Jong Yeob Jeon

Preparation of flame-retarding poly(propylene carbonate)

A preparative method for a flame-retarding poly(propylene carbonate) (PPC) was demonstrated by employing diphenylphosphinic acid (Ph2P(O)(OH)), phenylphosphonic acid (PhP(O)(OH)2), or phosphoric acid (P(O)(OH)3) as a chain transfer agent in the immortal CO2/propylene oxide copolymerization catalyzed by a highly active catalyst, a cobalt(III) complex of a Salen-type ligand tethered by four quarternary ammonium salts (1). High turnover frequencies of 10 000–20 000 h−1 (700–1300 g-polymer per g-cat·h) were maintained even in the presence of a large amount of the protic chain transfer agent ([–OH]/[1], 1600–200). Directly after the copolymerization using PhP(O)(OH)2 as a chain transfer agent, thermoplastic polyurethane (TPU) was formed by adding a stoichiometric amount of toluene-2,4-diisocynate. The TPU also was not inflammable. Cone calorimeter studies showed that PPC itself and TPU prepared using PPC-diol emitted significantly less smoke while burning than common plastics, such as polystyrene.

Preparation of thermoplastic polyurethanes using in situ generated poly(propylene carbonate)-diols

Low-molecular-weight poly(propylene carbonate)s bearing –OH groups at both ends (PPC-diols) are prepared by feeding protic chain-transfer agents (1,2-propanediol, terephthalic acid, 2,6-naphthalenedicarboxylic acid, and phenylphosphonic acid) in the CO2/propylene oxide copolymerization catalyzed by a highly active Salen–Co(III) complex tethered by four quaternary ammonium salts. The generated low-molecular-weight PPC-diols are used in situ for the formation of thermoplastic polyurethanes through subsequent feeding of diisocyanates (4,4′-methylenebis(phenyl isocyanate), 1,4-phenylene diisocyanate, and toluene 2,4-diisocyanate). The formation of polyurethanes is confirmed by 1H NMR spectroscopy and GPC studies. By varying the structure of the fed diisocyanate and chain-transfer agent, the glass transition temperature of the polyurethane can be tuned in the range 40–60 °C. A high glass transition temperature of up to 60 °C, which is 20 °C higher than that of high-molecular-weight PPC itself (40 °C), is attained when 2,6-naphthalenedicarboxylic acid (as the chain-transfer agent) and 4,4′-methylenebis(phenyl isocyanate) are employed. In addition, flame-retarding polyurethanes are generated by using an organophosphorus-based chain-transfer agent.

Copolymerization and terpolymerization of carbon dioxide/propylene oxide/phthalic anhydride using a (salen)Co(III) complex tethering four quaternary ammonium salts

Summary The (salen)Co(III) complex 1 tethering four quaternary ammonium salts, which is a highly active catalyst in CO2/epoxide copolymerizations, shows high activity for propylene oxide/phthalic anhydride (PO/PA) copolymerizations and PO/CO2/PA terpolymerizations. In the PO/PA copolymerizations, full conversion of PA was achieved within 5 h, and strictly alternating copolymers of poly(1,2-propylene phthalate)s were afforded without any formation of ether linkages. In the PO/CO2/PA terpolymerizations, full conversion of PA was also achieved within 4 h. The resulting polymers were gradient poly(1,2-propylene carbonate-co-phthalate)s because of the drift in the PA concentration during the terpolymerization. Both polymerizations showed immortal polymerization character; therefore, the molecular weights were determined by the activity (g/mol-1) and the number of chain-growing sites per 1 [anions in 1 (5) + water (present as impurity) + ethanol (deliberately fed)], and the molecular weight distributions were narrow (M w/M n, 1.05–1.5). Because of the extremely high activity of 1, high-molecular-weight polymers were generated (M n up to 170,000 and 350,000 for the PO/PA copolymerization and PO/CO2/PA terpolymerization, respectively). The terpolymers bearing a substantial number of PA units (f PA, 0.23) showed a higher glass-transition temperature (48 °C) than the CO2/PO alternating copolymer (40 °C).

Preparation of high-molecular-weight poly(1,4-butylene carbonate-co-terephthalate) and its thermal properties

Condensation copolymerizations of 1,4-butanediol (BD), dimethyl carbonate (DMC), and dimethyl terephthalate (DMT) were conducted by a two-step procedure using sodium alkoxide (0.1–0.2 mol%) as a catalyst with a variable [DMT]/[BD] feed ratio. In the first step, oligomers bearing almost equal numbers of hydroxyl and methoxycarbonyl end-groups were generated, which were polycondensed mostly by the elimination of methanol at 190–210 °C under reduced pressure. By this procedure, high-molecular-weight poly(1,4-butylene carbonate-co-terephthalate)s (PBCTs) were easily prepared with Mw 60 000–200 000 in a reasonably short reaction time (∼8.5 h) and even on a large scale (110 g polymer per batch) in a 250 mL glass reactor. The PBCTs prepared at a high [DMT]/[BD] feed ratio 0.30–0.50 were semi-crystalline polymers with fast crystallization rates and melting temperatures in the range 95–146 °C, which were adjustable by the [DMT]/[BD] feed ratio. The glass transition temperatures were rather high around 0 °C. These thermal properties were comparable to those of commercialized compostable polyesters such as PLA, PHA, PBAT, and PBSA.

Ring-opening metathesis polymerization of dicyclopentadiene and tricyclopentadiene

Abstract

Preparation of polystyrene–polyolefin multiblock copolymers by sequential coordination and anionic polymerization

Block copolymers of polyolefins (PO) and polystyrene (PS) are attractive materials that are not synthesized directly from the olefin and styrene monomers. A strategy for construction of PS-b-PO-b-PS triblock units directly from the olefin and styrene monomers is disclosed herein. PO chains (ethylene/1-octene or ethylene/1-pentene copolymers) were grown from dialkylzinc species bearing the α-methylstyrene moiety (i.e., [4-(isopropenyl)benzyl]2Zn) by ‘coordinative chain transfer polymerization (CCTP)’ using a typical ansa-metallocene catalyst, rac-[Me2Si(2-methylindenyl)2]ZrCl2 activated with modified-methylaluminoxane (MMAO). PS chains were subsequently grown from the Zn-alkyl sites and from the α-methylstyrene moieties of the resulting PO chains by switching to anionic polymerization. When nBuLi(tmeda)2 was fed into the system as an initiator in a quantity fulfilling the criterion [Li] > [Zn] + [Al in MMAO], nBuLi(tmeda)2 successfully attacked the α-methylstyrene moieties to initiate the anionic styrene polymerization at both ends of the PO chains generated in the CCTP process. However, in model studies, the attack of nBuLi(tmeda)2 on α-methylstyrene in the presence of (hexyl)2Zn consumed two molecules of α-methylstyrene per nBuLi to afford mainly R–CH2C(Ph)(Me)–CH2C(Ph)(Me)Li, where R is either an nbutyl or hexyl group originating from nBuLi or (hexyl)2Zn, respectively. This observation suggests that the block copolymer does not simply comprise the PS-b-PO-b-PS triblock, but instead comprises a multiblock containing PS-b-PO-b-PS units. The molecular weight of the polymer increased after performing anionic polymerization. Even though the phase separation of the PS and PO blocks observed in the TEM images is less regular in the multiblock copolymers, the elastomeric property of the multiblock copolymers observed in the hysteresis testing is better than that of the diblock analogue.