Design,Synthesis And Characterization Of High T_g Transparent Copolyesters

Due to its lightweight,beautiful appearance and unique optical properties,polymer transparent materials are widely used in water cups,food packaging,optical parts,furniture decoration and other fields,bringing a lot of convenience to people’s life.Polyethylene terephthalate(PET),as a kind of bulk polyester material,has attracted wide attention because its low price and excellent properties.But unfortunately,PET is a semi-crystalline polymer,so it is very easy to produce crystallization in its forming process,which affects the transmittance of the finished product.More importantly,although the glass transition temperature(T_g)of PET is already higher than most polyester materials,it is still difficult to meet the needs of daily life in medium and high temperature scenarios.Therefore,in this thesis,based on the structure of PET,two monomers of Bio-base 2,3-butanediol(2,3-BDO)and 1,4-cyclohexadiol(1,4-CHD)were introduced to design and synthesize a high T_g transparent polyester material with low-cost.It was expected to be used in fields such as optical devices.The main work of the thesis is as follows:In the first part of this thesis,on the basis of the molecular structure of PET,Bio-based 2,3-BDO was introduced for modification.2,3-BDO is a cheap Bio-based monomer with two asymmetric lateral methyl groups,which can effectively destroy the crystalline structure of PET.It can bring strong rigidity to the chain segment and has a significant effect on improving polyester T_g.Therefore,ternary transparent copolyesters,which were named poly(terephthalic acid/ethylene glycol/2,3-butanediol)ester(P23BET),were prepared by one-pot melting process by using it to partially replace ethylene glycol(EG).In order to solve the difficult polymerization problem caused by low reactivity of monomer,the influence of reaction device,catalyst and temperature on polymerization reaction was explored.The optimal polymerization reaction process was finally determined,and its Molecular Weight could reach up to 22,500 g/mol.The effects of 2,3-BDO ratio on the properties of materials were investigated by various testing methods.When the2,3-BDO feed ratio exceeds 50%,P23BET is an amorphous transparent material with T_g above 90℃,but its transmittance and impact strength decrease with the increase of 2,3-BDO.When the 2,3-BDO feed ratio is lower than 50%,the copolyester will crystallize.Therefore,P23BET-50%with the best comprehensive performance was selected to further improve its properties.In the second part of this thesis,on the basis of P23BET-50%,rigid 1,4-CHD monomer was introduced to partially replace EG to prepare the quaternary copolyesters which were named poly(terephthalate/ethylene glycol/2,3-butanediol/1,4-cyclohexadiol)ester(P23BECT)under the condition of constant molar ratio of 2,3-BDO.The introduction of 1,4-CHD into the copolyesters structure further inhibited the crystallization capacity,improved its T_g,and solved the problem of molecular weight reduction and yellowing caused by excessive introduction of 2,3-BDO.The successful introduction of 1,4-CHD monomer was characterized by ~1H-NMR and FT-IR,and the effects of different1,4-CHD feed ratios on the structure and properties of copolyesters were investigated by thermal,optical and mechanical tests.P23BECT is an amorphous transparent polyester,whose T_g is greatly improved without sacrificing molecular weight,and its transmittance is also increased from 88%to 92%.P23BECT has excellent performance and low cost,which is expected to be applied in optical devices and other fields.