超临界CO_2中陷落自由基引发聚合物整体接枝
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摘要
聚烯烃膜的整体接枝改性是优化其性能并增加附加值的重要途径之一。常用的方法是在溶液中或者熔融状态下均相接枝,但是对于那些既不溶解亦不熔融的聚合物,非均相接枝法将是最佳的选择。
本论文中我们着重研究了超临界CO2中聚合物无氧预辐射接枝法,该方法结合了γ射线预辐射接枝聚合和超临界CO2溶胀聚合两种方法的优势,能够在较低温度下对聚合物进行整体化学接枝改性。在氮气保护下,聚合物薄膜经辐射后将在其骨架上生成均匀稳定的大分子陷落自由基；然后在辐射场外于超临界C02中引发单体进行接枝聚合反应。由于超临界CO2既能溶解单体,又能溶胀聚合物,所以能够协助单体渗透进入聚合物的内部进行接枝聚合反应,从而达到整体接枝改性的目的。整个过程是在不锈钢高压釜中进行,通过调节反应时间、温度和辐射剂量等实验参数可以有效控制接枝程度。
在超临界CO2中聚合物无氧预辐射接枝的基础上,我们以苯乙烯为单体对聚丙烯进行整体接枝改性,接枝过程既无均聚物的产生,又没有单体、引发剂等残留。此外进一步探讨了辐射剂量、反应时间、压力、温度和单体浓度对接枝率的影响。元素分析、红外光谱、电镜表征证明聚苯乙烯是通过共价键以纳米尺度均匀地接枝到整个聚丙烯薄膜中。DSC和XRD分析显示接枝反应主要发生在聚丙烯的无定形区,并且接枝的聚苯乙烯链是非结晶性聚合物。
最后,我们充分利用在超临界CO2中能够实现苯乙烯和马来酸酐交替共聚以及Y射线对聚合物具有较强穿透能力的优势,实现了苯乙烯和马来酸酐对聚烯烃膜的交替共聚接枝。结果显示苯乙烯/马来酸酐双组分单体能够协同促进整体接枝过程。研究表明,苯乙烯和马来酸酐发生聚合前,能够形成电荷转移络合物,进而导致二者发生交替共聚。因此,当进料摩尔比1：1时,马来酸酐和苯乙烯具有强烈的交替共聚倾向,从而在相同条件下使接枝率达到最高值。采用DSC和元素分析验证了交替共聚接枝的结果。
Chemical modification of pre-existing polymer materials by functional monomers has always been an object of great interest as it offers an effective route to address some low cost commodity shaped-materials to higher added value applications. In traditional solution method, organic solvent is used to swell or dissolve the polymer matrix, and then the dissolved initiators initiate polymerization of monomers in polymer matrix. The high viscosity leads to the solvent, un-reacted monomers and initiators not be completely removed after the reaction. An alternative method is modification of polymers in the melt, but strong shear fields may be needed to conquer high viscosity polymers in extruders. In this research work, a novel process for graft copolymerization is studied by combining gamma (y)-rays pre-irradiation-induced graft copolymerization with supercritical carbon dioxide swelling polymerization techniques. Firstly, the trapped radicals on the polyolefin backbones would be uniformly distributed by y-rays radiation under nitrogen atmosphere. Subsequently, the produced polymer trapped-radicals were utilized to initiate graft-polymerization of vinyl monomers dissolved in scCO2 within polymer substrates. Finally, the un-reacted monomers trapped in polymer matrix were further removed via scCO2 extraction. The process offers many unique advantages over conventional methods for grafting reactions. Also, supercritical carbon dioxide serves dual purpose, being a solvent for monomers as well as the swelling agent for the polymer.
The bulk grafting modification of styrene onto polypropylene is the focus of the first project. Supercritical carbon dioxide is utilized as both solvent and swelling agent to promote this heterogeneous reaction and lead to successful grafting. The grafting composition is controlled by controlling reaction parameters. After polymerization reaction, the un-reacted monomers are further extracted via supercritical CO2 without any residues. Of importance, it is beneficial to diffuse the vinyl monomers to the internal layers of pre-existing polymer materials with the aid of supercritical CO2, which does not interfere with the chain-growth process during polymerization. Thereby, grafting component can be easily accomplished throughout the polymer matrix without homopolymer. Characterization of the composites shows polystyrene is covalently bonded to polymeric backbone in nanometer scale and the graft chains are uniformly dispersed throughout the thickness of polymer membranes. The crystalline domains of the polypropylene are unaffected. Styrene infuses into polypropylene and polymerizes within only the amorphous domains of polypropylene.
In the final project, our strategy takes advantage of the fact that well-defined alternating poly(styrene-alt-maleic anhydride) can be synthesized in supercritical CO2 and y-ray has high penetration depth to various polymers so that the pure graft copolymers with alternating trend can be obtained. The results indicate that styrene/maleic anhydride binary monomers synergistically promote the bulk grafting process. The maximum of grafting yield can be always attained at 1:1 molar feed ratio of maleic anhydride to styrene, indicating that the grafting process is attributed to the formation of charge transfer complex (CTC) between the binary monomers. DSC and element analysis support the conclusion that an alternative graft copolymer may be achieved.
