Headspace Gas Chromatography Applied To Emulsion Polymerization And Cellulose Modification Researches

To meet the needs of production and daily life, researchers are committed to developingenvironmentally friendly functional polymer and multifunctional biological materials withgood compatibility and natural degradation by grafting the function polymer chain on thecellulose. Two of the most effective routes to the successful synthesis of the functionalmaterials are based on emulsion polymerization and cellulose derivative reaction. For thesereactions, the conversion of monomer and the substitution degree (DS) of cellulose esters arecritical parameters to evaluate the reaction degree and product quality, rapid and accuratequantitative analysis is one of the key problems of the study. However, most of chemicalanalysis methods are not only complicated and time-consuming, but also with poor measuringaccuracy and reliability. The aims of this thesis, thus, were to be: a) firstly establishes rapidand accurate methods for determining the conversion of monomer in the reactions of unaryemulsion polymerization and binary emulsion polymerization, respectively, the conversion ofvinyl monomer and the degree of substitution of cellulose esters during cellulose graftreaction; b) preliminary discuss the influence of factors on the conversion of monomer andthe substitution degree.First, the study has been focused on the emulsion homopolymerization of methylmethacrylate (MMA). Because the viscosity of the reaction mixture was changed during thewhole emulsion polymerization process, the sampling based on volume would result insignificant error to the final results. In this chapter, the sample was withdrawn by the pipette,and then was accurately weighted. The weighted sample was diluted with deionized water forfurther analysis. This method precision was remarkably improved and was successfullyapplied to determining the conversion of MMA during the emulsion polymerization process.The results showed that the RSD of the present method is less than2%. The improved methodwas not only adapted to study the mechanism of emulsion polymerization at the early stage(the conversion <17%), but also used to determine a series of changes at a high monomerconversion (>90%). The effect of reaction parameters, such as the initiator dosage, thereaction temperature, on emulsion polymerization was studied in this work.Second, the main factor affects the monomer dissolve in water and the wall deposition of residual monomer droplets was also conducted in this work. We report an improvedheadspace gas chromatographic (HS-GC) technique for the determination of differentmonomers in polymer latex. The method is based on a HS-GC technique reported previously[Chai, Hou, and Schork, Journal of Applied Polymer Science, Vol.99,392–397(2006)] butincludes a major modification in the method of sample preparation. By using a weight-basedsampling method, coupled with initial dissolve in dimethyl sulfoxide (2ml), followed bywater dilution, the uncertainty in the sample preparation associated with previous method canbe significantly reduced (from20to5%). An equation for calculating the monomerconversion, based on the mass of the sample and GC peak area measured by HS-GC, wasderived. The method was applied to the emulsion copolymerization of MMA and vinylacetate (VAc) the course of which was followed by determination of the monomers remainingin the mixture. The effect of reaction parameters, such as the initiator dosage, the reactiontemperature, the mole ratio MMA to VAc, the total amount of monomers, on emulsioncopolymerization was also studied in this work.Generally, the optimization of reaction conditions in emulsion polymerization requireslots of experiments. On-line monitoring methods can rapidly obtain important parameters forthe study of the polymerization process, saving lots of time and reagents. However, thecurrently used on-line monitoring method, such as FT-IR, NMR method, vulnerable to theeffects sample properties during the emulsion polymerization process, causing greatlyuncertain of the final measurement results. We describe a novel multiple-headspaceextraction/gas chromatographic (MHE-GC) technique for monitoring monomer conversionduring a polymerization reaction in a water-based emulsion environment. The polymerizationreaction of MMA in an aqueous emulsion is used as an example. The reaction was performedin a closed headspace sample vial (22ml, as a mini-reactor), with pentane (1mg/L) as a tracer.In-situ monitoring of the vapor concentration of the tracer, employing a multiple headspaceextraction (sampling) scheme, coupled to a GC, makes it possible to quantitatively follow theconversion of MMA during the early stages of polymerization. Data on the integrated amountof the tracer vapor released from the monomer droplet phase during the polymerization isdescribed by a mathematic equation from which the monomer conversion can be calculated.The present method is simple, automated and economical, and provides an efficient tool in the investigation of the reaction kinetics and effects of the reaction conditions on the early stageof polymerization.What is more, a full evaporation headspace gas chromatographic method was establishedfor rapid determination of monomeric methyl methacrylate (MMA) in the cellulose graftpoly-methyl methacrylate (PMMA) via an atom transfer radical polymerization process. Thedata show that a near-complete mass transfer of MMA of the very small liquid sample (<30mg) to the vapor phase (headspace) was achieved within5min at a temperature of105oC.The results show that the method has excellent precision (RSD <0.3%) and accuracy(recovery=97%) for the quantification of the residual MMA in cellulose graft PMMA liquidsamples. This method is simple, rapid, practical, and suitable for use in cellulose graft vinylmonomer polymerization-related research. In this thesis, MMA was homogeneous-grafted ona cellulose based macro-initiator, cellulose chloroacetyl chloride by the atom transfer radicalpolymerization (ATRP) at a mild reaction temperature. The synthesized cellulose graftcopolymers were characterized by FT-IR,1H-NMR and13C-NMR spectroscopies. The linearfirst-order kinetics of monomer conversion was determined by headspace gas chromatography.The molecular weights and their distributions of the PMMA grafted onto the cellulosebackbone were determined by gel permeation chromatography, the thermal property wascharacterized by the TGA, and the Cell-PMMA in solution could aggregate was analyzed bySEM. The results confirmed that the generation of the cellulose grafted PMMA at50oC in thegiven solvent system was a "controlled/living" ATRP process.Finally, a HS-GC method was reported for rapid determination of DS, in succinicanhydride (SA) esterification with celluloses. The method is based on the reaction betweenthe carboxyl groups in SA modified cellulose and bicarbonate solution in a closed headspacesample vial. The CO2released from the reaction was measured by HS-GC using a thermalconductivity detector. The results showed that a complete reaction can be achieved within30min at80oC, in which a small sample size (<20mg) was used. The measurement precision(RSD) was less than5.0%and the relative differences were within8.0%when comparedwith a traditional titration method in DS quantification. The present method is simple,practical and automated, and is suitable for research on anhydride esterification withcelluloses. Based on the relationship between the DS and reaction parameters such as reaction temperature, reaction time and mole ratio cellulose to SA, an empirical model was proposed.The results showed that there is a good agreement (R2=0.946) between the measured andpredicted DS, indicating that the model is justifiable to be applied to predict DS during thecellulose esterification with SA.