Reversibly stealth QR code based on N-methylmaleimide-vinyl acetate copolymers under the condition of acid-base change

摘要

The Quick Response (QR) code has been widely used in many fields. While the information security of users will be endangered, if the QR code is illegally duplicated. So, the stealth QR code has the potential application in security printing. In this paper, a kind of stealth QR code that can be reversibly displayed by N-methylmaleimide (MMI) and vinyl acetate (VAc) copolymers as inkpad under the condition of acid-base change. The PVAc/MMI copolymers were synthesized by solution polymerization in methanol using VAc and different amount of MMI (MMI:VAc = 1, 2, 3 and 4 mol%). Because there is a big difference of the reactivity ratio of MMI (rMMI = 1.16) and VAc (r(VAc) = 1.90 x 10(-3)), the MMI were starved feeding into the polymerization system at a fixed rate over a period of 3 h. The actual mole ratio of MMI units in copolymers are 0.70 mol%, 1.91 mol%, 3.03 mol% and 5.83 mol% corresponding to the feeding ratios of MMI:VAc from 1 mol% to 4 mol%, respectively. The PVAc/MMI copolymers can be become to PVA/MMI by alcoholysis. The thermal properties of PVAc/MMI and PVA/MMI were investigated. The introduction of MMI in copolymers are helpful for improving the glass transition temperature (T-g) of PVAc/MMI and PVA/MMI, decreasing melting points (Tm) of PVA/MMI. The interesting thing is that the colorless PVAc/MMI showed color change under base condition in the alcoholysis process, further, the color showed reversibly change under acid/base condition change. This feature inspires us that using PVAc/MMI copolymer solution as inks, a kind of QR code patterns can be realized with fast color response, from blue color in alkaline condition to achromatous in acidic condition, which confirms the superior information encryption ability of the chemical-based QR pattern. Based on this feature, the QR code stamped by PVAc/MMI copolymers can be reversibly displayed in the actual information encryption application.