New catalysts for linear polydicyclopentadiene synthesis
Introduction
Of the cycloolefins polymerisable by ring-opening metathesis, dicyclopentadiene (DCPD) is one of the most accessible [1], [2]. In the ring-opening metathesis polymerization either both or one of the carbon–carbon double bonds from DCPD can be involved. In the first case a cross-linked polymer will result while in the second linear polydicyclopentadiene (LPDCPD) can be obtained.
Numerous patents and papers [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16] deal with metathesis polymerization of dicyclopentadiene involving ring-opening of both norbornene and cyclopentene units. The reaction is promoted by various complexes of W and Mo in conjunction with organometallic compounds of Al, Sn or Zn. The polymer thus obtained has a cross-linked structure and exhibits outstanding physical and mechanical properties. The commercial product has been manufactured via RIM (Reaction Injection Molding) technique.
Several authors [17], [18], [19], [20] have also reported metathesis polymerization of dicyclopentadiene involving selectively ring-opening of norbornene moiety to linear polymer. They employed either well-defined single-component catalysts [17], [18], [19] or certain selective binary catalytic systems [20]. In the last case, the linear polydicyclopentadiene has been accompanied by cross-linked polymer mainly when working at high monomer concentration.
Recently, a new class of quite active and selective catalysts for ring-opening polymerization of dicyclopentadiene to linear polymer has been disclosed [21].The present paper describes our results concerning synthesis, and structure of linear polydicyclopentadiene in the presence of this new class of catalyst.
Section snippets
Starting materials
Commercial dicyclopentadiene, (Aldrich, 95%) was purified by conversion in cyclopentadiene (CPD) and subsequent dimerization. Pure CPD was obtained by thermal cracking (170°C) and distillation through Vigreux column. It was stored for several days at 30°C, (under nitrogen atmosphere) when monomer dimerized to DCPD. Finally the mixture of cyclopentadiene with dicyclopentadiene was distilled under vacuum (p = 15 mm Hg, Vigreux column) immediately before carrying out the polymerization reaction.
Results and discussion
Several catalytic systems derived from WCl6 or related tungsten complexes and organometallic compounds such as iBu3Al, Et2AlCl, iBu4Sn, Ph4Sn, Me2Allyl2Si and Allyl4Si are active and selective in ring-opening polymerization of common monocyclic olefins: cyclopentene, cyclooctene, cyclooctadiene and cyclododecene [22], [23]. Numerous other catalytic systems have been shown to be effective in ring-opening polymerization of dicyclopentadiene, including those based IrCl3 and RuCl3 [24], ReCl5 [17],
Conclusions
- 1.
The endo-dicyclopentadiene polymerizes in the presence of the catalytic systems WOCl4/Me2All2Si or WOCl4/All4Si in toluene solution, selectively to linear polydicyclopentadiene within a rather wide range of monomer and catalyst concentration. The polymer yield is high.
- 2.
The microstructure of linear polydicyclopentadiene obtained in these conditions determined by IR and -NMR is predominantly cis.
- 3.
The glass transition temperature, Tg, determined by DSC has the value of 53°C.
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