Synthesis and cationic ring-opening polymerization of mono- and bifunctional spiro orthoesters containing ester groups and depolymerization of the obtained polymers: An approach to chemical recycling for polyesters as a model system

A spiro orthoester having an ester moiety, 2-acetoxymethyl-1,4,6-trioxaspiro[4.6]undecane (4) was synthesized, and its cationic polymerization and depolymerization of the obtained polymer (5) were carried out. The monomer 4 underwent cationic polymerization with a cationic catalyst to afford the corresponding poly(cyclic orthoester) 5. The obtained polymer 5 could be depolymerized with a cationic catalyst to regenerate the monomer 4 in an excellent yield. Further, bifunctional spiro orthoesters (6, 8, 9) having diester moieties were synthesized from terephthalic acid, succinic acid, and 1,4-cyclohexanedicarboxylic acid, and their acid-catalyzed reversible crosslinking–decrosslinking was examined. The bifunctional monomer 6 derived from terephthalic acid underwent cationic crosslinking to afford the corresponding network polymer (7), which could be also depolymerized to regenerate the original bifunctional monomer 6. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2551–2558, 1999     

Deoxycelluloses and related structures

The syntheses of various deoxycelluloses and related structures (cellulosenes and anhydrocelluloses) from the mid‐1920s to the present are critically reviewed. General synthetic strategies to prepare deoxycelluloses include nucleophilic displacement of good leaving groups. Distinctions are made between reaction of cellulosics under homogeneous and heterogeneous conditions. Recent advances in the preparation of halodeoxycelluloses have led to high degree of substitution fluorodeoxycelluloses and bromodeoxycelluloses. Applications for the deoxycelluloses are numerous and characterized by biological, chemical or physical end uses.     

First observation of equilibrium polymerization of cyclic sulfite

Cationic polymerization of a seven-membered cyclic sulfite ( 7CS ) was carried out with methyl trifluoromethanesulfonate as a catalyst in chlorobenzene. The final conversions of 7CS were 22, 41, 52, and 60% in the polymerizations at 25°C with the initial monomer concentrations of 3, 4, 5, and 6M, respectively. The calculated monomer concentration at equilibrium was evaluated as 2.4M in any case. The conversion of 7CS decreased as the polymerization temperature rose. These results support the fact that this polymerization is an equilibrium one. ΔH⁰ and ΔS⁰ in the polymerization were evaliuated as −0.765 kcal/mol and −4.18 cal/mol by Dainton's equation, respectively. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3235–3240, 1997     

Mechanisms of thermal degradation of polystyrene,polymethacrylonitrile, and their copolymers on flash pyrolysis

The mechanism of thermal degradation of homopolymers of styrene (St) and methacrylonitrile (MAN) and their copolymers was investigated theoretically and experimentally by the pyrolysis gas chromatography using a Curie-point pyrolyzer. Poly(St-co-MAN)s generate dimers and trimers as well as monomers by flash pyrolysis. Parameter α was proposed to account for the competition between the back-biting reaction and depolymerization. The back-biting parameter α is defined as the ratio of rate constants, α = k_bb/k_dp, where k_bb is the rate constant for the back-biting reaction and k_dp is that for depolymerization. The back-biting process is followed by β-scission, where dimer and trimer are generated, and directly correlated with the C—H bond dissociation energies in the polymer chain. Using the back-biting parameter α, where 1/α is equal to the zip length n in depolymerization, the boundary effect for the difference of monomer yields from the homopolymers of St and MAN and their copolymers is well explained. The calculated values of boundary effect parameters, β_St and β_MAN, agreed well with the experimental results. It was found that thermal degradation mechanisms of homo- and copolymers of vinyl compounds can be analyzed comprehensively using the back-biting parameter α and the boundary effect parameter β. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2315–2330, 1998     

Process Engineering for Production of Chiral Hydroxycarboxylic Acids from Bacterial Polyhydroxyalkanoates

An efficient process for the production of (R)‐hydroxycarboxylic acids (RHAs) from polyhydroxyalkanoates (PHAs) was developed. It involved the synthesis of PHA in bacteria, followed by bringing the culture broth directly to a pH optimal for in vivo PHA degradation, thus avoiding cell collection by centrifugation and pellet resuspension. The optimal pH was maintained to allow maximal release of RHAs. Using this process, cells having a dry weight (w) of 1.8 g · L⁻¹ and 45% (w/w) PHA exhibited a linear PHA degradation rate of about 0.059 g · L⁻¹ · h⁻¹ in the first 9 h. Concomitantly, RHAs were released with a rate of 0.057 g · L⁻¹ · h⁻¹. Further incubation of up to 15 h resulted in almost 90% (w/w) degradation of PHA. Based on this approach in combination with chemostat and a plug flow reactor a continuous process for the production of RHAs could be achieved.

     

A Novel Construction of Ring-Opening Polymerization and Chemical Recycling System

This article summarizes our recent efforts to chemical recycling of polymeric materials based on the equilibrium polymerization character of cyclic monomers. Spiro orthoesters ( SOE s), bicyclo orthoester, cyclic carbonates, and dithiocarbonates undergo ring-opening polymerization to afford the corresponding polymers, and the resulting polymers depolymerize to give the starting monomers under cationic or anionic conditions. Further, crosslinking and decrosslinking systems of bifunctional SOE s and a polymer having SOE moiety in the side chain are described.     

过氧化氢氧化降解壳聚糖的可控性研究

壳聚糖能被过氧化氢氧化降解得到低分子量壳聚糖,所得产物分子量分布随平均分子量的下降而逐渐变窄.其降解速度和产物特性受原料脱乙酰度、反应介质、H2O用量、温度和反应时间的影响.脱乙酰度越高的壳聚糖,降解反应越容易进行.在酸性介质中的降解,其起始速度比在水中的降解要快,所得产物的分散度要小,到一定程度后受到H+抑制.实验结果表明,制备分子量5万以上的壳聚糖产品在60～70℃、H2O2用量比小于0.25的中性体系中就可以完成;而制备分子量在1.5～5万之间的壳聚糖,采用反应温度70℃、H2O2用量比为0.5～1.5、介质为水的条件较适宜;盐酸体系有利于制备分子量7000左右的壳聚糖;要得到水溶性产物,可以使用2%醋酸或水两种介质.因此,通过选择反应条件,可制备特定分子量范围的壳聚糖.     

1,4丁二醇蒸馏底物的回收工艺

在Reppe法生产1,4丁二醇(BDO)的过程中,刮膜式蒸发器会产生一定量的黏稠蒸馏底物。提出了在加压条件下,以稀硫酸为催化剂,对该底物进行水解处理回收BDO并减少废物排放的工艺过程。最优工艺条件为：硫酸质量分数为15%,稀硫酸与底物质量比（配料比）为1.3〖DK〗∶1.0,反应温度为150　℃,反应时间为7 h。通过对水解产物的分离与分析,基于底物的BDO回收率可达39.1%。