以乙烯基酯树脂为多元醇制备聚氨酯硬质泡沫塑料的研究

Rigid Polyurethane Foams Prepared with Vinyl Ester Resin as Polyol

研究了用乙烯基酯树脂 (VER)直接代替通常的聚醚或聚酯型多元醇制备聚氨酯 (PU)硬质泡沫塑料的可能性。实验结果表明 ,发泡配方中促进氨酯化反应的催化剂N ,N -二甲基环己胺能与BPO复合形成室温引发体系 ,加速VER的共聚合反应 ,影响了PU硬质泡沫塑料形成过程中的发泡与凝胶反应 ,导致泡孔骨架基材的交联密度较低 ,泡孔结构不规整 ,并显示出较差的物理性能。以AIBN为引发剂时 ,反应初期主要进行氨酯化反应 ;仅当体系温度较高时才引起VER的自由基共聚反应 ,后者在聚氨酯泡沫骨架已初步形成的条件下进行 ,因而材料的泡孔结构较为均匀和规整。上述泡孔结构和基材交联密度上的差异导致两种材料具有不同的物理性能。

A new kind of rigid polyurethane(PU) foams were successfully prepared with vinyl ester resin containing hydroxyl groups as polyol directly. In this case, VER can not only react with isocyanate to form PU, but can also be copolymerized to form the network structure in the presence of free radical initiator, such as benzyl peroxide (BPO) or 2,2-azobis-isobutyronitrile (AIBN). It was found that the PU foam prepared with AIBN exhibited much better mechanical properties and lower thermal conductivity than the foam prepared with BPO. Further study shows that the catalyst used for preparing PU, N,N-dimethyl cyclohexyl amine, can complex with BPO to form a redox system and cause a rapid decomposition of BPO. Thus, the radical copolymerization of VER and the PU formation reaction take place at nearly the same time, especially at the early stage of the foam formation, but the foam stabilizer used is only favorable for the formation of cells of PU foam, so the cells of PU foam prepared with BPO are large and irregular. Furthermore, the cross-linking density of such a backbone of cells is lower. When AIBN is used as initiator, PU forms first in the early time, only when the temperature is high enough for AIBN to begin its decomposition, and the copolymerization of VER takes place on the framework of the PU cells. Thus, the cells of PU foam prepared with AIBN are small and regular. All these experimental results could be correlated with the discrepancy between the physical properties of two kinds of rigid PU foams prepared with these different initiators.