Shangan Lin

Preparation and characterization of maleic anhydride-functionalized syndiotactic polystyrene

Abstract The free radical-induced grafting of maleic anhydride (MA) onto syndiotactic polystyrene (sPS) has been accomplished in the solution process by using 1,1,2-trichloroethane as solvent and dicumyl peroxide as free radical initiator. The amount of MA grafted on sPS was evaluated by a titration method. Grafted products separated from the reaction mixture were purified and analyzed. Fourier transform infrared spectroscopy and 1 H NMR studies indicate that MA attaches to the sPS in the form of single succinic anhydride rings as well as short oligomers. The results obtained by GPC analysis suggest that the degradation and chain extension reaction do not occur under the reaction conditions. Moreover, the crystallization behavior of MA-functionalized sPS was also studied by means of differential scanning calorimetry. It was found that the crystallization behavior of the grafted polymer exhibited somewhat differences in comparison to the neat sPS. The MA-functionalized sPS crystallizes at higher rate than the unmodified polymer, on the other hand, the degree of crystallinity ( X c ) are lowered by the presence of the MA grafts.

Graft copolymerization of acrylamide onto carboxymethyl starch

Abstract Water absorption resins of carboxymethyl starch graft acrylamide (CMS-g-AM) were synthesized by copolymerization based on a free radical reaction. At first, CMS was prepared with starch and chloroacetic acid in an alkali–methanol media. Then, AM was grafted onto CMS by using ceric ammonium nitrate as an initiator. The resulting graft products were identified by infrared spectra. The effects of the preparation conditions on the substituent degree (SD) of starch and the water absorption capacities of CMS-g-AM were investigated. The results showed that SD of starch first increased remarkably and then decreased gradually with increased addition of sodium hydroxide, and the water absorption capacity of CMS-g-AM depended greatly on the SD of CMS and its maximum with 0.75 of SD of starch was 350 g/g.

Polymer blends of sPS/PA6 compatibilized by sulfonated syndiotactic polystyrene

Abstract Syndiotactic polystyrene (sPS) and polyamide-6 (PA6) are immiscible and incompatible and have been recognized. In this study, sulfonated syndiotactic polystyrene (SsPS-H) is employed as compatibilizer in the blend of sPS/PA6. During melt blending, the sulfonic acid groups of the SsPS-H can interact strongly with the amine end-groups of PA6 through acid–base interaction. In addition, SsPS-H is miscible with sPS when SsPS-H content is less than 20 wt.%. Therefore, the addition of SsPS-H to sPS/PA6 blends reduces the dispersed phase size and improves the adhesion between the phases. The glass transition temperatures of the PA6 component in the compatibilized blends shift progressively towards higher temperature with the content of SsPS-H-12 increase, indicating enhanced compatibility. On the other hand, the progressive lowering of the melting point and crystallization temperatures of PA6 in the blends with increasing SsPS-H contents compared to the incompatibilized blend, provide some insight into the level of interaction between the PA6 and SsPS-H. The compatibilized blends have significantly higher impact strength than the blends without SsPS-H. The best improvement in the impact strength of the blends was achieved with the content of the SsPS-H (11.9 mol%) about 5 wt.%.

Atactic polymerization of propylene catalyzed by mono(η5‐cyclopentadienyl)titanium tribenzyloxide combined with methylaluminoxane

Propylene has been polymerized with mono(η 5 -cyclopentadienyl)titanium tribenzyloxide activated with methylaluminoxane(MAO). It was found that the content of residual trimethylaluminium (TMA) in MAO has a determinative effect on the polymerization. An excess of TMA in the catalyst system reduces the Ti species to inactive lower valent states. The catalyst system gives medium molecular-weight atactic polypropylene (M, = 2-7 × 10 4 ) with narrow molecular weight distribution (M w / M n = 1.4-1.8). The polymer has a stereoirregular structure described by Bernoullian statistics. Statistical analysis of the regiotriad distribution of the polypropylene chains indicates a regioblock microstructure.

Novel monotitanocene and methylaluminoxane catalyst for syndiospecific polymerization of styrene

Syndiotactic polystyrene (sPS) was synthesized with a novel monotitanocene complex of η 5 -pentamethylcyclopentadienyltri-4-methoxyphenoxy titanium [Cp * Ti(OC 6 H 4 OCH 3 ) 3 ] activated by methylaluminoxane (MAO) in different polymerization media, including heptane, toluene, chlorobenzene, and neat styrene. In all cases bulk polymerization produced sPS with the highest activity and molecular weight. Solution polymerization produced much better activity in heptane than in the other solvents. Using a solvent with a higher dipole moment, such as chlorobenzene resulted in lower activity and syndiotacticity because of the stronger coordination of solvent with the Ti(III) active species, which controlled syndiospecific polymerization of styrene. With bulk polymerization at a higher polymerization temperature the Cp*Ti(OC 6 H 4 OCH 3 ) 3 -MAO catalyst produced sPS with high catalytic activity and molecular weight. The external addition of triisobutylaluminum (TIBA) to the Cp * Ti(OC 6 H 4 OCH 3 ) 3 -MAO system catalyzing styrene polymerization led to significant improvement of activity at a lower Al:Ti molar ratio, while the syndiotacticity and molecular weight of the yields were little affected.

