6-amino-1,3-dimethyl-5-nitrosouracil (NAU) is an important intermediate for the synthesis of caffeine and theophylline, usually in the form of monohydrate. However, NAU·H₂O is aggregated and has a plate-like habit, which is very unfavorable for downstream process such as filtration and transportation. In this work, carboxymethylcellulose (CMC), a very common polymer, was selected as an additive to manipulate the habit of NAU·H₂O. It was found that under acidic conditions, the addition of CMC can change the habit from plate-like to block-like and can significantly improve the aggregation. On the contrary, the additive cannot change the habit under neutral or weakly alkaline conditions. The underlying mechanism was analyzed by experiment and molecular dynamics simulation. It is found that, under neutral or alkaline conditions, CMC will dissociate into negatively charged polymer chains, which have a stronger interaction with water. But CMC will combine with hydrogen ions under acidic conditions, weakening the interaction with water, allowing it to adhere to the (0 0 1) face and inhibiting the growth of this face. The results of this study should be helpful in the selection and mechanism research of polymer additives for crystal habit.

6-amino-1,3-dimethyl-5-nitrosouracil (NAU) 是合成咖啡因和茶碱的重要中间体，通常以一水合物的形式存在。但NAU·H ₂ O呈团状，呈板状，不利于过滤、输送等下游工艺。在这项工作中，羧甲基纤维素（CMC）是一种非常常见的聚合物，被选为一种添加剂来控制 NAU·H _{2的习性。}O.发现在酸性条件下，CMC的加入可以将习性从板状变为块状，并能显着改善聚集。相反，添加剂在中性或弱碱性条件下不能改变习性。通过实验和分子动力学模拟分析了其潜在机制。研究发现，在中性或碱性条件下，CMC会解离成带负电荷的聚合物链，与水有更强的相互作用。但CMC在酸性条件下会与氢离子结合，减弱与水的相互作用，使其粘附在（0  0  1）面上，抑制该面的生长。本研究结果对聚合物晶习性助剂的选择和机理研究有一定的帮助。