PLVP. In a 50 ml Schlenk bottle, add 0.5 g methylene lactide (MLA), 2 mg AIBN, 0.46 g 2-vinylpyridine and 10 ml 1.4-dioxane. The mixture in the bottle was frozen and deoxygenated three times, and the reaction bottle was placed in an oil bath at 75 °C to react for 24 hours. After the reaction is over, cool to room temperature, and add 10 ml C frequency of 399.78 MHz and 100.53 MHz, respectively. The magic-anglespinning (MAS) rate was set as 12 kHz, and POST-C7 pulse sequence was used to excite and reconvert DQ coherences with a DQ recoupling time of 0.167ms. Windowed z-rotation Phase-modulated Lee-Goldburg (LG) decoupling pulses were used during the t1 and t2 evolution periods to suppress proton dipolar couplings, leading to significant enhancement of proton spectral resolution. The experimental pulse sequences can be found in the literature. The 1 H 90 o pulse length was 2.2 s. 128 t1