Organocatalytic Copolymerization Of Sulfur Containing One-carbon Monomers With Epoxides

In this paper,two new organic catalysis systems for the copolymerization of two sulfur-containing one-carbon compounds（C1:carbonyl sulfide（COS）and carbon disulfide（CS₂））with epoxides are investigated.Inspired by the concept of Frustrated Lewis Pairs（FLPs）in organic chemistry,organic Lewis acid-base pair systems that can efficiently catalyze the copolymerization of sulfur-containing C1 monomers and epoxides are designed,achieving the high efficiency and‘active copolymerization’of COS and epoxides.By copolymerization,polymonothiocarbonates with well-defined structure have been obtained,and the organic catalytic systems are extended to the copolymerization of CS₂and epoxides so that various polythiocarbonates are obtained.Through in-depth study of the organic catalyzed copolymerization mechanism based on alkylboron,the stabilizing effect of alkylboron on chain-growth anions and the activation of epoxides are revealed,and a controllable copolymerization strategy of‘supermolecular anions’is proposed.By using the Oxygen-Sulfur Exchange Reaction（O-S ER）in the CS₂copolymerization process,a series of CS₂-based polythiocarbonate materials with novel structures have been successfully obtained by using organic catalyst systems and the O-S ER process.First,an organic Lewis pair with triethylboron（TEB）as the Lewis acid and guanamine,quaternary ammonium salt,or quaternary phosphonium salt as the Lewis base are designed to successfully catalyze the copolymerization of COS with various epoxides.A variety of polymonothiocarbonates with well-defined structures are synthesized without the uncontrollable chain links caused by the O-S ER.Meanwhile,metal residue has been totally avoided.Organic Lewis pairs could catalyze the selective copolymerization of COS and PO in the temperature range of 25-60℃.The copolymer selectivity,altnenating structure and regioselectivity are all above 99%,and the number average molecular weight of the product reaches 9.2 kg/mol with the molecular weight distribution of 1.2.These indicators are superior to metal catalysts.Second,in order to solve the problem of the low initiator efficiency of Lewis pairs,the‘Immortal’polymerization mode has been adopted.In the presence of single-or double-terminal hydroxyl polyethylene glycol as a macromolecular chain transfer agent,organic catalysized COS/epoxides copolymerization provides polymonothiocarbonate-b-polyether block copolymer in a‘one-pot’maner.The molecular weight of the product and its distribution are controllable.When the chain transfer agent（CTA）/Lewis pair ratio is in the range of 5/1-50/1,conversion of the CTA is more than 99%,and there is a good linear relationship between the number average molecular weight of the product and the feeding ratio.This result also provides a new method for synthesizing sulfur-containing block copolymers with controlled sequences.Third,a double-base Lewis pair consisting of a di-tertiary amine and triethyl boron has been designed.The structure is simple,but the catalytic effect on COS/epoxide copolymerization has been significantly improved.Typical systems,such as Lewis pair consisting of triethylboron and N,N,N’,N’-tetraethylethylenediamine,catalyzing the copolymerization of COS/PO,the TOF can up to 10⁴h^-1,and showing‘living’copolymerization characters.The biggest advantage of this system is that it can quickly catalyze the copolymerization reaction and produce fully alternating copolymers under the condition of insufficient COS.Therefore,by continuously adding COS,the‘on-off’chain extension reaction has been achieved.When the B/N ratio is greater than 1,and the amount of COS is insufficient,the polymonothiocarbonate-b-polyether block copolymer can be prepared in a‘one-pot’maner.In this theses,the synergistic catalysis efffect of double-base Lewis pairs has been proposed,which can accelerate the chain initiation rate of the polymerization reaction and makes the copolymerization reaction a‘fast initiation and fast growth（R_i>R_p）’mode.The successful construction of double-base Lewis pairs provides a new idea for the construction of organic acid-base pairs.Fourth,organo-catalytic CS₂/ethylene oxide copolymerization has been studied in depth.The effect of organic Lewis pairs on the composition and structure of the copolymerization result is investigated.By regulating the O-S ER process,polythiocarbonate with crystalline segments has been obtained.By changing the catalyst and reaction conditions,two types of copolymers with melting points of117℃-138℃and 220℃-245℃are obtained correspondingly.The former mainly consists of polymonothiocarbonate linkages[-OC（=O）S-],while the latter has mainly polytrithiocarbonate linkages[-SC（=S）S-].The study find that CS₂/EO copolymer can be rapidly degraded in 30%H₂O₂solution.Within 24 h at room temperature,the weight average molecular weight of the copolymer decreases from30.5 kg/mol to 1.8 kg/mol.Organic Lewis pairs are also used to regulate the O-S ER process in the copolymerization of CS₂and phenyl glycidyl ether to prepare a structure-controllable polythiocarbonate.Sulfur-containing polymers containing only monothiocarbonate[-OC（=S）O-]and trithiocarbonate[-SC（=S）S-]linkages can be obtained,these copolymers have high refractive index of 1.73-1.79,making them possible to be used as a high-performance optical material.In summary,this paper successfully designes organic Lewis pairs with different structures and catalytic properties,which is effective for the copolymerization of two sulfur-containing C1 monomers（COS,CS₂）with epoxides.The fully atternating copolymerization of COS/epoxides can be conducted in a‘living’mode with high activity.Oxygen-Sulfur Exchange Reaction（O-S ER）in the CS₂/epoxide copolymerization has been utilized to synthesize polythiocarbonates with controllable structure.These results bring new opportunities in the study of catalytic polymerization of sulfur-containing C1 monomers.