Synthesis And 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 specially branched polymers, they become one of the recent research hotspots with useful prospects.Atom transfer radical polymerization (ATRP) is an important technique in polymer 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 etc. 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 star-shaped polystyrene(FASPS) has been synthesized as one of star-shaped polymers via ATRP 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. FASPS with an 1,2,4,5-tetra(bromomethyl benzene, TBMB) core were prepared by ATRP. Both bulk and solution polymerizations of styrene were performed by using TBMB as the multifunctional initiator and CuBr/2,2′-bipyridine (bpy) as the catalyst system. Through changing polymerization conditions, conversion of polymer was determined gravimetrically by sampling with an injector at different time in the course of polymerization system. Results indicated effect factors of polymerization system, which were monomer/initiator, catalysis system, temperature and time etc. Conversion increased along with increases of polymerization time, temperature and initiator, and ln[M]0/[M] versus time was linearity.2. For the complicated polymerization system, orthogonal, uniform and central experimental designs were employed to examine various effect 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.In bulk/solution polymerization, outstanding factors of effects of conversion were the same, namely polymerization temperature and time. The two polymerization systems were slightly different, so that their optimum conditions were a little different. For example: the optimum experimental conditions of orthogonal experimental designs: [M]/[I]: 14.4800g/0.0500g(1250), CuBr/bpy:0.06g/0.1960g(1:3), polymerization temperature: 100℃, polymerization time:10hours. 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, respectively.3. Viscidity of FASPS 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, and it showed that the prepared polymers were star polymers.4. Structures of polymers were analyzed with different spectroscopies, such as UV, IR, 1H-NMR, 13C-NMR and 1H-1H COSY, and it illuminate that the synthesized polyemers were well-defined FASPS. Number-average molecular weight and distribution of polymers were determined with GPC. Moreover, Mn,GPC was smaller than Mn,th, and it was conclusion that the prepared polymers were FASPS. 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) increased along with moleculal weight of polymer. 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 behaviors of FASPS were correlated with arm length of FASPS. Increase of decomposition temperature of the prepared polymers (T50%) followed increase of moleculal weight of polymer.In summary, FASPS cored with a TBMB as the multifunctional initiator has been synthesized via ATRP by using CuBr/bpy as the catalyst system under optimal experimental conditions. Results of various characterizations indicated that the prepared star-shaped polymers had well-defined four-arm structures and relatively narrow molecular weight distribution.