共查询到19条相似文献,搜索用时 171 毫秒
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聚乙醇酸(PGA)通常可通过乙交酯开环聚合和乙醇酸熔融缩聚制得,但乙交酯开环聚合工艺复杂,导致PGA成本高。相较而言,乙醇酸熔融缩聚制备PGA工艺简单,成本较低,但难以获得中高分子量的PGA。因此,本文基于熔融/固相缩聚路线,系统研究了催化剂种类与含量、酯化温度、固相缩聚温度等聚合工艺条件对PGA外观形态、特性黏度和热稳定性的影响。发现三氟甲烷磺酸铋对乙醇酸熔融缩聚具有较好的催化效果,优化熔融/固相缩聚条件如下:催化剂含量为0.20%(质量),酯化温度为180℃,熔融缩聚和固相缩聚温度为210℃,固相缩聚时间为12 h。在该熔融缩聚条件下,PGA的最高特性黏度为0.36 dl/g,进一步固相缩聚处理可以将PGA的特性黏度提高到0.59 dl/g。 相似文献
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以强酸性离子交换树脂为催化剂,进行了乙醇酸酯化制备乙醇酸甲酯的试验研究,考察反应温度、醇酸物质的量比、催化剂用量及是否搅拌等因素对乙醇酸转化率与反应速率的影响。结果表明,在反应温度100℃、醇酸物质的量比8∶1、催化剂用量为乙醇酸质量的5%和搅拌的条件下,乙醇酸转化率达93%以上。 相似文献
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以乙醇酸甲酯为原料,先通过熔融缩聚法得到低聚物,然后进行固相缩聚法制备出高分子量的聚乙醇酸甲酯(PMG)。考察了工艺过程中催化剂的种类和用量、反应温度以及反应时间对PMG分子量的影响。并通过正交试验得到较优的合成条件为:催化剂二水合氯化亚锡的质量分数为0.5%,压力70 Pa,反应温度180 ℃,反应时间100 h,合成的PMG的特性黏度可达0.802 dL/g。采用傅里叶红外光谱(FT-IR)表征了PMG基团的特征吸收峰,差示扫描量热仪(DSC)表征了PMG的玻璃化温度、结晶温度和熔点。 相似文献
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采用过硫酸铵、四甲基已二胺为催化剂,以丙烯酰胺为原料,通过冷冻聚合法合成聚丙烯酰胺,并正交实验探索最佳合成条件(催化剂用量、反应时间、反应温度等)对聚丙烯酰胺黏度的影响,结果表明:丙烯酰胺为2.65mol,催化剂用量为0.0075mol,反应时间为12h,反应温度为零下10度时聚丙烯酰胺的黏度为最大。产物的化学结构由FTIR进行表征。 相似文献
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[方法]利用中孔分子筛Al-MCM-41作催化剂,直接用反应物乙醇作带水剂,以乙醇和异戊烯酸为原料,采用分批补充乙醇的工艺方法合成农药异戊烯酸乙酯。考察了催化剂用量、反应物物质的量比、反应温度和反应时间对反应转化率和选择性的影响。[结果]该反应最佳的合成条件:异戊烯酸和乙醇的物质的量比为1∶8,催化剂的量为异戊烯酸质量的1.8%,反应时间为6 h,反应在剧烈回流温度下进行。在此条件下,异戊烯酸转化率可达89.9%,产品纯度大于99.7%。[结论]中孔分子筛Al-MCM-41可作为合成异戊烯酸乙酯高效而环保的固体酸催化剂。 相似文献
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硫酸氢钠催化甲醛与甲酸甲酯的偶联反应 总被引:1,自引:0,他引:1
在釜式反应器中研究了硫酸氢钠催化甲醛和甲酸甲酯的偶联反应,考察了反应温度、原料配比、催化剂用量、反应时间等因素对乙醇酸甲酯和甲氧基乙酸甲酯收率的影响,得到最佳反应条件为:反应温度160℃、反应物料配比n(甲醛):n(甲酸甲酯)=0.65、催化剂的用量为总反应物料质量的20.0%、反应时间4h,在此条件下,乙醇酸甲酯和甲氧基乙酸甲酯的收率最大,总收率达到42.15%。催化剂浓度和反应温度对活化甲醛分子,确保有效地进行羰基化反应,提高反应活性起重要作用。硫酸氢钠难溶于反应体系,后处理简单,副反应少,可重复使用,较其它相关催化剂具有突出的性能。 相似文献
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乙二醇选择性氧化制备乙醇酸催化剂体系的研究 总被引:2,自引:1,他引:2
制备了用于选择性氧化乙二醇制备乙醇酸的Pt—Bi/Al2O3、Pd—Bi/Al2O3催化剂;考察了负载金属催化剂的含量、氧气压力及反应温度等条件对目标反应产物催化性能的影响。试验结果表明,Pt—Bi/Al2O3催化剂比Pd—Bi/Al2O3具有更佳的催化性能,于343K及300kPa氧气分压等条件下,在含Pt2.0%的Pt—Bi/Al2O3催化剂体系中,乙醇酸的收率可达到93.60%。确定了最佳的乙二醇氧化制备乙醇酸的绿色氧化工艺条件。 相似文献
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《国际聚合物材料杂志》2012,61(8):587-595
The in-vitro degradation behavior of poly(glycolic acid) (PGA) rods and the composite rods containing poly(L-lactic acid) (PLLA) were investigated via mass loss, pH value change, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Since the degradation rate of PLLA is lower than that of PGA, PLLA/PGA composite rods exhibit a slower degradation rate in comparison with PGA. This finding indicated that it was possible to control the degradation rate of the composites by changing their composition. This result indicates that this kind of composite biomaterial may be applicable to devices for the need of prolonged degradation. 相似文献