Syntheses of multi‐stereoblock polybutene‐1 using novel monocyclopentadienyltitanium and modified methylaluminoxane catalysts

Butene-1 was polymerized using novel mono-(η 5 -pentamethylcyclopentadienyl) tribenzyloxy titanium[Cp * Ti(OBz) 3 ] complexes activated with three types of modified methylaluminoxanes (mMAO) containing different amounts of residual trimethylaluminum (TMA). The oxidation states of titanium in different Cp * Ti(OBz) 3 and mMAO catalytic systems were determined by redox titration method. The influences of various oxidation state of titanium active species on butene-1 polymerization were investigated. It is found that Ti(IV) active species is in favour of producing polybutene-1. The polymer obtained at 0°C and 30°C with melting temperature was shown by 13 C-NMR and DSC characterizations to comprise of multiple blocks of isotactic and atactic segments. 13 C-NMR analyses of polybutene-1 implies that chain propagation of butene-1 involves primarily head-to-tail 1,2-insertions, with involving negligible proportion of head-to-head and tail-to-tail 2,1-misinsertions. There is a remarkable decrease in 2,1-misinsertions with decreasing temperature of polymerization.

Ethylene/styrene copolymerization in the presence of cyclopentadienyltitanium tribenzyl oxide and various methylaluminoxanes

Copolymerizations of ethylene and styrene in the presence of CpTi(OBz) 3 and various MAOs have been investigated. It was found that the composition and structure of the copolymerization products are strongly dependent on the amount of free alkylaluminium, involving the residual trimethylaluminium (TMA) in MAO and external alkylaluminium (TIBA), in the systems. The catalyst system containing less free alkylaluminium affords an ethylene/styrene copolymer. while that containing plenty of free alkylaluminium affords a mixture of the corresponding homopolymers. This seems to be due to the existence of different Ti species caused by the free alkylaluminium content in the systems.

The synthesis of high molecular weight polybutene‐1 catalyzed by Cp★ Ti(OBz)3/MAO

A new stereoregular polybutene-1 was synthesized with a novel catalyst precursor η5-pentamethyl cyclopentadienyl titanium tribenzyloxide (Cp★Ti(OBz)3) and methylaluminoxane (MAO). The effects of polymerization conditions on the catalytic activity, molecular weight and stereoregularity of the products were investigated in detail. It was found the catalyst exhibited highest activity of 91.2 kgPB mol Ti−1 h−1 at T = 30 °C, Al/Ti = 200. The catalytic activity and molecular weight were sensitive to the Al/Ti (mole/mole), polymerization temperature; they also depended on the Ti concentration. The molecular weight of the products increased with decreasing temperature. The structure and properties of the polybutene-1 were characterized by 13C NMR, GPC, DSC and WAXD. The result showed the microstructure of polybutene-1 extracted by boiling heptane was stereoregular, whereas the ether-soluble fraction was atactic. The molecular weight of polybutene-1 was over one million g mol−1 and its molecular weight distribution (Mw/Mn) was from 1.1 to 1.2. © 2001 Society of Chemical Industry

High molecular weight atactic polypropene synthesized with (η5-pentamethylcyclopentadienyl)tribenzyl titanium activated with MAO

The half-titanocene (η5-pentamethylcyclopentadienyl)tribenzyl titanium (Cp*TiBz3) with methylaluminoxane (MAO) as the cocatalyst was employed to catalyze propene polymerization at ambient pressure. A novel atactic polypropene elastomer with a high molecular weight (Mw = 2 − 8 × 105) was produced. The effects of the polymerization conditions on the catalytic activity and polymer molecular weight are discussed. 13C NMR analysis confirmed that the catalyst system Cp*TiBz3/MAO produced atactic polypropenes, and the polymerization mechanism was in agreement with the Bernoullian process. The triad sequence distribution of the polymer was measured and found to be as follows: mm = 6.15%, mr = 40.87%, and rr = 52.98% (Bernoullian factor B = 1.03); this indicated that the insertion of propene with the catalyst system followed a chain-end control model.

Branched polyethylene prepared by in situ copolymerization of ethylene with monotitanocene and modified methylaluminoxane catalyst

Branched polyethylene was synthesized in heptane used as a polymerization medium with monotitanocene catalyst composed of η 5 -pentamethylcyclopentadienyl tribenzyloxy titanium and modified methylaluminoxane (mMAO) that contained different amounts of residual trimethylaluminum (TMA). The residual TMA more strongly reduced Ti(IV) complexes to Ti(III) and Ti(II) ones, and Ti(IV) active species were suggested to be more effective for ethylene polymerization. Influences of the polymerization temperature and Al/Ti molar ratio on the catalytic activity and the degree of branching, branch length, and molecular weight of polyethylene were investigated. The obtained polymers were confirmed by 13 C NMR to be higher molecular weight polyethylene containing significant amounts of isolated ethyl branches, butyl branches, or both. Branched polyethylene was prepared by the in situ copolymerization of ethylene with 1-butene and 1-hexene, which were formed through a proposed mechanism including metallcycloheptane and metallcyclopentane intermediates of Ti(II) species that were produced by the reaction of Ti(IV) complexes with TMA coexisting in mMAO. There was a remarkable increase in the chance of 1-butene being produced from metallcyclopentane of Ti(II) intermediates with an increase in the polymerization temperature.