Copolymerizations using pinenes

The monomer charge vs. copolymer composition data for a series of isobutylene and 0-pinene copolymerizations using EtAlCl2 in EtCl solvent between —50° and —130° are shown in Fig. 7. Evidently from —50° to —100°, 0-pinene is more reactive than isobutylene, and the copolymer is relatively richer in 0-pinene than the monomer charge. However, in the range from —110° to —130° the two monomers exhibit equal reactivities and the copolymer composition is equal to that of the monomer charge. Table 4 shows the reactivity ratios obtained together with the calculation methods employed. 

Copolymers of a-pinene and styrene have been obtained by cationic copolymerization using either AICI3, benzene, 10°C [82], or SbCls/AlCls, toluene, —80°C [83]. In the first case, copolymers with MWs = 2.3-3.1 kg/mol and softening temperatures of 82-85°C were obtained. 

The homopolymer and block copolymer macromonomers were copolymerized with MMA by free-radical polymerization in benzene at 60 °C using AIBN as an initiator typical concentration were [MMA]=1.2 mol 1 1 and [macromonomer] =0.020 mol l"1. MMA was completely converted in 18 h and the macromonomers conversion reached more than 70% as determined by lH NMR. Incomplete conversion was explained by steric hindrance. Free-radical copolymerization resulted in high MW graft copolymers with PMMA backbone and relatively rigid, nonpolar poly(P-pinene) branches. 

A detailed study of the reactivity ratios of the isobutylene and 0-pinene system has been undertaken. We found that the reactivity ratio product is dose to unity over the whole temperature range studied from —50° to —130°, indicating a random copolymer system. Further, we discovered that while the reactivity ratios are quite insensitive to the particular Lewis acid used, they can be controlled by temperature and that the individual reactivity ratios become equal to unity below about —110°. In other words, at very low temperatures the copolymerization becomes azeotropic (the composition of the feed and that of the copolymer become equal). 

Cationic copolymerization of i3-pinene with about 20% isobutylene produces impact-resistant thermoplasts, and vulcanizable elastomers when more than 90% isobutylene is used. 

There have been reports in which j3-pinene was copolymerized by a radical copolymerization, reversible addition-fragmentation chain transfer (RAFT). As comonomers, methyl acrylate or n-butyl acrylate have been used (9,10). 

The cationic copolymerization of a-pinene with several conventional monomers has been examined by various groups [38-41]. The reaction of a-pinene with isobutene using EtAlCl2 in ethyl chloride at-100°C yielded ran-... 

The synthesis of block, as well as random copolymers of 3-pinene with styrene and / -methylstyrene (pMeSt), was studied by living cationic polymerization, using both the styrene and vinyl ether adducts as initiators in the presence of Ti(OiPr)Cl3 in methylene chloride at —40°C [44,47]. For styrene (A) and 3-pinene (B), both AB and BA block copol3mers were obtained, as shown in Fig. 2.13, with Mn values of 4 000 and 3 600, respectively, and narrow Mw/Mn ratios (1.26 and 1.38, respectively). The efficiency of these block copolymerizations was attributed to the similar reactivity of the C—Cl bond derived from the two monomers [44]. 

This unfavourable situation is however reversed when pinenes and other monoterpenes are used as comonomers in free radical copolymerizations with monomers bearing structures other than theirs. These systems are described below as a function of the specific terpene comonomer. 

The conventional free radical copolymerization of 3-pinene and MMA or St, initiated by AIBN, yielded copolymers with Mw of about 11 600 and 25 400, respectively and MWD of 1.5 and 1.7, respectively [56]. When 2,3,4,5,6-pentafluorostyrene (PFS) was used as comonomer, and benzoyl peroxide as the initiator, a PFS-rich copolymer incorporating isolated isomerized 3-pinene units distributed between poly(PFS) segments was obtained [57]. This feature is related to the low reactivity of the 3-pinene free radicalar towards its monomer, that is to a reactivity ratio close to zero. These PFS-[3-pinene copol5miers were shown to combine the typical high water contact angles of perflourinated polymers (hydrophobicity) with the optical activity of polyOPESf) [57]. A recently published study indicated that the radical random copolymerization of both a- and 3-pinene with styrene under microwave irradiation yields materials with Mn values considerably higher than those obtained under conventional conditions, but still with very low conversions [18]. 

The AIBN-initiated radical copolymerization of P-pinene and methyl acrylate (MA) [58] with n-butyl acrylate (wBA) [60] produced results similar to those described above for AN [59] and thus the structure of the ensuing macro-molecules were characterized by the presence of MA or nBA blocks alternated with single P-pinene units but the incorporation of p-pinene could again be enhanced by the addition of Et2AlCl [58, 60]. When the authors attempted to turn this system into a controlled process by using RAFT reagents, the results were rather disappointing in the case of MA [58], whereas, when wBA was used [60], the results obtained were similar to those reported for AN [59]. 

Butadiene and myrcene have been copolymerized by either batch or continuous processes using finely divided alkali metal (Na or K) as catalyst and ether (preferably diethyl ether or 1,4-dioxane) as solvent at 25-95°C. Conversions of 90% or higher were obtained within 6-24 h. Other terpenes, like a-terpinene, dipentene (racemic limonene), or p-pinene, react little or not at all with 1,3-butadiene, while the copolymerization of alloocimene with 1,3-butadiene gives a low conversion of partially gelled copolymer [37]. 

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