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In this study, the thermogravimetric analysis (TGA) technique has been applied to determine the extent of in situ polymerization achievable in solid wood on treating with bio-polyester oligomers. Low-molecular-weight oligomers of poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(butylene succinate) (PBS), and poly(butylene adipate) (PBA) were impregnated and then thermally polymerized within solid wood to enhance the physical properties of wood. TGA revealed a similar degree of oligomer polymerization was achieved either with pure oligomers or within the wood structure. The influence of relatively acidic treatments, such as low-molecular-weight PGA oligomers, was observed to lead to degradation of the hemicellulose wood component. Polymerization of PLA and PGA oligomer treatments which penetrate the wood cell wall gave relatively lower wood thermal stability. Treatment and polymerization of lumen filling PBS and PBA oligomers contributed to increased wood thermal stability. 相似文献
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As a completely degradable material, poly(glycolic acid) (PGA) has excellent rigidity, barrier properties, degradability and biocompatibility. However, the inherent brittleness and easily hydrolysable characteristics limit its widespread application. Herein, we introduced chain extension ADR to modify PGA to ameliorate these defects. The results showed that ADR could react with PGA to form “comb-like” and “cross-linked” chain extension structures resulting in the improvement of complex viscosity and formation of gel. Because of the chain entanglement of chain extension structures, the toughness of modified PGA was improved (which was verified by the impact strength value of 4.3 kJ/m2 that was about 126% of virgin PGA) without sacrificing its rigidity. Furthermore, the hydrolysis results indicated that the representative PGA/1.0ADR had better hydrolysis stability, it had more complete morphology and slower degradation rate than virgin PGA in the 17-day hydrolysis experiment. Apart from better toughness and hydrolysis stability, there was also improvements in crystallization performance, the sample PGA/1.0ADR endowed with higher crystallization peak temperature (2.3°C higher than virgin PGA) and lower crystallization activation energy. In short, this work prepared a kind of modified PGA with rigidity toughness balance and better hydrolysis stability, which could expand the application range of PGA-based materials. 相似文献
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