Study On Preparation, Characterization And Properties Of Polymer-grafted Carbon Black

Carbon black has been widely applied in the preparations of chemically sensitive materials, electromagnetic interference shield, positive temperature coefficient materials, ink, coatings and rubber, etc. Carbon black is used as a pigment in ink and coating, and as reinforcing agent in the rubber industry. Improvement of dispersion of carbon black in solvents or polymer matrix is one of key points to its application. Grafting polymer onto carbon black surface can be one of practicable methods for improving its dispersion. In this article, all kinds of grafting polymerization methods and applications of carbon black have been first reviewed.To solve dispersion problem of carbon black, tailor its surface properties and exploit new applications, series of polymers were grafted onto carbon black surface by surface-initiated ring-opening polymerization (SI-ROP), surface-initiated atom transfer radical polymerization (SI-ATRP), surface-induced reversible addition-fragmentation chain transfer (SI-RAFT) polymerization and trapping polymer radicals.Pristine carbon black was firstly oxidized with nitric acid, producing CB-COOH with carboxyl group density controlled from 0.6mmol/g to 1.87mmol/g. Then, CB-COOH was successively reacted with thionyl chloride and glycol to introduce hydroxyl group, obtaining CB-OH. The density of hydroxyl group in CB-OH was adjusted from 0.94mmol/g to 1.56mmol/g. Finally, CB-OH was reacted with 2-bromo-2-methylpropionyl bromide to anchor ATRP initiator, obtaining CB-Br with ATRP initiator density from 0.28mmol/g to 0.89mmol/g.Using CB-OH as initiator, poly(e-caprolactone) (PCL) was grafted onto carbon black surface by SI-ROP. The PCL content in CB-g-PCL was controlled between 19.0% and 51.9%. Poly(2-hy -droxyethyl methacrylate) (PHEMA) was grafted onto carbon black surface. The prepared CB-g-PHEMA contained PHEMA from 35.6% to 71.8%. Then, PHEMA in CB-g-PHEMA as macroinitiator, two CB-g-(PHEMA-g-PCL) samples respectively containing 86.3% and 92.7% of PHEMA-g-PCL were prepared by Sl-ROP. CB-g-PCL and CB-g-(PHEMA-g-PCL) were systematically characterized by FT-IR, ¹H-NMR, ¹³C-NMR, POM, DSC and XRD. TEM and AFM measurements showed that CB-g-PCL and CB-g-(PHEMA-g-PCL) both formed core-shell structures in which carbon black constituted the "core" and PCL or PHEMA-g-PCL layer existed as the "shell". When crystallized at 20℃on carbon-coated substrate, CB-g-PCL and CB-g-(PHEMA-g-PCL) formed micrometer-sized lamellas with dendritic patterns, in which carbon black was oriented to some extent. Polystyrene (PS) chains were grown from carbon black surface by SI-ATRP, obtaining CB-g-PS. The PS content in the prepared CB-g-PS varied from 17.6% to 54.8%. Similarly, poly(methyl methacrylate) (PMMA) chains were also grown from carbon black surface by SI-ATRP. And the PMMA content in CB-g-PMMA varied from 64.0% to 90.9%. TGA, DSC and ¹H NMR were used to characterize CB-g-PS and CB-g-PMMA. By transesterifications, PMMA and PS were detached from carbon black surface. Their molecular weights and polydispersities (PDI) were determined by GPC. The GPC results showed the PDI of PMMA or PS detached from the grafted carbon black surface was relatively low. Morphologies of CB-g-PS and CB-g-PMMA were observed by TEM and AFM. Their particle sizes were about between 120nm and 400nm in THF determined by DLS. Dispersion experiments showed that the grafted carbon black had relatively good solubilities in organic solvents.A reversible addition and fragmentation chain transfer (RAFT) agent, 2-{[(dodecylsulfanyl) carbonothioyl] sulfanyl} propanoic acid (DSCTSP) was synthesized. The DSCTSP was charac -terized by FT-IR and ¹H NMR. And in the presence of 1,3-dicyclohexylcarbodiimide (DCC), the DSCTSP was immobilized onto CB-OH surface via a direct condensation reaction, producing CB-DSCTSP. The density of DSCTSP in CB-DSCTSP was about 0.33mmoVg, calculated by TGA. Then, using the CB-DSCTSP