Synthesis And Analytical Characterization Of Four-Arm Star-shaped Polystyrene

Star-shaped polymers are new important materials with unique three dimensional snowflake structures, unfamiliar configurations, various functions, special performances, particular capabilities and potential applications. As the simplest and specially branched polymers, they become one of the recent research hotspots with useful prospects.Atom transfer radical polymerization (ATRP) is an important technique in macromolecule chemistry and a useful pathway to realize molecular design and chemical synthesis of polymers with different structures and special performances. ATRP is applicable to various polymerizations in bulk, solution, emulsion, suspension and some others due to its many strong-points, for example, more monomers, milder conditions, unlimited methods and so forth. As a rule, there are two ways, namely, both"arm-first"and"core-first"methods in order to synthesize star-shaped polymers.In this thesis, four-arm polystyrene has been synthesized as one of star-shaped polymers via atom transfer radical polymerization by using"core-first"method through both solution and bulk polymerizations, respectively. The main contents and some conclusions are shown and made as follows:1. Four-arm star-shaped polystyrenes with an 1,2,4,5-tertra(bromomethyl benzene, TBMB) core were prepared by atom transfer radical polymerization (ATRP). Both bulk and solution polymerizations of styrene were performed by using 1,2,4,5-tertra(bromomethyl benzene) as the multifunctional initiator and CuBr/2,2′-bipyridine (2,2′-bpy) as the catalyst system. Through changing various conditions, the conversion of polymerization was determined gravimetrically by sampling with an injector at different time in the course of polymerization system and it was found that conversion was increased linearly firstly and non-linearly finally along with reaction time. Results indicated effect factors of polymerization system, which were monomer/initiator, catalysis system, temperature and time, Changed single polymeric condition and researched infection of polymeric conditions.2. For the complicated polymerization system, orthogonal, uniform and central experimental designs were employed to examine various influence factors such as monomer/initiator ratio, catalysis system, reaction temperature and polymerization time. Intuitive analysis, variance analysis, multiple linear and/or stepwise regressions were used to process experimental data to find the optimum experimental conditions(for example: the optimum experimental conditions of orthogonal experimental designs: [M]/[I]: 14.4800g/0.0500g, CuBr/Bpy: 0.06g/0.1960g(1:3), temperature:100℃, time:10 hours). And that stabilities, relativities and forecasting abilities of models were preferable (for instance: R=0.999, 0.996, 0.978 for the bulk polymerization; R=0.987, R=0.990, R=0.982 for the solution polymerization) by orthogonal, uniform and central experimental designs, respective. Both solution and bulk polymerizations were examined for optimum conditions; and it found that each had merits and faults, respectively.3. Viscidity of four arms star-shaped polystyrene was determined with Ubbelohde vislometer at 23°C, by using tetrahydrofuran as solvent. Viscidity average molecular weight (Mη) was calculated by formula [η]=KMα(K=3.5×10-3ml/g;α=0.74). While, viscidity of linear polystyrene was also determined simultaneously as the same viscidity average molecular weight and it was found the viscidity was much larger than that of star polystyrene.4. Various structures of polymers were analyzed with different spectroscopies, such as UV, IR, 1H-NMR, 13C-NMR and 1H-1H COSY. Number-average molecular weight and distribution of star-shaped polymers were determined with GPC characterization. Moreover, Mn,GPC was much smaller than Mn,th. Based on terminal functional groups analysis, Mn,NMR was calculated by NMR spectra and basically accorded with both Mn,NMR and Mn,th each other, which reveals the quantitative initiation efficiency. And steric tactility was then determined by NMR spectra. Syndiotactic rate of polymers was more than 80% for their relative contents.5. Thermal analysis was performed on thermometry model STA449C for star-shaped polymers. Glass transition was analyzed by differential scanning calorimetry (DSC), and glass transition temperature (Tg) was then obtained by multiple linear ingression (MLR) with correlation coefficients being R=0.973, and Rcv=0.923 from model estimation and cross verification, respectively. Decomposition course and thermal stability were evaluated with theremogravimetry (TG). It was found that four-arm star polymer behaviors were correlated with arm length of the four-arm star polymer.In summary, four-arm star-shaped polystyrene cored with an 1,2,4,5-tertra(bromomethyl benzene) as the multifunctional initiator has been synthesized via atom transfer radical polymerization by using CuBr/2,2′-bpy as the catalyst system under optimal experimental conditions. And that various characterization results indicated that the prepared star-shaped polymers had well-defined four-arm structures and relatively-narrow molecular weight distribution.