of adhesive performances of the dried films of the adhesives. Results showed that, in addition to the nature of chain extenders playing a role on the rheological behaviors and adhesive performances of polymer, the gel content could be used to adjust the macromolecular structure and molecular weight distribution of polymer, thus distinctly affected the adhesive performances of PSA. The relationship among rheological behaviors, macromolecular structure and adhesive performances was investigated, and the rational design of WPU was achieved with appropriate pressure sensitive adhesion properties for different working temperatures of 25 and 60 °C.

High-Performance Cyanate Ester Resins with Interpenetration Networks for 3D Printing.

As the 3D printing technology is getting more and more popular and useful, demands for materials for 3D printing have increased significantly. Cyanate ester (CE) resin possesses the characteristics of high heat distortion temperature and high glass transition temperature, outstanding mechanical properties, low dielectric constant, and excellent water uptake. However, CE resin has not been widely used in 3D printing of UV curing because it is difficult for photopolymerizable groups to graft onto the chains of CE resin. On the other hand, the glass transition temperature (Tg) of the homopolymer of the tris(2-hydroxyethyl)isocyanurate triacrylate (THEICTA) outclasses that of other acrylates. Although THEICTA is particularly advantageous to prepare a UV-curing prepolymer with high glass transition temperature, it also cannot be directly used for fabricating heat-resistant 3D-printed parts because it is solid and adding diluents will reduce the thermal stability of printed objects. This study is unique in producing 3D-printed materials, in which the THEICTA tactfully dissolves in low viscosity (about 100 mPa·s under 25 °C) bisphenol E cyanate (BECy) without sacrificing two kinds of bulk material properties. In the process of 3D printing, the carbon-carbon double bonds from THEICTA are cured by radical polymerization. Postprinting thermal treatment transforms three cyanate groups to a triazine ring structure. Additionally, the two kinds of structures are interpenetrating. The high-performance 3D-printing material has potential in fields ranging from space flight and aviation to the automotive and electronic industry.