Incorporating Organosilicon Modification into Waterborne Polyurethane

Due to their dendritic-like structure and properties, hyperbranched polymers exhibit numerous cavities, branching points, and a nearly spherical architecture. The preparation process of hyperbranched polymers is straightforward, without the need for purification. However, their direct use as materials is hindered by the absence of molecular chain entanglement. To address this limitation, grafting linear polyurethane onto hyperbranched polymers offers a dual benefit: enhancing mechanical properties and leveraging the branched structure and narrow hydrogen bonds of hyperbranched polymers.

Initially, hyperbranched polyurethane (HPU) with terminal tibial groups was synthesized using toluene 2,4-diisocyanate (TOI) and diethanolamine (DEOA) as raw materials, with DMAC as the solvent. Subsequently, raw materials including polycarbonate glycol CPCDL and TOI were utilized to produce a linear oligomer (A2) with an isocyanate terminal. A hyperbranched polyurethane terminated with isocyanate groups was then created by reacting these components, followed by generating a hybrid polyurethane through the introduction of an appropriate silane coupling agent (KH550).

The final step involved the wet curing of the unreacted isocyanate in an ambient environment, resulting in a hybrid polyurethane film. This product is denoted as HPU-KH550-n. In this notation, HPU represents the hyperbranched polyurethane, KH550 stands for the silane coupling agent, and n signifies the molar ratio of KH550 to isocyanate.

Analysis of functional groups, hydrogen bonds, thermogravimetric properties, and mechanical behavior via infrared analysis revealed that the abundant functional groups such as light groups, amino ester groups, and pulse groups within the hyperbranched polyurethane structure facilitated the formation of multiple hydrogen bonds within the molecule. The concentration of the silane coupling agent had a pronounced effect on the thermal and mechanical attributes of the polymers. The polymer components exhibited enhanced heat resistance as KH550 content increased, with the initiation of decomposition occurring at 200°C and the peak weight loss rate at 362°C. However, the tensile strength of the polymer gradually decreased with escalating KH550 content, reaching 44 MPa when n (NCO): n (NCO)=0.30.

Organosilicon-modified waterborne polyurethane synthesis involves two main steps. First, a polysiloxane polyurethane block copolymer is synthesized, which is then dispersed in water. The use of siloxane hydrolysis condensation crosslinking improves the performance of waterborne polyurethane, yielding a crosslinked waterborne polyurethane dispersion. This process can be categorized into a one-step feeding method and a step-by-step feeding method based on the feeding sequence of siloxane monomers or polysiloxane oligomers.

The one-step feeding method involves adding main raw materials and organosilicon monomers or polysiloxane oligomers to the reactor simultaneously during the prepolymer synthesis process. The prepolymerization reaction lasts 5-6 hours, with acetone added to reduce viscosity. After the -NCO group content approaches the theoretical value, the temperature is lowered, a solvent is introduced to reduce viscosity, and a neutralization salifying agent is added after thorough mixing. Subsequently, distilled water is added to achieve dispersion, and chain extension with ethylene diamine (EDA) results in the production of amino siloxane-modified waterborne polyurethane composite solution.

It's important to note that this sequence does not yield a stable lotion. The resulting lotion exhibits a milky appearance with large particle size and inadequate film-forming performance.