Synthesis and polymerization of 2‐cyano‐2‐methyltrimethylene carbonate

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Abstract
2‐Cyano ‐methyltrimethylene carbonate (CMTC, 2) was synthesized starting from 2‐methylacrolein (6), propionaldehyde (8) or 2‐hydroxymethyl‐2‐methyl‐1,3‐propanediol (9). A key position in this synthesis is held by 2,2‐bis(hydroxymethyl)propionitrile (3), which in a first step, is reacted — in conjunction with 2,2‐dimethyl‐1,3‐propanediol (200) — with diphenyl carbonate (17) to result in a statistical copolycarbonate. Ring‐closing depolymerization of this polymer, with a catalyst based on tin, yields in a second step the title monomer, CMTC (2), along with 2,2‐dimethyltrimethylene carbonate (DTC, 1b). Separation of the two monomers can be achieved by selective solubilization of the latter in toluene. Polymerization of CMTC is performed preferentially by using weak nucleophiles as initiators, such as Et2AlOEt, Al(O‐secBu)3 or MgBu2, since strong nucleophiles such as BuLi or ZnEt2 tend to give side reactions with the cyano group. Copolymerization of CMTC with DTC results in statistical copolymers. With Et2AlOEt as initiator copolymers with Bernoulli statistics are obtained, with a ratio of diads DTC/DTC : (DTC/CMTC + CMTC/DTC) : CMTC/CMTC equal to 1:2:1 for equimolar feed composition. With MgBu2 as initiator and the same feed composition, a copolymer with the diad ratio 1:5:1 is obtained. Poly(CMTC) is a crystalline polymer with a melting point of 132.9°C and a glass transition temperature of 68.8 °C.