高分子量聚丙二醇在微通道反应器中的制备

Preparation of high molecular weight polypropylene glycol in microchannel reactor

高分子量聚醚多元醇应用广泛,但用传统的半连续釜式法制备不仅反应热风险大,而且反应时间漫长。采用微通道反应器(MCR)具有传热效率高、过程安全的特点,但反应物料黏稠、放热量大也使聚醚多元醇的分子量难以提高。本研究以双金属氰化络合物(DMC)为催化剂、正己烷为溶剂,在MCR中进行了环氧丙烷的开环聚合,制备出了分子量在2000~8000之间的聚丙二醇(PPG)。通过对流速、通道长度、温度和进料方式影响的考察,发现在停留时间足够长时,产品分子量基本等于理论分子量;当起始剂流速固定,单体流速增加时,分子量分布(MWD)先变宽再变窄;当管长较长时,分子量较高且MWD较宽;温度升高会使聚合反应的诱导期缩短;分段进料比一段进料更易制备高分子量PPG,但MWD变宽。这些均可用DMC催化的环氧丙烷的开环聚合机理和物料在MCR中微观混合强度的变化来解释。微观混合强度越低,聚合反应中链转移与链增长的速率比越小,聚合物的分子量分布也越宽。

High molecular weight polyether polyols are widely used.However,there is not only a large risk of reaction heat,but also a long reaction time in its traditional production process by using the semi-continuous reactor.The microchannel reactor(MCR)has the characteristics of high heat transfer efficiency and process safety,but the viscous material and high reaction heat release make it difficult to produce the high molecular weight polyether polyols.In this work,using double metal complex(DMC)as catalyst and n-hexane as solvent,the ringopening polymerization of propylene oxide(PO)was carried out in MCR.Polypropylene glycol(PPG)with molecular weight ranging from 2000 to 8000 was prepared.Effects of reaction conditions,such as flow rate,channel length,reaction temperature and feed policy,were investigated.It has been found that when the residence time is long enough,the molecular weight of the produced PPG is basically equal to the theoretical molecular weight.When the flow rate of initiator is fixed,an increase in flow rate of monomer will result in the molecular weight distribution(MWD)first widened and then narrowed.If the tube length is longer,the molecular weight is larger and the MWD is wider.If the temperature increases,the induction period of the polymerization can be shortened.Using the segmented feed,it is easier to prepare high molecular weight PPG with higher conversion than using the single feed,but the MWD is wider.These rules can be explained from the mechanism of PO ring-opening polymerization catalyzed by DMC and micro-mixing strength of materials in MCR.The lower the micro-mixing strength,and the smaller the rate ratio of chain transfer to chain propagation in polymerization,the wider the molecular weight distribution is.