Ring Opening Metathesis Polymerization (ROMP) of cis‐ and trans‐3,4‐Bis(acetyloxymethyl)cyclobut‐1‐enes and Synthesis of Block Copolymers

Abstract

Summary: The synthesis and living ring opening metathesis polymerization (ROMP) of diacetate functionalized cyclobutene derivatives cis‐3,4‐bis(acetyloxymethyl)cyclobutene (2) and trans‐3,4‐bis(acetyloxymethyl)cyclobutene (3) were investigated with the functional group tolerant initiators (PCy3)2(Cl)2RuCHPh (I) and (SIMes)(PCy3)(Cl)2RuCHPh (II) (SIMes: 1,3‐dimesityl‐4,5‐dihydroimidazol‐2‐ylidene). The kinetic parameters of the ROMP initiated by the ruthenium alkylidene complexes I and II were determined and correlated to monomer stereochemistry. The cis isomer 2 was found to be more reactive than the trans isomer 3 and to generate functional polymers of narrow molecular weight distribution especially with the classical “first generation Grubbs catalyst” I. Block copolymers containing 2 and cyclooctadiene (COD) or norbornene (NBE) were synthesized. Block copolymer poly(2‐b‐COD) was hydrolyzed and converted to a material with a block bearing hydrophilic alcohol functional groups and hydrophobic block.SEC elution profiles: poly(2) prepolymer and block copolymer poly(2‐b‐COD).magnified imageSEC elution profiles: poly(2) prepolymer and block copolymer poly(2‐b‐COD).

Scope of the Ring-Opening Metathesis Polymerization (ROMP) Reaction of 1-Substituted Cyclobutenes

“…The polymerization rates of substrates 2 are approximately 4 times slower than those of 1,2-unsubstituted, 3-substituted cyclobutenes,18 in which the olefinic bond is disubstituted and the substituents are one atom removed from the carbons that undergo metathesis.…”

Norbornene‐functionalized PEO‐b‐PCL: A versatile platform for mikto‐arm star, umbrella‐like, and comb‐like graft copolymers

“…The exo isomer was chosen since exo-diastereoisomers are much more reactive in ROMP than their endo-counterparts. [41][42][43][44] Moreover, compound 2 and subsequent macromonomers include the norbornenol anchor group that is known to be more reactive in ROMP compared to carboxylic and imide analogs. 45,46 2 was prepared by esterification of 1 with 5hexynoic acid in a 1/1 molar ratio using N,N 0 -dicyclohexylcarbodiimide (DCC)/4-(N,N-dimethylamino) pyridine (DMAP) as the catalytic system 47 at room temperature in 45% yield after column chromatography.…”

Ring opening metathesis polymerization of triazole‐bearing cyclobutenes: Diblock copolymer synthesis and evaluation of the effect of side group size on polymerization kinetics

“…Cyclobutene‐based monomers were synthesized by adapting procedures from the literature, as illustrated in Scheme . (detailed synthetic procedures and data are available in the experimental section and Supporting Information).…”

“…Examples include stimuli responsive materials, biologically active polymers, high strength materials, and ionically conducting membranes . This process is very well understood for norbornene and cyclooctene derivatives, but it has not been explored in depth for cyclobutene‐based molecules due to their relatively more complex synthesis and lower thermal stability …”

“…In the latter case, the fusion of the cyclobutene rings with N‐arylpyrrolidene moieties provided the necessary steric hindrance for a controlled ROMP. There have also been a few reports of ROMP using 1‐alkyl‐functionalized, 3‐alkyl‐functionalized, and 3,4–alkyl‐functionalized cyclobutenes with G1 or G3 catalysts. However, these reactions worked well only when either the substituents were small, bore a fused ring structure or if there was only one pendant group per ring.…”