| Pressure sensitive adhesive (PSA) which possesses excellent construction technology and adaptability is a kind of adhesive with extensive use. This kind of materials is rare, mainly including rubber and acrylate. PSA is a type of unique viscoelastic material which must be provided with both strong viscosity and cohesion strength. While, generally speaking, most polymers are difficult to meet the viscoelastic requirements of PSA. Polyurethane is a kind of strong polar material with a structural characteristic of micro-phase separation which causes strong cohesion strength but poor viscosity and that is why the polyurethane PSA is rare. Nonetheless, polyurethane PSA products have broad applications in the medical, nursing and other areas, therefore, the research of polyurethane PSAs to solve the contradiction between structure and properties has become an important direction and research focus of polyurethane PSAs.In this paper,4,4’-azobis (4-cyano-1-pentanol) was used to extend the isocyanate-terminated oligomers to synthesize two kinds of polyurethane macroinitiaters with different structure and same molecular weight. After that, polyurethane-poly (butyl acrylate) block copolymers with different structure and molecular weight were prepared by method of radical polymerization of polyurethane macroinitiators and butyl acrylate, also, the performances of PSAs based on polyurethane-poly (butyl acrylate) block copolymers were evaluated. Pressure sensitive adhesive synthesized in this paper, the introduction of poly (butyl acrylate) decrease the hydrogen bond in polymer which resulted decrease of cohesion strength and increase of free volume to provide viscosity for polymer. Meanwhile, urethane groups in polyurethane can form hydrogen bond to each other which can provide cohesion strength for polymer by physical crosslinking. Through the research of structure and properties, we found the law of structure and properties. Meanwhile, a pressure sensitive adhesive with excellent performance was got by evaluating the performance of pressure sensitive adhesive. The main work of this paper is as follows:1. Through designed of molecular weight of polyurethane, two kinds of polyurethane macroinitiators PUMIs with different structure and same molecular weights were synthesized. GPC and FT-IR showed that two kinds of PUMIs were synthesized successfully. DSC showed that the thermal decomposition activation energy of two kinds of PUMIs are 114.9 kJ·mol-1 and 106.5 kJ·mol-1 respectively, which is consistent with other literature. Mechanical characterization of two kinds of PUMIs showed that the mechanical property of PUMI-2 is better than PUMI-1, which indicates that PUMI-2 has more hydrogen bonds in its structure compared with PUMI-2.2. Polyurethane-poly (butyl acrylate) block copolymers with different structures and different molecular weights were synthesized. The results showed that the optimum reaction temperature and reaction time is 85℃ and 200 min. DSC, FT-IT and 1H-NMR were used to characterize polymerization products and the results showed that the polyurethane-poly (butyl acrylate) block copolymers were synthesized successfully. Meanwhile, we found that with the increase of content of poly (butyl acrylate) PBA, the hydrogen bonds decreased which caused the decrease of cohesion strength, at the same time, the molecular free volume increased which caused the increase of viscosity. The phase compatibility of polyurethane and poly (butyl acrylic) decreased but changes little with the increase of content of PBA. TGA studies have shown that the introduction of poly (butyl acrylate) reduced thermal stability of PSA.3. Pressure-sensitive adhesive properties were evaluated and the results showed that tack of PSAs was closely related to the content of poly (butyl acrylate), tack increases with the increase of content of PBA. The holding power of PSAs increased firstly and decreased then which was influenced by both tack and cohesive strength, holding power maximized when pressure sensitive adhesive showed both excellent viscosity and cohesive strength.180° peel strength also showed a decreasing trend after the first increase, which was influenced by tack and cohesion strength. The polymer with code of PU2-PBA3 exhibited the best performance pressure sensitive adhesive. |
PDF Full Text Request