Copolymerization of Cyclic Monomers
Many copolymers have been prepared from cyclic monomers. These can form through ring-opening copolymerizations of monomers with similar functional groups as well as with different ones. Some cyclic monomers can also copolymerize with some linear monomers. Only a few copolymers of cyclic monomers, however, are currently used industrially.
The composition of the copolymers depends upon the reaction conditions, the counter ions, the solvents, and the reaction temperatures. The initiator system can be very important when cyclic monomers with different functional groups are copolymerized. Also, if different propagating centers are involved in the propagation process, copolymerizations can be very difficult to achieve.
Prominent among copolymers of cyclic ethers are interpolymers of oxiranes with tetrahydrofuran. Thus, ethylene oxide copolymerizes with tetrahydrofuran with the aid of boron trifluoride-ethylene glycol catalytic system [200]. The resultant copolyether diol contains virtually no unsaturation. Another example is a copolymer of allyl glycidyl ether with tetrahydrofuran formed with antimony pentachloride catalyst [201]:
In addition to the above, liquid copolymers form from 1,3-dioxolane with ethylene oxide, when boron trifluoride is used as the catalyst [1]. Also, a rubbery copolymer forms from tetrahydrofuran and 3,3-diethoxycyclobutane with phosphorus pentafluoride catalyst [202]. A 3,3-bis(chloromethyl) oxacyclobutane copolymerizes with tetrahydrofuran with boron fluoride or with ferric chloride catalysis. The product is also a rubbery material [1].
Various copolymers were reported from trioxane with dioxolane or with glycidyl ethers [2, 3]. For instance, a copolymer of trioxane and dioxolane forms with SnCl4, BF3, or HCIO, catalysts. The products from each reaction differ in molecular weights and in molecular weight distributions. Copolymerizations of trioxane with phenylglycidyl ether yield random copolymers [203].
Different lactones can be made to interpolymerize [204]. The same is true of different lactams [205-207]. The products are copolyesters and copolyamides, respectively.
More interesting are copolymers from cyclic monomers of different chemical types. For instance, cyclic phosphite will copolymerize with lactone at 150°C or above in the presence of basic catalysts [208]:
Aziridine copolymerizes with succinimide to form a crystalline polyamide that melts at 300C [209]:
Terpolymers form from epoxides, anhydrides, and tetrahydrofuran or oxetane with a trialkylaluminum catalyst [211]:
Copolymerizations of caprolactone with caprolactam in various ratios take place with lithium tetraalkylaluminate as the catalyst [212]. The products are mainly random copolymers with some block homopolymers.
When lactones copolymerize with cyclic ethers, such as ẞ-propiolactone with tetrahydrofuran, in the early steps of the reaction the cyclic ethers polymerize almost exclusively [213]. This is due to the greater basicity of the ethers. When the concentration of the cyclic ethers is depleted to equilibrium value, their consumption decreases markedly. Polymerizations of the lactams commence. The products are block copolymer [213].