as a chain transfer agent, poly(N-isopropylacrylamide) (PNIPAAm) chains were grown from carbon black surface by SI-RAFT polymerization. The PNIPAAm content in CB-g-PNIPAAm was between 37.3% and 83.1%. CB-g-PNIPAAm was characterized by FT-IR and ¹H NMR. By TEM, it was found that CB-g-PNIPAAm formed spherically nano-sized agglomerates with core-shell structures. Variable ¹H NMR and variable DLS measurements showed that CB-g-PNIPAAm behaved a reversible temperature-responsive property in water. On the other hand, series of CB-g-PNIPAAm samples with PNIPAAm from 43.2% to 68.7% were prepared by SI-ATRP. Chemical structure, morphology and temperature -responsive property of CB-g-PNIPAAm were also characterized by FT-IR, ¹H NMR, TEM and variable ¹H NMR.Polystyrene (PS), poly(styrene-co-maleic anhydride) [P(St-co-MA)], poly(4-vinylpyridine) (P4VP) and poly[styrene-co-(4-vinylpyridine)][P(St-co-4VP)] were synthesized using 4-hydroxyl -2,2,6,6-tetramethylpiperidin-l-oxyl(HTEMPO)-mediated radical polymerizations. The resultant HTEMPO-terminated polymers were characterized by FT-IR, ¹H NMR and GPC. These HTEMPO-terminated polymers were grafted onto carbon black surface through radical trapping reactions. The PS content in CB-g-PS varied from 4.4% to 19.6%. The P(St-co-MA) content in CB-g-P(St-co-MA) was between 4.9% and 31.8%. The P4VP content in CB-g-P4VP was between 7.7% and 34.0%. The P(St-co-4VP) content in CB-g-P(St-co-4VP) was between 10.6% to 18.7%. Particle sizes and morphologies of these grafted carbon black samples were studied by DLS, TEM and AFM. Dispersion experiments showed that CB-g-PS and CB-g-P(St-co-MA) could be dispersed in THE CB-g-P4VP and CB-g-P(St-co-4VP) could be well dispersed in ethanol.3-Ethyl-3-hydroxymethyl oxetane was synthesized by a closed loop reaction of trimethylopropane. Hydroxy methyl group was introduced onto carbon black surface through a reaction between carbon black and formaldehyde in alkali condition, obtaining CB-CH₂OH. Using CB-CH2OH as initiator, multihydroxyl hyperbranched polyether (HP) was grafted onto carbon black surface by surface-initiated ring-opening polymerization of 3-ethyl-3-hydroxymethyl oxetane, obtaining CB-g-HP. The HP content in CB-g-HP was between 21.4% and 83.7%. CB-g-HP was characterized by FT-IR and ¹H NMR. Their particle sizes were about 350nm in ethanol determined by DLS. Morphologies of CB-g-HP samples were studied by SEM.Poly(sodium 4-styrenesulfonate) (PSS), poly(N,N-dimethylacrylamide) (PDMA) and poly (tert-butyl methacrylate) (PrBMA) were grown from carbon black surface by SI-ATRP. The PSS content in CB-g-PSS was between 15.5% and 46.4%. The PDMA content in CB-g-PDMA was between 17.6% and 26.3%. The PtBMA content in CB-g-P/BMA was between 35.6% and 89.2%. CB-g-PMAA was obtained after hydrolysis of PtBMA in the presence of CF3COOH. CB-g-PSS, CB-g-PDMA, CB-g-PtBMA and CB-g-PMAA were chacterized by FT-IR and ¹H NMR. Their particle sizes of CB-g-PSS, CB-g-PDMA and CB-g-PMAA were mostly about between 300nm and 500nm in water determined by DLS. TEM and AFM observations showed that these water-dispersible carbon black formed spherically nano-sized agglomerates with core-shell structures. Water dispersion experiments showed that they possessed relatively good stabilities in water.CB-g-PSS and CB-g-PDMA were used to immobilize glucose oxidase, preparing disposal glucose biosensors. The application experimental results indicated that CB-g-PSS could enhance the sensitivity of biosensor with three orders magnitude and CB-g-PSS could only improve the sensitivity a little. We have also applied CB-g-PSS and CB-g-PDMA to prepare two kinds of gel ink and gel pens. Major physical properties of gel ink including specific gravity, surface tension, pH and thixotropy were studied, and writing performance of gel pens was also studied. The experimental results showed that two kinds of gel pens both behaved good writing performance. Thus, these two kinds of gel ink possess hopefully good application potentials.