Semicrystalline Polymers via Ring-Opening Polymerization:  Preparation and Polymerization of Alkylene Phthalate Cyclic Oligomers

Abstract

Preparation of cyclic oligomeric alkylene phthalates via pseudo-high dilution condensation of alkylene diols with iso- and terephthaloyl chlorides and conversion to high molecular weight polyesters via ring-opening polymerization is described. Sterically unhindered amines such as quinuclidine or 1,4-diazabicyclo[2.2.2]octane (DABCO) catalyze the condensation significantly faster than other tertiary amines and are useful for carrying out this conversion in high yield, in the first direct reaction of diol and diacid chloride to form cyclic polyesters. The mixtures of oligomeric cyclics melt at 150-200 degrees C, providing liquids of low viscosity. Ring-opening polymerization using tin or titanate catalysts affords high molecular weight polymers within minutes. Complete polymerization of PBT oligomeric cyclics can be achieved at 180-200 degreesC, significantly below the polymer's melting point of 225 degreesC, and with molecular weights as high as 445 x 10(3). Polymers formed via such a process are more crystalline than conventionally prepared polyesters.

Poly(hexamethylene terephthalate-co-caprolactone) copolymers: Influence of cycle size on ring-opening polymerization

“…This distribution of cycle sizes was in all cases close to that reported by Brunelle et al [7] for a cyclic fraction prepared by reaction of terephthaloyl chloride with hexamethylene glycol in solution at high dilution conditions. Such fraction consisted of species ranging from the dimer to the heptamer with percentage contents decreasing with the increase of cycle size.…”

“…found that each hexamethylene terephthalate cyclic oligomer of M mass was accompanied by a minor amount of the M+100 compound, which was identified by NMR as the corresponding oligomer with one hexamethylene glycol unit replaced by one di(hexamethylene glycol) unit. As it can be expected, these di(hexamethylene glycol) containing oligomers were not reported to be present in the cyclic fractions produced by chemical synthesis from diadic chlorides and diols due to milder conditions used for the synthesis [7].…”

“…The intrinsic viscosities of the resulting polymers are listed in Table 2 and data available for fraction c(HT) [6][7] [19] were included for comparison. The viscosity of the cyclic oligomers was 0.09 dL·g -1 and it increased significantly upon heating indicating that the ring opening polymerization reaction proceeded.…”

“…However, the potential of ROP is strongly constrained by the limited availability of suitable cyclic monomers. Increasing attention is being paid recently to the utilization of cyclic oligoesters as feedstock for the synthesis and processing of aromatic polyesters [3,[7][8][9]. One source of cyclic oligoesters of great interest is cyclo-depolymerization of linear polyesters, which in combination with ROP, would provide an environmentally friendly route for the chemical recycling of currently important thermoplastics as poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT) and other closely related industrial aromatic polyesters and copolyesters [10][11][12][13][14].…”

“…Recently we succeeded in preparing copolyesters of HT and ε-caprolactone (CL) by ROP. A fraction of hexamethylene terephthalate cyclic oligomers consisting of a mixture of hexamer and heptamer c(HT) [6][7] prepared by cyclo-depolymerization of PHT was used for this synthesis [19].…”