Laszlo Sipos

Optimum conditions for the synthesis of linear polylactic acid-based urethanes

The reactions of polylactic acid (PLA) oligomers and isocyanates (4,4′-diphenylmethane diisocyanate and toluene diisocyanate) are reported. The effects of the reaction conditions, that is, the reaction time, reaction temperature, molar ratios, isocyanates, and catalyst, on the number-average molecular weight (Mn ) are demonstrated. The optimum reaction conditions are determined by the synthesis of relatively high Mn PLA-based linear polyurethanes. The structure of the polymer samples was investigated with dynamic light scattering, 1H NMR, IR, and matrix-assisted laser-desorption ionization time-of-flight mass spectroscopy (MALDI-TOF MS).

Living ring-opening polymerization of l,l-lactide initiated with potassium t-butoxide and its 18-crown-6 complex

SummaryLiving polymerization of L,L-lactide initiated by potasium t-butoxide and its 18-crown-6 complex was investigated in THF solution at room temperature. The results support a reversible polymerization mechanism consisting of first order in monomer propagation and of unimolecular depropagation. The presence of 18-crown-6 has a strong MWD narrowing effect (Mw/Mn<1.2), slows down the overall rate of polymerization and gives rise to slow initiation. The polymerizations yield optically pure polymers both in the presence and absence of 18-crown-6.

Living Cationic Sequential Block Copolymerization of Isobutylene with 4‐tert‐Butoxystyrene: Synthesis and Characterization of Poly(p‐hydroxystyrene‐b‐isobutylene‐b‐p‐hydroxystyrene) Triblock Copolymers

The living polymerization of p‐tert‐butoxystyrene (tBuOS) was studied in methylcyclohexane (MeChx)/methylchloride (MeCl) 60/40 v/v solvent mixture at –80°C. The model initiator 1,1,‐ditolylethylene (DTE) capped 2‐chloro‐2,4,4‐trimethylpentane (TMPCl) was formed in situ in conjunction with TiCl4. Lowering the Lewis acidity by the addition of Ti(OIp)4 was necessary to induce a rapid and controlled polymerization of tBuOS. Well‐defined polymers with controlled molecular weights, however, were only obtained at a narrow [Ti(OIp)4]/[TiCl4]=0.83–0.86 ratio. Above this ratio, the polymerization of tBuOS was slow and became absent at [Ti(OIp)4]/[TiCl4]≥1.18. At ratios lower than 0.83, the polymerization was too rapid and the initiator efficiency was lower than 100%. The living polymerization of tBuOS was also studied with SnBr4 as Lewis acid. After capping TMPCl with DTE, Ti(OIp)4 was added to reach [Ti(OIp)4]/[TiCl4]=1.2, followed by the addition of tBuOS and SnBr4. SnBr4 induced a well‐controlled living polymerization approximately first order in [SnBr4], and the polymers exhibited close to theoretical M ns and low polydispersity indices (PDI<1.2). The success of the method was also demonstrated by the clean synthesis of poly(isobutylene‐b‐p‐tert‐butoxystyrene) PIB‐b‐PtBuOS diblock copolymers. PtBuOS‐b‐PIB‐b‐PtBuOS triblock copolymer thermoplastic elastomers were prepared by employing 5‐tert‐butyl‐1,3‐bis(1‐methoxy‐1‐methylethyl)benzene (DCE) as a difunctional initiator for the living polymerization of IB followed by capping with DTE and substitution of TiCl4 with SnBr4 for the polymerization of tBuOS. Deprotection of the triblock copolymer in the presence of catalytic amount of HCl yielded poly(p‐hydroxystyrene‐b‐isobutylene‐b‐p‐hydroxystyrene) (PHOS‐b‐PIB‐b‐PHOS). PHOS‐b‐PIB‐b‐PHOS with 39.3 wt% p‐hydroxystyrene content exhibited typical characteristic of a thermoplastic elastomers (TPEs) with tensile strength of 18 MPa and ultimate elongation of 300%.

Anionic polymerization of L-lactide effect of lithium and potassium as counterions

Abstract The polymerization of L-lactide was carried out with t-BuOK and t-BuOLi in the presence and absence of crown ethers. Each polymerization showed living nature only in the limited sense of having a decreasing amount of active species at high conversion. The initiator efficiency was low in each case because of the deprotonation reaction between the tert-butoxide ion and L-lactide. Although termination did not take place with lithium containing initiators to 90% conversion, intra- and intermolecular transesterification was observed to a significant degree. With potassium containing initiators both termination and transesterification occurred.