TMC-CL Copolymers

In contrast to TMC-DLLA, the mechanical properties at equilibrium water uptake of TMC-CL copolymers are not significantly different from those in the dry state as shown in Table 8.1. 

Like the in vitro studies, the in vivo degradation of the TMC-CL copolymers containing 89% CL showed no change in shape or size after one year. As the degradation of the TMC-CL copolymers was so slow, a mature fibrous capsule remained throughout the year. Histological results of the TMC-CL copolymers were similar to those obtained from TMC-DLLA or other commonly used biodegradable polymers. 

The syntheses of block copolymers of mono- or difunctional PEO with various lactones such as TMC, CL, and LL... 

P(TMC-co-CL) copolymers have also been studied. Albertsson et al. reported the in vitro degradation of a P(TMC-co-CL) 12/88 in comparison with PTMC (Albertsson and Eklund, 1995). Degradation was found to proceed in the bulk. The copolymer showed a higher degradation rate compared to PTMC. Preferential degradation of amorphous parts led to an increase in crystallinity. 

Grijpma et al. (1994) studied blends of PLA and a rubbery copolymer of caprolactone (CL) and trimethylene carbonate (TMC) (poly(TMC/CL)). They reported an increase in the notched Izod impact strength of neat PLA with the addition of 20wt% copolymer (from 40J/m to a maximum of 520 J/m). 

However, for homopolymer poly(TMC) and PLA blends, the corresponding wt% of mbber phase did not improve the notched Izod impact strength. Joziasse et al. (1998) have investigated blends of PLA homopolymer with poly(trimethylene carbonate) (poly(TMC)) mbbery copolymers. They found that the samples with 21 wt% of the mbber block of poly(TMC) in PLA did not break in an unnotched impact test. Diblock copolymers of L-lactide and caprolactone (P(LA/CL)) were also blended with PLA to determine their influence on the mechanical properties. The addition of 20 wt% of diblock copolymer improved the unnotched impact strength of the blend from 5 kJ/m to 50 kJ/m. ... 

Lipases not only catalyze ROP but also catalyze transacylation reactions. This was exploited by preparing random copolymers of TMC with CL or PDL [91, 92, 159]. The PDL-TMC poly (carbonate-esters) show co-crystallization behavior of... 

Copolymers of DXO and d,l-LA were synthesized in different molar concentrations in their recent attempts [245]. In vitro hydrolysis studies on the copolymers showed degradation times up to 250 days. Microspheres intended for drug delivery were prepared from poly[TMC-co-CL], PAA and PLGA [245]. SEM studies showed that the microsphere morphology depends on the concentration at the time of preparation and on the choice of polymer. The drug release profiles showed dependence on the polymer degradation behavior and on the water penetration into the microsphere [245]. 

Segmented copolymers as low modulus materials comprising polymeric CL or TMC soft segments... 

On the other hand, Joziasse et al. [243] investigated the NHD of linear and branched P(LLA-C6>-DLA-C6>-GA)/Iinear poly (TMC-C6 -CL) blends and found that the blends of branched copolymers retained their mechanical properties for longer periods than did the linear copolymers. 

Poly(TMC-co-ethylene ethyl phosphate) was prepared by ring-opening copolymerization catalyzed by lipase enzymes (pancreas lipase, PPL and Candida rugosa lipase, CL) as catalysts in bulk at 100 °C with molecular weight (Mn) from 3200 to 10 200. Degradation experiments showed that introducing phosphate groups into the TMC chain increases the hydrolysis rate of the copolymer. 

The syntheses of triblock PEG-CL-TMC copolymers methoxypoly[(ethylene oxide)-b-(CL)-l7-(trimethylene carbonate)] were reported by Ould-Ouali et al and Danhier and co-workers. These copolymers spontaneously formed micelles and significantly increased the solubility of poorly water-soluble drugs. 

The first example of biodegradable segmented copolymers introduced in 1980s as a monofilament suture was Maxon (Syneture), also containing a random poIy(TMC-co-GL) middle block. The copolymer was prepared by ring-opening copolymerization of CL and TMC, the final composition being defined by a 67.5 wt.% of CL (Scheme 91). ... 

The synthesis of multiblock cyclic carbonate copolymers was presented by Kricheldorf and Rost. First, telechelic random copolymers were prepared by copolymerization of CL and TMC in bulk using bismuth(III) hexanoate [Bi(OHex)3] as an initiator. A-B-A triblock copolymers were synthesized by chain extension of these random copolymers with l-LA. Finally, the triblock copolymers were transformed into multiblock copolymers by chain extension with 1,6-hexamethylene diisocyanate. It is worth mentioning that all three synthetic steps were performed in a one-pot procedure. ... 

Similar star-shaped poly[(TMC)-co-(CL)j and its block copolymers with lactide/GL were investigated by Joziasse et When dipentaerythritol was used as a six-functional initiator, cross-linked rubbers were obtained, swelling in chloroform. Star-shaped lactide/GL block copolymers with a poly [(TMC)-CO-(CL)] rubber core based on o-sorbitol exhibited good mechanical properties. 

The abiUty of Upases to catalyze not only ROPs but also transesterification/ transacylation reactions was exploited by preparing random copolymers of TMC with CL or co-pentadecalactone, and copolymers of cycUc dicarbonates with CL and 12-dodecanolactone [91-94]. The introduction of substituents at the cycUc carbonate (1-MeTMC and 2-MeTMC Scheme 15.4) has also been studied, and their homopolymers and copolymers with TMC have been prepared [95-99]. The use of protected functional groups at the TMC ring (BTMC and MBM Scheme 15.4) allowed for easy access to the hydroxy-functional or carboxy-functional polycarbonates, which may be used to tune the degradation behavior of these polymers. 

---