本论文中我们着重研究了超临界CO2中聚合物无氧预辐射接枝法,该方法结合了γ射线预辐射接枝聚合和超临界CO2溶胀聚合两种方法的优势,能够在较低温度下对聚合物进行整体化学接枝改性。在氮气保护下,聚合物薄膜经辐射后将在其骨架上生成均匀稳定的大分子陷落自由基；然后在辐射场外于超临界C02中引发单体进行接枝聚合反应。由于超临界CO2既能溶解单体,又能溶胀聚合物,所以能够协助单体渗透进入聚合物的内部进行接枝聚合反应,从而达到整体接枝改性的目的。整个过程是在不锈钢高压釜中进行,通过调节反应时间、温度和辐射剂量等实验参数可以有效控制接枝程度。
在超临界CO2中聚合物无氧预辐射接枝的基础上,我们以苯乙烯为单体对聚丙烯进行整体接枝改性,接枝过程既无均聚物的产生,又没有单体、引发剂等残留。此外进一步探讨了辐射剂量、反应时间、压力、温度和单体浓度对接枝率的影响。元素分析、红外光谱、电镜表征证明聚苯乙烯是通过共价键以纳米尺度均匀地接枝到整个聚丙烯薄膜中。DSC和XRD分析显示接枝反应主要发生在聚丙烯的无定形区,并且接枝的聚苯乙烯链是非结晶性聚合物。
最后,我们充分利用在超临界CO2中能够实现苯乙烯和马来酸酐交替共聚以及Y射线对聚合物具有较强穿透能力的优势,实现了苯乙烯和马来酸酐对聚烯烃膜的交替共聚接枝。结果显示苯乙烯/马来酸酐双组分单体能够协同促进整体接枝过程。研究表明,苯乙烯和马来酸酐发生聚合前,能够形成电荷转移络合物,进而导致二者发生交替共聚。因此,当进料摩尔比1：1时,马来酸酐和苯乙烯具有强烈的交替共聚倾向,从而在相同条件下使接枝率达到最高值。采用DSC和元素分析验证了交替共聚接枝的结果。
Chemical modification of pre-existing polymer materials by functional monomers has always been an object of great interest as it offers an effective route to address some low cost commodity shaped-materials to higher added value applications. In traditional solution method, organic solvent is used to swell or dissolve the polymer matrix, and then the dissolved initiators initiate polymerization of monomers in polymer matrix. The high viscosity leads to the solvent, un-reacted monomers and initiators not be completely removed after the reaction. An alternative method is modification of polymers in the melt, but strong shear fields may be needed to conquer high viscosity polymers in extruders. In this research work, a novel process for graft copolymerization is studied by combining gamma (y)-rays pre-irradiation-induced graft copolymerization with supercritical carbon dioxide swelling polymerization techniques. Firstly, the trapped radicals on the polyolefin backbones would be uniformly distributed by y-rays radiation under nitrogen atmosphere. Subsequently, the produced polymer trapped-radicals were utilized to initiate graft-polymerization of vinyl monomers dissolved in scCO2 within polymer substrates. Finally, the un-reacted monomers trapped in polymer matrix were further removed via scCO2 extraction. The process offers many unique advantages over conventional methods for grafting reactions. Also, supercritical carbon dioxide serves dual purpose, being a solvent for monomers as well as the swelling agent for the polymer.
The bulk grafting modification of styrene onto polypropylene is the focus of the first project. Supercritical carbon dioxide is utilized as both solvent and swelling agent to promote this heterogeneous reaction and lead to successful grafting. The grafting composition is controlled by controlling reaction parameters. After polymerization reaction, the un-reacted monomers are further extracted via supercritical CO2 without any residues. Of importance, it is beneficial to diffuse the vinyl monomers to the internal layers of pre-existing polymer materials with the aid of supercritical CO2, which does not interfere with the chain-growth process during polymerization. Thereby, grafting component can be easily accomplished throughout the polymer matrix without homopolymer. Characterization of the composites shows polystyrene is covalently bonded to polymeric backbone in nanometer scale and the graft chains are uniformly dispersed throughout the thickness of polymer membranes. The crystalline domains of the polypropylene are unaffected. Styrene infuses into polypropylene and polymerizes within only the amorphous domains of polypropylene.
In the final project, our strategy takes advantage of the fact that well-defined alternating poly(styrene-alt-maleic anhydride) can be synthesized in supercritical CO2 and y-ray has high penetration depth to various polymers so that the pure graft copolymers with alternating trend can be obtained. The results indicate that styrene/maleic anhydride binary monomers synergistically promote the bulk grafting process. The maximum of grafting yield can be always attained at 1:1 molar feed ratio of maleic anhydride to styrene, indicating that the grafting process is attributed to the formation of charge transfer complex (CTC) between the binary monomers. DSC and element analysis support the conclusion that an alternative graft copolymer may be achieved.
