|摘要: ||本研究成功以商業易取得的4-氯-甲基-苯乙烯(4-vinylbenzyl chloride，簡稱4-VBC)為起始原料，經兩步置換反應製備4-異氰酸鹽-甲基-苯乙烯(4-vinylbenzyl isocyanate，簡稱4-VBI)。第一步以碘化鉀在丙酮溶劑中，將4-VBC之氯原子置換成碘原子，形成4-碘-甲基-苯乙烯(4-vinylbenzyl iodide，簡稱4-VBIodide)。接著在甲苯溶劑中，利用氰酸銀(AgCNO)與4-VBIodide反應製得4-VBI，此兩步驟反應均使用溫和的反應條件且產率都可達80%。另外，4-VBI是第一次經由非光氣法所製備出，同時完成單體的純化與結構鑑定。|
4-VBI分子結構具有活性雙鍵及異氰酸鹽兩種不同反應機制的官能基，其自由基聚合及異氰酸鹽加成兩個反應皆可獨立進行，不會彼此相互影響，因此，造就4-VBI在應用上的多樣性。在本研究中，依照反應機制的不同而有兩種不同先後順序的聚合方式。第一種聚合方式，先利用2,2,6,6-tetramethylpiperidinoxy(簡稱TEMPO)作為起始劑進行自由基聚合反應，將4-VBI在130℃分別以莫耳比例為5、10及15%含量與苯乙烯進行共聚合，此共聚物簡稱r-PS-PVBI。接著導入帶有醇類的壓克力單體(2-hydroxyethyl methacrylate，簡稱HEMA)與前面製備的三種不同比例共聚物r-PS-PVBIs之異氰酸鹽官能基反應，形成具有胺酯壓克力官能基的共聚物r-PS-PVBH。經由1H NMR結構分析，可利用r-PS-PVBH共聚物上胺酯官能基的含量，間接證明r-PS-PVBI共聚物中4-VBI含量分別為3.0、7.2及10.5%(接支率為0.7)。另外，r-PS-PVBH共聚物的分子量分布(polydispersity)隨著4-VBI含量增加而有增加的趨勢，從1.75(4-VBI含量3 mol%)增加到2.01(4-VBI含量10.5 mol%)，這個現象可能是由於4-VBI上異氰酸鹽官能基的拉電子效應，造成活性雙鍵反應性下降所造成。另外，不可避免的有部份共聚物上之異氰酸鹽官能基與水氣反應。
第二種聚合方式，是先將4-VBI與帶有單一胺基的aminopropylisobutyl POSS (簡稱API-POSS)進行反應，形成具有尿素的衍生物4-VBUP，接著分別以莫耳比例為1到5%含量與苯乙烯進行共聚合，並純化取得此共聚物r-PS-PVBUP。最後經由1H NMR結構分析，得到r-PS-PVBUPs的POSS含量為1.5到4.4 mol%。同時r-PS-PVBUPs隨著POSS的導入，玻璃轉化溫度(Tg)由純聚苯乙烯的86℃提升至r-PS-PVBUP含量為4.4 mol%的104℃。
A two-step synthetic scheme of 4-vinylbenzyl isocyanate (4-VBI) has been successfully accomplished in this study using a commercially available 4-vinylbenzyl chloride (4-VBC) as the starting material. In the first-step of reaction, the chloride atom in 4-VBC was replaced by iodine through the action of potassium iodide (KI) in acetone solution. Subsequently, the 4-vinylbenzyl iodide (4-VBIodide) was reacted with silver cyanate (AgCNO) in toluene solution, and this substitution reaction affords 4-vinylbenzyl isocyanate (VBI) readily. Both steps were carried out under mild condition with an overall yield of about 80% for the two-steps. For the first time, this two-step scheme provided the isolation as well as complete structure-proof of the pure 4-VBI through our non-phosgene route.
Dual functional groups of 4-VBI with an isocyanate group and an active-vinyl group at the opposite ends of the VBI molecule are of significant application interests, since they could independently undergo reactions/polymerizations in tandem to form polymers of diverse properties. In this research, two trial polymerizations have been carried out to find out which orders of reaction will be preferred. In the first trial, TEMPO-mediated free-radical co-polymerizations of styrene with 4-VBI in three weight ratios of 5, 10, 15% were carried out first at 130℃, and was followed by addition of 2-hydroxyethyl methacrylate (HEMA) to each of the three random r-PS-PVBIs to consume the isocyanate to form the urethane-acrylate functionalized co-polymers. 1H NMR analyses of the co-polymers showed 3.0, 7.2 and 10.5% of urethane contents in the respective cases indicating lower than expected 4-VBI incorporations (by a factor of 0.7) in the co-polymers. The polydipersity of the co-polymers increases with increasing 4-VBI incorporations ranging from 1.75 (in 5% case) to 2.10(in 15% case). These observations indicate a slight de-activation of vinyl group of 4-VBI in free-radical reaction due to the electronic–withdrawing effect of isocyanate-group. In addition, some loss of isocyanate groups in the copolymers due to moisture reaction also seems inevitable.
In the other approach, 4-VBI was reacted first with mono-functionalized aminopropylisobutyl POSS (API-POSS) to form a urea-POSS adduct before carrying out the co-polymerization with styrene in mole-concentrations of 1 to 5%, and was followed by the isolation of the resulting co-polymer, r-PS-PVBUP. In this case, the r-PS-PVBUPs showed POSS incorporation of 1.5 to 4.4 mol %. As might be expected, POSS groups in the r-PS-PVBUPs show a substantial enhancement of Tg from 86℃ in polystyrene to 104℃ for the r-PS-PVBUP with 4.4 mole % of POSS.
Through our preliminary research, it appears that polymerizations of 4-VBI by both approaches are feasible and invaluable, and both can introduce multiple urea or urethane groups into its styrene-copolymers by free-radical reactions.