趙冰潔，鄭思珣

(上海交通大學(xué)化學(xué)化工學(xué)院，上海 200240)

（接上期）

1.4 基于POSS的聚降冰片烯（PN）形狀記憶材料研究進(jìn)展

Yang等人[52]首次通過(guò)開(kāi)環(huán)易位聚合制備了聚辛烯（PCOE）和雙羧基的聚降冰片烯（PNBEDCA）的嵌段共聚物，然后將含氨基官能團(tuán)的POSS與該嵌段共聚物上的酸酐進(jìn)行反應(yīng)，從而得到一種新型的功能化的P（COE-co-NBEDCA-g-POSS)，其中羧基和POSS作為側(cè)鏈接枝到降冰片烯上。反應(yīng)過(guò)程如圖14所示，通過(guò)DMA和形狀恢復(fù)速度進(jìn)行了表征了其形狀記憶性能。Yang等人認(rèn)為，玻璃態(tài)的彈性模量與橡膠態(tài)的彈性模量下降的程度可用來(lái)衡量形狀記憶性能的好壞，下降程度越大，說(shuō)明共聚物在降溫時(shí)表現(xiàn)出更好的形狀固定性，升溫時(shí)表現(xiàn)出更大的形狀回復(fù)。通常采用分別比Tg高與低20℃的彈性模量的比值來(lái)衡量彈性模量下降的程度。其中POSS含量為20%的P（COE-co-NBEDCA-g-POSS20)其比值為45.6，POSS含量為10%的P（COE-co-NBEDCA-g-POSS10)比值為27.0，并且P（COE-co-NBEDCA-g-POSS 20)僅需44 s便可恢復(fù)其初始形狀，而P（COE-co-NBEDCA-g-POSS10)需58 s。說(shuō)明，POSS含量更高的聚合物具有更好的形狀記憶性能。

Mather等人[53]將一個(gè)角為降冰片烯剩下七個(gè)角為環(huán)己基或環(huán)戊基的POSS與降冰片烯通過(guò)開(kāi)環(huán)易位聚合制備了降冰片烯-POSS雜化復(fù)合材料，通過(guò)熱機(jī)械分析測(cè)得的Tg上的回復(fù)應(yīng)變表征了這種拉伸的樣品的形狀記憶性能。結(jié)果發(fā)現(xiàn)引入POSS后，聚降冰片烯材料的應(yīng)變回復(fù)率有輕微的下降，這可能是因?yàn)榫劢当╂湹乃沙谟捎赑OSS分子的體積位阻和聚集的存在受到阻礙。他們還發(fā)現(xiàn)，POSS端基官能團(tuán)的類型同樣影響著形狀記憶行為，含端基為環(huán)己基POSS的雜化復(fù)合材料的應(yīng)變回復(fù)率要比含端基為環(huán)戊基POSS的低，這主要是因?yàn)榄h(huán)己基POSS的聚集。

1.5 基于POSS的其他聚合物形狀記憶材料研究進(jìn)展

Mather課題組對(duì)含有POSS的SMP研究作了大量工作。2011年，他們[54]利用側(cè)基帶有雙鍵的生物降解性聚酯[Poly(3-hydroxyoctanoate-co-3-hydroxyundecenoate)，PHOU]與含巰基 (-SH)的POSS通過(guò)光交聯(lián)點(diǎn)擊反應(yīng)合成了具有柔軟彈性的網(wǎng)絡(luò)狀PHOU-POSS新型SMP納米復(fù)合材料，過(guò)程如圖15(a)所示。與其他一次固定成型的SMP不同，PHOU-POSS納米復(fù)合材料的納米結(jié)構(gòu)具有重構(gòu)性，這是由于PHOU與POSS之間的共價(jià)鍵隨外部熱力學(xué)條件的變化表現(xiàn)為解聚態(tài)和聚合態(tài)。這一特點(diǎn)賦予了PHOU-POSS納米復(fù)合材料優(yōu)異的形狀固定和恢復(fù)性（圖15(b)）。對(duì)于本體系，在POSS重量含量較低時(shí)（＜20%）的PHOU-POSS聚合物，由于缺乏POSS的結(jié)晶結(jié)構(gòu)，形變的固定性較差，外力撤消后便可回復(fù)。而隨著POSS含量的增加，當(dāng)含量大于30%時(shí)，聚合物表現(xiàn)出較良好的形狀記憶性能（Rf＞=96%，Rr＞=98%），在加熱到POSS的熔融溫度上后，在5 s內(nèi)就迅速回復(fù)其初始形狀。

圖14 含POSS的共聚物的制備

圖15 (a)柔軟彈性的PHOU-POSS復(fù)合材料的合成 (b)PHOU-POSS膜的形狀記憶行為

POSS也被引入到纖維素中對(duì)其形狀記憶性能進(jìn)行改性。Xie等人[55]利用含多個(gè)羥甲基的POSS作為交聯(lián)劑，制備了POSS/纖維素的交聯(lián)網(wǎng)絡(luò)體系，發(fā)現(xiàn)將POSS引入后，纖維素的折皺回復(fù)角明顯增加，且SEM圖顯示，與不含POSS的纖維素相比，含有POSS的體系表現(xiàn)出更為光滑有韌性的表面。

2 結(jié)論及展望

基于POSS的形狀記憶聚合物中具有良好的形狀記憶效果，POSS的的引入對(duì)傳統(tǒng)SMPs材料機(jī)械強(qiáng)度低和形變回復(fù)驅(qū)動(dòng)力小等缺點(diǎn)有較大的改善，同時(shí)還提高了聚合物形變回復(fù)率及回復(fù)速度。目前報(bào)導(dǎo)的基于POSS的形狀記憶聚合物大多數(shù)為只有一元形狀記憶行為的聚合物，關(guān)于二元、三元甚至多元的還很少，因此未來(lái)的研究方向可能會(huì)多關(guān)注基于POSS的具有多元形狀記憶行為的SMPs，并且，目前報(bào)導(dǎo)的基于POSS的SMPs均為熱響應(yīng)的聚合物，其他如光、電磁等響應(yīng)的基于POSS的SMPs可能也是未來(lái)的發(fā)展方向之一。

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