引文
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[3]MCHUGH M A, KRUKONIS V J. Supercritical fluid extraction. Boston: Butterworth-Heinemann,1994[C].
[4]YILGOR I, MCGRATH J E, KRUKONIS V J. Novel supercritical techniques for polymer fractionation and purification.2. Fractionation and characterization of functional siloxane oligomers [J]. Polym. Bull.,1984,12:499-506.
[5]GUAN Z, COMBS J R, MENCELOGLU Y Z, DESIMONE J M. Homogeneous free radical polymerizations in supercritical carbon dioxide.2. Thermal decomposition of 2,2'-Azobis(isobutyronitrile) [J]. Macromolecules,1993,26:2663-2669.
[6]HOEFLING T A, NEWMAN D A, ENICK R M, BECKMAN E J. Effect of structure on the cloud-point curves of silicone-based amphiphiles in supercritical carbon dioxide [J]. J. Supercrit. Fluids,1993,6:165-171.
[7]COOPER A I. Synthesis and processing of polymers using supercritical carbon dioxide [J]. J. Mater. Chem.,2000,10:207-234.
[8]TOMASKO D L, Li H, LIU D, HAN X, WINGERT M J, LEE L J, et al. A review of CO2 applications in the processing of polymers [J]. Ind. Eng. Chem. Res.,2003,42:6431-6456.
[9]ALSOY S, DUDA J L. Processing of polymers with supercritical fluids [J]. Chem. Eng. Technol.,1999,22:971-973.
[10]KENDALL J L, CANELAS D A, YOUNG J L, DESIMONE J M. Polymerizations in supercritical carbon dioxide [J]. Chem. Rev.,1999,99:543-564.
[11]ADAMSKY F A, BECKMAN E J. Inverse emulsion polymerization of acrylamide in supercritical carbon dioxide [J]. Macromolecules,1994,27:312-314.
[12]廖传华,柴本银.超临界流体与新材料制备[M].北京：中国石化出版社,2007.
[13]韩布兴.超临界流体科学与技术[M].北京：中国石化出版社,2005.
[14]DESIMONE J M, MAURY E E, MENCELOGLU Y Z, MCCLAIN J B, ROMACK T R, COMBES J R. Dispersion polymerizations in supercritical carbon dioxide [J]. Science,1994,265: 356-359.
[15]ROMACK T J, MAURY E E, DESIMONE J M. Precipitation polymerization of acrylic Acid in supercritical carbon dioxide [J]. Macromolecules,1995,28:912-915.
[16]LEPILLEUR C, BECKMAN E J. Dispersion polymerization of methyl methacrylate in supercritical CO2[J]. Macromolecules,1997,30:745-750.
[17]BUNGERT B, SADOWSKI G, ARLT W. Separations and material processing in solutions with dense gases [J]. Ind. Eng. Chem. Res.,1998,37:3208-3220.
[18]HEBB A K, SENOO K, BHAT R, COOPER A I. Structural control in porous cross-linked poly(methacrylate) monoliths using supercritical carbon dioxide as a "pressure-adjustable" porogenic solvent [J]. Chem. Mater.,2003,15:2061-2069.
[19]DUXBURY C J, WANG W, DEGEUS M, HEISE A, HOWDLE S M. Can block copolymers be synthesized by a single-step chemoenzymatic route in supercritical carbon dioxide? [J]. J. Am. Chem. Soc.,2005,127:2384-2385.
[20]BERENS A R, HUVARD G S, KORSMEYER R W. Goodrich Co B F:US,4820752[P/OL].
[21]WATKINS J J, MCCARTHY T J. Polymerization in supercritical fluid-swollen polymers: A new route to polymer blends [J]. Macromolecules,1994,27:4845-4847.
[22]KUNG E, LESSER A J, MCCARTHY T J. Composites prepared by the anionic polymerization of ethyl 2-cyanoacrylate within supercritical carbon dioxide-swollen poly(tetrafluoroethylene-co-hexafluoro propylene) [J]. Macromolecules,2000,33: 8192-8199.
[23]KUNG E. Bulk and surface polymer composites prepared in supercritical carbon dioxide [D]. Amherst:Univ. of Massachusetts,1999.
[24]RAJAGOPALAN P, MCCARTHY T J. Two-step surface modification of chemically resistant polymers:Blend formation and subsequent chemistry [J]. Macromolecules,1998,31: 4791-4797.
[25]TSUJII Y, OHNO K, YAMAMOTO S, GOTO A, FUKUDA T. Structure and properties of high-density polymer brushes prepared by surface-initiated living radical polymerization [J]. Adv. Polym. Sci.,2006,197:1-45.
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